Gas Chromatographic Peaks Research Articles

Volatiles from thermal decomposition of isomeric methyl (12S, 13S)‐(E)‐12,13‐epoxy‐9‐hydroperoxy‐10‐octadecenoates

AbstractTwo epimers of methyl (12S,13S)‐(E)‐12,13‐epoxy‐9‐hydroperoxy‐10‐octadecenoate were isolated after esterification of a mixture of fatty acids obtained from decomposition of (13S)‐(9Z,11E)‐13‐hydroperoxy‐9,11‐octadecadienoic acid by an Fe++‐cysteine catalyst. These epimeric epoxyhydro‐peroxyoctadecenoates were decomposed by heat (210 C) in the injection port of a gas chromatograph, and the cleavage fragments were subsequently separated by gas chromatography (GC) and identified by mass spectrometry (MS). Among the scission products obtained, the most prominent in the GC peak profile were methyl octanoate and methyl 9‐oxononanoate. Other peaks were identified as pentane, 1‐pentanol, hexanal, 2‐heptanone, 2‐pentylfuran, methyl heptanoate, 2‐octenal, 4,5‐epoxy‐2‐decenal, methyl 8‐(2‐furyl)‐octanoate, 11‐oxo‐9‐undecenoate and methyl 13‐oxo‐9,11‐tridecadienoate. In addition, 3,4‐epoxynonanal, methyl 8‐oxooctanoate, 3‐hydroxy‐2‐pentyl‐2,3‐dihydrofuran and methyl 10‐oxodecanoate were tentatively identified. Except for the furan compounds, the formation of the fragmentation products could be explained by conventional free‐radical scission mechanisms.

Determination of highly volatile organic contaminants in water by the closed-loop gaseous stripping technique followed by thermal desorption of the activated carbon filters

Very volatile organic contaminants in water were determined by using closed-loop gaseous stripping combined with thermal desorption from the activated carbon filter into a high-resolution gas chromatograph. The operating parameters for quantitative applications were evaluated. The solvent-free thermal desorption procedure permits the determination of compounds that normally elute under the gas chromatographic solvent peak ( e.g., dichloromethane and Freons). Sixteen volatile compounds with boiling points in the range −30 to 120°C were determined with an overall recovery of 12–52%. Qualitative determinations of volatiles from a secondary sewage effluent were in good agreement with the results found by two more established methods.

Aroma analysis of apple juice: Influence of salt addition on headspace volatile composition as measured by gas chromatography and corresponding sensory evaluations

Sensory response to the aroma of a food depends on the composition and concentrations of the volatiles of the headspace. When analyzing the headspace composition by gas chromatography, salts are often added to the sample as a means of increasing the concentration of the aroma compounds in the vapor phase (e.g. enrichment of the vapor phase). This will only give a correct impression of the original aroma when all volatile components are affected equally. In this study on apple juice aroma, it is demonstrated that the degree of headspace enrichment resulting from salt addition is different for esters, aldehydes and alcohols, In our collection system, the average degree of enrichment at 40°C (described in terms of Relative Peak Areas—RPA) was greater than 4 for alcohols, between 1·75 and 3·50 for aldehydes and less than 1·75 for esters. How these differences can be useful when trying to identify gas chromatography peaks is also discussed. Sensory evaluations showed that aroma response is changed when salt is added to the juice, resulting in an increased aroma intensity and off-aroma. Fruit aroma was not affected. A comparison of the sensory responses with headspace gas chromatographic measurements indicates that increase in off-aroma can be related to the increase in alcohol percentage in the headspace. From these results it can be noted that, when attempting to correlate sensory scores with aroma component concentrations as measured by headspace gas chromatography, it is most important that the test conditions utilized for each analysis correspond as closely as possible with each other.

Systematic management and analysis of fatty acid data from multiple tissue samples.

A systematic approach has been developed for the collection and analysis of gas chromatographic (GC) data from multiple fatty acid profiles. The approach was applied to a series of polar and nonpolar tissue lipids generated in animal feeding studies to allow a comparison of mean fatty acid profiles as a function of either dietary regimen or tissue location. The magnitude of the studies, sufficiently large to minimize error from animal variabilities, mandated the use of computer assistance. Nevertheless, manual input was essential due to the complexity of the GC patterns, and was invoked for peak assignment and report editing. The approach discussed here allowed for the consolidation and statistical analysis of data from over 30,000 GC peaks, and generated results in both tabular and graphic formats. It should be extendable to other chromatographic studies of lipid components.

