Before collecting samples, filters must be pre-combusted at 450°C for 30 minutes. Whatman filters, either GFC or GFF, provide low background contamination and are highly preferred. Filters up to 25mm in diameter are analyzed whole and are considered as 'Regular' on our rate schedule. Larger filters up to 47mm in diameter are too big to analyze whole and must be cut in half for analysis. Both halves are analyzed simultaneously, but these samples fall under the "Double-drop" analysis on our rate schedule.
After collection, filters should be placed in a 60°C drying oven and must be submitted completely dry. They should contain no more than 4mg of dried material. If more than 4mg of material is present, or if you have other concerns, please contact the Analytical Lab. Be sure to include filter blanks along with the samples.
Filters submitted to the Analytical Lab for Organic Carbon analysis (TOC) should be treated with 10% v/v hydrochloric acid (HCl) to remove inorganic carbonates. After acidification, filters should be placed in a 60°C drying oven and must be submitted completely dry. The Analytical Lab can provide the acidification service upon request.
Glass or plastic scintillation-type vials are the preferred containers, but plastic petri dishes with lids or glassine envelopes work well also. Wrapping filters in aluminum foil is not recommended as filters have a tendency to stick to the foil during drying and sample losses may occur.