Researchers from Helmholtz-Zentrum Dresden-Rossendorf (HZDR), a research institute based in Dresden, Germany, developed a gas chromatography–mass spectrometry (GC–MS) method for analyzing reaction products of partial isobutane oxidation. Their findings were published in the Journal of Chromatography A (1).
Hydroperoxides are the first stable reaction products in the reaction chain of non-catalyzed hydrocarbon oxidation processes, which can occur in the atmosphere, food, or fragrances. It is important to determine what methods are being used during analysis. This knowledge is useful when tracking how certain approaches are affected by industrial oxidation processes that use gaseous oxygen, such as hydroperoxide and peroxide. Some methods for determining hydroperoxides at low concentrations have been published, but very few have focused on products of isobutane (1). Publications on analytical methods for complex reaction mixtures, such as those obtained by multiphase oxidation processes, are also rare.
Reaction products obtained in industrial processes often need to be measured at much higher concentrations and absorbed in a solvent, since direct online analysis in the liquid phase is not yet possible. However, due to impurities, mixtures frequently become more complex, due to complex reaction mechanisms.
In this study, an improved gas chromatography–mass spectrometry (GC–MS) method was created for analyzing reaction products of the non-catalytic partial oxidation of isobutane at a starting temperature of 25 °C has been developed and compared to a previously published method. Two green GC-solvents (dimethyl carbonate (DMC), diethyl carbonate (DEC) and several internal standards (hexane, benzene, toluene, DEC) were tested.
The product separation occurring at low retention times (methanol, isobutane, isobutene) could be significantly improved. For liquid main products, such as t-butyl hydroperoxide (TBHP), di-t-butyl peroxide (DTBP), t-butanol (TBA), propanone and most trace products (isopropanol, isobutanal, methyl formate, isopropyl formate, t-butyl formate and some acetates–24 compounds in total), a coefficient of determination (CoD) greater than 0.999 was achieved. Uncertainties were calculated for all weighing and GC–MS measurements. The peaks of the peak pair t-butyl formate (CoD > 0.999) and isobutanol (CoD > 0.99), were also simulated and used for calibrations.
An improved GC method allowed for better separation, simultaneous determination, and a more exact quantitative analysis (correlation coefficients CoD ≥ 0.999 for the calibrations of the liquid reaction products) including a wider range of by-products, such as methanol and formic acid, among others. The peaks of isobutanol and t-butyl formate, which creates a strongly overlapping peak pair, could be separated and evaluated through simulations. Validating this model should be possible for most liquid organic products with a linear calibration.
DEC was not usable as a solvent, since TBHP decomposition took place, causing a strongly deformed peak, the researchers wrote. DMC was utilized instead. For both solvents, a special purification procedure was developed, with DMC stability towards TBHP and small concentrations of formic acid has been verified. After various attempts, the best calibration quality was obtained using benzene as an internal standard.
Based on measurements at lower temperatures between 19 and 31 ºC, an oven temperature of 25 ºC and DMC as solvent were selected to calibrate all liquid products with an excellent precision (CoD > 99.9 %) using benzene as internal standard. The method should be appropriate for performing a complete validation and studying reactions and their kinetics with good accuracy and precision.
(1) Willms, T.; Kryk, H.; Hampel, U. An Improved Method for the Analysis of the Reaction Products of the Partial Isobutane Oxidation by Gas Chromatography Using a Green Solvent. J. Chromatogr. A 2025, 1753, 465982. DOI:
