Suspended particulate matter: Collection methods for gravimetric and trace metal analysis.

Abstract

Filtration is the most commonly used method for separating the dissolved and particulate fractions of seawater samples. A wide variety of filter types with different pore sizes has been used for this purpose. Filtration of water samples for trace metal analysis has generally been done using either Millipore 0.45~m cellulose acetate/nitrate filter membranes, Nuclepore 0.4~m polycarbonate filter membranes, or similar filter membranes produced by other companies. Several studies have shown that the concentrations of suspended particulate matter (SPM) measured using different types of filters can vary significantly. For example, Tambiev and Demina (1982) have shown, using samples from the Baltic Sea, that 0.7~m cellulose nitrate filters can give a suspended particulate matter concentration that is five times that found with 0.4~m Nuclepore polycarbonate or 0.5~m Dubna polyethylene-terephthalate membranes. The metal blanks were also higher for the cellulose nitrate membranes. Likewise, Brzezinska-Paudyn et al (1985) observed that 0.45~m cellulose acetate and 0.45~m glass fibre filters gave significantly higher particulate matter concentrations than did 0.4~m Nuclepore filters. Danielsson (1982) found that 0.45~m Millipore membrane filters introduce large errors due to changing pore size during filtration. He also showed that the iron concentrations in the filtrates decreased with time and became nearly zero when the filters clogged.