Outline of CHN Elementary and CN Environmental Analysis

A C T A U N I V E R S I T A T I S L O D Z I E N S I S

FOLIA CHI MICA 1 3 ,2 0 0 4

O U T L IN E O F C IIN E L E M E N T A R Y AND C N E N V IR O N M E N T A L A N A L Y SIS

by Zbigniew H. Kudzin* and Bogdan W aśkow ski

U n iversity o f Łódź, Institute o f C hem istry, 68 N a ru to w icza Sir., 9 1-360 Łódź, P o la n d

A review on the CHN analysis o f organic com pounds and the CN environmental analysis is described. The review contains outline o f the evolutionary developm ent o f elem entary analysis, since G ay-Lussac, Dumas and Liebig era until a present slate analysis, with computer controlled, fully automated analyzers. Physical principles o f high temperature and low temperature com bustions are discussed. Technical foundations on conjunctions o f the high temperature com bustion with chromatographic separations o f the ultimate com bustion products o f organic sam ples, is delineated. Com m ercially available elem ental analyzers are compared and their construction and operating principles are described. The basic m ethods o f determination o f environmental carbon and nitrogen are discussed. The representative analyzers for environmental carbon and nitrogen analysis are presented and their operating principles are described. K ey w ord s: elem entary analysis, simultaneous CH and CHN determ inations, high temperature com bustion, low temperature com bustion, com bustion products, gas chromatographic separation, thermal conductivity detection, infra-red detection, chem ilum iniscence deteciion, m icrocoulometric detection, elem ental analyzers, environmental analysis.

1. Outline of History of Elementary Analysis Development

A fast developm ent o f the organic chem istry in XX age was a result o f earlier accom plishm ents on ground o f elem entary analysis o f organic com pounds. T he first quantitative analysis o f organic com pounds (determ inations o f carbon and hydrogen) was elaborated by G ay-L ussac and Thenard, in 1805-1815 [ 1,2 ], The determ ination was carried oul in an apparatus an ideological schem e o f which is illustrated in Fig. 1.

Fig. 1. Ideological schem e o f apparatus to elementary analysis (C ,H ) o f organic com pounds by G ay-Lussac and Thenard:

i - com bustion tube; 2 - spirit lamp; 3 - pipe connecting the com bustion tube with calibrated cylinder; 4 - calibrated cylinder; 5 - dish with mercury; 6 - lock o f (he com bustion tube.

Analysis: a sam ple (S*: 1-5 g) was mixed with perchlorate, placed into the com bustion tube I , and heated for the full therm al-oxidative degradation (schem e 1) o f the com pound analyzed. The com bustion products - carbon dioxide, aqueous vapor, and derived from decom position o f perchlorate oxygen (schem e I), were collected in the graduated cylinder 4, sealed hydraulically by means o f m ercury.

KCIO,

S* (C H 2yOz) --- --- ► x CO, + y H20 + 0 2

Schem e 1

The analysis o f the gaseous com bustion products, was labor-consum ing and led to charged with considerable errors results.

T he m ethod o f analysis providing far more accurate results on the determ ination o f carbon and hydrogen was elaborated by Berzelius in 1814-1817 [3 8 5 1. The m ethod o f Berzelius, considered as the real creator o f the elem entary analysis, depended on "the com bustion” o f a substance sam ple on the way o f therm ally induced reaction with potassium chlorate and the sequent gravim etric determ ination o f form ed water steam (increase o f the mass o f w ater absorber charged with anhydrous calcium chloride) as well as carbon dioxide (increase of the mass o f carbon dioxide absorber, charged with potassium hydroxide).

Joseph L. G ay-L ussac (1 7 7 8 -1 8 5 0 ) Jean A. Dum as (1 8 0 9 -1 8 8 4 )

A considerable im provem ent o f the m ethod o f carbon and hydrogen determ ination, was achieved with the w ork o f Liebig, w ho in 1831 published the procedure differing fundam entally from m ethods o f G ay-L ussac - T henard and Berzelius. T he com bustions, Liebig carried out in an air atm osphere using copper oxide as the oxidant, in the apparatus schem atically presented in Fig. 2. In this, Liebig applied for the com bustion copper oxide (schem e 2), a new type o f the com bustion tube I , and to heating the coal perm issive on a zone heating furnace 3 [4,5],

CuO

S * (C xH2yOz) --- ► x CO, + y H20 Temperature

Schem e 2

A special shape o f the com bustion tube (situated horizontally and sealed on one end) perm itted after the com bustions to rinse the tube w ith an air-stream , in order to achieve the quantitative absorption o f the com bustion products in the absorbers 5 - for w ater vapor (determ ined gravim etrically) as well as the 6 - for carbon dioxide (determ ined alkacim etrically). An ideological schem e o f the apparatus o f Liebig is presented in Fig. 2.

s

H

L2J

l = t

Fig. 2. Ideological schem e o f the apparatus o f L iebig for determination o f carbon and hydrogen: i - com bustion tube; 2 - porcelain boat to placing mixture o f substance and oxidant; 3 - coal oven to zone heating; 4 - link; 5 - water vapor absorber (CaCI>); 6 - carbon d ioxide absorber (a ball absorber filled with solution o f potassium hydroxide); 7 - outlet o f the apparatus (connection with vacuum); 8 - end o f the com bustion tube, broken o ff after com bustion with aim o f washout o f the com bustion products passed in an air stream through absorbers.

T he apparatus o f Liebig, requiring for the analysis at least 0.2 g quantities o f analyzed substance, m ade possible the analysis o f new organic com pounds on m ass scale and played in the developm ent o f organic chem istry the significant part [385], The apparatus o f Liebig was applied w idely by many decades w ithout substantial principle changes.

Jons J. B erzelius (1 779-1848)

The m odifications, introduced successively concerned the construction o f a furnace for com bustions m ainly, the way o f heating o f the com bustion tube, and som e details, influencing, how ever, the precision o f determ ination. The essential m odification o f the apparatus o f Liebig was introduced in 1870 by Low e [10], w ho applied for com bustions the tube bipartitely open. The m ethod which introduction caused essential im provem ents in the CH determ ination, was elaborated by D ennstedt [17]. Dennsted carries out the com bustion in the tube

devoid o f solid oxidative fillings. T he com bustion was carried out in the oxygen atm osphere, in a presence o f the platinum catalyst (schem e 3).

0 2/ Pt

S * (CxH2yOz) — — --- x C 0 2 + y H 20 I emperature

Schem e 3

T he apparatus o f D ennstedt facilitated the sim ultaneous carbon and hydrogen determ ination, and additionally, m ade possible the determ inations of sulfur and halogens, which w ere im possible in the apparatus o f Liebig.

T he paradigm from the gram to m illigram scale in the elem entary analysis is ow ed to pioneer w orks o f Pregl, published in 1912-1916 [25,28] and aw arded by N obel’s prize in 1923.

Fritz Pregl (1 8 69-1930)

T he results o f w orks o f Pregl (the mass o f analyzed substance in a range 5-10 mg at error 0.3 %), consisted not only the largest achievem ent in the field ° f elem entary analysis from the tim e o f Liebig, but also a m ile-stone event in the history o f organic chem istry developm ent, especially in chem istry o f natural products.

In 1890, M essinger [15] elaborated depending on so called "wet com bustion” the m ethod o f analysis o f organic com pounds, w hich perm itted on the carbon determ ination in explosives as well as organom etallic com pounds and also salts, that is, the com pounds which com bustion on the “d ry ” way, was not Possible. T he m ethod o f M essinger, was based on the com bustion o f organic

substance occurring during heating in a mixture o f sulfuric and chrom ic acid. Because products o f the reaction contained carbon m onoxide (schem e 4), the re­ oxidation o f the form ed gas products was necessary, achieved by the passage through a layer o f glow ing-hot copper oxide.

