Methyl Silicone Column Research Articles

Identification of free disaccharides and other glycosides in wine

Free soluble carbohydrates of different wine samples were analyzed by GC–MS as their trimethylsilyloximes using a methylsilicone column. Besides α,α-trehalose, several β-glucosylglucoses such as cellobiose, sophorose, laminaribiose and gentiobiose were the main disaccharides identified. With the exception of gentiobiose, these disaccharides are now reported for the first time in wine. Lactose (4-O-β- d-galactopyranosyl- d-glucose), previously described in this product, was also tentatively identified. Several free glycosides: β-ethyl-glucoside and seven glyceryl-glycosides (including glucosides and galactosides) were also identified for the first time in wine. On the contrary, disaccharides in grape juice were mainly constituted of fructose derivatives, including sucrose, and no glycosides were detected. Although the total amount of disaccharides was different in white wines (<50 mg/L) from those in rosé and red wines (80–130 mg/L), the chromatographic profile was noticeably similar in all wine samples. The method here reported allows the identification of several carbohydrates which have not been previously detected in wines and could contribute to increase the understanding of enzymatic activity during winemaking.

Determination of petroleum contamination in shellfish using solid phase micro-extraction with gas chromatography-mass spectrometry.

Headspace solid phase micro-extraction (HS-SPME) has been applied as a sampling technique for the determination of petroleum contamination in shellfish using capillary gas chromatography-mass spectrometry (GC-MS). A poly(dimethylsiloxane) fused silica fibre (100 microm thickness) was found to be satisfactory for the extraction of a range of aliphatic hydrocarbons (HCs) from homogenised shellfish tissues. The SPME conditions, including temperature, salt content, extraction time and desorption temperature, were optimised for a range of aliphatic HCs (C9-C20). A methyl silicone column GC (12 m x 0.20 mm, 0.33 microm layer thickness) was used with a temperature programme from 40 to 260 degrees C and the HCs were determined within a mass range of m/ z=50-550 in electron impact mode. Calibration range was from 10 to 5000 ng/g with linear correlation coefficients ( r(2)) of 0.982 for nonane to 0.997 for octadecane. Detection limits for aliphatic HCs, spiked into shellfish (mussel) tissues, varied from 3.6 ng/g (tetradecane) to 51 ng/g (eicosane) and relative standard deviation (% RSD) values ranged from 1.4% (hexadecane) to 24.3%(eicosane).

Packed column supercritical fluid chromatography of oligoethers using pure carbon dioxide with flame ionization and ultraviolet detection

TMS derivatives of ethoxylates and proproxylates were separated with high resolution, on standard bore and 2 mm packed columns, using both UV and FID detection. A methyl silicone column was found to dramatically decrease retention and allow the elution of heavier oligomers, compared to C18 or C8. Standard bore columns eliminated pre-column splits, and allowed full loop injections. Reproducibility for individual homologs was found to be 0.2–0.3% in retention time and 0.85 to 1.3% in area, over 10 consecutive automated injections. The UV data was found to be equivalent to “corrected” FID data. Switching to the UV detector at 191 nm, eliminated any need for a fixed restrictor. Slow and fast program rates were shown to provide equivalent mass distribution information.

Gas chromatographic and mass spectrometric analysis of 36 lignin-related methoxyphenols from uncontrolled combustion of wood

Eighteen 4-hydroxy-3-methoxyphenyl (guaiacyl) compounds in wood smoke from spruce, and 18 4-hydroxy-3,5-dimethoxyphenyl (syringyl) analogues in birchwood smoke were analysed. Smoke samples were taken by a gas syringe from wood burning under varying but more or less choked conditions in laboratory pot experiments. Retention index data for a methylsilicone column and basic mass spectral data are given for all compounds. Retention index in combination with molecular mass and structure-specific fragment ions greatly facilitates qualitative analysis. The syringyl and guaiacyl analogues differ by 240 units in retention index and the matching structure-specific ions in their mass spectra by 30 mass units. The identified methoxyphenols differ in the structure of the sidechain, which may be lacking, an alkyl group, an alkenyl group, a carbonyl-containing group or an alcoholic moiety. The proportions between these groups of compounds varied strongly with combustion conditions whereas the proportions of phenols within them were quite specific for each group. The phenols with reactive olefinic linkages in the sidechain were present in larger proportions than reported in other studies of methoxyphenols.