Effects of contaminants in blood-collection devices on measurements of therapeutic drugs.

Substances in evacuated blood-collection devices produce gas-chromatographic peaks with retention times similar to those of drugs. All tubes tested except the serum separator tubes contained tris(2-butoxyethyl) phosphate, as determined by mass spectrometry. In addition, the partition coefficient during the solvent-extraction step increased for some drugs by as much as 40%, while for other drugs it decreased by as much as 30%, depending on the drug and the collection tube. The Becton Dickinson serum separator tube also contains several other compounds identified by mass spectrometry to be dibasic esters used in the preparation of the polyester gel. The Corning serum separator tube and the Venoject serum tube contain still other impurities. The Becton Dickinson royal-blue-stoppered tube contained the least amount of impurities of the tubes tested. CVs of 25 commonly measured drugs in plasma pools increased from 5% for samples collected in glass tubes to greater than 20% for samples collected in evacuated blood-collection tubes. Clearly, accuracy and precision of measurements of therapeutic drugs can be seriously compromised if an inappropriate blood-collection device is used.

Gas—solid chromatographic characterization of active carbons

The characterization of two active carbons was carried out by using gas chromatographic (GC) peak parameters (mean and variance) obtained by fitting experimental data with the Edgeworth-Cramér series. These results were then compared with those obtained from mercury porosimetry, low-temperature nitrogen adsorption measurements, small-angle X-ray diffraction, scanning electron microscopy and transmission electron microscopy. With regard to mass exchange processes, the chromatographic technique yields results which agree with those obtained by the other techniques. In regard to adsorption capacity, the GC characterization is more direct and unambiguous.

Gas Chromatographic Determination of Butylated Hydroxyanisole, Butylated Hydroxytoluene and Tertiarybutyl Hydroquinone in Soybean Oil

ABSTRACTOils containing different levels of the most common phenolic antioxidants, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and tertiarybutyl hydroquinone (TBHQ) from 0–200 ppm were analyzed by a new gas chromatographic method. The antioxidants in oils were isolated by nitrogen gas purging, collected on Tenax GC coated with polymetaphenoxylene, and then separated and quantitated by gas chromatography. This method requires neither extraction of antioxidants from oil nor derivatization of antioxidants. The correlation coefficients (r) between gas chromatographic peak heights or peak area and their concentrations in oils were 0.99 for BHA, BHT, and TBHQ. This simple gas chromatographic method can determine as little as 10 ppm pf BHA, BHT, or TBHQ in oils in an hour.

Pattern recognition for analysis of cigarette smoke by capillary gas chromatography. Part 1: Total particulate matter (TPM)

AbstractComplex smoke profiles from fused silica capillary gas chromatography of different cigarette types produce rich information requiring computer and sophisticated statistical analysis to reveal the hidden correlation patterns. In our technique, a Cambridge pad containing total particulate matter (TPM) is extracted with Freon‐11 in a micro‐Soxhlet apparatus. The condenser is maintained at −15°C. After extraction, Freon‐11 is allowed to evaporate under mild conditions. Bis(trimethylsilyl)trifuoroacetamide (BSTFA) is subsequently added to the extract. Trimethylsilylation is completed by maintaining the reaction vessel at 60°C for two hours. A microprocessor‐controlled capillary gas chromatograph with an automatic sampler is used to generate profiles. A link to a host computer provides for transmission of profile reports and access to various statistical and graphic packages. Factor and discriminant analyses are applied to gas chromatographic data from TPM extracts because of their ability in data reduction, pattern extraction and ranking the importance of the gas chromatographic peaks. Some preliminary results from these statistical analyses are discussed.

Gas chromatographic identification of common drugs by their mulitiple peaks and those of their trimethylsilyl derivatives

The extent to which common drugs procedure multiple peaks in gas chromatography on an OV-17 column at an injection port temperature of 300°C and temperature programme from 120 to 270°C or at an isothermal temperature of 300°C was studied. Forty-six out of 116 drugs tested produced more than one peak either as the parent compounds or as their trimethylsilyl derivatives. The retention times provide a useful means of identification.

