Abstract
Concentration differences of soluble constituents in precipitation samples, under five different preservation methods, were compared. The samples collected at Niigata, Japan in early winter and spring were preserved 21 to 59 days in 100 mL polyethylene bottles. Examined preservation methods were as follows:(A) Untreated, preserved at room temperature;(B) Filtrated (using a well washed membrane filter, pore size: 0.45μm), preserved at room temperature;(C) Added thymol (40 mg/100 mL), preserved at room temperature;(D) Untreated, preserved in a refrigerator (4°C) and (E) Filtered, preserved in a refrigerator.
Thymol-addiiton, which did not intefere with determination of constituents in precipitation, was an effective method for original H+ (organic acids, such as formic and acetic acids) and the NH4+ cncentratiorn. Refrigeration was the next useful preservation method except for organic acids. Filtration was effective in reducing Ca2+ concentration change induced by dissolution of suspended matter in precipitation samples. From these results, it is recommended that when a refrigerator is not available even if samples are collected by wet-only sampler and/or organic acids are involved in measuring parameters, thymol should be placed in the sample collection bottles beforehand, and after collection, suspended substances in precipitation samples and residual crystals of thymol should be eliminated by filtration at a laboratory as a pretreatment for ion chromatography.