Analysis of sn‐1(3)‐ and sn‐2‐short‐chain acyl isomers of triacylglycerols in butteroil by gas‐liquid chromatography

AbstractThe aim of the study was to determine major triacylglycerols (TG), and sn‐1(3) and sn‐2 isomers of butyryl and caproyl TG in butteroil (BO) and interesterified butteroil (IBO) by gas‐liquid chromatography (GLC) and silver ion column chromatography. Altogether, 112 molecular species of TG were synthesized by interesterification and their retention indices were determined. Molar empirical correction factors for TG were determined using linear calibration. Retention indices showed that sn‐1(3) and sn‐2 isomers of the TG containing one short‐chain acyl (butyrate, caproate) and two long‐chain acyls (lauroate, myristate, palmitate, stearate, and oleate) were separated on a phenyl (65%) methylsilicone column. The difference between retention indices of 1(3)‐ and 2‐short‐chain acyl isomers ranged from 14 to 19, and from 9 to 16 for butyrates and caproates, respectively. The proportion of sn‐2 isomers of butyrates averaged 1.4%, but only traces of sn‐2 isomers of caproates were detected in butteroil. The ratio of sn‐1(3)‐ to sn‐2‐butyrates and caproates in interesterified butteroil averaged 2.0:1. The most abundant molecular species of mono‐short‐chain TG in butteroil were BPP + BMS (5.6 mol%), BPO + BSPo (4.8 mol%), BMP + BLaS (3.4 mol%), BMO + BPPo (2.7 mol%), BPS (2.5 mol%), and CoPP + CoMS (2.3 mol%).

Determination of positional distribution of butyryl groups in milkfat triacylglycerols, triacylglycerol mixtures, and isolated positional isomers of triacylglycerols by gas chromatography and 1H nuclear magnetic resonance spectroscopy.

Positional isomers (1-butyryl-2X-3Y-rac-glycerol and 2-butyryl-1X-3Y-rac-glycerol; X,Y = long-chain acyls) of saturated triacylglycerols (TAG) within 34 and 40 acyl carbons were shown to separate in two chromatographic peaks on immobilized phenyl(65%)methylsilicone column by gas-liquid chromatography, and on reversed-phase ODS-1 column by high-performance liquid chromatography. The analysis of 500-MHz 1H nuclear magnetic resonance (NMR) spectra showed distinct differences between 2-butyryl-1X-3Y-rac-glycerol and 1-butyryl-2X-3Y-rac-glycerol isomers in the resonance signals of methylene and methine protons of glycerol backbone, and carbon-2 methylene of acyl groups, and methyl protons of butyryl group. The 1H NMR spectra of three interesterified mixtures of three monacid TAG containing saturated butyrate and caproate TAG and unsaturated butyrate TAG showed that triplets of methyl protons of butyryl groups at sn-1(3)- and sn-2-positions in saturated and unsaturated TAG had similar chemical shifts and that the chemical shift of caproyl methyl protons was different from those of butyryl methyl protons. The positional distribution of butyryl groups in isolated positional isomers of butyrate TAG, interesterified TAG mixtures, and natural and interesterified butteroil can be determined by integration of these signals.

Properties of chlorinated dihydroxybenzenes — Components of pulp bleaching effluents

Gas chromatography and mass spectrometry data are given for the acetates of the chlorodihydroxybenzenes which are components of wood pulp bleaching effluents and biologically-treated effluents, and are proposed intermediates in the chlorination of humic acids. The chlorohydroxybenzenes include the nine chlorocatechols, the six chlorohydroquinones and the seven known chlororesorcinols. The 22 chlorinated compounds were generally well separated on a phenyl methyl silicone column with the exception of three dichloro compounds. The chloro compounds with the same level of chlorine substitution were not able to be distinguished on the basis of their electron impact mass spectra.