In the m odifications made by Van Slyke and Folch [83,104,134,135], Me Cready and Hassidy [91], and also by Binkowski [271J, to "wet” com bustions, an addition of iodic and chrom ic acids into a m ixture o f sulfuric and phosphoric acids, were applied. Form ed quantitatively from the organic carbon o f the sam ple carbon dioxide, it was then determ ined m anom etrically [37,105], gravim etrically [91,109] or alkacim etrically [115],

H2C r 04 / H , S 04 C 02 + C O C uQ

5 0 - 2 0 0 °C Cr2( S 04 ) 3 + H , 0 5 0 0 -6 0 0 "C

co2

Schem e 4

Bobranski introduced in 1928 a speed com bustion autom atic regulation [43], preventing overheating o f the com busted substance, and so elim inating too quick evaporation or decom position o f the substance in the com bustion tube, the cause o f incom plete com bustions or explosions. In 1961, Ingram w orked out the method o f instant com bustion {flash com bustion) of organic com pounds, depending thereon, that an analyzed substance is mixed with an oxidant in a foil metal capsule (foil o f Al, Ag, Sn or Cu) and the capsule is introduced into the com bustion tube (situated perpendicularly) [206], D uring the com bustion, the m etallic capsule undergoes the oxidation, elevating considerably the com bustion tem perature (a few hundreds degree over tem perature o f the tube), which favours a quick and total com bustion of the substance.

The endeavor to im provem ent of the m ethods o f elem entary analysis, concerned tests o f render independent from the operator's manual predispositions analyze m ainly, in m ajority, in the direction o f autom ation. As a result, it was published in hundreds of works within the topic o f elem entary analysis, in this 1289 papers quoted in the handbook o f quantitative analysis of organic com pounds written by Bobrnski [385], and edited in 1979. More advanced m odifications depended on the utilization for heating o f a boat with com busted substance by means o f electric high-frequencies currents furnace [167], as well as further innovations applied in the com bustion control [193,198],

On special attention deserve the methods o f com bustion carried out in an em pty quartz tube at tem perature 800-1100 °C, with the speed o f the oxygen

stream - 10-lbld higher than in the classic m ethod of Pregl [385|, introduced in 1940-thies by B elcher [74-76] and Titov [82], as well as applied by another explorers [238,276], T he evolution o f construction o f the com bustion tube in the last two centuries was presented recently by Burns [4 6 5 1.

In addition to above described m ethods - called dynam ic and characterized by a continuous movem ent o f gases inside an apparatus during the com bustion, static m ethods were also introduced. In these, the com bustion is carried out in a closed space in an oxygen atm osphere and/or by means o f added to the substance some type o f oxygen donors (solid oxidants). An instant com bustion presents a special variant o f com bustion, introduced to m icroanalysis by Ingram [206], and adopted by other explorers [209,236,242, 260,287,347,4631.

In the m odification carried out by Koziow ski - called "ignition m ineralization” , the instant com bustion was applied, for m ixtures o f oxidant and analyzed substance [326,331]. In this case, the com bustion is partially and therefore obtained products of incom plete com bustion (CH.|, C O ) are necessary to convert quantitatively to carbon dioxide, prior to their final determ ination. This is achieved by the passage of formed fum es in a m ixture with oxygen, through layers o f oxidants and/or catalysts.

At present, the carbon determ ination in sam ples o f diverse origin, in these in chem ical substances, biological m aterials and/or in environm ental samples, can be achieved by the use of a wide spectrum o f com m ercially accessible carbon analyzers [440] and/or autom atic CHN analyzers [385,440],

The first m ethod o f the quantitative nitrogen determ ination in organic com pounds, was elaborated in 1831 by Dumas [3], and applied the com bustion o f m ixtures o f analyzed substances with copper oxide, inside the com bustion « ib e in a carbon dioxide atm osphere (schem e 5).

D um as placed in the com bustion tube a copper m etallic layer, reducing formed during com bustion nitrogen oxides to m olecular nitrogen, determ ined subsequently in an eudiom eter (azotom eter) filled with an aqueous solution of Potassium hydroxide (schem e 6 ).

s * (C xH 2vN O ) Tem perature C u O / CO x C 02 + y H 20 + z/2 N Schem e 5 m N O x C 02 + y H , 0 + x C 02 + y I I2 O + z/2 N Tem perature Schem e 6

Here, carbon dioxide underwent chem isorption; so a volum etric m easurem ent o f com ing into the azotom eter gas, afforded directly the volum e o f form ed in the com bustion nitrogen, and on this way the nitrogen content (schem e 7).

k o hui]

x C 0 2 + y H 20 + zn N2 --- ► z/2 N2

Schem e 7

The m ethod o f Dumas, after numerous m odifications and adaptations in centigram , m illigram and m icrogram (6,25,28,385) scales, constitutes to today the basic m ethod o f nitrogen determ ination in solid substances:

Kjeldahl, in 1883, described a straight line m ethod o f nitrogen determ ination in organic substances, depending on the m ineralization o f a sam ple by heating it in sulfuric acid [13], In process o f the m ineralization, the "organic nitrogen” underw ent to am m onium sulfate quantitative conversion, follow ed by the determ ination o f ammonia, usually after its release by alkalization.

Kirsten, in 1946, introduced the com bustion in a quartz tube at tem perature 1050 UC [107]. To oxygenation o f organic com pounds he applied nickelous oxide (NiO), m eanw hile nickel to the reduction o f nitrogen oxides instead o f m etallic copper was used [123,124], Schoniger introduced dry com bustion o f organic sam ples in an oxygen atm osphere and in the presence of platinum catalyst [164,176,192], FijSC), --- ► BaS( ) 4 HNOj S * --- --- ► ^ ---► 2 X -T > 1 0 0 °C h 3p o 4 --- (N H ,),P04(M 0 3)12 Schem e 8

Carius, in 1860-1865, introduced a classic m ethod o f determ ination o f sulfur [7], halogens (Cl2, Br2, I2) as well as phosphorus [9], He carried out the m ineralization by heating ot sam ples in a concentrated nitrogenous acid under elevated pressure (sealed ampoule).

T he m icroanalytical m odifications o f C arius procedure, accom plished by Emich and Donau [21], as well as others |385], find the use to nowadays (schem e 8).

B aubigny and C havanne [19] worked out the m ethod o f m ineralization o f halogeno-organic com pounds in a m ixture o f concentrated sulfuric and chrom ic acids, Volhard 1111 applied the fusion o f analyzed substances in m ixtures with sodium carbonate and potassium nitrate, Pringsheim 12 0 1 in sodium peroxide. Kekule | 8 | halogen splintered o ff in result o f the reduction with soda am algam . T he num erous m odifications of above m entioned m ethods (79,118,158], as well as the present m ethods o f determ ination o f sulfur, phosphorus and halogens, were discussed in the review work o f Bobranski [385],

T he first m ethod of oxygen determ ination was published in 1922, by ter M eulen [33]. It applied a prelim inary pyrolysis o f analyzed com pounds carried out in a quartz com bustion lube (schem e 9).

S * (C xH ,y N , O m) ---► x ( C 02 + C O ) + y H 20 + z N O ,, T em p eratu re

Schem e 9

O xygen containing gas products o f pyrolysis - C 0 2 and CO, was subject to further reduction to water, determ ined gravim etrically (schem e 10).

H2 / N i

x ( C 02 + C O ) + y H 2O + z N O ,, ---1--- m H 20 + z/2 N2

3 0 0 ° C Schem e 1 0

In the procedure published by Schutze, - organic substance is subject to a prelim inary pyrolysis in an nitrogen atm osphere (void o f oxygen) [72], The pyrolysis products ( C 0 2 and CO) are passed over carbon glow ing-hot to bright reddens, w hat causes full reduction of carbon dioxide to carbon m onoxide (schem e 11).

