Evaluation of 3,5-stigmastadiene content of edible oils: Comparison between the traditional capillary gas chromatographic method and the on-line high performance liquid chromatography-capillary gas chromatographic analysis

Summary The quantitation of 3,5-stigmastadiene and other steroidal hydrocarbons, commonly known as steradienes, is a valid tool for the recognition of refining (in particular bleaching) of edible oils; the evidence of this process is nowadays of a great interest due to growing market for virgin, cold-pressed, natural oils. Due to the long time required (about 4 hours) and the amount of solvents employed (about 650 mL) to perform the official analysis, other methods have been recently proposed, the most important of which involves high performance liquid chromatography coupled with capillary gas chromatography (HPLC-GC). In this study the results of ten oil samples, analysed by both the official method and HPLC-GC, are reported and the two methods compared and discussed, for routine use, in terms of sample preparation, time of analysis and setting up, difficulty and reproducibility.     

Determination of Volatile Sulfur Compounds in Beverage and Coffee Samples by Purge-and-Trap On-Line Coupling with a Gas Chromatography-Flame Photometric Detector

A sensitive and fast analytical method using purge-and-trap on-line coupling with gas chromatography was developed for the determination of trace volatile sulfur compounds including dimethyl sulfide (DMS), ethyl-methyl sulfide (EMS), and dimethyl disulfide (DMDS) in beverage and coffee samples. The analytes were purged for 12min from the sample by high purity nitrogen at a flow rate of 35KPa and preconcentrated in the cooled fused-silica capillary trap at –75°C. The NaCl content in the samples was maintained at 10%. The volatile sulfur compounds were separated with an Agilent-6890 gas chromatograph by a suitable temperature program and detected by means of a flame photometric detector (FPD). The detection limits were 80ngL^–1 for DMS, 80ngL^–1 for EMS, and 100ngL^–1 for DMDS, respectively. This method was successfully applied to the determination of volatile sulfur compounds in different beverage and coffee samples.     

Selection of a Trio of Different Selective Gas Chromatographic Stationary Phases, and Use of Retention Ratios Between Phase Pairs to Indicate Some Solute Structures: “MPMS” Liquid Crystal Polysiloxane Re-assessed

Summary MPMS is a commercially marketed capillary liquid crystal Mesogenic Polymeric Methyl (poly-) Siloxane stationary phase which is selective to solute molecular shapes. It is chemically different to other types of molecularly selective phases, such as the peptide methyl-polysiloxane Chirasil-Val and the various modified cyclodextrins (CD). This study measures how different in chromatographic behaviour are the phase trio of a CD to be selected here, and the above two methyl polysiloxanes. Ten selected solutes from volatile oils are used to record relative retentions to n-undecane on each phase, and these are used in a procedure previously itemised for Chirasil-Val to seek the lowest correlation coefficients between results for pairs of phases, which leads to Chiraldex G-DA being the selected most different CD (out of 14) to MPMS and Chirasil-Val. Another 21 solutes are also examined on this phase trio, and retention ratios of the 31 solutes between pairs of phases are calculated. These are indicative of an unknown solute being an aromatic substance, or a bicyclic monoterpenoid.     

Comparison of GC and HPLC Methods for Quantitative Analysis of Tinuvin 622 After Saponification in Polyethylene

This study describes the sample preparation and two chromatographic techniques for determination of Tinuvin 622 in polyethylene. The first part of the two methods consisting of dissolving the polyethylene in boiling xylene is followed by addition of a methanolic solution of potassium hydroxide. The polymeric light stabilizer, Tinuvin 622, is thereby saponified to 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol (diol). Addition of the methanolic solution of the saponification reagent simultaneously precipitates the polyethylene matrix. Then the diol is quantified using either gas chromatography (GC) or high performance liquid chromatography (HPLC). For GC, a Macherey Nagel Optima-17 capillary column (30m×0.25mm ID, film thickness 0.25µm) is used. Nitrogen is used as carrier gas and make-up gas. The detection system is a flame ionization detector. For HPLC, an octadecyl silane (ODS) column (30cm×4mm, particle size 5µm) and a mobile phase methanol: water mixture (3:97, v/v) are used. Detection of analyte is carried out at 215nm. Both methods can be used to determine Tinuvin 622 in polyethylene in the concentration range of 0.02–1%, which represents the usual application concentration.     