Confirmation of Chloramphenicol Residues in Bovine Milk by Gas Chromatography/Mass Spectrometry

Abstract A gas chromatographic/mass spectrometric method was developed to confirm the presence of chloramphenicol (CAP) at 0.5 ng/mL in bovine milk. meta-Nitrochloramphenicol (20 ng) is added to 10 mL milk as a surrogate standard. The milk is mixed with ethyl acetate and then loaded onto a diatomaceous earth-filled, solid-phase extraction (SPE) column; CAP is eluted with additional ethyl acetate. A solution of 4% NaCI in water is added to the eluant, and ethyl acetate is removed by evaporation under a flow of N2. The sample is defatted with hexane and then loaded onto a C18-SPE column. The column is washed with water, and CAP is eluted with methanol. The methanol is evaporated under a flow of N2, and the trimethylsilyl derivative is prepared with Sylon HTP (hexamethyldisilazane–trimethylchlorosilane–pyridine, 3 + 1 + 9). The excess reagent is evaporated under N2, and the residue is taken up in cyclohexane-hexane (60 + 40). CAP is separated on a 30 m × 0.25 mm id methylsilicone column having a film thickness of 0.25 pm and analyzed by methane negative chemical ionization with selected ion monitoring. The ions with m/z 304, 322, 358, 360, 466, and 468 are monitored. Confirmation is based on the presence of 5 ions with relative ion abundances within 10% of that obtained by using standards.

Mass spectrometric identification of triacylglycerols of enzymatically modified butterfat separated on a polarizable phenylmethylsilicone column

AbstractOriginal butter oil, butter oil interesterified withPseudomonas fluorescens lipase as catalyst, and the saturated, monoene, diene and triene fractions of interesterified butter oil from silver ion chromatography on ap‐propylbenzene sulfonic acid column were analyzed on a polarizable phenyl(65%)methylsilicone column. Major and also some minor molecular species of triacylglycerols (TG) were identified from the electron‐impact (EI) gas chromatography/mass spectrometry analytical data for the original and lipase‐modified butter oil and the four fractions. Acyl + 74 and acyl + 128 fragments of EI mass spectral data proved useful, in addition to acyl and M ‐ RCOO fragments, in the identification of molecular species of TG. The TG compositions of the modified butter oils were compared with the composition calculated according to random distribution and with the TG composition of original butter oil.

Simultaneous screening and quantitation of alpidem, zolpidem, buspirone and benzodiazepines by dual-channel gas chromatography using electron-capture and nitrogen-phosphorus detection after solid-phase extraction.

A rapid twin-column gas chromatographic (GC) method for simultaneous screening and determination of commonly prescribed benzodiazepines and other new anxiolytics from plasma is described. Identical fused-silica Ultra 2 (5% phenyl methyl silicone) columns were connected to nitrogen-phosphorus and electron-capture detectors. The drugs were isolated from 1 ml of plasma by solid-phase extraction (SPE) onto a C8 reversed-phase sorbent and recovered with 0.5% acetic acid in methanol. The eluate was reconstituted with isopropanol which was found suitable for on-column injection. Prazepam was used as internal standard. The method was found appropriate for the quantification in a single run of alpidem, alprazolam, buspirone, chlordiazepoxide, clobazam, clotiazepam, diazepam, estazolam, flunitrazepam, lorazepam, midazolam, oxazepam, tofisopam, triazolam, and zolpidem within 30 min. Limits of quantification allow toxicological or pharmacological determinations, except for buspirone: only toxic blood levels can be quantified by this method. This first SPE of imidazopyridines (alpidem and zolpidem) provides faster, more efficient and cheaper sample preparation than the traditional liquid-liquid procedure. This GC analysis of alpidem and zolpidem is also the first described procedure for simultaneous quantification of all different classes of anxiolytics.

