Trace gas analysis by mobility separation

(1)

December,

1971.

TRACE GAS ANALYS IS

TECHtJlS(

1E

HOGau

OOL DnA

UEGTU~EOUWIWNO

BmUOTHEfK

BY MOBILITY SEPARATION

by

George Peter Laszlo

(2)

TRACE GAS ANALYSlS BY MOBlLlTY SEPARATION

by

George Peter Lasz10

Manuscript received October, ~971.

(3)

\

ACKNOWLEDGEMENT

It is a pleasure to acknowledge the able guidance, advice, and encourage-ment of Dr. J. B. French who bath initiated and supervised this investigation in an enthusiastic and tireless manner.

Special thanks are due to Dr.Neil Reid of the UTIAS staff and to my fellow students for their direct and indirect contributions to this work.

The UT I,AP , research fellowship granted for the duration of this work is gratefully acknowledged. This project was supported by the Department of Energy, Mines and Resources under Contract HO

88719.

The assistance of Mrs. Claudette ~aszlo and Mrs. Barbara Waddell in preparing the manuscript is sincerely appreciated.

(4)

SUMMARY

Alpha and beta partic~es or ion pairs are formed by placing a radioactive

source in a sample air stream. The charges then first complex with water vapour

and finally end up on any highly polarizable or electronegative i~urity species

present. Pulses of ions so formed can be drifted down a tube by ~ one-dimensional

field and a time-of-arrival spectrum is generated. This is known as a plasma

chromatogram by analogy to an ordinary gas chromatogram.

This project was designed to be a feasibility study of a continuous flow

analogue to this device because of the désire to utilize large sample gas rates

and extremely high scavenging efficiency for impurity atoms. For this purpose

a modern version of the old "El-ikson Air-Blast Method" (Ref. 1) was used. The

system, originally used in the 1920's for measuring mobilities, is comprised of

a uniform velocity flow of sample gas through a rec~angular cross-section tube,

with astrong potential difference applied between the top and the bettom. A

mixture of ions introduced at one point at the top separates out in the crossed

potential and velocity fields on account of mobility differences. Ion spectra

can be obtained by sliding an ion detector along the floor of the tube. The peaks

are due to typical water cOmPlexes such as (H20)nHT , (H₂0)OH-, etc, in the

ambient laboratory air samples, and to other trace ions present in the air.

The identification of the ion species is made by calculating the mobility

corresponding to the location of the current distribution peaks. In this paper

the Langevin equation was used ~o calculate the ionic masses corresponding to the

calculated mobilities. This theory predicts a limiting mobility for high masses.

This connection between mass and mobility was found to be inadequate for the

posi-tive identification of trace gas ions present in air at atmospheric pressure.

However, just af ter the conclusion of this paper an empirical relation between

ionic ~ss and mobility was presented by Carroll and Kilpatrick at the Nineteenth

Annual Conferençe on Mass Spectrometry and Allied Topics in Atlanta (May, 1971).

This formula is reported to be valid at atmospheric pressure up to masses of

10,000 a.m.u. It is evident that the experimental method presented in this paper

and the empirical formula of Carroll and Kilpatrick can be used for trace gas

analysis by mobility separation.

(5)

TABLE OF CONTENTS PAGE Acknowledgements Summary Not at ion 1. INTRODUCTION 1 2. EXPERIMENT 1 2.1 Apparatus 1 2.2 Procedure 2 3. THEORY 2 3.1 Calculation of Mobility 2 3.2 Calcuj.ation of Mass 4 4. RESULTS ₅ 4.1 Experimental Results 5

4.2 Errors in Mobility Calculations

6

4.3 Errors in Mass Calculations

8

4.4 Evaluation of the Experiment

8

5. C ONCLUS I ONS 10

(6)

K

h D V H

E

u v o t m

M

E p

P

R

r NCITATION mobility of ion

reduced mobility of ion

average distance travelled by ions perpendicular to air flow downstream distance corresponding to peak on mobility curve potential difference between top and bottom of duct

distance between top and bottom of duct electric field strength between plates drift velocity of ions

velocity of stream of carrier gas time

mass of trace gas ion mass of gas molecule

dielectric constant of gas gas density

gas pressure

sum of radii of ion and molecule

radius of ion or molecule differentiated by subscripts i or m charge on an electron

(7)

1. INTRODUCTION

In recent years a new type of analytical instrument was designed for the direct and rapid measurements of trace gases at sensitivities several orders of magnitude greater than those previously available. This so=called plasma

chromatograph-mass spectrometer has applications in several fields of research. The concentration levels of water vapour, insecticides, pollutants, etc. in the atmosphere can be monitored by the use of such an instrument. In the field of medical diagnosis this appratus can be used to classify human odors characteristic of disorders caused by enzyme blocks. Sensing the naturally emanating odors from drugs and explosives renders this method useful for contraband detection. Mineral prospecting can be performed by an air-borne instrument that can detect the low concentration of vapours originating in subterranean ore deposits. Biological insect control can be aided by detection of animal scents present in the air at very low levels of concentration.

