Filtering Procedure

Now that we have samples, the next step is to filter them.  Because organic matter can break down rapidly, runoff samples need to be processed as quickly as possible.  We filter about 150 mL of each sample through 0.7 µm glass fiber filters.  The filters are pre-combusted in a furnace to destroy any organic contaminants.  The filtration apparatus is thoroughly rinsed between each sample.  Ultra pure (Milli-Q) water is passed through the filter paper before any sample.  The filtration is expedited by a vacuum pump (Büchner-style).

In order to determine the concentration of particulate matter in each sample, each filter is pre-weighed.  After filtration, each filter is dried overnight at 105°C.  The dried filters are weighed again.  The differences between pre- and post-filtration masses are divided by the volume of initial filtered sample to determine the concentration of suspended sediment.  The filtrate is preserved for later analysis for inorganic ions, absorbance properties, and total dissolved organic carbon.