Evaluation of capillary gas chromatography for the measurement Of C 2–C 10 hydrocarbons in urban air samples for air pollution research

A method for the determination of speciated non-methane hydrocarbons (C 2–C 10, range) in ambient air samples was evaluated. The method involves a two-step cryogenic procedure: preconcentration (air sample volumes of 100–1000 cm 3) and prefocusing combined with capillary GC with flame ionization detection. GC columns were used under optimized temperature programming conditions (GC oven starting at above ambient temperature). Two systems were used to monitor hydrocarbon concentrations in urban air. The first system uses a megabore capillary column with a thick film of bonded non-polar silicone stationary phase (5 μm, SPB-1), which was found to be suitable for the chromatographic separation of hydrocarbons in ambient air samples without removing the moisture. To obtain a reasonable separation of volatile hydrocarbons in the C 2–C 5, range, a methylsilicone column was connected in series with a megabore methylphenylsilicone column. Better resolution of C 2–C 6, hydrocarbons was achieved on the latter system using an Al 2, O 3-KCl porous-layer open tubular (PLOT) colunm. A dry-ice-cooled water trap was devised to remove moisture from ambient air samples. The PLOT column was not suitable for α- and β-pinene owing to decomposition. The reproducibility of GC performance ( i.e., retention time and peak-area integration) is discussed in detail. Both systems showed good long-term stability and gave good results for the determination of hydrocarbon concentrations ranging from several ppt to 100 ppb by volume in air samples from the Toronto urban area.

Identification of compounds in an HPLC fraction from female extracts that elicit mating responses in male screwworm flies,Cochliomyia hominivorax

When hexane extracts of mature screwworm females were chromatographed on a silica gel column, mating stimulant activity was concentrated in a fraction that eluted with hexane-ether (94∶6, v/v). Separation of this fraction with HPLC (acetonitrile-acetone; 60∶40, isocratic) resulted in a chromatogram of some 20 peaks. Only peaks 4-11 elicited mating responses. Peaks 5-10 had most of the activity, with peak 8 producing the highest response. Sixteen compounds were characterized from peak 8 by gas chromatography-mass spectrometry: six unbranched secondary acetates (C31H62O2); seven previously unreported methyl-branched secondary acetates (C32H64O2); one unbranched ketone (C31H62O); and one methyl-branched ketone (C32H64O). The isomeric acetates were not completely resolved from each other by capillary gas chromatography (CGC) on methyl silicone columns. The sixteenth compound was an aldehyde (C30H60O) that was present only in occasional peak 8 preparations. These compounds and several derivatives were characterized by capillary gas chromatography-mass spectrometry (CGC-MS). The position of the acetate group was ascertained by conversion to a keto group or by replacement of the acetate with a methyl group. Pheromone activity was not observed in peaks trapped either from CGC or by recombination of the trapped CGC peaks from HPLC peak 8. This apparent loss of activity from CGC peaks or from TLC cannot currently be explained.

On the mechanisms of the formation of L-alloisoleucine and the 2-hydroxy-3-methylvaleric acid stereoisomers from L-isoleucine in maple syrup urine disease patients and in normal humans.

2-Keto-3-methylvaleric acid (KMVA) has been found not to undergo spontaneous keto-enol tautomerization in neutral aqueous solution, alone or in the presence of large concentrations of pyridoxamine or pyridoxamine-5-phosphate. This finding denies the commonly held suppositions that 3R-KMVA is derived spontaneously from 3S-KMVA in vivo, and that L-alloisoleucine is the product of the reamination of this 3R-KMVA. Evidence presented here suggests that racemization of the 3-carbon of L-isoleucine occurs during transamination, that L-alloisoleucine is an inherently unavoidable by-product of L-isoleucine transamination (and vice versa), and that a KMVA enol is not obligate in this racemization. The four stereoisomers of 2-hydroxy-3-methylvaleric acid have been synthesized and the mass spectra of their trimethylsilyl derivatives recorded. An achiral methylsilicone column was used to separate the diastereomeric pairs and to determine their relative ratios in plasma and urine from normal controls and two maple syrup urine disease (MSUD) patients. The urinary ratio of the two diastereomers is different from that for plasma, both in normals and in MSUD patients. The plasma ratios may provide a rapid and simple measure of residual branched chain 2-keto acid dehydrogenase activity in MSUD patients.