Gas chromatographic peak splitting due to subambient accessory

Gas chromatographic peak splitting due to subambient accessory

Analysis of antioxidants in oil

AbstractOils containing from 0 to 200 ppm of the most common phenolic antioxidants, BHA, BHT and TBHQ, were analyzed by a new gas chromatographic method. This method requires neither extraction of antioxidants from oil nor derivatization of antioxidants. The correlation coefficients (r) between gas chromatographic peak heights or peak area and their concentrations in oils were 0.99 for BHA, BHT and TBHQ. This simple gas chromatographic method can accurately determine as little as 10 ppm of BHA, BHT and TBHQ in oils in 1 hr.

Quantitative analysis of components of unresolved gas chromatographic peaks by electron-capture detection with oxygen sensitization

Abstract A method for the quantitative analysis of unresolved gas chromatographic peaks is described which should be useful in manny instances for the trace analysis of structural isomers which are sensed by the electron-capture detector (ECD). A determination of unseparated isomeric components of a peak is made by obtaining a chromatogram of the sample without and with added oxygen in the ECD. The method is shown to be successful if the magnitude of the response enhancement caused by oxygen is dependent on the structural differences within the set of isomers. The method is applied here to mixtures of the three isomers of chloroanthracene.

Gas chromatographic determination of biphenyl and phenyl ether in oil

AbstractOils containing 0~100 ppm biphenyl and phenyl ether were analyzed by a new gas chromatographic method. Correlation coefficients (r) between gas chromatographic peak heights and biphenyl and phenyl ether concentrations were 0.99 and 0.98, respectively. As little as 5 ppm biphenyl and phenyl ether in oils could be determined rapidly and efficiently in 90 min by this new method.

Simultaneous analysis of imipramine and its metabolite desipramine in biological fluids

A method for the simultaneous quantitation of imipramine and its N-demethylated metabolite desipramine at the nanogram level in a single gas chromatograph peak is presented, utilizing gas chromatography-mass spectrometry with selected ion recording. The assay is specific and quantitation is achieved using [ 2H 4]imipramine as the internal standard. The method involves the in situ methylation of desipramine with [ 2H 2]formaldehyde and sodium borohydride to give [ 2H 2]imipramine. Quantitation is then achieved by selected ion recording at m/z 280, 282 and 284, whence the ratio of the ion currents at 280 284 and at 282 284 gives the quantities of imipramine and desipramine respectively.

Pyrolysis-Gas Chromatography as an Exploration Tool for Geochemical Evaluation of Source-Rock Potential: ABSTRACT

A pyrolysis system was developed to identify the possible production type (oil, condensate, and gas) and the presence of contamination (by migrated oil or drilling additives) in rock samples. This is accomplished by incorporating gas chromatography (GC) in the pyrolysis system so that a direct analysis can be made of the hydrocarbons in the pyrolysis products from sediments samples. This analytical capability of making a positive identification of pyrolysis products is one of the important advantages of this system. Because of this additional feature, this pyrolysis system can overcome problems related to the interpretation of indirect production type indicators such as the oxygen and hydrogen indices used by the commercially available ROCK-EVAL system. The productive type is recognized either qualitatively by GC fingerprint traces or quantitatively by hydrocarbon composition (C1-C4, C5-C14, and C15+) from the kerogen (Peak II) pyrolysate. Oil-prone sediments are recognized by GC traces with a full spectrum of C1 to C28 hydrocarbons, or by high amounts of C15+ hydrocarbons. In contrast, gas-prone sediments are characterized by the predominance of light hydrocarbons from C1 to C7 in the GC trace, or by low amounts of C5-C14 and C15+ hydrocarbons. Condensate or mixed type production is intermediate in character between the two. Migrated oil or liquid contaminants are detected by a stepwise heating of the rock samples and GC analysis or Peak I (solvent extractables) and Peak II (kerogen decomposition) products. The application of this pyrolysis system over the past four years as a rapid method for evaluation of organic richness, maturation, and production type using well or outcrop samples along with the limitations of the techniques will also be discussed. End_of_Article - Last_Page 582------------

Reconstruction of mass spectra of components of unknown mixtures based on factor analysis

A method is described for the spectral resolution of combined gas chromatographic—mass spectrometric data. Factor analysis is applied to the identification of a second species in a single gas chromatographic peak. A plot can be constructed from the region of the non-negative values of spectral lines in the factor space. Feasible locations for the spectra of these constituents in the plot can be identified and give recognizable spectra of the separated constituents.