C / N j

x ( C O , + C O ) + y 1 -1 ,0 + z N O „ ---1---*► m C O + z/2 N ,

1000°C

Schem e 1 1

T he form ed carbon oxide, treated with iodic anhydride, released stoichiom etrically iodine (schem e 12), subsequently determ ined by the iodom etric titration [132].

i2o 5

5 C O --- ► l2 + 5 C O 2

Schem e 12

D ifferent m odifications o f this m ethod function to today; the introduction o f the physical m ethods to quantitative determ ination o f carbon oxide form ed (G C -IR, G C -TC D ) perm it considerable shortening o f the method as well as its considerable autom ation [278,380,385,405,409,440],

During the past two centuries the elem entary analysis passed a huge evolution. W hen as 150 years ago were the need, according from a qualitative com position, from 1 to 5 g o f the analyzed substance [1-10], at present, applying the m icrom ethods the quantity of milligram and even m icrogram range is sufficient [51,84,126,144,241,267,293,311,312,317,339,354,372,385,441,473],

The endeavour to econom ization o f the analytical process, dictated with growth o f dem and on elem entary analysis determ ination im plied the research developm ent over m odification o f earlier worked out procedures in direction of shortening o f the time o f analysis. Since most time consum e gravim etric determ inations o f com bustion products, it was tried to cut down these parts of an analytic process by the replacem ent o f weighing o f absorptive apparatuses by certain physical m easurem ents, perm issive on determ ination o f C 0 2, H20 w hether N 2, directly or indirectly in the com bustion products. T he elem entary analysis, dom inated by usage o f the com m ercially accessible analyzers at present, pursuant the m ajority o f analytic actions autom atically, and so w ithout the experim enter who stays only w eighing substance's part [399,410], periodical tests o f the apparatus, as well as an interpretation o f the results. The exactitude o f results increased also, so that the average error o f m icroanalytical determ inations does not exceed ± 0.2 %.

At the beginning of I960., the elem entary analysis becom es united with gas chrom atography [196,202,209,229,232], what stim ulated a dynam ic developm ent o f constructed analyzers' autom ation, illustrated by the expanding scope ot available analytical configurations, nam ely starting from the CH, through CHN, C H N O and/or CHNOS [183,256,273,281,282,284,299,304,305, 312-314,317,321,337,354,360]. In 1970., elem entary analysis was conjuncted with com puter processing m ethods [329,330,344], An im portance of this application increased successively in next decades [498],

T he progress in the field o f elem entary analysis [151,177,186,192,339, 340,362,385,405,517,571] constitutes one of the m ost effective factors, influenced the present developm ent o f organic chem istry. T he m illigram or centigram range m ethods oi elem entary analysis pushed out the m acro-chem ical m ethods, m aking possible shortening oi the time of analysis, m ore rational

handling with the determ ined substances as well as chem ical reagents, and also on the analyst's m ore convenient and m ore safe work.

A lthough introduction to the organic chem istry research a mass spectroscopy technique 1297,407,464, 467,492,515,518,520,523,539,557,5781 makes possible the settlem ent o f the m olecular form ula o f analyzed com pound, and also the isotopic ratio o f carbon and nitrogen atom s, the exact m easurem ent of m olecular ion mass does not replace the elem entary analysis [557], Induced, from second side, the utilization o f the laser spectroscopy perm its on a settlem ent o f the C : H : N atom s ratios [5681.

These techniques, however, do not deliver sufficient inform ation, relating to a chem ical purity of com pounds analyzed. In contrary, the result of elem entary analysis state both the purity degree o f com pound, as and the test of m olecular mass. Therefore elem entary analysis keeps fully its im portance in organic chem istry.

2. Elementary Analysis of Carbon, Hydrogen and Nitrogen

D eterm ination o f carbon, hydrogen and nitrogen (CH N ) belong to the most im portant signs of elem entary analysis. The analytical procedures applied for these determ inations underw ent the evolution from G ay-Lussac, Dumas and Liebig era. This is reflected by their continuous developm ent, across the determ inations o f carbon and hydrogen (CH) as well as the nitrogen (N), across sim ultaneous determ inations o f carbon, hydrogen and nitrogen (CH N ) and since two decades the sim ultaneous determ inations of carbon, hydrogen, nitrogen, sulfur and oxygen (CHNSO).

2.1. Determination o f Carbon and Hydrogen

B eginning from the classic works o f Gay - Lussac, Liebig and Pregl - the CH analysis applied the com bustion the organic substance to carbon dioxide and w ater (schem e 1-3) and subsequent determ ination o f these com ponents. The

sine quanon requirem ent o f correct CH analysis was assurance o f the

quantitative course o f both stages o f the analytic procedure applied. 2.1.1. Combustion Process of Organic Compounds

The com bustion o f organic substance can be perform ed using one o f the following variants:

b. the com bustion in an atm osphere of oxygen in the presence o f a catalyst (Pt);

c. the com bustion carried out by m eans o f solid oxidant in the presence o f oxygen;

d. the com bustion in an atm osphere of oxygen at tem perature 1000 “C. Kainz and Horvatish [211,213,214) revealed that the oxidative activity of different solid oxidants applied for the com bustion in the oxygenic atm osphere is different than exhibited in the anaerobic atm osphere. And so, in the atm osphere o f oxygen the efficiency o f oxygenation o f representative oxidants changes in follow ing order:

Pd / 0 2 > C 03O4 > M n 0 2 > Pt / 0 2 > Ni / 0 2 > CuO > C r20 3 > Fe20;, > M n20 3 > C e 0 2 > ZnO > WO., > S i0 2

The lowest tem perature o f oxidation activity o f solid oxidants depends on a kind o f oxide, and carries out 345 °C for C 03O4; 410 °C for M n 0 2; and 445 °C for C uO [199],

The list o f representative solid oxidants applied in the com bustion analysis is given in Table 1. T he com parison and profile o f physico-chem ical proprieties o f various metal oxides applied in the elem entary-com bustion analysis (Cu, Co, Mn, Ni, Mg, Ag i Pb) was presented by Kirsten [239J. Kainz and Horvatish [199] as well as Vecera [315] introduced to the elem entary analysis mixed catalysts (CuO + Cr20 3; CuO + C o ^0 4; C uO + Ag; C o 3 0 4 + asbestos).

Table 1. Representative oxidants applied in combustion analysis.

No O x id a n t“’1' P rod u cts o f com b u stion '1'1 A n aly

-sis L iteratu re

1 KClOj S* + KCIO., — KCI + C 0 2+ H 20 S* + KCIOi -> KCI + C 0 2+ H20 + NO*

CH N

1

276

2 CuO S* + CuO — Cu20 + C 02 + H 20 S* + CuO — Cu20 + C 02 + H20 + N O z CH N 2,28,43,185 179,277 3 CuO + KClOj

S* + CuO + KCIO3 — Cu20 + KCI + C 02 + HjO + N O z N 276 4 CuO + V 2 O 5 S* + 2 CuO + V205 - * Cu20 + V20 , + C 02 + h2o S* + 2 CuO + V20 , — Cu20 + V2Ot + C O , + H20 + N O , CH N 2 0 13

5 CuO + C e 02 + P bC r04

S* + CuO + C e 02 + PbCrO., — Cu20 + C e20 , + PbO + Cr2Oj + C( ) 2 + HjC) CH 70 6 _{CuO +} M (O A c), S* + CuO + M (O A c) 2 - * M 20 + C 02 + h 2o + N O , N 6 6 7 8

M nOj S* + MnOj — MnO + C 02 + l l 2() S* + M nO: — MnO + C 02 + H20 + N O , CH N 28 35,65 A gM nO i S* + A g M n 04 —» A g 20 + Mn207 —* A g 20 + MnO + C 02 + H jO + N O , S* + A g M n 04 —► A g 20 + Mn207 —* A g 20 + MnO + C 02 + 1I20 + NO,.

