Gas chromatography-Fourier Transform Infrared Spectroscopy Research Articles

Relationships in Gas Chromatography—Fourier Transform Infrared Spectroscopy—Comprehensive and Multilinear Analysis

Molecular spectroscopic detection techniques, such as Fourier transform infrared spectroscopy (FTIR), provides additional specificity for isomers where often mass spectrometry (MS) fails, due to similar fragmentation patterns. A hyphenated system of gas chromatography (GC) with FTIR via a light-pipe interface is reported in this study to explore a number of GC–FTIR analytical capabilities. Various compound classes were analyzed—aromatics, essential oils and oximes. Variation in chromatographic peak parameters due to the light-pipe was observed via sequentially-located flame ionization detection data. Unique FTIR spectra were observed for separated mixtures of essential oil isomers having similar mass spectra. Presentation of GC×FTIR allows a ‘comprehensive’-style experiment to be developed. This was used to obtain spectroscopic/separation profiles for interconverting oxime species with their individual spectra in the overlap region being displayed on a color contour plot. Partial least square regression provides multivariate quantitative analysis of co-eluting cresol isomers derived from GC–FTIR data. The model resulted in an R2 of 0.99. Prediction was obtained with R2 prediction value of 0.88 and RMSEP of 0.57, confirming the method’s suitability. This study explores the potential of GC–FTIR hyphenation and re-iterates its value to derive unambiguous and detailed molecular information which is complementary to MS.

Prediction of designer drugs: Synthesis and spectroscopic analysis of synthetic cathinone analogs that may appear on the Swedish drug market.

The use of hyphenated analytical techniques in forensic drug screening enables simultaneous identification of a wide range of different compounds. However, the appearance of drug seizures containing new substances, mainly new psychoactive substances (NPS), is steadily increasing. These new and other already known substances often possess structural similarities and consequently they exhibit spectral data with slight differences. This situation has made the criteria that ensure indubitable identification of compounds increasingly important. In this work, 6 new synthetic cathinones that have not yet appeared in any Swedish drug seizures were synthesized. Their chemical structures were similar to those of already known cathinone analogs of which 42 were also included in the study. Hence, a total of 48 synthetic cathinones making up sets of homologous and regioisomeric compounds were used to challenge the capabilities of various analytical techniques commonly applied in forensic drug screening, ie, gas chromatography-mass spectrometry (GC-MS), gas chromatography-Fourier transform infrared spectroscopy (GC-FTIR), nuclear magnetic resonance (NMR), and liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS). Special attention was paid to the capabilities of GC-MS and GC-FTIR to distinguish between the synthetic cathinones and the results showed that neither GC-MS nor GC-FTIR alone can successfully differentiate between all synthetic cathinones. However, the 2 techniques proved to be complementary and their combined use is therefore beneficial. For example, the structural homologs were better differentiated by GC-MS, while GC-FTIR performed better for the regioisomers. Further, new spectroscopic data of the synthesized cathinone analogs is hereby presented for the forensic community. The synthetic work also showed that cathinone reference compounds can be produced in few reaction steps.

Separation and Characterization of Trace Phosphorus Compounds in Hydrotreated Lube Base Oil

In this article, a kind of method was described for separation and characterization of the trace organic phosphorus compounds in hydrotreated lube base oil. First, the base oil was extracted with methanol containing 2% hydrochloric acid, and then the extracted portion was adsorbed on neutral aluminum oxide and eluted with petroleum ether, benzene, chloroform, and 9:1 tetrahydrofuran-ethanol in sequence; finally the fraction acquired was characterized by gas chromatography-mass spectrometry, respectively. The result of the test indicates that only one kind of organic phosphorus was found in hydrotreated lube base oil, gas chromatography-mass spectrometry and gas chromatography-Fourier transform infrared spectroscopy (GC-FTIR) were used to characterize the organic phosphorus compound, and its molecular structure is tributyl phosphate.

Novel Method for Identification and Quantification of Methanol and Ethanol in Alcoholic Beverages by Gas Chromatography-Fourier Transform Infrared Spectroscopy and Horizontal Attenuated Total ReflectanceFourier Transform Infrared Spectroscopy