Quantitative Determination of Mono- and Diglycerides with and without Derivatization by Capillary Supercritical Fluid Chromatography

Abstract Mono- and diglycerides, as well as commercial monoglyceride emulsifiers, were analyzed by capillary supercritical fluid chromatography (SFC). Carbon dioxide without modifier was used as the mobile phase in the chromatography. Samples were prepared by simply being dissolved in solvents or by propionyl ester derivatization. A capillary SFC methyl silicone column (SB-methyl 100, 100 μm X 10 m, 0.5 μm film thickness, Lee Scientific) was used for the separation, and a flame ionization detector was used for the detection. A calibration standard containing known concentrations of monomyristln, monopalmitin, monostearin, dimyristin, dlpalmitin, and distearin were used for the determination of the response factor (unit weight per peak area) of each analyte. The response factors were used in the quantitation of the analytes in the test samples from their respective integrated peak areas. Monomyristin was used as an internal standard for the quantitation of monoglycerides In commercial emulsifiers. The accuracy of the methods was demonstrated by comparing the percent area (%A) determined by the chromatography with the percent weight (%W) of each of the components in the standard mixture, and the precision of the methods was indicated by the relative standard deviation (RSD). The mean ratio and RSD of %A/%W were 0.98 ± 0.09 (&amp;lt;5%) and 1.01 ± 0.03 (&amp;lt;2.5%) for underlvatized and derivatized samples, respectively. Two lots of commercial monoglyceride emulsifiers were analyzed with and without derivatization, and the results were compared to those obtained by gas chromatography (GC). 7-tests comparing the method means did not indicate any significant mean differences (95% confidence level) between the GC and SFC methods. Nor did the variance ratio F-test indicate that the overall variances of the methods were significantly different. However, the error variance of the SFC-underivatized method was significantly higher than that of the GC and SFCderivatized methods. These results demonstrated the feasibility of applying the SFC technology in the analysis of monoand diglycerides with and without derivatization

Quantification of PCBs in Environmental Samples: Comparison of Results Obtained with Different Analytical Instruments (GC—ECD, GC—MS) and Standards

Abstract Polychlorinated biphenyls have been determined in sediments, macroalgae, mussels and worms sampled in the lagoon of Venice, Italy. Sample preparation included hexane extraction, clean-up with sulphuric acid, Florisil and copper and separation from pesticides by column chromatography with silica gel. Analyses were performed using methylsilicone and phenyl-methylsilicone capillary columns. A GC—ECD and a computer-assisted GC—MS performing selected ion monitoring (SIM) were employed. Quantification was based on standards prepared by combining Aroclor formulations and on mixtures prepared with selected biphenyls of different degree of chlorination (7 PCB mix). Recovery tests conducted with an internal standard added to the samples before extraction yielded values between 79 and 102%. The precisions obtained on quadruplicate samples by using the combination HRGC—LRMS with Aroclor standards and with the 7 PCB mix were 18% and 15%, respectively. Imprecision was mainly due to uncertainties in measuring a...