One of the factors responsible for the high price of such a commercial~y available instrument is the complex electronic instrumentation and vacuum system necessary for the operation of a mass spectrometer. The following investigation is a feasibility study of a system that avoids the use of mass spectrometers by separation by mobility differences. The object is to determine the amount of mass resolution that is sacrificed by the use of such a system that can be built for less than 1% of the cost of the other one. Further simplifications in the electronic signal handling are the result of the higher signal levels due to large sample gas rates. The scavenging efficiency of this system is very high as the trace gas is nearly completely ionized in the ion-molecule reaction induced by passing it along a radioactive sourceo

A simple apparatus can be constructed to perform this function. The gas sample is drawn into a rectangular tube by means of a fan. A radioactive source placed near the intake end of the duet ionizes the trace gas molecules. A DC

potential difference applied be~ween the top and bottom plates of the tube together with the flow velocity perpendicular to it have the combined effect of forcing the trace gas ions to strike the duet floor. The location of the point of im-pact can be related to the ion mobility which, in turn, can be used to calculate the corresponding mass. The trace gas concentration ean he monitored by measuring the ion current with an electrometer connected to a probe placed at the point of

impact on the duet floor.

2. EXPERIMENT

2.1 Apparatus

A schematic diagram of the experimental setup is shown in Fig. 7.1. The atmospheric sample containing the trace gas is introdueed. into the system at two places. The main portion is drawn into the tube by the fan F through a bell-mouth orifice to ensure laminar gas flmw in the duet. This part of the sample acts as the carrier gas. Now it must be remembered that the entire apparatus is surrounded by the atmosphere to be analyzed. Thus the portion of it near the radioactive source S is ionized as it is wafted through the slit in the duct roof beneath the source. A small DC potential difference applied between

the top of the duct and the curved metal screen svrrounding the ionization region focusses the ions at the slit to increase the trace gas ion scavenging efficiency of the system.

(8)

· Hapart. The sides of the tube are made of a dielectric material which must not

react with any of the trace gases under study. The length of the tube must be

long compared to H; the width can be made any convenient size. A DC potential

difference is applied between the top plate and the grounded duct floor. The

polarity of the top plate with respect to ground corresponds tG that of the metal screen with respect to the top plate. Positive ion collection is achieved by

making the top plate and the grid positive; they must be biased negative to collect negat.ive ions.

The ions hitting the duct floor are detected by means of a metal probe P that is weIl insulated from the bottom plate. The trace gas concentration can be monitored by the ion current registered by the electrometer connected to the

probe.

2.2 Procedure

Air was drawn through the duct by the fan at velocities ranging up to

30 fps. The flow velocity was monitored by a Betz manometer connected to the

side of the duct as shown in Fig. 7.1. A fine thread suspended in the tube near the slit under the radioactive source was a yisual aid used to verify that the gas flow was horizontal as stipulated by the theory that is discussed in the following section.

For the experiments performed the De potential difference between the

top and bottom plates of the duct was varied from -5kV to +5kV. The DC potential between the metal screen around the ionization region was kept at + 90V depending on the polarity of the ions that were collected.

The ion current can be detected using two methods. One way is to have

a movable probe. This method makes it possible to give a graphical representation

of the ion current.distribution along the duct floor: current is plotted as a

function of downstream distance with flow velocity and electric field as the independent parameters. From the family of curves plotted by this method the location of the ion peak for any combination of flow velocity and electric field is known. The alternate approach is to have the probe fixed at a convenient

point downstream from the ionization region. Using the data found from the first method the correct combination of flow velocity and electric field can be selected to move any ion current peak to the location of the fixed detector. Consequently

this method can be used for the quantitative analysis of known trace gas constituents

in the carrier gas, while the movable probe method can be used to locate the current peak for any desired trace gas.

For the experiments involving wa~er vapour at arbitrary concentrations

the ambient laboratory air was used. Saturated water vapour conditions were established by passing the ambient atmosphere through a moist cotton wad before

introducing it into the apparatus. For other trace gas samples the flow rate of the constituents was regulated by means of a micrometer needIe valve or by the use of a motorized syringe driven at a convenient const.ant speed.

3.

THEORY

3.1 Calculation of Mobility

(9)

to make the following simple argument valid. A uniform electric field applied

simultaneously with a laminar flow velocity perpendicular to it will force an ion to move downstream a distance D as shown in Fig.

7.2.

The ion traverses the distance h in the same time t as the stream moves it along a distance D:

h D =

ut

vt ( 1)

Now the mobility is defined as the drift velocity per unit electric field:

u uH

K =

Ë

= V (2)

Substituting Equation (2) into (~),

h KVt

=

-D vHt

Rearranging Equation

(3),

the mobility in terms of the downstream distance D corresponding to the observed peak in the ion c~rent distribution is:

K = hHv

VD (4)

The reduced mobility is then obtained by expressing Kunder conditions of standard temperature and pressure:

In the experimental setup the following values are used: p

₌

1 atmosphere 760 mmHg T

₌

220C

=

2950K h == 2 in. H

₌

2 in. v

₌

v ft/sec V

=

V x 103 volt D

=

P cm

Substi tut,ing these into Equation (5),

=

(76QD (273) (2in)(2in)(v ftjsec)(12 injft)(2.54 cmjin)3

Ko 760· 295 • 3 V x 10 volt x D cm i.e., K

=

0.73 o v VD 2 cm /volt-sec

For convenience in calculation this equation can be rewritten as Ko

=

X

(~)

cm2/volt-sec

where

x

0.73

D

(6)

(10)

The coefficient X is plotted for various values of D in Fig. 7.3. The reduced mobility corresponding to a peak in the ion current distribution can be found by multiplying this coefficient by the ratio of the flow velocity and the electric field according to Equation (7)0

It is of interest to note that mobility is constant with respect to variations in Elp provided that Elp

<

2 volt/cm-mmHg. In the experiments pe r-formed the maximum voltage was 5 kV, so that

5000 volt

2in x 2.54 cm/in x 760 mmHg i.e.,

(~)max

= 1.295 volt/cm-mmHg

Thus for purposes of this analysis mobility can be taken to be invariant with

Elp·

302 Calculation of Mass

In the theory derived by Langevin, a dimensionless temperature ,,2 is defined as the thermal energy divided by the energy of attraction when the ion and the molecule are in contact:

8171'R4

(E_l)e2

(10)

Corresponding to À a coefficient A is tabulated by Langevin (Ref. 3, Table 111) where the value of A depends on the comparative effect of the attractive forces and the elastic collisionso Based on this value the reduced mobility is given

in cgs units by the relation where K o M 1/2 = Y (1 + -) m

. (%ö)

.(2~3

) (11) ( 12)

Now Equation (11) can be rearranged so that the mass of the ion can be calculated in terms of the reduced mobility:

M

( 13)

m

(11)

- - - -- - -- - - " P 1 atmosphere

=

1.0132 x 105 kg/sec2m E = 1.00059 E 8.85 x

10-~2

coU10mb2/newton

m~

o e = 1.602 x 10-19 coulomb

M

= 28.9 a.m.u. T

=

220C

=

2950K

Thus Equation (10) becomes, cgs units,

5 2 -10 2 =12

8~ x (1.0132 x 10 kg/sec m) x (R x 10 m) x (8.85 coul /newt-m x 10 )

0.59 x 10-3 x (1.602 x 10-19 coulomb)2 i.

e.,

À == 0.0122 R2 R ( À ) 1/2 0.0122 (14 )

The coefficient Y from Equation (12) becomes

i.e. ,

y

=

3.67 A (15)

Using Table 111 from Hasse's paper (Ref. 3) that lists values of Aand À, Fig.

7.4 was plotted from Equations (14) and (15). I t gives the variation of the

coefficient Y with the combined radius of the ion plus the molecule. Knowledge

of this coefficient leads to the calculation of the ionic mass from the reduced

mobility:

m= M (16)

4.

RESULTS

4.1 Experimental Results

Using the procedure described in a previous section a series of +

experiments was performed. lonized water complex molecules of the form (H20)nH ,

(H20)nOH-, (H20)nO; , etc. were formed by passing the ambient atmospheric

sample along the radioactive source. The size of these water molecule complexes

(i.e., the value of n) was increased for some measurements by using air saturated

with water vapour. In addition to the experiments performed with water vapour,

other known trace gases were added to ambient air. Sulphur hexafluoride was

selected for analysis because of the very high electronegativity of the SF

(12)

molecule assures that the entire negative current in an ionized sample of air and SF

6 is due to the presence of SF

6

ions. This experiment then provides a definite link between the results and the theoretical values because the mass corresponding to the SF

₆

current distribution peak is known to be 146 a.m.u.

To examine the behaviour of the ionic current distribution with changes in flow velocity and electric field strength, families of such curves were plotted. One typical set of graphical results is shown in Fig. 7.5. It shows the negative current distribution dueto_,the presence of SF

₆

ions in air. The effect of chang-ing the applied potential in 1 kV steps from 0 to -5kV is demonstrated for flow velocities of approximately 15, 20 and 25 fps. The ion current distribution should be of the form of an isoceles triangle, symmetrical about the ionic

impact on the duct floor in the absence of diffusion. Bepartures from the ideal can be attributed to nonuniformities in any or all of the following: ionization,

e~ectric field strength, or flow velocity. Another fundamental reason for any non-ideality is caused by ion diffusion, for which no provision was made in the theoretical treatment leading up to the mobility equation. Decreasing the magnitude of the voltage and increasing the flow velocity both have the ef~ect

of diffusing the triangular current distribution. Examination of the experi-mental curves in Fig. 7.5 reveals a generally good agreement with the above

des-cription. The diffusio~ of the current distribution manifests itself as an

increase in the base length of the triangular current distributio~ accompanied

by a decrease in the peak height.

The location of the apex of the triangular current distribution can be used to calculate the mobility as discussed in the section devo~ed to the theoretical aspects of the problem. The mobilities calculated based on the graphical results are tabulated in Fig's. 7.6 and 7.7.