Numerous methods are being used to identify and quantify methanol and ethanol in alcoholic beverages, including country liquors. Some of the known methods are density and refractive index measurements, and spectrophotometric measurements using Schiff's reagent or chromatropic acid. Other advanced techniques involve head space gas chromatography (GC), GC-flame ionization detection, high-performance liquid chromatography, enzymatic reactions, and biosensors. However, identification and quantification of methanol and ethanol in beverages can be accurately done using GC-Fourier transform infrared spectroscopy (FTIR) and horizontal attenuated total reflectance (HATR)-FTIR. Identification of alcohols is possible from library matching of the IR spectra obtained from GC-FTIR. In water, methanol and ethanol show a very strong peak for C-O, stretching at 1015.3 and 1044.2 cm(-1), respectively. The strong absorption of vibrational stretching frequency of C-O present in alcohols was used for quantification purposes. The absorptions of C-O group frequency of alcohols in water mixtures were measured using HATR-FTIR with a zinc-selenide crystal. Samples were placed directly on the HATR crystal, with alcohol concentrations ranging from 0.2 to 50.0% (v/v). The plot of absorptions against concentrations of methanol and ethanol obeyed Beer's law (r2 = 0.9998 and 0.9987, respectively), from which alcohol in the mixtures was quantified. Propan-2-ol and n-butanol showed no interference. The method is validated from absorption measurements of known mixtures of standard ethanol in water. This is a simple, specific, rapid, accurate, and nondestructive method of identification and quantification of methanol and ethanol in mixtures. It can be used to ascertain methanol contamination in alcoholic beverages that can lead to death or methanol poisoning by alcohol consumption.

Isomer Identification of Monohydroxylated Polycyclic Aromatic Hydrocarbon Metabolites by Gas Chromatography/Fourier Transform Infrared Spectroscopy and Carbon-13 Nuclear Magnetic Resonance Spectroscopy

The foundation for a systematic approach utilizing spectral/structural correlations was established for unambiguous identification of monohydroxylated polyaromatic hydrocarbon metabolite (PAHm) isomers. Using elements of a theoretical/empirical valence-bond model developed earlier in our laboratory for isomer identification of chlorinated dibenzo- p -dioxin isomers, both gas chromatography/Fourier transform infrared spectroscopy (GC/FTIR) and carbon-13 nuclear magnetic resonance ( 13 C NMR) spectroscopy were employed for PAHm isomer identification. Results indicate that PAHm isomers also can be systematically identified by these techniques. However, many of the parameters leading to the success of the dioxin analysis (high symmetry of the parent dioxin molecule and laterally stabilized delocalization from chlorine substituents through ether linkage oxonium ions) are not generally present in the PAHm ring systems under investigation. The observed infrared parameters in PAH metabolites are C--O stretch, O--H stretching and bending vibrations, along with C=C skeletal stretching vibrations. In addition, 13 C NMR parameters such as chemical shift perturbations for carbons adjacent to functional groups have been observed.

Computer-aided screening for hallucinogenic and stimulant amphetamines with gas chromatography-Fourier transform infrared spectroscopy (GC-FTIR).

An expert system applied as a screening test for amphetamine analogues found in recreational-drug exhibits (tablets or powders) is described. The knowledge base defining the reference Fourier transform infrared spectroscopic (FTIR) spectral patterns has been built according to criteria encompassing toxicological, pharmacological, and neurochemical aspects. The class identity of a compound is determined within seconds using soft independent modeling of class analogy (SIMCA). The predictive value of the system, as assessed at a testing accuracy of 95%, is expressed by a total correct classification rate of 93.93% and by a 96.30% rate of true-positive amphetamines. The specificity and the selectivity of the screening test, evaluated by testing 159 toxicologically relevant compounds, are discussed, emphasizing the chemical and physical factors affecting these parameters. Medicinal amphetamines giving cross-reactions with traditional screening techniques produce a negative result. The specificity of the system characterizes the expert system as a highly sensitive, selective, fast, and user-friendly screening test that screens for amphetamines with prediction accuracy adequate for investigations in analytical toxicology.

Identification limits for volatile organic compounds in the blood by purge-and-trap GC-FTIR.

An analysis method for volatile organic compounds in blood based on purge-and-trap extraction coupled with gas chromatography-Fourier transform infrared spectroscopy (GC-FTIR) was developed. The sample volume was 5 mL, and the internal standard was diethyl ketone. The chromatographic separation was carried out on a PoraPLOT Q capillary column, and the effluent was first directed to the FTIR and then to a flame ionization detector (FID). FTIR identification limits were measured for 27 volatile organic compounds; the criteria for the limit were that the first hit-list position should be obtained against the Sadtler library, which contains 3240 spectra, and that the correlation value should exceed 0.5. It was required that the peak be seen by FID but not necessarily by a Gram-Schmidt chromatogram. The FTIR identification limits, ranging from 0.01 mg/L for ethyl acetate, methylethyl ketone, and sevoflurane to 24 mg/L for methanol, generally allowed the detection of volatile-substance exposure at a lower level than is acutely toxic. Quantitative calibration data were presented for selected substances, based on the FID response, which shows that the method is also amenable to quantitative analysis. The throughput of the method without additional automation is five samples per day, the purge-and-trap stage being the limiting factor.

