Theoretical principles of thin layer headspace analysis

Abstract

Theoretical principles of thin layer headspace (TLHS) analysis are reviewed. TLHS utilizes a special heated column in which a continuously flowing thin film of a liquid sample is contacted with a continuously flowing pure gas. Volatile analytes contained in the liquid sample pass to the gas phase and are carried away from the column. For the determination of volatile organic halogen (VOX), the analytes in the gas are mineralized at 900°C, and the mineralization products (hydrogen halides) are absorbed in an appropriate solvent in a second TLHS column kept at ambient or sub-ambient temperature. The mineralization products can be quantified in the liquid sorbent using conductometric, spectrophotometric, as well as direct and indirect potentiometric methods. The unique feature of this method is the dynamic preconcentration of the analyte in the liquid sorbent. When analyte speciation is required, the liquid sorbent can be generated in TLHS column II by condensation of the water vapour carried by the gas from TLHS column I, and the condensed phase can be analyzed by direct liquid injection gas chromatography. General equations describing the recovery of the analyte or its conversion products in TLHS column II are given, followed by general and partial solutions yielding insight into the nature of the processes and being useful for optimization of the operating parameters of the method. Conditions under which TLHS analysis can be used to separate two compounds are discussed.

Selected concentration techniques for gas chromatographic analysis of environmental samples

“…The spectrum of matrices, which can be analysed with the use of DAI-GC, has been noticeably widened since the development of a special variety of head space technique at the Department of Analytical Chemistry, Chemical Faculty, Technical University of Gdafisk [21 ]. Figure 4 presents a schematic diagram of an apparatus for the generation of aqueous concentrates by means of thin layer head space (TLHS).…”

Monitoring of Occupational Exposure to Volatile Organohalogen Solvents (VOXs) in Human Urine Samples of Dry-cleaner Workers by TLHS-DAI-GC-ECD Procedure

“…The biological monitoring of unchanged forms of solvents sampled from exposed workers has been investigated in many laboratories [1][2][3] but occupational exposure of dry-clean workers is still a pressing problem 4,5) .…”