Determination of fosfomycin in human urine by capillary gas chromatography: Application to clinical pharmacokinetic studies

Summary A capillary gas chromatographic method for the determination of fosfomycin in human urine is described. After dilution of the sample and derivatization, analysis was on a HP-1 capillary column and a flame ionization detector was used to determine the bistrimethylsilyl derivative of fosfomycin. Response was linear in the range 50–5000 g mL^–1. The detection limit was about 10 g mL^–1. The within and between day coefficients of variation did not exceed 6%. The method was applied to the determination of fosfomycin in urine samples collected during clinical pharmacokinetic studies.     

Selectivity of Fischer-Tropsch synthesis on supported nickel catalysts

Alumina supported Ni as well as Ni²⁺ exchanged CaNaX zeolites were used to study Fischer-Tropsch synthesis. Two significant selectivity effects can be distinguished, which are related to the different structures and acidities of the catalysts.

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CaNaX, Ni, Ni⁺² , -. , .

     

Chromatographic analysis of penstemide and serrulatoloside by high-performance liquid chromatography and gradient thin-layer chromatography

Summary A sensitive capillary gas chromatographic method is described for the simultaneous determination of lidocaine, tetracaine, procaine and dibucaine. The method was applied to the determination of anesthetics in tissue homogenates incubated at 38°C at doses between 10 and 400 mg/kg. In the liver tissue thein vitro metabolization of the studied anesthetics is most rapid for tetracaine, also fast for procaine, while for lidocaine and dibucaine the metabolization is very slow. In brain tissue thein vitro metabolization of anesthetics is very slow.The method shows good analytical parameters: linearity between 5 and 40 g/ml; day-to-day reproducibility ca. 8% for a concentration of 20 g/ml, precision ca. 7% for a concentration of 20g/ml. Accuracy is also very good.     

Some effective solvents for rapid and reliable characterization of phenylthiohydantoin-amino acids

Summary One-dimensional chromatography with internal standards permits reliable identification of the phenylthiohydantoins from all the common amino acids with the following TLC systems: silica gel — chloroform/n-butyl acetate (9010), di-isopropylether/ethanol (955), dichloromethane/ethanol/acetic acid (9082) ortrans-dichloroethylene/ethanol/acetic acid (88102); and cellulose with 25% formic acid — heptane/isobutanol/75% fromic acid (40309) or silica gel — chloroform/ ethanol/acetic acid/water (50470.52.5).Abbreviations: PTH=phenylthiohydantoin, TLC=thin-layer chromatography, HPTLC=high-performance TLC; other abbreviations: see end of text. Proportions in solvent mixtures are v/v except where otherwise indicated.     

Characterization,evaluation and in-situ cross-linking of new polar phases in capillary gas chromatography

Summary The possibilities of OV-1701 and RSL-310, two new stationary phases, have been evaluated for capillary gas chromatography in fused silica columns. OV-1701 is a cyanopropylphenyldimethyl polysiloxane of moderate polarity possessing excellent chromatographic characteristics. The phase exhibits high coating and chromatographic efficiencies, high temperature stability and is suitable for cross-linking. RSL-310 is a polar liquid stationary phase yet to be permanently bonded in a capillary column. The selectivity of both phases extends the applicability of fused silica columns.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Reversed phase liquid chromatographic retention behavior of polystyrene homopolymers

Summary Isocratic and gradient elution high performance liquid chromatographic measurements of the retention behavior of polystyrene homopolymers with molecular weights ranging from 2 kD to 390 kD were performed using mixed methylene chloride-methanol mobile phases of varying composition and a C-18 chemically bonded stationary phase supported on either 100 Å or 300 Å mean pore diameter silica. Isocratic measurements of the capacity factor, k, for different molecular weight homopolymers as a function of the volume fraction of methylene chloride, , permit determination of the critical composition, _c, which renders k=1 and the local slope, S=–lnk/_c of the lnk- isotherm at =_c, and also the dependence of _c and S on the degree of polymerization, M. Linear gradient elution measurements of _c and S were also performed and compared to the corresponding isocratic measurements. The general retention behavior and the dependence of _c and S on M compare favorably to the predictions of the theory of homopolymer retention and fractionation developed by Boehm, Martire, Armstrong, and Bui (BMAB). Comparison is also made between the present work and the experimental observations of other workers on related chromatographic systems involving hompolymer retention.     