Biodegradation of Alkylnaphthalenes in Sediments Adjacent to an Off-Shore Petroleum Production Platform

Abstract Sediments adjacent to an off-shore petroleum production platform in North Western Australia contain kerosene-like hydrocarbons from oil-based drilling mud. The hydrocarbons in these sediments were examined by gas chromatography-mass spectrometry (GC-MS) and direct deposition gas chromatography-Fourier transform infrared spectroscopy (GC-FTIR). As distance from the platform increased, the hydrocarbons exhibited an increasingly biodegraded signature. The relative susceptibility to biodegradation for the individual dimethylnaphthalene (DMN), trimethylnaphthalene (TMN) and tetramethylnaphthalene (TeMN) isomers present in the samples were determined using GC-MS and GC-FTIR as complementary analytical techniques.

The Analysis of Dimethylphenanthrenes by Direct Deposition Gas Chromatography – Fourier Transform Infrared Spectroscopy (GC-FTIR)

Abstract Dimethylphenanthrenes (DMPs) occur as complex mixtures in crude oils and sedimentary rock extracts. Conventionally these mixtures are analysed using gas chromatography-mass spectrometry (GC-MS) employing a column with a medium polarity stationary phase. Under these conditions, complete resolution of the mixture is not achieved and several isomers co-elute. Furthermore, the mass spectra of these co-eluting isomers may be so similar that one is unable to differentiate between them, and their abundance may therefore not be determined. In this paper, we describe the application of GC-FTIR as a complementary technique to GC-MS in the analysis of three co-eluting DMP isomers. Since each isomer has a unique infrared spectrum, the proportion of each in the mixture was determined by comparing the spectrum of the co-eluting compounds with the spectrum of each of the isomers. The result of this analysis was confirmed by the use of mordenite molecular sieves to separate the mixture into simpler fractions, an...

Identification of monosaccharides and related compounds by gas chromatography-Fourier transform infrared spectroscopy of their trimethylsilyl ethers

Trimethylsilyl (TMS) ethers are widely used in gas chromatography (GC) and gas chromatography-mass spectroscopy (GC-MS) for the identification of carbohydrates; this work shows that gas chromatography-Fourier transform infrared spectroscopy (GC-FT-IR) can also be used, with some advantages, for this purpose. A selection of 42 monosaccharides and related compounds were examined and in each case unique spectra were obtained for the differing compounds and their isomeric forms, allowing unambiguous identification. No relationship between the observed spectra and anomer form was seen. There was a statistically significant difference in the intensity of the peak at 1108±25 cm −1 distinguishing the furanose and pyranose conformers.

Analysis of Alkyl Nitrites by Gas Chromatography-Infrared Spectroscopy

Abstract Gas chromatography-Fourier transform infrared spectroscopy (GC/IR) was used to analyze a series of alkyl nitrites (butyl and pentyl) as well as some typical “street products” containing alkyl nitrites. The vapor phase IR spectra of the nitrites exhibited strong absorbances near 1665 and 1620 cm-1 (anti and syn R-O-N = O stretches) and 780 cm-1 (O-N stretch); yet enough variation exists to distinguish between them. Street samples, or purposely “aged” nitrites, showed mixtures of readily separated components consisting of alkyl nitrites and nitrous oxide.

Polychlorobiphenyls differentiation and identification by gas chromatography/fourier transform infrared spectroscopy

Reference infrared vapour phase spectra of 20 polychlorobiphenyls (PCBs) have been obtained by gas chromatography/Fourier transform infrared spectroscopy (GC/FTIR). These spectra are consistent with those of PCB obtained by diffuse reflectance IR spectroscopy (DRIFT) and with those of more simple molecular structures (iodochlorobenzenes, 1-bromodichlorobenzenes). The IR frequencies of the GC/FTIR spectra of PCB are assigned in terms of substitution patterns. This work shows that GC/FTIR can be a good approach for differentiation and identification of PCB in complex mixtures.

