Gas chromatography-vacuum ultraviolet spectroscopic analysis of organosilanes.

Organosilanes are used in a broad range of industrial, cosmetic, and personal care products. They serve as bridges between inorganic or organic substrates and organic/polymeric matrices. They are also versatile intermediates and can be used for a variety of synthetic applications. They do not exist naturally and have to be synthesized. Evaluation of intermediates and products resulting from the synthesis processes of organosilanes can be challenging. In this study, gas chromatography with vacuum ultraviolet spectroscopic detection (VUV) was used to analyze Si-containing compounds that are commercially available or were synthetically prepared. VUV measures full scan absorption in the range of 120-240 nm, a region that provides unique absorption signatures for chemical compounds. VUV absorption spectra of organosilanes showed rich and featured characteristics in this wavelength range. Theoretical computations of VUV absorption spectra based on time-dependent density functional theory were also explored as a complementary tool for identification. In addition, the synthesis process of isomeric benzodioxasiline compounds (ortho-, meta-, and para-) was monitored by GC-VUV. It was demonstrated that GC-VUV can be used for easy and rapid differentiation of organosilanes, including structural isomers.

Comparative study of ink photoinitiators in food packages using gas chromatography with vacuum ultraviolet detection and gas chromatography with mass spectrometry.

This work focused on the development and validation of the analytical procedure using gas chromatography equipped with vacuum-ultraviolet detection for the specific and sensitive determination of nine photoinitiators in food packages. Subsequently, a comparison of the combination of vacuum ultraviolet spectroscopy with gas chromatography and a developed gas chromatography with mass spectrometry method was performed. The vacuum-ultraviolet spectra of all tested photoinitiators were collected and found to be highly distinct, even for isomers. Under the optimal conditions, the limits of detection for nine photoinitiators ranged from 1 to 5 mg/L using vacuum ultraviolet detection and from 0.15 to 0.5 mg/L using mass spectrometric detection. Both techniques were successfully applied for screening of photoinitiators in seven kinds of food packages and the obtained data showed good agreement (the relative difference was between 3 and 18%). The variability in concentrations found in triplicate samples was assessed to be below 18%. Predominantly benzophenone was found in all analysed samples in the range of 0.31-4.23 mg/kg. It appears to be preferably selected by food packaging manufacturers. This study proposes a new simple and sensitive technique used for analysis of photoinitiators that could be a good alternative to gas chromatography with mass spectrometry.

Resolution of isomeric new designer stimulants using gas chromatography - Vacuum ultraviolet spectroscopy and theoretical computations.

Distinguishing isomeric representatives of "bath salts", "plant food", "spice", or "legal high" remains a challenge for analytical chemistry. In this work, we used vacuum ultraviolet spectroscopy combined with gas chromatography to address this issue on a set of forty-three designer drugs. All compounds, including many isomers, returned differentiable vacuum ultraviolet/ultraviolet spectra. The pair of 3- and 4-fluoromethcathinones (m/z 181.0903), as well as the methoxetamine/meperidine/ethylphenidate (m/z 247.1572) triad, provided very distinctive vacuum ultraviolet spectral features. On the contrary, spectra of 4-methylethcathinone, 4-ethylmethcathinone, 3,4-dimethylmethcathinone triad (m/z 191.1310) displayed much higher similarities. Their resolution was possible only if pure standards were probed. A similar situation occurred with the ethylone and butylone pair (m/z 221.1052). On the other hand, majority of forty-three drugs was successfully separated by gas chromatography. The detection limits for all the drug standards were in the 2-4 ng range (on-column amount), which is sufficient for determinations of seized drugs during forensics analysis. Further, state-of-the-art time-dependent density functional theory was evaluated for computation of theoretical absorption spectra in the 125-240 nm range as a complementary tool.

Gas chromatography-vacuum ultraviolet detection for classification and speciation of polychlorinated biphenyls in industrial mixtures.

