Analysis of silyl peroxides with post-column chemiluminescence reaction of luminol
Stefan BAJ, Roksana SŁUPSKA, Tomasz KRAWCZYK
Silesian University of Technology, Faculty of Chemistry, Department of Chemical Organic Technology and Petrochemistry ul. Krzywoustego 4, 44-100 Gliwice, Poland
Silyl peroxides are an organometallic group of compounds with the peroxy group bonded directly to the silicon atom. These kinds of compounds can be used as free-radical polymerisation initiators or cross- linking and vulcanisation agents [1]. They are also widely used as oxidation agents and bis(trimethylsilyl) peroxide (BTMSPO) is considered an anhydrous, safe form of hydrogen peroxide [1].
The abovementioned, wide practical applications of silylperoxides require adequate methods for their detection and quantification.
A method that is used for organic peroxides analysis is HPLC, followed by post-column chemiluminescent (CL) reactions [2,3]. CL is especially useful because it allows the detection of substances that lack chromophores and are therefore not visible by UV detectors. The most widely applied CL reaction in peroxides analysis is luminol oxidation, catalyzed by iron complexes or enzymes.
The general mechanism of luminol oxidation.
Process variables Uncoded values
Bissilyl peroxides Alkyl-silyl peroxides
Base concentration 0.03 0.03
Luminol concentration 0.4 0.4
Hemin concentration 0.3 0.3
Flow rate 0.9 0.3
Compound Correlation coefficient (r2)
Linear dynamic range (nmol)
LOD (nmol)
LOQ (nmol) Bissilyl peroxides 0.9928 - 0.9843 0.25 - 2.0 0.07 - 0.16 0.21 - 0.35 t-Bu-silyl peroxides 0.9914 - 0.9793 2.5 - 15 0.53 - 0.93 1.63 - 2.80 Cumyl-silyl peroxides 0.9984 - 0.9907 3 - 25 0.55 - 1.01 1.66 - 3.06
H2O2 0.9976 0.1 - 2 0.02 0.07
tBuOOH 0.9934 2 - 15 0.51 1.57
CumylOOH 0.9936 2 - 25 0.13 0.40
Schematic diagram of the HPLC-CL system: (A), (B) - eluents; (W 600E) - eluents pump;(W 717) – autosampler; (W 2487) - UV detector; (W 474) - CL detector; (WRM) - reagents pump; (T) –
T-connector; (W) - waste.
Formulae of investigated silyl peroxides.
The main variables which have an impact on CL emission are concentration of luminol, hemin and a base and a flow rate of its solution. To evaluate the optimal conditions the experiments were designed by Central Composite Design using STATISTICA software.
OPTIMAL CONDITIONS
QUANTITATIVE ANALYSIS
RESPONSE SURFACE METHODOLOGY
POSSIBLE REACTION MECHANISM 1. For each of investigated peroxides a regression equation with linear, square and
interaction coefficients were obtained.
2. The values of r2, depending on the investigated compound, were in the range of 0.86-0.95.
3. For the base and luminol concentration no optimum was found
4. For the hemin concentration, the broad maximum was observed
5. In the case of the dependence of light intensity on the flow rate, there were significant differences for:
alkyl-silyl peroxides, the maximum was observed in the center of the investigated range
bissilyl peroxides CL emission decreased with flow rate in the entire investigated range
According to obtained data it was possible to use the same mixture of reagents for both groups of peroxide compounds. Only the required flow rate was different - for alkyl-silyl
1. The method was evaluated for LOD, LOQ, linearity range, precision and accuracy.
2. A five-point linear curves (three replications of each injection) was plotted.
3. Both intra-day and inter-day precision were lower than 5.5% for each tested concentration level.
4. The intra-day accuracy for each concentration level was: 4.5 - 8.1% for the low concentration level, 1.3 - 3.6% for the middle concentration level, and 0.5 - 2.3%
for the high concentration level. The inter-day accuracy ranged from 0.8 to 7.8%.
It is very probable that the bond between silicon and oxygen must be cleaved with the formation of corresponding hydroperoxides or
The proposition of the hydrolysis of bissilyl and alkyl-silyl peroxides with the formation of an active oxidant.
[1] Yu. A. Aleksandrov, J. Organomet. Chem. 238 (1982) 1-78. [2] S. Baj, A. Chrobok, M. Cieślik, T. Krawczyk, Anal. Bioanal. Chem. 375 (2003) 327-330. [3] S. Baj, S. T. Krawczyk, Anal. Chim. Acta 585 (2007) 147-153.
Effects of the concentration of base, luminol, hemin and flow rate on the CL peak area for (Me3SiO)2.
INTRODUCTION
INVESTIGATED COMPOUNDS
Column: Nova-Pak C18 3.9mm x 150mm 4mm Cartridge RP Mobile phase: acetonitrile/ water 85% v/v
Concentration of silyl peroxides in acetonitrile: 10 mM Injection volume: 2 µL
Flow rate: 1 mL min-1.
EXPERIMENTAL DESIGN AND HPLC SYSTEM
RESULTS AND CONCLUSIONS
peroxides the value was higher and was 0.9 mL/min when for bissilyl peroxides the value was 0.3 mL/min
hydrogen peroxide prior to the reaction with hemin.