The essential oil of taurus cedar (Cedrus libani A. rich): Recent results

Water and steam distilled essential oils from wood and roots of Taurus Cedar (Cedrus libani A. Rich) obtained from Antalya and Içel (Tarsus) provinces were analyzed by GC and GCIMS. 37 components were characterized representing 90–93% of the oils. Himachalenes (-, -, and -) constituted 58.6% of the oils. In order to isolate minor sesquiterpenes, the oils were subjected to fractional distillation and chromatographic techniques. The isolated constituents were characterized by spectral analysis (IR, MS,¹H and¹³C-NMR). Cis- and trans-10,11-dihydroatlantones, cis- and trans--atlantones, 8, 9-dehydroneoisolongifolene, longipinene, -ylangene, camphor, sativene,-guijunene, longifolene (=junipene), -cedrene, -calacorene, oxidohimachalene, isohimachalone, nerolidol, longiborneol, cadalene, limonene, and terpinolene were found as constituents ofCedrus libani oil for the first time.     

Analysis of steroids XXXIX. Estimation of the impurity profile of 5α-androst-2-ene-17-one

Summary The impurity profile of 5-androst-2-ene-17-one was investigated by using two different capillary gas chromatographic (GC) and a reverse phase high performance liquid chromatographic systems (HPLC). The impurities were identified by retention matching with authentic standards, diode-array UV spectroscopy, on-line gas chromatography-mass spectrometry (GC-MS), off-line HPLC-MS and NMR spectroscopy. The following impurities were identified and quantitated: ring A saturated, isomeric (1-ene, 3-ene, 4-ene, 5-ene) analogues, 3 and 3-hydroxy as well as 3-phenyl derivatives.For Part XXXVIII, see Reference [1]. This paper is Part III in a series of papers Estimation of Impurity Profiles of Drugs and Related Materials. For Part II, see Reference [2].     

Determination of piribedil in pharmaceutical formulations by micellar electrokinetic capillary chromatography

A fast and simple micellar electrokinetic capillary chromatographic method was developed for the analysis of piribedil in pharmaceutical formulations. The effects of buffer concentration, buffer pH, sodium dodecyl sulphate (SDS) concentration, organic modifier, applied voltage and injection time were investigated. Optimum results were obtained with a 50 mM borate buffer at pH 8.0 containing 50 mM SDS by using a fused silica capillary (50 m internal diameter, 72 cm effective length). The sample was injected hydrodynamically for 4 s at 50 mbar pressure and the applied voltage was +30 kV. The detection wavelength was set at 205 nm. Diflunisal was used as an internal standard. The analysis was performed at 25 °C and the total run time was 14 min. The method was suitably validated with respect to linearity range, limit of detection and quantification, precision, accuracy, specificity and robustness. The linear calibration range was 5–100 g mL^–1 and the limit of detection was determined as 1 g mL^–1. The method developed was successfully applied to the determination of piribedil in pharmaceutical formulations. The results were compared with a spectrophotometric method reported in the literature and no significant difference was found statistically.     

AlPO4 as catalyst in organic reactions, III. transesterification of EtOAc with n-BuOH

The transesterification of EtOAc with n-BuOH, catalyzed by AlPO₄-B is analyzed. In gas phase, the process is favored by low reaction temperatures and an excess of alcohol. Better yields are obtained in solid-liquid than in gas phase conditions.

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- EtOAc n-BuOH, AlPO₄-B.B . -, .

