Passive capillary samplers (PCAPS) use the capillary potential generated by hanging fiberglass wicks to exert a sampling suction on soil water. Impurities on the fiberglass affect the capillary properties of the wick and the chemical properties of the samples collected. To determine the need, and a method, for cleaning the wicks, capillary rise and moisture contents were measured using four preparations: uncleaned, detergent washed, acetone extracted, and combusted. Wicks were made with fibers produced by PPG Industries and Manville Company. Results showed that wicks made from PPG fibers lost up to 3.4% of original mass during combustion while Manville fiber wicks lost <0.6%. These losses are assumed to have been due to combustion of organic compounds applied by the manufacturers. All cleaning methods had higher capillary rise than obtained with uncleaned wicks. Combustion at 400 °C for 4 h was the best cleaning method, removing 98 to 100% of impurities.
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Knutson et al. (1993) studied this question.