Polychlorinated biphenyls (PCBs) are a group of synthetic chlorinated compounds that have been widely used as dielectric fluids in capacitors and transformers. Due to their toxicity, persistence, and bioaccumulation in the food chain, PCBs are an environmental concern and among the most analyzed compounds in environmental analysis. The most common analytical methods for analysis of PCBs are based on gas chromatography-electron capture detection (GC-ECD) and gas chromatography-mass spectrometry (GC-MS). However, the number of possible congeners (209), similarities of physical and chemical properties, and complexity of sample matrices make it difficult to distinguish and accurately speciate PCB congeners using existing methods. This study presents a new method using gas chromatography with vacuum ultraviolet detection (GC-VUV), which offers absorption detection in the range of 120-240nm, where all chemical species have absorption. The VUV absorption spectra for all 209 PCB congeners were collected and shown to be differentiable. The capability of VUV data analysis software for deconvolution of co-eluting signals was also demonstrated. An automated time interval deconvolution (TID) procedure was applied to rapidly speciate individual PCBs, as well as classify commercial Aroclor mixtures based on their degree of chlorination. The data showed excellent agreement between the stated nominal and determined degrees of chlorination (less than 1% deviation for highly chlorinated mixtures). GC-VUV was verified to provide excellent specificity, high sensitivity (100-150pg limit of detection), and fast data acquisition for this application.

Analysis of terpenes and turpentines using gas chromatography with vacuum ultraviolet detection.

The separation and identification of natural mixtures of terpenes is challenging and laborious. A gas chromatographic method based on vacuum ultraviolet spectroscopic detection, which is characterized by full-scan absorption in the range of 125-240 nm, was developed and applied to analyze terpenes. In this study, the vacuum ultraviolet absorption spectra of 41 different standard terpenes were investigated and compared. The spectra were found to be highly featured and easily differentiated. Several commercial turpentine samples were analyzed and the vacuum ultraviolet detector demonstrated good specificity for qualitative identification of constituent terpenes. A total of 31 terpenes were detected in the four turpentine samples. α-Pinene was the predominant terpene ranging from 744.2 ± 9.7 to 917 ± 21 mg/mL. The other major constituents in the turpentines included ß-pinene, δ-3-carene, camphene, and p-isopropyltoluene. Deconvolution of co-eluting signals of terpenes was achieved utilizing the data analysis software. The technique has been demonstrated to be a powerful tool for reliable and accurate qualitative and quantitative analysis of terpenes from complex natural mixtures.

Pseudo-absolute quantitative analysis using gas chromatography - Vacuum ultraviolet spectroscopy - A tutorial.

The vacuum ultraviolet detector (VUV) is a new non-destructive mass sensitive detector for gas chromatography that continuously and rapidly collects full wavelength range absorption between 120 and 240 nm. In addition to conventional methods of quantification (internal and external standard), gas chromatography - vacuum ultraviolet spectroscopy has the potential for pseudo-absolute quantification of analytes based on pre-recorded cross sections (well-defined absorptivity across the 120-240 nm wavelength range recorded by the detector) without the need for traditional calibration. The pseudo-absolute method was used in this research to experimentally evaluate the sources of sample loss and gain associated with sample introduction into a typical gas chromatograph. Standard samples of benzene and natural gas were used to assess precision and accuracy for the analysis of liquid and gaseous samples, respectively, based on the amount of analyte loaded on-column. Results indicate that injection volume, split ratio, and sampling times for splitless analysis can all contribute to inaccurate, yet precise sample introduction. For instance, an autosampler can very reproducibly inject a designated volume, but there are significant systematic errors (here, a consistently larger volume than that designated) in the actual volume introduced. The pseudo-absolute quantification capability of the vacuum ultraviolet detector provides a new means for carrying out system performance checks and potentially for solving challenging quantitative analytical problems. For practical purposes, an internal standardized approach to normalize systematic errors can be used to perform quantitative analysis with the pseudo-absolute method.