On-column injection in the stopped-flow mode with open-tubular columns

Summary A simple, inexpensive, on-column injector of the septum moving-needle kind is described for quantitative analysis using open-tubular columsn. when operated in the stopped-flow mode an improvement incolumn efficiency is observed combined wit a diminished tendency to produce split-top peaks, particularly for late eluting peaks. Using electronic integration a relative error of about 2.7% was observed for peaks spanning a wide range of sample concentrations and volatilities.Dedicated to Professor A. Zlatkis on the occastion of his 60th birthday.     

柱头进样结合气相色谱质谱分析动物源食品中热不稳定性氨基甲酸酯类农药

对柱头进样结合气相色谱-质谱法(GC/MS)应用于复杂基体中热不稳定性氨基甲酸酯农药检测的可行性及可靠性进行了探讨.在常规不分流进样和柱头进样模式下,对13种氨基甲酸酯类农药的热不稳定性进行了比较.以猪肉、鸡蛋、牛奶为研究基体,采用乙腈提取,凝胶渗透色谱结合中性氧化铝固相萃取柱净化,柱头进样-GC/MS检测.研究表明:...     

On-column endcapping and derivatization in reversed-phase high-performance liquid chromatography

Summary On-column endcapping and derivatization or regeneration of C₈ and C₁₈ reversed-phase HPLC columns with newly introduced reagents were studied. These treatments can increase column life expectancy by restoring retention times and original chromatographic characteristics of the columns. This is illustrated by examples. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Injection temperature effects using On-column and split sampling in capillary gas chromatography

The effect of sample injection temperature on quantitation is examined for on-column and conventional split modes of sampling in capillary gas chromatography. Discrimination effects can be observed even with on-column injection if the injection temperature is too far above the boiling point of the solvent (or that of a major low boiling constituent(. This is attributed to higher boiling components being left behind in the syringe needle, and a set of simulation experiments are described to illustrate this effect. Various discrimination patterns using conventional split injection were observed, depending on temperature of injection. Apart from syringe needle effects, discrimination is probably due to the preferential venting of higher boiling components as liquid sample droplets, which can have a lifetime greater than the time of transit to the splitter. With such a two-phase system, involving variable droplet size, the flow distribution in the splitter will be critical to uniform sampling. The use of combination on-column/split sampling, with the appropriate temperature control to provide sample uniformity to the splitter is discussed as an advantageous alternative to conventional split sampling.     

Direct gas chromatographic analysis of halogenated hydrocarbons at the part-per-trillion level

Large sample volume on-column injection (up to 250 μL) of n-pentane solutions of halogenated hydrocarbons has been employed for the direct measurement of both low-boiling and high-boiling compounds in what is essentially a single run. Two-bonded phase, fused-silica capillary columns are joined in series, through which the low-boiling compounds are first chromatographed and detected with an electron capture detector. High-boiling compounds are then trapped in a section joining the two columns, and subsequently chromatographed in the second column, using the same detector. This procedure permits analysis at the ppt level.     

Determination of carbofuran in a nutrient solution by GLC/NPD and HPLC

Summary Two analytical methods using GC/NPD and HPLC to analyse carbofuran in a nutrient solution used in hydroponic culture are described. Both methods show a high recovery, (greater than 90%), and their limits of detection are low.     

GLC assay of khellin in human serum and urine

Summary A sensitive, specific and rapid GLC assay for khellin in serum and urine has been developed using flame ionization The method involves the addition of hyoscine as an internal standard, extraction with chloroform and the use of a 3% OV-17 on Gas Chromosorb column. The suitability of this procedure for serum sample analysis from rats after oral administration of the drug is reported.     

On-column injection onto capillary columns. Part 2: Study of sampling conditions; practical recommendations

During one year continuous use of on-column injection, the typical advantages described in our first report have fully been confirmed. In addition the analysis of large sample volumes has proved promising. Only minor modifications have been applied to the on-column injector device. Broad evidence has been gathered showing that full separation efficiency of the capillary columns after on-column injection is attained only when cold trapping or the solvent effect, as band shortening mechanisms, are working- While, under the conditions of on-column injection, cold trapping is less efficient than with other injection techniques, the opposite holds true for the solvent effect. Compared with splitless injection, the danger of excessive solvent condensation on the column is increased. A working rule is presented for establishing the optimal chromatographic conditions for handling large sample volumes while ensuring full separation efficiency yet avoiding harm to the column.