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Subject: search.filters.subject.Gas chromatography

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    Concurrent analysis of the mycotoxins, cyclopiazonic acid, moniliformin and ochratoxin A using capillary zone electrophoresis
    (2000) Govender, Urishani; Odhav, Bharti
    Mycotoxins are a group of natural poisons produced by certain strains of fungal species when they grow under favourable conditions on a wide variety of different substrates. These toxins have been implicated in a wide range of acute diseases in man and animals. Their toxic effects include oesophageal cancer and liver diseases in humans, and carcinogenic effects in experimental rats and poultry. Hence, there is a need to monitor toxin levels in food commodities.
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    Thermo-physical properties and activity coefficients at infinite dilution for ionic liquid systems at several temperatures
    (2017) Singh, Sangeeta; Redhi, Gyanasivan Govindsamy; Ramjugernath, Deresh
    The thermodynamic properties of mixtures involving ionic liquids (ILs) with organic acid (acetic acid or propanoic acid) or acetonitrile at different temperatures were determined. The ILs used were imidazolium-based: 1-ethyl-3-methylimidazolium ethyl sulphate [EMIM]+[EtSO4]-, 1-butyl- 3-methylimidazolium thiocyanate [BMIM]+[SCN]- and 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide ([BMIM]+[Tf2N]-. The ternary excess molar volume (V E ), isentropic compressibility (ks) and deviation in isentropic compressibility ( ks123 ) were determined for four ternary liquid mixtures of {[EMIM]+[EtSO4]- or [BMIM]+[SCN]− + acetic or propionic acid + acetonitrile} at different temperatures (293.15, 298.15, 303.15, 308.15 and 313.15) K and at a pressure of 0.1 MPa with aid of the experimental density (ρ), speed of sound (u) data. The calculated data were correlated by using the Cibulka equation with the help of Redlich–Kister parameters obtained from fitting the Redlich–Kister equation for the corresponding binary systems. Furthermore, the density and speed of sound were also measured for eight corresponding binary systems at the same experimental conditions. The binary excess molar volume, isentropic compressibility and deviation in isentropic compressibility were also calculated for measured systems and fitted to the Redlich–Kister equation to obtain the Redlich–Kister parameters as well as to check the accuracy of measured data which were used to correlated experimental data using Cibulka equation. These results were discussed, in terms of how the sign and magnitude of thermodynamic functions were influenced by the addition of a third component to liquid systems. Also, the possible molecular and pair-wise interactions between component molecules and the effect of temperature on the thermophysical and thermodynamic properties were predicted. In addition, the work focussed on application of ([BMIM]+[Tf2N]-) ionic liquid for the separations of (alkane/aromatic), (alkane/alk-1-ene), (cycloalkane/aromatic) and (water/alkan-1-ol) using gas- liquid chromatography (GLC) technique. The activity coefficients at infinite dilution, , for 31 organic solutes (alkanes, cycloalkanes, alkenes, alkynes, aromatics, alkanol and ketones) and water in ionic liquid were measured at temperatures of (323.15, 333.15, 343.15, 353.15 and 363.15) K. Stationary phase loadings of (42.83 and 68.66) % by mass were used to ensure repeatability of E , measurements. Partial molar excess enthalpies at infinite dilution, H1 , were also determined. The selectivities, S , and capacities, k , were determined for the above separations. The separating ij j ability of the investigated ionic liquid was compared with previously investigated ionic liquids and industrial solvents such as sulfolane, n-methyl-2-pyrrolidine (NMP) and n-formylmorpholine (NFM). The results obtained suggested that in general, the [BMIM]+[Tf2N]− had outperformed the conventional solvents such as sulfolane, NMP and NFM in terms of selectivity, while the [BMIM][Tf2N] had in general, performed better overall when the performance index was used for comparison.