S* + A g M n 04 —► A g 20 + Mn207 —► A g 20 + MnO + C 02 + H 20 + N O , CH N CHN 160-162,173, 175,326,343, 352 99,100,107 581 9 M nO i + S i 02 + K2Cr207 S* + K2Cr207 + M n 02 + S i 0 2 -> M n S iO ,+ Cr2O i + C 02 + H 20 + N O , CHN 461 1 0 _{M nO i +} A g 20 + infusorial earth S* + M n 02 + A g 20 —* MnO + A g 20 + C 02 + H 20 + N O , CHN 279,293 11

v2o.

s*

v2o5

v2o ,

c o 2

v2o,+ c o 2

n2o

H2Q

17 C o ,0 , S* + C o , 04 — CoO + C 02 + H 20 S* + C0 3O4 — CoO + C 02 + H20 + N O , S* + C o . A -* CoO + C 02 + II20 + N O , CH N CHN 23,9 6 ,1 8 4 ,1 8 5 , 187,236,243, 245 169-172,194, 220, 264,397, 400,406,581 201,382 18 C0 1O4 + Al + Fe20 , S* + C o ,04 —* CoO + c o2 + h 2o + n o , 2 Al + F e ,0 , —► 2 Fe + A120 , N 4 2 9 ,5 8 0 19 Pt + 02 S* + 02- * C 02+ H 20 s * + o2 — c o2 + H20 + NO., S* + 02 -> C 02 + H 20 + N O , CH N CHN 17,167,214, 227, 308,237 356 582 2 0 0 2 s * + o 2 -> c o2 + h 2o S* + 02 — C 02 + H20 + N O , S* + 02 -H. C 02 + H 20 + N O , CH N CHN 22,53 ,1 0 8 ,1 1 3 , 119,238 249,267,277 250,331 2 1 W O , s * + w o , — w2o , + c o2 + h 2o S* + w o , — W jOj + c o2 + h 2o + N O , CH CHN 206 582 2 2 W O ,+ A g2S 03 S* + w o , - * A gW0 2 + C0 2 + H20 + N O , CHN 311 23 A g2W 04 + A g 20 S* + A g2W 04 + A g20 — A g W 02 + A g20 + C 02 + h2o + CH 262 24 M n 02 + W O , + S i 02 + Cr203 S* + W O3 + M n 02 + S i 02 + Cr20 , —► M nSiO , + w 20, + C 0 2 + H 20 + N O , CHN 386

“ M - Cu or Hg; AcO - acetate. b S* - analyzed sample. cN O , were subsequently reduced into N 3.

Particularly interesting m ethods were introduced by M arek and based on the com bustion o f substance in a quartz tube without solid oxidants [22 ], developed subsequently by Bennett [113], Belcher and Ingram [119], and others [385]. The oxygen balance occurring during com bustion o f organic sam ples containing carbon, hydrogen and oxygen was investigated by Rezl [448],

Utilization o f gaseous oxygen to the com bustion, involved the requirem ent o f careful purification o f the applied gas from any organic substances (passing over layers CuO, C o ,0 4 or Korbl catalyst [98]), and also its desiccation and decarbonization [385],

During the com bustion o f organic containing-nitrogen, sulfur, phosphorus and halogens substance the form ed undesired products o f these

elem ents oxidation - lias to be rem oved from the com bustion products com position (by absorption on corresponding reactive filling o f the tube). Thus, halogens and sulfur oxides are caught quantitatively on a silver gauze, situated in the term inal part o f the com bustion lube and warmed to tem perature o f 400-500 °C [71,79,118,156]. A nother effective halogen and sulphur scavenger are Ag as well as Ag2W 0 4 (em bedded on Chrom osorb) [262[ or Ag /A120 3 [288J.

Particularly large com plications accom pany the com bustion o f organic, fluorine-containing substances. This results from large durability of the C-F bond, and also from poor com bustibility of this type o f com pounds. From other side, the products o f com bustion of fluorine-containing com pounds react with quartz form ing volatile silicon fluorides (SiF.() and by this way shorten the lime of use o f the com bustion tube; and also overstating carbon determ ination data (reaction with C 0 2 absorbents) [125].

A removal o f fluorine from com bustion gases was achieved by application o f M gO [148,149,174,275,280], P b ,0 4 11811, C e 0 2 [289], A g V 0 3 [255,327], M n 0 2 [244), or granulated NaF [203,346]. Pechanec for absorption of HF applied A g2C 0 3 and P b C 0 3 (500 UC) [257],

D uring the com bustion of phosphorus-containing com pounds one need the neutralization o f phosphorus oxides during com bustion form ed. For this porpoise, according to Kasler, MgO is suitable perfectly [275], Kozłowski and co. [342] determ ined the phosphorus oxides binding value exhibited by series o f sorbents, in these, various metals and their oxides. These, in tem perature o f 750- 900 UC w ere changed in the follow ing order:

M gO > Ag > A gM n04 > M n 0 2 ~ Ni > A120 3 > C e 0 2 > C uO > C o30 4 > W 0 3 > S i 0 2

A ccording to Binkowski and Gizinski [364,369,392], the ability to bond phosphorus oxides exhibited by various reagents (com ponents o f reactive fillings of the com bustion tube) is in accordance with the follow ing row:

Ag—pum ice > Ag—M n 0 2 > M n 0 2 > ZnO > C o30 4 > asbestos > pum ice > A g - A l 20 3 > Z r 0 2 > A l- S i > A120 3 > M gO > CuO > C e 0 2 > Si > W 0 3

On the ground o f these investigations Giziński and W aśkow ski worked out the com position o f a reactive filling neutralizing effectively phosphorus oxides in products o f com bustion o f different phosphorus-containing com pounds [423],

The largest difficulties in the carbon determ ination appear in the case o f analysis o f nitrogen-containing com pounds with regard to the form ation of nitrogen oxides (N -> N O z), overstating the carbon determ inations. These nitrogen oxides can be rem oved from com bustion gases, by the 1 eduction or by chemical ligature with the help o f suitable binding substances. C hronologically,

the first used nitrogen oxides reducer was m etallic copper, originally applied by Gay - Lussac [1,2] and Dumas [3], as and by other explorers [34,55,60,113,121, 139,172,210,263], From other effective nitrogen oxides scavengers were applied: Ag [385], Ni [159], C e 0 2 [86,89], M n 0 2 [116,144,172,326,343], PbO [284] as well as very frequently P b 0 2 [12,25,28,215,225-227],

Lead dioxide reacts with nitrogen oxides already at a tem perature o f 180-200 °C, binding it quantitatively in the form o f lead (II) nitrate (schem e 13),

NO ---► PbO + N 0 2 N O P b O , ---— N 0 2 --- -— ► P b ( N 0 3) , Schem e 13

It was found, that som e substances, for instance hopcalites (hopcalite I: M n 0 2—CuO—C o2O r~ A g 20 ; hopcalite II: M n 0 2—CuO) bind nitrogen oxides already at a room tem perature. For their removal liquid absorbing solutions were also applied [385], Detailed investigations on the nitrogen oxides absorption by application o f a large num ber of various substances were undertaken by Kainz and Zidek [2 6 8 1.

The com position o f representative reactive fillings o f com bustion analysis for the analysis o f carbon and hydrogen (CH), nitrogen (N), and carbon, hydrogen and nitrogen (CHN), is presented in Table 2.

Table 2. Representative reactive fillin gs applied in elementary analysis.