As discussed in a previous portion of this paper, a knowledge of the sum of the radii of the trace gas ion and the carrier gas molecule (denoted

by R) is necessary in order to calculate the ionic mass from the tabulateQ values of the mobility. A series of interatomic dista~ces pertaining to the ions and molecules of interest in the above experiments ~s given in Fig. 7.8. As stated earl ier , for the cases involving sulphur hexafluoride in air the entire current is du~ to the presence of the SF

6

ions. Thus the value of R is one-half the sum of the S-F bond length in SF

₆

and the N-N bond length in N

2 (where air is assumed to be pure nitrogen gas for the purposes of specification of the mole-cular size of air). The a priori identification of the water complex ions is

rather more arbitrary. These calculations are summarized in Fig. 7.9. In

order to determine the causes of the large percentages of error a detailed analysis of the possible sources of error was conducted.

4.2 Errors in Mobility Calculations

In this section the effect of measurement errors in the VèLocity,

voltage, and distance upon the calculated reduced mobility is examined. The

notation is the same as in the section on theory with the addition of the symbol 6 which is used to denote a deviation from the actual value of the quantity

that follows the symbol.

(13)

where

x

=

.0.73

D

(8)

Thus a change in each of the measured constituents of Equations (7) and (8) leads to a net change in the theoretically predicted value of the reduced mobility given by the relation Now (V 1 v 6. -)= - 6.v - - 6.V V V 2 v Also, X+6.X= D + 6.D 0.73

Substituting Equation (8) into (18),

i.e., 0.73 D + 6.X = 0.73 D + 6.D 6.X= _{D + 6.D}0.73 0.73

(D )

D D+6.D

Substituting Equations (18) and (19) into (17),

6.K = X 1 6..v v 6.V)

-

(

v ) _{X ( 1 +}

0 v

-

v

2 V

= X ( v _V) ( 6.v _v

_-

--

_V6.V

_{D (}

lill. _{1 + 6.D!D) )}1

Substitute Equation (7) into (20) and rearrange: 6.K _6..v _6.V 6.D 1 0 - = - - - _{(1 + 6.D!D)} K v V D 0 ( 18) 1 ) 6.D!D (20) (21)

Thus the error in mobility calculated from the experimental data is a linear combination of the measurement errors in velocity, voltage and distanceo The effect of velocity errors on mobility calculations is opposite to that due to voltage and distance deviations. It is useful to nete that the magnitude of the dis~ance error is diminished by a factor of (1 + 6.D/D)-l in its effect on the reduced mobilityo Thus a slightly greater leaway can be tolerated in measurements of the peak height distance thaN. in, the other experimental data.

(14)

4.3 Errors in Mass Ca1cu1ations

Equation (21) derived in the previous section shows the effect of ex-perimental errors on the ca1cu1ation of the reduced mobi1ity. H0wever, since the object of the experiment is to identify the unknewn ions using their mobi1ity to ca1cu1ate the mass, it is of interest to trace the effect of the mobi1ity errors on the corresponding mass.

Reca11ing the equation re1ating mobi1ity and mass,

m= 28.9

Introducing an error K into this re1ation resu1ts in the fo11owing:

o = +m i.e. , 6m =( 28.9 ) ( (K

/y)'2.

_

1 o

Now substitute Equation (16) into (22) and rearrange:

6m (K /y)2 _ (K o 0 + 6K )2/y2 0 - = (K + 6K )2/y2 - 1 o 0 m

1 -

K 2/(K

+ 6K)2 o 0 0 = i.

e.,

6m (K + 6K )2 _ K 2 0 0 0 - = -m _(K + 6K )2 y2 0 0 6m

_-

6K 2 + (6K /K )

(

0 ) o 0 m K _6K _{/K )2 _ (y/K )2} 0 (1 + o 0 0 ( 16) (22) (23)

Figure 7.10 is a graph of (6ill/m) vs. (6K /K ) for the case of su1phur hexaf1uoride o 0

in air, where Y

=

1.975 and K

=

2.16 cm2/vo1t-sec.

o

4.4 Eva1uation of the Experiment

A cursory examination of the graph in Fig. 7.10 revea1s the undesirab1e amp1ification of mobi1ity errors. Another comp1ication is that theerror curve is

(15)

not symmetrical about the 6rn/m axis, but has an asymptote at tJ( y 0 - 1 = K K

(24)

0 0

Now it is evident that the experimental errors in mobility can only be expressed

as ranges about the origin, i.e., + tJ(

IK.

Thus if the asymptote lies near

- 0 0

this range, the mass error will greatly exceed that in the mobility, and may even

be unbounded for those cases where the asymptote lies within the mobility error

range. The asymptote in the error curve for the case of sulphur hexafluoride in

air occurs at

6K

IK

=

-8.5%

as can be seen in Fig.

7.10.

Thus even an acceptable

error of ~

5%

inomoBility will result in mass errors ra~ging up to

130%.

Based on the above theoretical treatment of errors the large mass errors shown in Fig.

