The use of cartridges for solid-phase extraction in the analysis of organic compounds in natural waters

The article presents the main stages of the solid-phase extraction process as a method of sample preparation of natural thermal and mineral cold waters for subsequent instrumental analysis of medium volatility organic matter by gas chromatography, in combination with mass spectrometry. The use of standard polypropylene cartridges, equipped with frits, has a high risk of the extract contamination with adventitious impurities, which appear as separate peaks on the chromatogram. The paper examines cartridges from two major manufacturers: DSC-18 Supelco and Strata C18-E Phenomenex. Dichloromethane (methylene chloride), used as an eluting solvent, reacts with the walls of the cartridge, resulted in the extraction of n-alkanes and siloxanes from the polypropylene the cartridge is made of. Replacing dichloromethane with methanol, on the one hand, helps to reduce or completely prevent the occurrence of this type of instrumental contamination, but, on the other hand, it carries the risk of ineffective extraction of non-polar organic compounds of medium volatility from the sorbent and causing damage to the capillary gas column, which is used in gas chromatography. The use of homemade glass cartridges, equipped with deactivated glass wool as frits, helps to avoid the above-mentioned disadvantages. Dichloromethane does not extract unwanted impurities from glass walls of homemade cartridges and successfully extracts non-polar and weakly polar organic compounds of medium volatility from the C18 sorbent. The natural water analyzes from a stagnant reservoir in the town of Birobidzhan, when using a homemade glass cartridge have shown in the extract a large number of various organic compounds (115 components) of bacterial and plant origin, with a complete absence of foreign impurities. The dominant compounds include terpenes, heteroaromatic hydrocarbons, oxygen-containing compounds and normal alkanes, the origin of which is associated with biogenic processes. The man-made pollution compounds are presented there by phthalic acid esters, with a relative content of about 9%.