Sulphites analytical methods

The within- and between-bottle homogeneity was verified and the variances were compared with the method variance (assessed on the basis of replicate analyses of an extract). A 500 mg portion of the sediment was extracted in a Soxhlet apparatus with 120 mL of a mixture of n-hexane and acetone 90/10 (v/v) for 6 h. The extract was concentrated and taken into a volume of 1 mL iso-octane. The concentrated extract was eluted over 2 g deactivated silica (with 15% water) with 15 mL of petroleum ether. The eluate was concentrated to a volume of 1 mL and treated with 1 mL of a solution containing 34 g L tetrabutylammonium sulphate, and sodium sulphite and isopropanol for the removal of sulphur. The concentrated eluate was cleaned over a column packed with 1.5 g deactivated silica (with 5% water). An internal standard solution (CB 198) was added to the clean extract. The mixture was separated on an Ultra-2 column (length 50 m, internal diameter 0.2 mm, film thickness 0.33 mm. He carrier gas, 65 min gradient from 90 to 275°C) with electron capture detection. No significant difference in the variance of the between- and the within-bottle series and the analytical method itself Therefore, it was concluded that the material is homogeneous for CBs. 

Compared with classical analytical methods such as gas chromatt raphy, HPLC, atomic absorption or mass spectrometry, the detection of pollutants by biosensors is generally less specific. These devices provide valuable information on a class of pollutants rather than a mere information about a specific compound, although the use of mutants that are resistant to specific pollutants can render them more selective. Biosensors provide valuable information about the real biological effects of the pollutants in a sample since phytotoxicity is determined from the measurement of electron transport activity, photocurrent or photosynthetic oxj en evolution. It is important to note that althoi the PSII complex is sensitive to various pollutants (herbicides, heavy metals, sulphites, nitrates, carbonates), its susceptibility to these compounds is highly variable, tanging from nanomolar to milhmolar concentrations. 

---