7.9

can be readily explained. The errors for the ionized water complexes is greater than that for sulphur hexafluoride because of

the arbitrary a priori identification of the ions responsible for the current

flow. As discussed earlier, only the SF

6

ion can be definitely identified (due to its high electronegativity) without recourse to mass spectrometric analysis. That alternative was thought to defeai the purpose of the experiment: the ide nti-fication of trace gas ions from the mobility corresponding to their current d

is-tribution peaks. The fact that the results obtained seem inconclusive as far as

identification is concerned is one of the shortcomings of the methode This fact

was experimentally evident and theoretically proven by the error analysis in the

previous section.

The mobility data presented by the Franklin GNO Corporation (Ref. 7)

is tabulated in Fig. 7.11. Here the ion species were identified by passing them

through a mass spectrometer. The last two columns were calculated using the

theory presented in the previous sections; the data supplied in the first two

columns was used to calculate Y and r . • A marked difference exists between

1. on

these values f0r the ionic radii and those given in Fig.

7.8. An

asterisk

denotes the cases where the coefficient Y calculated from the given data exceeds

2.17,

the maximum value in Fig.

7.4.

These instances indicate the serious

short-comings of relying on the interatomic distances for mass calculations without

taking into account the kinetic theory governing the collision distance distr

i-bution in ion-molecule reactions. A plot of mass versus mobility based on this

data shows no definite functional relation. The dispersion in the experimental

data precludes the positive identification of the ionic species based on mobility

data alone in the paper presented by the Franklin GNO Corporation as well as in

Fig.

7.9

of this paper.

These results supported by the analysis of errors involved in calcula

-ting mass from mobility suggest that mobility is ~ot very sensitive to mass

changes.

A

plot of Kvs. m by Chanin and Biondi (Ref. 5) shown in Fig.

7.12

confirms this. A cargful consideration of the error plot, Fig.

7.10,

also leads

to the same conclusion: from this graph it is evident that for the case of sulphur

hexafluoride in air, as long as the error in mass is greater than

-

40%,

the

mo-bility error is less than

5%

in magnitude. Consequently, the calculation of

mobility from mass using the Langevin theory is far more fruitful for experimental

purposes than trying to identify the ionic species based on the mobility data alone.

(16)

at the Nineteenth Annual Conference on Mass Spectrometry and Allied Topics in Atlanta (May, 1971) by Carroll and Kilpatrick. In agreement with the discussion

in the preceeding sections they also found that the Langevin equation predicts that a limiting mobility will be reached at high ion masses. Based on the assumption that this behaviour is not correct due to the direct relationships between mobility and ionic radius and that between radius and mass Kilpatrick developed an empirical relationship between the mass of the ion and its mobility in air at standard conditions. Their data covering a mass range of about 50 to lD,OOO a.m.u. is an extension of the results presented by earlier research work performed at pressures wel 1 below atmospheric. It is then apparent that the application of this new empirical formula to calculate the ionic mass from mo -bility data Fan be used to sort the data obtained by the experimental method described in this paper. Consequently this is a potentially good and, inexpensive method of trace gas analysis.

5. CONCLUSION

The potentially large sample gas rates and the very high scavenging efficiency were the motivating factors for the investigation of trace gas analysis by ion diffusion at atmospheric pressures. A simple experiment was devised based on the air-blast method used by Erikson in the 1920's for mobility measurements. The ion current distribution peak locations combined with other experimental data was used to calculate the mobility of the ions. The Langevin theory for mobility calculation from mass was used to compute the mass corresponding to each ion peak.

A careful analysis of the Langevin theory revealed that mobility is a relatively insensitive function of mass. Concurrent with this work Carroll and Kilpàtrick have devised an empirical formula based on the Langevin equation. Their formula is an extension of the relationship between mass and mobility of ions that does not suffer from the misleading conclusion that mobility is not a sensitive function of mass at high values of mass. It is evident, therefore, that the experimental results based on the method described in this paper can be recalculated using this recently proposed formula. Thus the apparatus is a potentially inexpensive trace gas analyzer that works on the principle of mobility separation of ions present in air at atmospheric pressure.

(17)

1. Loeb, L. B. 2. McDaniel, E.

w.

3. Rasse, R. R. 4. Langevin, P. 5. Chanin, L. M. Biondi, M. A. 6. Karasek, F-:' W. 7. 8. Cohen, M. J. 9. Karasek, F. W. Cohen, M. J. 10. Mahoney, J. J.

H.

Erikson,

H.

A. 12. Loeb, L. B.

13.

Erikson,

H.

A. 14. Erikson,

H.

A. 15. Erikson,

H.

A. 16. Chapman, S. 17. Karasek, F. W. 18. 19. 20. Carroll, D. I. 21. Kilpatriek, W. D. REFERENCES

"Basic Processes of Gaseous Electronics", University of California Press (1955), p.10.

"Collision Phenomena in Ionized Gases", John Wiley

&

Sons, New York (1964), pp.426-524. Phil. Mag.

l,

(1926), p.139.