Determination of Cyclohexanol in Urine and Its Use in Environmental Monitoring of Cyclohexanone Exposure

A simple and sensitive method for determining urinary cyclohexanol, the main metabolite of cyclohexanone, by hydrolysis and gas chromatography (GC) with a flame ionization detector was developed. A 2-mL urine sample was hydrolyzed with 0.4 mL of concentrated HCl and followed by extracting twice with diethylether. Two microL of the filtrate was injected into the GC with a methyl silicone column. The detection limit is estimated to be 0.4 mg/L. The coefficient of variation for the procedure is 8% and 10% for the range of concentration 5 and 50 mg/L, respectively. The within-run variation was 5.4% and between-day variation was 9.67%. The method was verified with urine samples collected from workers exposed to cyclohexanone. An excellent correlation (r = 0.88) was observed between environmental cyclohexanone exposure and cyclohexanol in urine. The procedure is relatively simple and reproducible and it can be applied for occupational health measurement of cyclohexanone exposure.

Optimizing temperature program and flow rates for apillary GC analysis of EPA‐608 pesticides

AbstractAn approach is described for optimizing chromatographic conditions for dual‐column analysis of U.S. EPA Method 608 pesticides. Sample throughput for environmental analysis of pesticides can be increased by performing the screening and confirmation analyses at the same time. This requires simultaneous injection, separation, and detection in a GC with dual inlets, columns, and detectors. Resolution maps for flow rate and temperature relationships of poorly resolved peak pairs for 5%‐phenyl methyl silicone and 7%‐cyanopropyl 7%‐phenyl methyl silicone capillary columns are presented. Resolution of target pesticides on the 5%‐phenyl methyl silicone column was much more sensitive to changes in flow and temperature‐ramp rates than was the 7%‐cyanopropyl 7%‐phenyl methyl silicone column. Optimal conditions resulted in a run time of approximately 20 min.

Further applications for capillary gas chromatography in routine quantitative toxicological analyses

AbstractThe use of capillary column gas chromatography for drug screening in forensic toxicology has become increasingly widespread. Screening procedures however are often lengthy and unsuitable for rapid confirmatory or quantitative applications. In order to develop a practical scheme for confirmatory/quantitative analysis, we have optimized a series of temperature profiles to allow the rapid quantitative determination of a wide range of acid/neutral and basic drugs in extracts from post mortem fluids and tissue. The appropriate profile is selected based on the retention index on a standard crosslinked methyl silicone column used to screen extracts. The use of a 5% phenyl methyl silicone phase allows complementary identification, and allows the separation of some pairs of compounds with identical retention indices in the screning procedure.

Interlaboratory Reproducibility of Retention Indices in Capillary Gas Chromatography

Abstract Because of the temperature-dependent behavior of Kovat's retention indices (RI), based on straight-chain alkane homologues and a liquid phase such as SE-30. OV-1. or methyl silicone, the interlaboratory reproducibility of these RIs determined on capillary columns is comparable to those determined on packed columns. Other homologue series investigated—including diisopropyl-n-alkylamines (DIPA), tri-n-alkylamines (TAA), and 1-nitro-n-alkanes (NIA)—showed the same phenomenon. However, by using a carefully selected reference drug mixture, a dramatic gain in the interlaboratory reproducibility of RI values can be obtained, even under vastly different operational conditions. This allows a search window of ±25 RI units for capillary methyl silicone columns, which is much better than the ±60 RI units that must be applied when using alkane or substituted alkane homologues.

High-performance liquid and gas chromatographic methods for the determination of cicloprolol

Two methods, one based on high-performance liquid chromatography (HPLC) and the other on gas chromatography (GC), were developed for the quantification of the partial adrenergic receptor antagonist cicloprolol. In the GC method, samples are cleaned up by back-extraction, then derivatized with heptafluorobutyric anhydride and separated on a capillary cross-linked methylsilicone column. This GC method is time-consuming but, with electron-capture detection, cicloprolol can be quantified at levels down to 1 ng/ml. The HPLC method, using a reversed ODS stationary phase and fluorimetric detection, is less sensitive (5 ng/ml) but, with a single-step extraction, is faster and simpler. The determination of cicloprolol in human blood samples by the two methods gave comparable results. Routine monitoring of cicloprolol can be done easily with the HPLC method, whereas the time-consuming GC method may be reserved for pharmacokinetic studies where late-sampled tubes, with low concentrations, must be analysed.