N o A n a ly ­ sis

C o m b u stio n

co n d itio n s C om b u stion tub e rea ctiv e fillin gs

L itera tu re /A n a ly zer 1 CH S * b + A g2W 0 4b + A g2O b + 02 (10 0 0 °C) S i 02-A g20 - A g2WO4-M g 0 -A g2W 0 j- A g20 - S i 02 (8 0 0 °C) 254 2 CH S * + Ptb + 0 2c (1 0 5 0 °C) Pt-Cu-Ag (8 6 0 -8 8 0 °C); Cu (500 °C) 308 3 CH (NPSO X) S * + S i 0 2b + 0 2d Pt-CuO-Ag (700 °C); P b 0 2- A g ( I 9 0 UC) 167 4 CH S *+ A la + V205 + 0 2c (A g M n 0 4)f (8 0 0 °C) S i 02- C o ,04 + S i 02- S i 02 (8 0 0 °C); A g M n O / (500 " Q 3 26,343

5 CH S* + Sn" + 02 (1 0 0 0 °C) Ag (5 0 0 °C); M n 02 (20 °C) 242,2 6 0 6 N S *+ Ptb+ 0 2 (9 0 0 °C ) C o j 04 (7 5 0 BC); H j/BTA (5 0 0 °C ) 356 7 N S* + CuO + C 02 (7 0 0 HC) CuO-Cu (700 °C); CuO (2 0 0 -3 0 0 “C) 385 8 N S* + Ptb + NiO + COi (1 0 5 0 ° C ) NiO-Ni (1 0 0 0 “C); hopcalite (1 0 0 -1 5 0 UC) 107,123,141

9 N S* + AI" (or Sn ") CuO + 02 (10 5 0 °C) S i 02-C u 0 -A g (950 °C); A g-tC uO + S i 0 2|-[Cu + S i 02]-[C u 0 + S i 0 2)-Ag (500 °C) Heraus Rapid N 1 0 N S* + AI" + C o ,04 (1 0 5 0 UC) Cu (800 °C)-CuO (5 5 0 °C )-A g (250 °C) 397,581 11 CHN S* + A lh + He (1050 UC) CuO (1050 °C); Cu (500 °C) HP 185 1 2 CHN S* + A g “ + He + 0 2d (1 0 5 0 °C) C uO -A g-M gO (8 5 0 °C); Cu (5 0 0 °C); S i 02 (200 °C) Technicon 13 CHN S* + A g1’ + C0 3O4 + He + 02 (900 °C)

Pt-A g2W 04(M g 0 )-A g20 - A g2W 0 4-A g (900 °C); Cu (500 °C) PE 240 14 CHN S* + A1“ + V205 + He + 0 2c (1 0 5 0 UC) Cr20 .r C o30 4-A g (10 5 0 °C); Cu-CuO- Cu (640 °C) C E m 1104 15 O S* + Ag" + He (1 0 0 0 °C) C-Ni-Pt (10 0 0 °C) CE in 1104 16 CH NS S* + Sn“ + He + 0 2c (9 0 0 °C)

Oxido-reductive catalysts (900 °C) 8 Flash 1112 EA 17 O S* + Sna + He (1 0 0 0 °C) Ni-C (900 °C) Flash 1112 EA 18 CHN S* + AIJ+ AgMnOV + 03 + He (8 0 0 °C) A g2W 04-Z r 02-M n 0 (6 0 0 °C) 455 19 CHN S *+ A lu+ A g M n 0 4' + Cr20 3 + H e (8 0 0 UC) Pt-Cu0 -C0 30 4-Cu0 (6 0 0 °C) 393 2 0 N S *+ H2S 04 + H2C r 04 (2 0 -2 0 0 °C) CuO-A g (500 °C) 3 81,421,422, 443,444

“ M etallic capsule. b Boat. c Injection o f a determined oxygen amount. d Air. c O xygen (3%) in a helium carrier gas. 1 Product o f decom position in 500 °C. 1 As result ot metallic capsule combustion (Sn) the temperature locally increased to 1800 °C.

The investigations over suppression o f nitrogen oxides form ation accom panied by catalytic com bustions of nitrogen-containing com pounds, were conducted by Pechanec [290,291,302,303],

O btained ultim ate com bustion products, namely w ater and carbon dioxide - w ere determ ined subsequently; gravim etrically using a selective chem isorption/absorption ( C 0 2 on lim e-soda and/or ascarite) and/or water (C a S 0 4, M g(C 104)2, C oC l2), and also gasom etrically and/or volum etrically [385 J. Presently, in an endeavor to autom ation o f analytic process, frequently are applied electrochem ical methods, in this coulom etric and conductom etric methods, also the therm al conductom etric (TCD) and infra-red based detection (IRD) [385, T able 8 ] methods.

A representative exam ple o f the volum etric m icro-m ethod o f hydrogen determ ination presents the method elaborated by L indner 132,38,49,50,64J. This m ethod is based on the reaction o f hydrolysis of not volatile 1 -napthy 1- dichlorophosphine oxide, generating hydrogen chloride. The passage o f the com bustion gases by series-connected washers filled with w ater (absorption o f HC1) and baryta w ater (absorption o f C 0 2), perm its volum etric determ ination o f both com ponents (schem e 14).

S*

Schem e 14

Num erous exam ples o f the volum etric determ inations o f carbon and hydrogen were discussed in the review work o f Bobranski [385],

T he exact results were possible to get by applying the conductom etric m ethod o f C ain [29], basing on a decrease o f electrochem ical conductivity of absorption solution occurring in result o f the absorption o f carbon dioxide, involving the reaction course:

2 HO + C 0 2 —> C O 3* + H20

Schem e 15

The conductom etric m ethod was successfully applied in several works [194,197,198,200, 228,240,251,258,310], Accurate results o f carbon dioxide determ ination were obtained also applying the coulom etric-alkacim etric [233,310,324,332,351] or potentiom etric [435] titrations. T he w ater content was

determ ined, by utilization o f a Keidel hygrom eter [189,207,235] o r the reagent o f F ischer ( K-F reagent) [61 ].

H20 + l2 + S 0 2 + 3 Py - » 2 Py x HI + Py xSO .,

Schem e 16

The reaction o f w ater with the K-F reagent runs with a stoichiom etric consum ption o f iodine, in accordance with the presented equation (schem e 16) [73], The subsequent water determ ination can be perform ed on the way of coulom etric regeneration (oxidation) o f consum ed in the reaction iodine (schem e

17) [190],

21' - » I2 + 2e

Schem e 17

Q uick determ ination o f C 0 2 is possible by application o f infra-red absorbance based detectors (1RD) [216,269,337,385] as well thermal conductom etric detectors (TCD) [222,240,280,385,388,419, T able 8].

The apparatus o f Libieg-Pregl for determ inations o f carbon and hydrogen, underw ent constant m odifications directed on a grow th o f precision o f signs, a decrease o f the mass of analyzed sam ple as well as shortening o f the time o f analysis and its sim plification, which was possible to reach by continuous developm ent o f autom ation. The representative CH analyzers, applied in the period preceding appearance of trade autom atic analyzers, in this number: the analyzers o f Bobranski [167], Gustin and H oim an [254], the apparatus o f Binkowski [308] as well as Kozlowski [326,352], reflect the increasing level o f autom ation.

The principle o f w orking o f apparatus for carbon and hydrogen determ ination (CH) according to Binkowski, the representative for its period, is presented in Fig. 3.

A nalysis according to Binkowski:

An analyzed sam ple (3 mg) is placed in the boat I into the com bustion tube 2 o f the apparatus (Fig. 3), and burns up in an air stream , carefully cleaned by a prior passage through the purifying gas system 9-13. Thi s consists ol the dryer 9, the oxidation tube JO and its furnace JT, and the absorbers 12 (ascarite) and J 3 (anhydrone). The products of com bustion (in m ajority consisted o f CO, C 0 2, N O z and H20 in a m ixture with air) are transferred in the air stream through C uO and Ag layers (warmed to temp. 800-880 °C), then through a copper layer (w arm ed to tem perature 500 C) and subjected to luilhet specific absorption: the w ater in the absorber 7 (tilled with anhydrone) and the carbon

dioxide in the absorber 6 (filled with ascarite), respectively. The content of carbon and hydrogen in the com busted sam ple was counted on the basis o f mass increases o f the corresponding absorbers (6 and/or 7 ).