Ann. Chim. Phys.

L'

(1905), p.245. Phys. Rev. 107, (1957), p.1219.

Research/Pevelopment 21, (March, 1970), p.34.

Report A/II, January 1970, Franklin GNO Corporation, P.O.Box 3250, West Palm Beach, Florida, 33402, USA.

Transactions, American Geophysical Union, 51, NO.ll,

(Nov, 1970), p.760.

J. Chromatog. Sci., ~, (June, 1970), p.330.

Phys. Rev. 33, (1929) , p.217.

The American Phys. Soc. 17, No.3 (1921), p.400. The American Phys. Soc. 17, No. 3 (1921), p.400. Phys. Rev. 18, (1921) , p.100.

Phys. Rev. 23, (1924) , p.llO. I

Phys. Rev. 19,

(1922~,

p.275. Phys. Rev. 52, (1937), p.184.

Research/Development, 21, (1970), p.25.

"Tables of Interatomic Distances and Configurations in Molecules and Ions", The Chemical Society,

London (1958).

"Tab les of Interatomie Distances and Configura~ions

in Molecules and Ions- Supplement 1956-59", The Chemical Society, London (1965).

"The Theoretical Relationship Between Ion Mobility

and Mass", Nineteenth Annual Conference on Mass

Spectrometry and Allied Topics, Atlanta, (May, 1971).

"An Experimental Mass-Mobili ty Relation for Ions in

Air at Atmospheric Pressure", Nineteenth Annual Conference on Mass Spectrometry and Al1ied Topics, Atlanta (May, 1971).

(18)

- - - -- - - ,

II

Fi9·7.1. Schemaiic Dia9ram

Ot

t,he

Appara~us.

D=~

I

I I

Flow

velocily=v

Ion

L _ _ _ _ _ _ _ _ _ _ ..;. __ _

h=ut.

A

B

Carrier

-

Gas

(19)

0.& 0.4 0.2

o

( cm' )

y

volt-sec 2.0 1.6 x-~

_o

r::-ig.

7.3 :

Variation

o~

Coe.uicient.

X wit.h

Distance.

O.8~----~---~----~---L---~---~----~~---e"

o

4 6 8 10 12 14

R(A)

(20)

-I

(nA)

4 2

-I

(nA)

6 -2kV V0l20~ps.

LL.tI....J'-~~~::aIa...:~i....l _ _ _ L..:::!:=:a... _ _ .J.. _ _ -1._-~ O(cm)

o 2 4 6 8 10 12 I.

-I

"Al

(21)

· F'g.7.6. Ne9a:bive Mobtl,ty

ReSt.llts.

TablQ

7.6.1. Moblliiies

of

Ne9ative lons in

L~ Air (c\'l'\~/volt-sec).

~

14.96 fps.

20.7S

+ps.

26.

25ks. -I kV l,94· 1.7S 1.77; 1.60 2.0~ 1.84; 1.71 -2kV 2.02 l. 9'2.

1.97

-3kV 2.04 .

1.93

1.98 -4kV

2.06

1.86 l,94 -SkV 2.06

1.99

l.

9'

Tab\~ l.b.

2. Mobilities

of

NagativQ Ions in

lab

Air

Satut'atecl

wlth

Wate.~

VapotAr (c.""'/vott-Sec).

\T--..:!.

14. 96 tps.

20.75

~ps.

'25. 4

\j'es. -'kV 1.7.5 1.60. 1.:39 1.9\· 1.1"; 1.60; 1.53 -2kV

2.02

1.92

1.99

-3kV 2.04 1.87 1.93

-4kV

2.15

2.07

1.88

-SkV

2.09

2.~9 2.09

Tab\Q.

7.6.3. Mobilities

of Nt9i.iiVQ Ions in

Lab

Air

Mi~ed

with

Sulphur

He)t.Af'uorid~ (('",~lvolt-$ec).

V---'"

14.96.(ps.

'20.15

fp$.

23. e4

.frs

-IkV 1.50; US 2.39 2.'!>6) I.S!>; 1.57; 1.43

-2kV

2.71

2.46

2.071 1.76; l.40 -~kV 2.04 2 . .53

1.97

-4 kV 2.08

2.54

l.94 -SkV

2.09

2 . .53 l.9B

(22)

J=i9.7.7.

Positive

Mobtli~y

Results.

Tab\a 77.1. Mobi\ities of Posi-\:.iv" fons in Lab Air (c;Oo\"/voll-sec).

v~

14.96.(.ps.

'20.75

+P5.

24.90-le

s.

+\k\l

1.50, 1.'27; I.IS 1.~71 1.25 I. 9'2J

1.,

l; 1.4Z. I. 3Z

+2

kV

I.~O l. 2'2 1.53;

1.43

+3

kV

1.:!>4 l.35

1.37 +4kV

1.37

1.40

1.41 ... 5

kV

I.

47

1.3S

l.47

Tab'e

7.7.2. Mob,\ities

Ot

Positi"e

rons

in

Lab

Air

Saturat.d

wlth

Water

Vapour

(c~~

/volt-sec).