Reconstruction of gas chromatograms from digitally filtered Fourier-transform infrared interferograms

Two methods have commonly been used to reconstruct gas chromatograms from interferograms collected during gas chromatography/Fourier transform infrared spectroscopy (GC/FTIR) experiments. Gram-Schmidt orthogonalization has been applied to a section of the raw interferograms, or the fast Fourier transform has been applied to the interferogram followed by absorbance calculations over specific frequency windows

Fluorimetric determination of vitamin k 3 (menadione sodium bisulfite) in synthetic animal feed by high-performance liquid chromatography using a post-column zinc reducer

A high-performance liquid chromatographic (HPLC) method for analysis of vitamin K 3 (menadione), as the water-soluble sodium bisulfite salt, in synthetic animal feed is described. The menadione sodium bisulfite (MSB) is extracted with acqueous methanol, converted to oil-soluble menadione with sodium carbonate, and partitioned into n-pentane. After evaporation, the menadione is dissolved in methanol and analyzed by revered-phase HPLC. The menadione is reduced on-line to its fluorescent 1,4-dihydroxy analogue by zinc reduction prior to fluorescence determination at 325 nm excitation wavelength and 425 nm emission wavelength. The fluorescence response was linear in the range 1 to 100 ng of menadione injected. Recovery experiments were performed on synthetic animal feed spiked at 20 and 200 mg/kg levels of MSB. Average recoveries from feed were greater than 90% with an average relative standard deviation of 5.5%. Additional confirmation of menadione in actual feed extracts was performed using capillary gas chromatography-Fourier transform infrared spectroscopy (GC-FT-IR). The HPLC-fluorescence and GC-FT-IR methods had lower limits of detection of 20 μg/kg and2 mg/kg, respectively.

Identification of amphetamine isomers by GC/IR/MS.

The methods of gas chromatography/Fourier transform infrared spectroscopy (GC/FTIR) and gas chromatography/infrared spectroscopy/mass spectrometry (GC/IR/MS) are evaluated for their ability to differentiate side chain isomers of amphetamine. It is found that absorption bands from 3000 to 2850 cm-1 and 900 to 650 cm-1 are most useful for differentiating the alkyl amines, while the bands from 1600 to 900 cm-1 are only useful for differentiating primary amines from the other substituted amines. The combination of GC/IR/MS is superior for differentiating these side chain isomers.

Forensic Drug Analysis by GC/FT-IR

Gas chromatography Fourier transform infrared spectroscopy (GC/FT-IR) has been examined as a new forensic drug identification technique. The method is found to be specific for many closely related isomers including cocaine and pseudococaine or phentermine and methamphet-amine. Distinguishing some isomers may require spectral subtraction or examination of band positions. The useful range of GC/FT-IR sensitivities was determined to be from 5O to 500 nanograms per component.

Gas chromatography/Fourier transform infrared spectroscopy for determining traces of methane from biodegradation of methylmercury

A sensitive and specific technique, gas chromatography/Fourier transform infrared spectroscopy (GC/FTIR), has been used to detect traces of methane from the biodegradation of methylmercury due to the detoxification process of Pseudomonas putida strain FB1, which was isolated from cinnabar mines in southern Tuscany (Italy). The cured strain FB4 was used together with uninoculated samples as controls for the experiment. The calibration curve of methane was linear up to 1.3 ..mu..g/mL when 0.3 mL of headspace was injected into the GC/FTIR. The detection limit of methane determination in the closed system was 10 ng/mL. The biodegradation of methylmercury was measured during the 130-min experiment by means of elemental mercury analysis, which was determined specifically in the headspace by atomic absorption spectroscopy (AAS), by methylmercury analysis, and by consideration also of the growth rate of the bacterial strains.

Systematic approach to coupled gas chromatography Fourier transform infrared spectroscopy using two wide bore capillary columns

The approach to coupled gas chromatography Fourier transform infrared spectroscopy (GC-FTIR) described in this paper is designed to achieve good separation with pre-set column parameters, allowing fast and precise identification of the components. For this reason the sample is separated on a gas chromatograph fitted with two wide bore (530 µm) capillary columns of different polarities. The use of two columns allows a definite statement about the number of components in the mixture to be made. Infrared (IR) spectra can then simply be taken from the centre of each peak. The wide bore capillary columns were necessary to achieve the desired peak volume, peak shape and sample loading to match the light pipe volume. Temperature gradients were developed which kept the peak width constant and relatively narrow throughout the separation, thus maximising the concentration of components passing through the IR cell. This systematic approach provides a methodology for the technique, which, if adopted, would result in an increased sample throughput and greater reliability.

Analysis of Terpenes by Capillary Gas Chromatography/Fourier Transform Infrared Spectroscopy (GC/FTIR)

Analysis of Terpenes by Capillary Gas Chromatography/Fourier Transform Infrared Spectroscopy (GC/FTIR)

Gold Coating of Glass Tubes for Gas Chromatography/Fourier Transform Infrared Spectroscopy “Light-Pipe” Gas Cells

The sensitivity of gas chromatography/Fourier transform infrared spectroscopy (GC/FT-IR) may be significantly improved by use of small bore gold-coated glass gas cells. This note describes the method of preparing internally gold-coated glass or quartz tubes for GC-IR applications.