Fig. 3. Schem e o f working o f the apparatus for determination o f carbon and hydrogen on m illigram scale, according to Binkowski [308]:

i - porcelain boat; 2 - com bustion tube; 3 - electric m ovable furnace (1 0 5 0 -1 0 7 0 °C); 4 - electric furnace (8 6 0 -8 8 0 °C); 5 - reduction tube (Cu); 6 - reduction tube electric furnace (500 °C); 7 - water absorption pipe (anhydrone); 8 - carbon dioxide absorption pipe (ascarite); 9-J3 - cleaning system for applied air [9 - dryer (conc. H2S 0 4), 10 - oxidation tube for air (CuO), J 1 - electric furnace (8 0 0 °C), 12 - absorber (anhydrone), 13 - absorber (ascarite)]; 14 - valves.

C hem ical transform ations, occurring during this com bustion analysis, are illustrated in schem e 18.

CO + CO 2 C 02 c o O , / C u O + CuO /A g + + 2 — *--- ► H , 0 --- H o Cu , „ _ Ron ° r ^ HjO + suu L + 500 "C + N O z N O ?_ + N2 N , S chem e 18

2.1.2. Carbon Determination by Wet Combustion Method

D espite advantages ot a dry com bustion m ethod, the com bustion of som e organic substances are accom panied by serious difficulties. Exam ples o f these are explosives, exacting o f a special conduct application. Also, the com bustion o f sam ples bearing alkaline and alkaline-earth elem ents, requires the

com plicating the analytic procedure modifications. M oreover the com bustion o f organom etallics including As, Sb, Hi, B or Ta, causes a durable dam age o f the tube or deactivation o f the tube reactive fillings. In such cases, the carbon determ ination by the com bustion carried out in a solution, so called “w et” com bustion, introduced to elem entary analysis by M essiner [151 presents a more profitable option.

M essinger oxidized by heating organic substance in a m ixture o f sulfuric and chrom ic acids. The carbon m onoxide forming as a result o f the reaction (schem e 19), is oxidized further to dioxide by a passage through the tube containing a glow ing-hot copper oxide. The method o f M essinger, being the conjunction o f technique of com bustion on wet (in solution in H2S 0 4) and on dry (in gas phase), in the original version o f procedure [15], or in its m odifications [16,42,44,48,54, 56,68], required therefore a rather enough com plicated apparatus.

Schem e 19 H2Cr04/H2S 04 5 0 - 200 “C c o 2 + CO HlOj/HjCrO^/H-jSOj/HjPOj 50-200 UC CuO 500-600 “C CO, CO,

An essential im provem ent, which perm itted the om ission o f additional oxidation by the dry m ethod, was the m odification, carried out by van Slyke and Folch, based on application o f the mixture o f chrom ic and iodic acid as oxidative reagents in an anhydrous solution (m ixture o f smoky sulfuric and phosphoric acids). This reagent perm its quantitative com bustions of the organic carbon to carbon dioxide, w ithout need o f additional oxidation (CO —► C 0 2) carried out in earlier versions in gas phase, in order to full conversion to dioxide. The form ed carbon dioxide was determ ined subsequently m anom etrically [37,104], gravim etrically [91,109] or alkacim etrically [115].

W ide usage o f Van S lyke’s method disclosed its num erous lim itations. Ihus, the analysis o f substance containing a high carbon contents (anthracene, cam phor) usually leads to understated results o f carbon content with errors exceeding 1%. M ethod is not suitable either to analysis o f com pounds insoluble >n the Van S ly k e’s reagent, and also for volatile and/or subjected degradations to volatile derivatives com pounds (com pounds including N -m ethyl group, aryl halides, organophosphorus com pounds) [385], In the m odification introduced by Minkowski [234], the method was adapted to determ inations in the m illigram

scale, expanding also a range o f its applicability. Ideological schem e o f the apparatus applied by Binkowski for carbon determ ination by the wet com bustion m ethod, is presented in Fig. 4.

Fig. 4. Schem e o f an apparatus for carbon wet determination in m illigram scale, according to the method o f Binkow ski [234]:

1 - m ineralization flask; 2 - condenser; 3 - bubbles-meter; 4 - gas drainage (filled with layers: asbestos, anhydrone, copper wire and particles o f zinc); 5 - absorptive tube (ascarite); 6 - cutting o ff bolts; 7 - inlet and outlet o f cleaned air; 8 - inlet and outlet o f water o f the condenser.

A nalysis according to Binkowski 12341:

An analyzed substance (3-10 mg) is placed into the round bottom flask i , follow ed by addition o f K I0 3 (0.4 g), and after rinsing o f the apparatus with an air stream (dried and devoid o f C 0 2) and checking of its tightness, the oxidative reagent [5 ml; m ixture o f K I0 3 (5 g), C r 0 3 (25 g), H3P 0 4 (85% ; 167 ml) and oleum (20% ; 333 ml) heated in 150 °C to hom ogenization] is added. The flask is heated with a m icroburner up to the decom position o f K 1 03, controlling the speed o f process with the help o f the bubble-m eter 3 (8-10 ml / min). After com bustion o f the substance (about 20 min), the apparatus is rinsed with a stream o f air, (20 m l/m in), in order to washout the w hole quantity o f produced C 0 2 (20 min). T he form ed gas m ixture is passed through the drying pipe 5 (rem oval o f w ater vapor and volatile acids) and then through the absorptive pipe 6 , w here the quantitative absorption o f C 0 2, subsequently determ ined gravim etrically, occurs. The carbon content was counted on the ground o f the increase o f mass o f the absorber 6 , after deduction o f the background (0.1 to 0.15 mg). T he tim e o f analysis: ca. 40 min.

Other, present m ethods o f analysis of the carbon content in organic substances, as and in environm ental samples (OC, TC, TO C , TIC ) using the wet- com bustion m ethod o f m ineralization (in solution), are discussed in the chapter 4.1.

2.2. Determination of Nitrogen

D eterm ination o f nitrogen in nitrogen-containing organic com pounds can be achieved after prelim inary degradation (m ineralization) to sim ple nitrogenous inorganic com pounds, in these am m onia, m olecular nitrogen, nitrogen oxides (NO or N 0 2) or to ions o f nitric acid (NOV and / or N 0 3 ).

T he degradation was usually carried out according to three fundam ental methods: the m ethod o f Dumas, the method o f Kjeldahl as well as the m ethod of catalytic hydrogenation.

In the classic m ethod o f Dumas, the organic substance is mixed with copper oxide (CuO ) and it burned in the com bustion tube in a carbon dioxide atm osphere [3]. T he formed com bustion products ( C 0 2, H20 and N O z) are passed through a glow ing-hot copper layer; where nitrogen oxides are reduced into m olecular nitrogen, and the obtained m ixture o f transform ed products o f the com bustion ( C 0 2, H20 and N2) is directed to the azotom eter. Here in a solution o f KOH, carbon dioxide underw ent quantitative absorption, and due to this, the measured volum e corresponded to formed nitrogen (schem e 2 0 ).

n C 02 n C 02 + C it + K O H S * (c „H mN yO x) C u Q - y N O , --- -- y/2N2 ---— y/2 N2 ■f* 4" m/2 H20 m/2 H 20 Schem e 2 0

In the present m odifications ot Dumas m ethod, the iorm ed products ol com bustion ( C 0 2) H20 , N O , w hether N2) are subject to an autom atic analysis. During this, the com bustion products are separated chrom atographically with subsequent post-colum n instrum ental determ ination, using usually thermal conductom etric detectors [TCD] ( C 0 2, H20 , N2) [385,572, T able 8] and/or infra­ red detectors [1RDJ ( C 0 2, H20 ) [385,572, Table 8], and/or chem ilum iniscence detectors [CLD] (N O z) [436,440, 483,484,489,502],

In K jeldahl’s m ethod [13], the organic substance is m ineralized by 'vanning in a solution o f concentrated sulfuric acid, during which the oiganic nitrogen (TO N - total organic nitrogen-, TBN - total bound nitrogen) converts into am m onium sullate. T he formed solution is alkalized, and ieleased am m onia *s determ ined in a separate flask, most often by m eans ol the alkacim etiic titration (schem e 21).

n co2

In the m ethod o f catalytic hydrogenation, the organic substance was heated in a stream o f hydrogen in the presence o f suitable m etallic catalysts, causing the reduction o f organic nitrogen (nitrogen bounded) to am m onia [80,1201, determ ined further by titration (schem e 2 2 ).