Regulatory mass spectrometry.

The history of regulatory mass spectrometry at the Food and Drug Administration began in the early 1960s and was initiated by J. N. Damico using a time-of-flight instrument with limited mass range, resolution and sensitivity. Early work involved confirmation of identity of compounds using direct probe introduction and full mass scans. From 1964 to 1969 an important application of mass spectrometry was the analysis of pesticides and elucidation of their fragmentation pathways. Regulatory mass spectrometry was used to confirm manually trapped gas chromatographic peaks, and it solved the problem of false positive identifications based solely on gas chromatographic retention time. In time the mass spectrometer became viewed as the ultimate gas chromatographic detector. Another important early regulatory case involved the question of Krebiozen as a cancer cure. Krebiozen was analyzed by mass spectrometry and found to consist of creatinine, which was known to have no activity as an anti-cancer drug. Such basic information as the identity of a substance demonstrated the indispensable regulatory use of mass spectrometry. The basic problem of identification has broadened in scope to include multicomponent analyses, trace level detection, quantitation, and newer ionization techniques. Two examples illustrate the continuing development of regulatory mass spectrometry, Negative ion chemical ionization mass spectrometry in the analysis of aflatoxin B1 involves use of a newer ionization technique. The requirements of trace level detection and specificity are further stretched in the gas chromatographic mass spectrometric selected ion monitoring detection, confirmation and quantitation of tetrachlorodibenzo-p-dioxins.

The adsorption of hydrocarbons on cellophane

Weak-kneed type II adsorption isotherms were obtained for n-heptane, n-octane, n-nonane, n-decane, and mesitylene on cellophane using the gas chromatographic peak maxima elution method. Monolayer capacities and molecular areas of the hydrocarbons were calculated from the isotherms using the BET method. The molecular areas were found to be larger on cellophane than on cellulose paper, suggesting a dependence on the strength of adsorption. From the temperature dependence of the n-nonane isotherms, the variation of the thermodynamic adsorption quantities with surface coverage was determined. The low net adsorption heats (<3.4 kJ mole−1) indicated that cellophane is a low-energy surface for hydrocarbons. Integration of the isotherms gave the spreading pressures of the hydrocarbons, from which the London force component of the cellophane surface free energy was estimated to be ∼46 mN m−1 and ∼42 mN m−1 using the geometric mean and arithmetic mean approximations, respectively.

Pyrolysis of transvaal kerogens I. Diagenesis of kerogen in a stromatolite near Zeerust, South Africa: One possible chemical evolution process

Abstract This study represents an attempt to understand some of the many post-lithification chemical processes which affect the evolution of kerogen. Kerogens separated from four carbonate stromatolites, collected over a horizontal distance of ∼ 350 km from the Malmani Dolomite of the Olifants River Group in the Transvaal Supergroup, were characterized by combined vacuum pyrolysis—gas chromatography-mass spectrometry. The relative profiles of the gas chromatographic peak distributions and intensities (·finger print patterns’) of three of the kerogen pyrolyzates were closely similar. The Zeerust stromatolite kerogen yielded a different pattern, showing a greater abundance of higher molecular weight aliphatic and alkyl aromatic hydrocarbon moieties than the other three samples. Many of the stromatolites near the Zeerust area contain epigenetic fluorite introduced by aqueous solutions. Fluid inclusion homogenization analysis showed that the emplacement temperature of fluorite in the sample studied was 100–200°C. Fluoride ion initiated base catalyzed condensations may have been a feasible cause for the production of higher molecular weight aliphatic and (indirectly) some alkyl aromatic moieties in this stromatolite, as compared to those in the other three samples. Acid-catalyzed condensations may also achieve similar results in aqueous diagenetic environments.

Statistical analysis of gas chromatographic peaks by the Gram-Charlier series of type A and the Edgeworth-Cramer series

Statistical analysis of gas chromatographic peaks by the Gram-Charlier series of type A and the Edgeworth-Cramer series