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    Activity coefficients at infinite dilution for ILs : methyltrioctylammonium cation and bis(trifluoromethylsulfonyl)imide or thiosalicylate anions using glc
    (2009) Gwala, Nobuhle V.; Deenadayalu, Nirmala
    The activity coefficients at infinite dilution ( γ13 ) were calculated for alkanes, alkenes, cycloalkanes, alkynes, ketones, alcohols and aromatic compounds from gas liquid chromatography (glc) measurements at three temperatures (303.15 and 313.15 and 323.15) K. The γ13 values were calculated from the retention data for two ionic liquids (ILs) with the same cation but different anions. The ionic liquids: [methyltrioctylammonium bis(trifluoromethylsulfonyl)imide and methyltrioctylammonium thiosalicylate] were used as the stationary phase. The γ13 data for methyltrioctylammonium thiosalicylate were higher than for methyltrioctylammonium bis(trifluoromethylsulfonyl)imide. For each temperature and each ionic liquid, γ13 values were determined for two columns and the average γ13 values were used for the calculation of the partial molar excess enthalpies at infinite dilution, H E 1 Δ , using the Gibbs-Helmholtz equation. Graphs of In γ13 vs 1/T were plotted to determine H E 1 Δ at T = 303.15 K. The selectivity, S12 , value for the hexane/benzene separation was calculated from the ratio of the avarage γ13 values to determine the suitability of the ILs as an entrainer for extractive distillation in the separation of aromatic and aliphatic compounds.The S12 values were also compared to the literature values for other ionic liquids. It was found that the longer chain alkyl group attached to the cation or anion gave lower S12 values. Both ILs have S12 values greater than one and in theory can be used as an entrainer for the hexane/ benzene separation. The capacities at infinite dilutions, k1 , were also calculated from the inverse of the avarage γ13 values for each IL at each temperature.
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    Evaluation of bacteriological techniques, sensory evaluation, gas chromatography, and electronic nose technology for the early detection of Alicyclobacillus acidoterrestris in fruit juices
    (2007) Harrichandparsad, Zeenat
    Alicyclobacillus acidoterrestris is a spore-forming spoilage micro-organism found in fruit juices whose spores are not destroyed by typical pasteurisation. Once its spores outgrow and multiply in finished juice products, they produce two volatile taint compounds namely guaiacol and 2,6-dibromophenol. In the food industry margins for errors are small and monitoring of products to avert such errors is crucial. Conventional microbiological monitoring is one such technique for spoilage micro-organisms another being automated systems which can detect taints. Both these categories were evaluated in this study with the electronic nose and gas chromatograph being the specific automated systems being assessed. Sensory evaluation was also assessed as a diagnostic tool in the detection of taints. Isolation and identification of what was thought to be A. acidoterrestris was a laborious and expensive exercise which eventually proved inconclusive. A pure culture was purchased and juices were then inoculated with two levels of A. acidoterrestris spores and incubated. Juices from each level of inoculation were evaluated at different time intervals via the above-mentioned monitoring techniques. Of the three media assessed in the microbiological method, Bacillus acidoterrestris medium (BAM) was found to be the most effective for enumerating A. acidoterrestris followed by K-medium (KM) then Orange Serum Agar (OSA). While BAM was still indicating the presence of A. acidoterrestris KM and OSA were not (counts of <10cfu/g). This illustrated that this micro-organism could be easily overlooked if KM or OSA were being used to enumerate them. Considering that many workers actually do use KM and OSA as their media of choice in enumerating A. acidoterrestris (perhaps because BAM is very tedious to prepare) the cause for concern is a real one. Assessment of the resultant taints via sensory evaluation after inoculation and incubation reveals the inability of many panellists to detect taints at levels (as assessed by GC) far above their documented threshold values. While GC is an extremely useful and powerful tool, the level of expertise and skill required to use such an instrument cannot be overlooked nor can the expense involved. With regard to the electronic nose assessment for the presence of the volatile taint compounds, an important finding was that the electronic nose indicated significant differences between test and control samples when panellists performing sensory evaluation did not. This also correlated to an interval when enumeration on OSA illustrated no A. acidoterrestris after several days of inoculation and incubation and BAM and KM did. Without implying that the electronic nose has no drawbacks, it has proved, in this instance to be a simple and easy piece of equipment to use. It can be used to detect taints produced under simulated spoilage conditions at reduced analysis times, levels of expertise, cost and energy.