Modification of hydrophobic sorbents by cobalt chloride in order to concentrate low molecular polar organic substances from the air for subsequent gas chromatographic determination.

The article presents a new method of modification of hydrophobic sorbents. To improve sorption pre-concentration of polar organic compounds in the air analysis, these sorbents are coated with cobalt chloride. This modification increases retention volume of lower alcohols by 5-10 fold as compared to that of unmodified sorbents and solves the problem of gas-chromatographic determination at 1-2 ppb (micrograms/m(3)) by using the most common flame ionization detector. It should be noted that the modification of hydrophobic sorbents by cobalt chloride has little influence on their porosimetry parameters (specific surface area, proportions of meso- and micropores) and modified sorbents are capable of retaining hydrophobic nonpolar and weakly polar analytes as well as original unmodified sorbents. Thus, a fairly simple procedure leads to a large positive effect.

Compositional surface-layered sorbents for pre-concentration of organic substances in the air analysis.

We juxtapose methods of synthesis of non-polar surface-layered sorbents on the platform of a carrier, which combines macro-porous coarse-dispersed polytetrafluoroethylene with micro-dispersed activated carbon. Further, we present data about the sorption properties of the said materials alongside perspectives of their analytical applications. Our study established that with respect to efficacy of dynamic sorption from gaseous phases these sorbents outperform bulk-porous analogues in their normal, granular form.

The properties of chromatomembrane cells in flow systems coupled to gas chromatography-analysis of volatile organic compounds.

The economical use of modern analytical instrumentation requires an online-coupling of efficiently working flow-systems which automate both sampling and sample pretreatment. Whenever extraction and preconcentration procedures are necessary the application of chromatomembrane cells proved to be very worthwhile. On this occasion the analyte exchange takes place inside a block of biporous PTFE wherein the two immiscible phases come into contact with each other. A special enclosure enables water and the extracting nitrogen to flow independently through that block. In case of gaseous extractants the behavior of the biporous PTFE and its mechanical parameter have to be investigated precisely in order to overcome the special problems of trace analysis in gases. The gas-chromatographic detection of volatile organic compounds (VOC's) requires a discussion on the effects of gas-sorption and the kinetics of equilibration which should be taken into consideration for using the chromatomembrane cell as an extractor from waste water. The investigation realizes at least that a quick pretreatment is made possible and, however, sample sizes decrease remarkably in comparison with competing methods as head space analysis or purge and trap technique. The application of chromatomembrane cells permits reasonable accuracies with a limit of detection on the ng/l level.

Dissolved oxygen removal from aqueous media by the chromatomembrane method.

The possibilities of the new chromatomembrane method in the removal of oxygen dissolved in water are studied. The scheme of the water deoxygenation process is determined. The new reagent-free method allows production of water with oxygen content at the level of a few ppb.