     

Practical Evaluation of Sol-gel and Hydrothermal Fritting Technologies for Rapid Column Fabrication and its Application in Capillary Electrochromatography and Micro-Liquid Chromatography

Summary Tetraethoxysilane (TEOS) sol-gel technology was investigated as an alternative fritting methodology. It allowed a wide range of silica based stationary phase materials of differing particle sizes (3–12 m) in capillaries of differing lengths (7.4–25 cm) and internal diameters (100–375 m) to be investigated. Experiments comparing coupled with continuous capillaries illustrated a loss of approximately 7% in chromatographic peak efficiency for the coupled capillary format. Continuous column architecture experiments showed that it is possible to detect through the packed bed without losing the peak efficiency when optimised detector settings were employed. TEOS fritting technology was fast and reliable, allowing rapid stationary phase screening for CEC or micro-LC.     

The autocatalytic character of the reaction methanol to hydrocarbons over amorphous silica-alumina catalysts

Conversion of methanol to hydrocarbons was studied on an amorphous silica-alumina over the 330–420°C temperature range and contact times up to 8 h. The reaction was confirmed as autocatalytic from the results of varying both contact time and temperature.

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330–420°C 8 . , , , .

     

Essential Oils of Nepeta Species Growing in Turkey

Essential oils from 22Nepetaspecies growing in Turkey have been studied. Results of GC/MS analyses of the essential oils have shown that four Nepeta species contain 4a-7-7a-nepetalactone as the major component. 4a-7-7a-Nepetalactone was the main constituent in N. racemosa. Seven Nepeta species contained caryophyllene oxide as the main constituent in their essential oils. 1,8-Cineole/linalool were the major components in the essential oils of six species. -Pinene,-terpineol,germacrene-D,and spathulenol were the main constituents in the essential oils fromN. phyllochlamys, N. viscida, N. sorgerae, andN. trachonitica, respectively.     

Factors affecting reproducibility in the manufacture of glass and siliceous glass open tubular (capillary) columns

Summary Column characteristics affecting the chromatographic behavior of glass and siliceous glass (fused silica) capillary columns include the dimensional uniformity of the column, the physical and chemical characteristics of the column wall and the characteristics of the liquid phase. In the case of the coated column the uniformity and thickness of the liquid phase film are the most important criteria affecting column reproducibility. The paper discusses these factors and their influence on column performance.Presented in part at the Symposium on Standardized Materials for Chromatography, 181 st National American Chemical Society Meeting, Atlanta, Georgia, March 29–April 3, 1981.     

Liquid-phase hydrogenation on new AlPO4?SiO2 supported rhodium catalysts

The liquid-phase catalytic hydrogenation of various organic compounds was carried out using new rhodium catalysts supported on AlPO₄–SiO₂ (2080 wt. %) system, in methanol as solvent, under low hydrogen pressure (0.55 MPa) and at 293 K. Neither alkene isomerization nor hydrogenolysis products were detected in any of the cases.

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AlPO₄–SiO₂ (2080 . %), , , (0,55 MPa) 293 . , .

     

Multi-residue procedure for the analysis of pesticides in groundwater: Application to samples from the comunidad Valenciana,Spain

Summary A simple multi-residue procedure has been developed and applied to the analysis of pesticides in groundwater samples from the Comunidad Valenciana, a predominantly agricultural area on the Mediterranean coast of Spain. The procedure includes a liquid-liquid extraction, after addition of NaCl on the samples, and a subsequent analysis by capillary gas chromatography using a dual detection system with electron capture and nitrogen-phosphorous detectors. This allows the determination of more than 30 compounds (organophosphorous, organochlorine and pyrethroid pesticides) at the low ppb (g l^–1) levels. Detection limits obtained varied between 0.01 g l^–1 (lindane, fonofos) and 0.5 g l^–1 (cypermethrin). An additional injection of the sample extracts into a gas chromatograph equipped with a column of different polarity and electron capture detector is used for the confirmation of chromatographic peaks. The recommended procedure has been applied to 66 ground water samples. Pesticides, including organophosphorus and organochlorine compounds were detected in 31 of them, in levels ranging from 0.02 to 0.7 g l^–1.