Applications of the deferred standard technique in process gas chromatography

Three applications of the deferred standard (DS) technique in on-line gas chromatographic analysis with a rotary injection valve are reported. It is demonstrated how both absolute and relative measurements are affected by several deviations of the experimental conditions, such as atmospheric pressure, sample injection during either flow or stopped-flow conditions and instrumental settings (carrier gas flow-rate, column oven temperature, detector bridge current) of the analytical system. It is shown that the relative DS concept provides an excellent means of improving the reliability of the analytical equipment. Under standard conditions, accurate results were obtained with a relative standard deviation < 1%. Significant deviations in the instrumental settings affected the accuracy of the final analytical results by less than 4%. It is further shown how the DS technique can be applied to obtain early information on maintenance requirements of the system. A diagnostic table is included that relates observed changes with time of the signals, obtained with a thermal conductivity detector, to possible maintenance requirements.     

On-line single column capillary gas chromatographic analysis of all reactants and products in the synthesis of fuel methanol from hydrogen and oxides of carbon

The main problems with complete analysis of the components of fuel methanol, or in Fischer-Tropsch studies, are the several classes of compound present in the sample (permanent gases, water, alcohols, hydrocarbons), its wide range of components, its boiling point range, and the wide range of component concentrations. A flexible on-line GC method has been developed for kinetic study of catalyzed chemical reactions of hydrogen and oxides of carbon. The single capillary column, temperature programmed method was designed for complete analysis of reactants and products (hydrogen, carbon monoxide, carbon dioxide, water, C₁-C₁₀ hydrocarbons, and C₁-C₆ alcohols): a sample selection valve is used to switch between either the heated line used for input of the synthesis gases or the heated line used to transport reaction products from the reactor. Sample is introduced to the capillary column by means of a 10-port heated gas sampling valve with two external injection loops (0.07 and 1.95 cm³); this results in the determination of components over a wide range of concentrations in the sample (ppm to percentage levels). Helium from a pressure-controlled supply is used as carrier gas and detection of the components is performed by serial connection of thermal conductivity and flame ionization detectors. Peak identification is performed by mass spectrometry and by comparison of component retention times. The automated analytical equipment is integrated with a process control computer and delivers repeatable analytical results for the individual components (RSDs varying between 0.3 and 10% depending strongly on the concentration of the component and the accuracy of the determination of its peak area).     

Automated on-line gas chromatographic injection of samples completely liquified by pressure

Summary A modified on-line liquid injection technique with rotary valves for gas chromatography has been developed. Applications for the on-line analysis of 2-methylpropene, cyclohexene and 1-butene are described. All samples were loaded under pressure. The results obtained show excellent reproducibility with less than 0.1% relative standard deviation (r.s.d.; n=6) for the peak areas measured. The method is particularly advantageous for samples containing both gas and liquid ccomponents at one bar.     

Ion-exchange chromatography of lactose-lactulose isomerization mixtures using a boric acid-borate eluent

Mixtures obtained by the isomerization of lactose on anion exchangers have been analysed by ion-exchange chromatography. With a 57-mm column of Aminex A-25 and 0.400 M H₃BO₃-0.005 M Na₂B₄O₇ as eluent, a complete separation of actose, epilactose (4-O-β-d-galactopyranosyl-d-mannose), lactulose, galactose and tagatose is obtained in about 50 min. The influence of various factors on the qualitative and quantitative results is given. The ratio of Na₂B₄O₇ to H₃BO₃ in the eluent has an important influence on the order of elution of ketoses and aldoses, especially at low ratios. A special device is described for removing excess of lactose during the analysis. The method describe is also applicable to the analysis of lactulose syrups.