V----"

14.

96

.fps.

20.54.{ps.

'24.75

fps.

... 'k.

\I

/.S4~I.SO. 1..39t I.IS 1 . .sO· 1.3t>. I.l~ l.09 1.731l.G~·1.49.l.41

+~kV 1.46 loSI. l. 3~ I.S2· l.:53

+3k\l

L.47

\.34

1.44 +4kV

1.42 l.39

1.39

~SkV 1.50 1.30

1.46 Tab\e

7.7.3. Mobilities of Positive

10ns

in

Lab

Air

MilC.ed

with

Sulph\.lr

~elC.afluo

...

;(h

(c""Yvolt-sec).

1\1---"

14.96

fp~.

20.75

fps .

23.84 i,.s.

• lkV l. :39. I. 24. l. 15 '.S~. I.4S·

l.:35.

1.'24

1.79· 1.67·

I.SS; t

.43

+'2k.V

1.'30

1.3S

':?>ï

.3kV

1.47 l.34-

1.:!>8

+4kV

l.38

1.40

1.47

+SkV

1.47 \."37

1.41

(23)

~'9.

7.

8. Tables

Ot

Intera!omic Distances.

N--N

Su\phur

Hexafluoride

F

I

r

F-S~F (5~)

~/I

F

OXY9~

0 - 0

(O~)

Water (crystalhne

.(orm)

/0,

(H

₂

O)

H

/ 0 ,

H

~

H

(H

₂

O)H4-H

0

(OH)-o

0-0

bond

\en~th

-=

1.208 A

o-H

bond len9th:O.957À

0

O-H bond

len,9th=O.960

A

O-H

_bQnd

_'Qn9th=O.9B4

_Ä

(24)

_ . - - - . ,

Fig. 7.9. Analysis

Ot

ExperiMentai Results.

(H~O)14+

(~~O)O~- (~~O)Ot.-

5~-•

I'"iol\

(A)

0.480 _1.096

lO63

1.570

• R(A)

1 .

038

1.654 \.641

2.128

( cm~ )

Y volt-sec

1.923

1.953 J

.

95?>

L975

( c_~ )

\<0

volt - sec

1.40

2 .

10

1.90

2.45

mup'ol

(a

.

m

.

u.l

'/I.

193

11

.53.5

\'V\

(a

.

",,-"" )

19 3S

50

146 ~(~)

00

+450k

00 -63.5CZ

(25)

-

.

200

1$0

.

~m

:

f(A~)

Ol ~ . ..,a

CL,

~I

100

"'I

<l

I I -I SO I I I I -100 -.50 I 100

~O{%)

0 -100 -ISO -200

(26)

Franklin GNO Corp. Rf.su'ts Calcu\att.d Va\ues

Ion

l'Y\ (a.m.u.) K. (c",'I"oll-scc) ,«(",a/volt-se,) non (&.)

lH

1. 0)

H

1

'9

3.2

2.17 ().5

(H'O):I~+ 37

3.'2

2.39

_'*

(DMSO)~1

₇₉

2 .

3

l.97

8.8

(DMSO~1r 157 1.7 1.56 lO.8 01.-

₃₂

2.7 - 3.0 1.96 - 2.l7 I.t -

b.4

l(HaO)O;

50

?7 -3.0 2.15 - 2. :!>9

_5.5-

*

CO:a-

₆₀

_{'Z.7 - 3.0} 2.~2 ~

2.47

1t - 1#

co.-

76

2.7 - 3.0 2.30- 2.56

• - *

(DMSO)<f

₉₄

2.4 t 0.1 2.01- 2.19

as-

'JI.

~OUSO)o;

,fo

'2.4! 0.1 2.0S - 2.'22 8.3 - 11

'It No r"ion ~x'sts

tor

y~ 2.17

a

ccordit'\9 to ~'9.

7.4.

3.0

2.5

2.0

I.S ~ _ _ - - L _ _ _ - L . _ _ _ - ' - -_ _ . - .

(27)

25 o

o

IS 10 0

s

0 Li+ ~+ K+ Rb· Cs· Hs+ m

(a.m.u.)

0 50 '00 ISO 200

(28)

..

UTIAS TECHNICAL NarE NO. 166

Institute for Aerospace Studies, University of T oronto

TRACE GAS ANALYSIS BY MOBILITY SEPARATION

Laszlo, George Peter 11 pages 10 figures

1. Ion-Mobility 2. Plasma Chromatograph 3. Mobility Separation

4. Trace Gas Analysis

I. Laszlo, George Peter H. UTIAS Technical Note No. 166

Alpha end beta partieles or ion pairs are formed by placing a radioacti ve source in a sample air stream. The charges then first complex wi th water

vapeur and finally end up on any highly polar:!,zable or electronegati ve impurity species present. Pulses of lans sa formed can be drifted down a tube by a one-dimensional field and a time-of-arrival spectrum is generated.