*C„Hn,2 H ,/ C a t ./H ,0 + S* ( C H N O ) _ 2 --- 2_ _ ^ y T > 3 1 0 "C + z H , 0 Schem e 22

The num erous m odifications o f Dumas and K jeldahFs m ethods were the subject o f several reports [246,316, & 2.2.1., & 2.2.2.J as well as the experim ental com parison o f their analytic param eters [373,437,480,487,507, 526,566,577,579],

In other, so called "wet ” degradative procedures (schem e 23), the m ineralization o f nitrogenous com pounds were carried out on the way of UV- photo-oxidation (U V / K2S2OK/H2O) [484, Table 11], dichrom ate oxidation (H2S0 4 /K 2C r207) [516, Table 11], or with m icrow aves-induced m ineralization [434,437,456,466,528,529, Table 11], n C O 2 0 x i d a n t / H ,0 + S * ( C nH mN yO x) --- ?--- ^ y N O / T < 100 °C + m/2 H’® Schem e 23

Created as a result o f the oxidative degradation (photo-oxidation or m icrow ave-prom oted oxidation) o f organic substance - the ions o f nitric (III and/or V) acids, were determ ined spectro-photom etrically [494,501,555] or electrochem ically [526].

An interesting method o f the nitrogen determ ination by the “w et” oxidative degradation, follow ed by subsequent reduction o f nitrogen oxides

form ed to m olecular nitrogen, and its final TCD determ ination was presented by V entura [381,421,443,444].

Several m ethods o f nitrogen determ ination applied radiochem ical procedures [286,370,371,436,475,539,561,5671, mass spectroscopy (407,464, 523,578] or other physico-chem ical m ethods [479,538,574],

2.2.1. Determination of Nitrogen by the Method of Dumas

The first, m illigram scale method o f nitrogen determ ination, based on Dumas procedure, cam e into being thanks to Pregl works [25]. And here, sim ilarly as in the case o f the CH determ ination, a decrease o f the substance analyzed quantity disclosed many im perfections o f D um as apparatus.

T he investigations carried out by Pregl exhibited, that copper used for the reduction o f nitrogen oxides, at a tem perature 650 °C reduced also carbon dioxide to m onoxide - unsolvable in an solution absorbing o f the azotom eter, and therethrough elevating the results of nitrogen determ ination. T o prevent this, Pregl introduced to D um as com bustion tube a third layer, folded from copper oxide, the task o f which was the conversion of carbon oxide to dioxide (Fig. 5).

CuO Cu CuO Cu CuO

(a)

Fig, 5. Profile o f distribution o f reactive filling layers o f the com bustion tube: (a) according to Dumas, (b) - in Pregl’s m odification

T hese processes setting in the com bustion tube by Pregl, occurred in accordance with schem e 24.

C O , S*

Schem e 24

Cu C ° ; + C 0 CuO CO,

n 2 + n o z 650 üC n 2 650 °C N

Halla [45] revealed, that the location o f the additional layer o f CuO leads to extortionate results o f the nitrogen, resulting from the reaction ol dissociation o f copper oxide, setting in tem perature o f 650 °C (schem e 25).

2 CuO

650 °C

C u ,0 + 0.5 O .

Due to this, Fisher [7 8 1 recom m ended heating o f the term inal layer with C uO only to 200 °C tem perature, in which the oxidation o f carbon oxide to dioxide (CO —> C O 2) was quantitative whereas the dissociation of copper oxide (2C uO —* C u20 + 0 .5 0 2) did not run (scheme 26).

C 0 = Cu C 0 ’ + C° _{+ ---}CuO _^ CO- ₊

N2 + N O z 6 5 0 ° C N2 2 ° 0 ° C n2

Schem e 26

Hozumi and Amako [188] conducted the investigation over the relationship between the tem perature o f the reduction layer and its thickness. O ther sources o f overstating the results o f nitrogen determ ination resulted from porosity o f applied oxidants and/or sorbents, as a result o f which, air contained in them was w ashed out to a carrier gas during the analysis. Elim ination o f these factors w orks o f Flaschentrager [41] and other explorers [39,46,52,53! were consecrated.

In time, other limitations of Dumas m ethod, depending m ainly on understating o f the nitrogen content results in heterocyclic arom atic com pounds, were exhibited [8 1 ,105,276|. Thus, the derivatives o f chlorophyl [65.262J, pterynes and carboranes [323] did not it burn up in the standard conditions entirely; a coke formed after the com bustion contained chem ically bounded nitrogen. H ow ever, in the case o f long chain aliphatic com pounds, m ethane during the com bustion was formed, overstating the azotom eter indication 1107,123,124,133]. In the case o f analysis o f this type o f com pounds, the substance analyzed was mixed with com posites of C uO and KCIO^ [276], or C uO and V2O 5 [20], or CuO and the salts of copper or m ercury [6 6 ],

In investigations o f Kainz [213], the oxygenation effectiveness exhibited by typical metal oxide oxidants in a carbon dioxide atm osphere and tem perature 650 °C represented itself as follows:

M n 0 2 > CuO - C 03O4 > Fe20 , > NiO

M itsui [152] investigated the therm ochem ical equilibria established betw een C u20 , C uO and C 0 2, at a tem perature 750-800 °C, affirm ing the course o f follow ing reactions (schem e 27).

In connection with above m entioned, M itsui the usage o f a copper layer, heated to 550 °C, as the term inal layer recom m ended. Fischer [78] heated the final part o f the com bustion tube, containing CuO, to 200 °C, in which carbon oxide underw ent a quantitative oxidation (CO -> C 0 2) w hereas copper oxide did not undergo a therm al dissociation (CuO —> C u20 + O).

C 0 2 2 CuO --- ► C u ,0 + 0.5 O, 750-800 °C CO, 2 Cu + CO, --- ► C u ,0 + CO 750-800 °C Schem e 27

D uring the com bustion process, organic nitrogen is converted to a m ixture o f nitrogen and oxides o f nitrogen exhibiting different degrees o f oxidation (N 2 + N20 + NO + N 0 2 + N20 5) (schem e 28).

S* ---► N, + N ,0 + NO + NO, + N ,0

650 °C + 2 2

H20

Schem e 28

Nitrogen oxides (N 20 , NO and/or N 0 2) formed during the com bustion, exhibit different solubility in alkaline solutions, they contain in the particle o f oxide also different num ber o f nitrogen atoms (N 20 vs N 0 2). Therefore, the prior reduction o f nitrogen oxides to m olecular nitrogen, carried out before entrance o f the com bustion gases to the azotom eter, is necessary.

A considerable influence of the structure as well as the way o f com bustion o f nitrogen-containing com pounds on the conversion degree of organic nitrogen to nitrogen oxides was affirm ed (Table 3).

Table 3. Influence o f the structure o f the combusted nitrogen-containing com pounds and the type o f applied com bustion on the formation o f nitrogen oxides.

