Cross-contamination avoidance, water analyses

C prior to analysis. The jars should not be overfilled because breakage can easily occur for samples with high-water content. The plastic lids of the jars should be covered inside with solvent-rinsed aluminum foil to avoid the introduction of plasticizers in the sample. Sediment samples can also be dried before analysis, but several procedures carry a risk for the integrity of the samples due to evaporation losses or introduction of interferences or cross-contamination. 

Tables 116-120 show results obtained by this procedure in the analysis of water, shell and human urine samples for organotin compounds. All samples were analyzed without pretreatment. Samples which were not analyzed immediately, were frozen until analysis was possible. Polyethylene bottles, 500-ml volume, were used for sample acquisition and storage. No contamination of samples by the bottles was observed and no cross contamination was noted between uses. Poly(vinyl chloride) materials must be avoided to prevent tin contamination from the organotin plasticizers used in its production. Approximately 17-60% of the total tin present was found to be in the methylated forms. The saline waters appear to have the highest percentage of methylated tin compounds, 60% of the total tin present was found to be in the methylated forms, the dimethyltin form contributes approximately half of this value.

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