Temperature chromatographic methods

Ethylenethiourea (ETU) is a toxic decomposition product/metabolite of alky-lenebis(dithiocarbamates). This compound could be generated during processing of treated crops at elevated temperature. Different chromatographic methods to determine the residue levels of ETU have been published. After extraction with methanol, clean-up on a Gas-Chrom S/alumina column and derivatization (alkylation) with bro-mobutane, ETU residues can be determined by GC with a flame photometric detector in the sulfur mode. Alternatively, ETU residues can also be determined by an HPLC method with UV detection at 240 nm or by liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/tandem mass spectrometry (LC/MS/MS) (molecular ion m/z 103). ... 

Guo et al. [53] developed a gas chromatographic method for the analysis of miconazole nitrate in creams and injections. The conditions were flame ionization detector, stationary phase of 5% SE 30 support of Chromosorb W (AS-DMCS, 80—100 mesh) packed column 3 m x 3 mm column temperature 275 °C injection temperature 290 °C and diisooctyl sebacate and internal standard. The average recoveries for creams and injections were 97.7 and 101.4%, respectively. The relative standard deviations were 2.2 and 1.3%, respectively. 

Reza, J., Trejo, A., Vera-Avila, L.E. (2002) Determination of the temperature dependence of water solubilities of polycyclic aromatic hydrocarbons by a generator column-on-line solid-phase extraction-liquid chromatographic method. Chemosphere 47, 933-945. 

Supercritical fluid chromatography is the name for all chromatographic methods in which the mobile phase is supercritical under the conditions of analysis and the solvating properties of the fluid have a measurable effect on the separation. SFC has some advantages over GC and HPLC it extends the molecular weight range of GC, thermally labile compounds can be separated at lower temperatures, compounds without chromophores can be sensitively detected, and the use of open-tubular and packed columns is feasible. SFC can be employed in both the analysis of natural pigments and synthetic dyes, however it has not been frequently applied in up-to-date analytical practice. 

Trace hydrocarbons that may be regarded as contaminants may be determined by the gas chromatographic methods already discussed. Heavier hydrocarbons in small amounts may not be removed completely from the column. If accurate information is required about the nature and amount of heavy ends, temperature programming or a concentration procedure may be used. 

Clark described another gas chromatographic method, which used a 2 m x 4 mm glass column with 2.5% SE-30 on 100 mesh Chromosorb G 80 [4]. An oven temperature of about 118°C and a nitrogen carrier flow rate of 45 mL/min. were used. 

Rao et al. reported a high performance liquid chromatographic method to determine diloxanide furoate and metronidazole in single and in combined dosage forms [41]. A 30 mg equivalent of diloxanide furoate and 25 mg of metronidazole (either as the bulk drug substances or in powdered tablets) was dissolved in methanol, amidopyrine added as the internal standard, and the mixture analyzed by HPLC at room temperature. The analytical column (30 cm x 3.9 mm) consisted of p-Bondapak Cig, with 9 9 1 1 methanol water 0.05 M KH2PO4 0.05 M NaH2P04 as the mobile phase. The flow rate was 1 mL/min), and detection was performed at 254 nm. 

Most early gas-chromatographic methods for corticosteroid analysis in foods involved use of an OV-17 275 cm column at high temperature and an electron capture detector for separation of the analytes in form of their TMS... 

An attractive alternative to the direct measurement of vapor pressure is the use of gas chromatographic retention to estimate p (e.g., Hinckley et al., 1990). This method is based on the evaluation of the partitioning behavior of a given compound between the gas phase (i.e., the mobile phase) and a bulk organic phase (i.e., the stationary phase) at different temperatures. The method hinges on the selection of an... 

Reversed-phase HPLC can separate polyphenolics of extracts on the basis of polarity. HPLC easily produces better resolution among chemically similar compounds in extracts than conventional chromatographic methods. The operating temperature of the column during reversed-phase HPLC analysis should be controlled for data reproducibility. A change in temperature produces only a minor effect, however, on band spacing in reversed-phase HPLC and produces essentially no effect in normal-phase HPLC (Lee and Widmer, 1996). A range of ambient temperatures is widely used, and elevated temperatures are often applied. The retention times of the peaks are dependent upon the type of column and the combination of various solvents used in the method. 

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