N o C lass o f an a ly zed co m p o u n d s C om b u stion D egree o f co n v ersio n [% ] N -> N O , L iteratu re

1 A m ines Thermal decom position 26% 62

Combustion in a stream o f oxygen

1-17% 106

3 Nitro com pounds Thermal decom position 59% 62 Combustion in a stream o f oxygen 82-97% 106 4 H eterocyclic com pounds

Thermal decom position 59% 62

Combustion in a stream o f oxygen 7-40% 106 5 Aromatic nitro com pounds Ignition combustion (Oi/Pt; 900 "C) Up to 13% 287 6 Various nitrogen- containing com pounds

Combustion in empty tube (Oi/Pt; 900 °C) - 108 Pyrolysis in nitrogen atmosphere (1000 °C) and subsequent combustion 292

Combustion in empty tube ( 02/Pt; 900 °C)

1-8% 291

C zum aszenko [223] subjected the substance analyzed to the prelim inary pyrolysis; in result o f which, the m ajority o f organic nitrogen was converted into m olecular nitrogen (reductive action of organic carbon).

The tem perature o f CuO layer exerted a large influence on the exactitude o f m easurem ents. Thus, usually higher than 650 HC [385], in several works in range 700-800 °C [262], and for hardly com bustible com pounds and/or giving underestim ated results at least 1000 °C [99,114,138],

O ne o f the com plete com bustion substance (hardly-com bustible com pounds) affirm er ways, consists the com bustion in an carbon dioxide including, the adm ixture o f oxygen, atm osphere [69,99,127,129,131,136,154, 170,249,267,275,277,351]. For absorption o f an oxygen excess, the reactive filling, equipped with situated in the end o f the com bustion tube copper layer (m etallic or on m ineral carrier), is applied [232].

The apparatus to the volum etric determ inations o f nitrogen according to Dumas m ethod, based on described procedure (chem ical reactions occurring during the procedure are presented on schem e 29) is illustrated in Fig. 6 .

Schem e 29 C u 0 /C 0 2 + 0 2 650 °C CO, n 2 + o 2 h2o Cu 650 °C CO, + N, H20

Fig. 6. Schem e o f apparatus for Dumas nitrogen determination:

i - carbon dioxide bottle; 2 - needle valve; 3 - combustion tube; 4 - electric furnace (7 0 0 "C); 5 - electric furnace (2 0 0 -3 0 0 °C); 6 - layer o f CuO; 7 - copper gauze; 8 - layer o f CuO; 9 - azotometer; JO - connection with reservoir o f KOH solution.

In the m ethod elaborated by Trutnow ski [356], the sam ple is burnt out in oxygen, the form ed nitrogen oxides along with an oxygen excess are reduced by means o f hydrogen, which excess in turn is removed on a copper oxide layer (schem e 30). S* 0 2 / P t 900 °C

co2

A ccording to Kirsten [151], this course o f action leads to extortionate results o f nitrogen determ ination. This statem ent is in opposition to works o f M auser and Egli [155], as well as other explorers [385].

Kirsten [107,123,141] introduced a m odification to the m ethod of Dumas, which perm itted an enlargem ent o f its generality, especially in reference to the com bustion analysis o f hardly-com bustible substances. Kirsten carried out com bustions at tem perature o f line 1000 °C; in this aim replaced traditional glass tube with one made from quartz. Based on the results o f investigations of K urtenacker [23] and Kapustinski [59], he replaced the layer arrangem ent consisted o f CuO—Cu by the layer NiO—Ni. The m odified m ethod o f Kirsten- Dumas (schem e 31) was also adapted to the m illigram scale [179].

C 02

M n 0 2 / C u O + --- *" N

100 "C + 2

h2o

For settlem ent o f the optim um conditions for com bustions o f organic sam ples - the wide spectrum of investigations on the com bustion process, including the influence of used oxidants, as well as the process tem perature, were explored. B ehavior o f the CHN sam ples in tem peratures adequate to com bustion conditions was also studied by the utilization o f TG A as well as term ogravim etrical m ethods [425],

2.2.2. Nitrogen Determination by the Method of Kjeldahl

T he m ethod o f Dumas, though presents the m ost general m ethod of nitrogen determ ination, is not useful for the sam ples occurring in a form of aqueous solutions (in urine, blood, tissue hom ogenizates, physiological liquids, etc.). In such cases more profitable is the method o f K jeldahl, as quicker and using less com plicated apparatus.

K jeldahl’s m ethod is based on the degradation o f organic nitrogen- containing com pounds (m ineralization) in concentrated sulfuric acid (stage 1), in result o f which the bounded nitrogen converts by the reduction to am m onium sulfate. A fter alkalization o f a reactionary mixture, the released am m onia is most often distilled o ff in water vapor [385] to a receiver flask containing a solution o f salt acid [25], sulfuric [31], boric [90,94] or other acids [385] or water [191] (stage 2 ), and is subsequently determ ined (stage 3), the m ost often by m eans o f the alkacim etric titration.

The m ethod o f Kjeldahl presenting in the classical elaboration (1883) the lim ited use, as result o f subsequent im provem ents becam e one o f more

C 0 2 C 0 2 + C0 N iO + N i S * --- -- N O , --- -- N , 1050 °C + 1050 °C + h2o h2o Schem e 31

practical analytic m ethods [13,573,576]. The details relating the various m odifications o f the m ethod o f Kjeldahl were described by B radstreet [246], The evolution o f the m ethod o f Kjeldahl, and its analytic potential was recently discussed by M cK enzie [472]. The problem o f superiority or com patibility of Dumas and Kjeldahl m ethods [373,437,480,487,507,526,566,577], or the m ethod o f Kjeldahl and other m ethods [296,573], presents the object o f constant considerations.

A ccording to present standards, the range o f applicability o f K jeldahl’s method, retreats still the enhanced versions o f the m ethod o f Dum as. It can not be applied, for instance, without additional interventions for the determ ination o f nitrogen exhibiting the positive degrees o f oxidation (nitro-, nitrozo-, azo- and azoxy-com pounds), or/and in the determ ination o f a high volatility com pounds or/and for certain heterocyclic compounds.

T he reaction can be accelerated by addition to the degradation solution o f som e type o f oxidants, for example, perchloric acid [92,93] or hydrogen peroxide [77,87,88,97], In the case o f analysis of com pounds containing the nitrogen-oxygen (-N -0 ) or nitrogen-nitrogen (-N-N) linkage system s, the substance is degradated in a tw o-stage process, with prelim inary reduction (stage I), follow ed by ultim ate degradation in sulfuric acid.

Tem perature exerts essential part as influencing the integrity of degradation factor [153,218]. The degradation tem perature can be increased by the addition o f K2S 0 4 (can not be replaced by Na2S 0 4 [178]) to 410 °C, and must not be low er than 380 °C [18,111,130].

D ecom positions usually are com pleted after ca. 15 min; in case of derivatives o f pyridine can last even up to 4 h [101]. The com pounds containing nitrogen on the higher than -3 degree of oxidation (occurring in functions: -N O z, -N-N-, -N =N -, etc.) do not undergo the quantitative degradation to am m onia (understated results o f nitrogen). In these cases, the degradation solution was supplied by various additions, in these by phenols, salicylic or thiosalicylic acid, glucose, alone or as the com binations of these com pounds (table 4). T he most effective m ethod turned out the two-stage procedure, in w hich, before the ultim ate degradation in sulfuric acid, the prelim inary reduction o f nitrogenous functions by m eans o f hydrogen iodide was applied [57,87,137,145,180], K jeldahl’s digestion procedure was also facilitated by the m icrow ave radiation [457,466],

The com position o f various variants o f K jeldahl’s m ethod and the applied m ineralizing reagents is presented in Table 4.