This is known as a plasma chromatogram by analogy to an ordinary gas chroma-togram. This project was designed to be a feaslbl1ity study of a continuous

flow analogue to tbls device because of tbe desire to utilize large sample gas rates and extremely high scavenglng efficiency for impurity atol!lS. For

this llurpose a modern version of the old "Erikson Air-Blast Method" (Ref. 1) was used. The system, originally used in the 1920's for measuring mobil1ties,

is comprised of a uniform velocity flow of sample gas through a rectangular cross-section tube, with astrong potential difference applied between the top and the bottom. A mixture of ions intraduced at one point at the top sepa-rates out in the crossed potential and velocity fields on account of mobility

differences. Ion spectra can be obtained by sliding an ion detector along the floor of tbe tube. The peaks are due to typical water complexes such as

(~O)nH+, (~O)OH-, etc, in th. ambient laboratory air samples, and to other

trace lans present in the air.

Available co pies of this report are limited. Return this card to UTIAS, if you

Instil:ul:e for Aerospace Sl:udies, University of T oronto

1. Ion-Mobil1 ty 2. Plasma Chromatograph 3. MObility Separation 4. Trace Gas Analysis

Alpha and beta partieles or ion pairs are formed by placing a radioacti ve

source in a sample air stream. The charges then first complex ... itb water

vapeur and finally end up on eny highly polarizable or electronegati ve impurity species present. Pulses of ions sa formed can be drifted down a

tube by a one-d1mensional field end a time-of-arrival spectrum is generated.

This is known as a plasma chromatogram by analogy to en ordinary gas chroma

-togram. This project was designed to be a feasibili ty study of a continuous flow analogue to this device because of the desire to utilize large sample

gas rates and extremely high scavenging efficiency for impurity atoms. For

this purpose a modern version of the old "Erikson Air-Blast Method" (Ref. 1) was used. The system, originally used in the 1920's for measuring mobillties,

is comprised of a uniform velocity flow of sample gas through a rectangular

cross-section tube, with astrong potentiaJ. difference applied between the

top and the bottom. A mixture of 10ns introduced at one point at the top sepa-rates out in the crossed potential and velocity fields on account of mobili ty

differences. Ion sp.ctra can be obtained by sliding en ion detector along

the floor of the tube. The peaks are due to typical water complexes such as

~

reqUire a copy.

~

-~

Institute for Aerospace Studies, University of T oronto

1. Ion-lolobill ty 2. Plasma Chromatograph 3. Mobili ty Separation

Alpha end beta partieles or ion pairs are formed by placing a radioactive source in a sample air stream. The charges then first canplex with water vapour and finally end up on any highly pOlarizable or electronegati ve impurity species present. Pulses of 10ns so formed can be drifted down a

tube by a one-dlmensional field and a time-of-arrlval s'Pectrum ls generated. This is known as a plasma. chromatogram by analogy to aD. ordinary gas clu'oma-togram. This project was designed to be a feasibility study of a continuous

flow analogue to this device because of the de sire to utilize large sample

gas rates and extremely high sca.venging efficiency for impurity atoms. For

this purpose a modern version of the old "Erikson Air-Blast Method" (Ref. 1)

was used. The system, originally used in the 1920's for measuring mobilities,

is comprised of a uniform velocity flow of sample gas through a rectangular

cross-section tube, with astrong potential difference applied between the

top and the bottom. A mixture of ions introduced at one point at the top sepa-ra.tes out in the crossed potentiel and velocity fields on account of mobility dif:ferences. Ion spectra cao be obtained by sliding an ion detector along

~

the flo~r of the tube. The peaks are due to typ1cal. water complexes such as

(~O)nH , (~O)OH-, etc, in the ambient laboratory air samples, and to other trace ions present in the air.

Available copies o~ this report are limited. Return this card to UTIAS, if you require a copy.

Instil:ul:e for Aerospace Studies, University of T oronl:o

L Ion-Mobility 2. Plasma Chromatograph 3. Mobility Separation

Alph .. and beta partieles or ion pairs are formed by placing a radio .. ctive

source in a sample air stream. The charges then first complex wl th water

vapoW" and finally end up on any highly polarizable or electronegati ve impurity species present. Pulses of ions so formed can be drifted down a tube by a one-d1mensional field and a time-of-arrival spectrum is generated. This is known as a plasma chroma.togram by analogy to an ordinary gas

chroma-togram. This project was designed to be a feasibility study of a continuous

flow analogue to this device because of tbe desire te utilize large sample

gas rates and extremely high scavenging efficiency for impurity atoms. For

this purpose a modern version of the old "Erikson Air-Blast Method" (Ref. 1)

... as used. The system, originally used in tbe 1920's for measuring IrOb111ties, is comprised of a uniform velocity fIo'"" of sample gas through a rectangular

cross-section tube, with astrong potentiaJ.. d1fference applied between the top atld the bottom. A mixture of 10ns introduced at one point at the top

sepa-rates out in the crossed potential and velocity fields on account of mobility differences. Ion spectra can be obtained by sliding an ion detector along the floor of tbe tube. The peaks are due to typical water complexes such as (~O)nH+, (~O)OH-,