The Applications of Chemical Analyses of Sediments and Soils in ...

eference samples are included in each run for quality control. Problems occurred dueto contamination and high blanks which have been largely corrected by protectingsamples in the fumehood from contamination by a baffle and overnight soaking ofglassware in 50% nitric acid.* Millipore filters were previously used by these have beenreplaced by filtering through paper in long stemmed glass funnels, both quicker andless subject to contamination. The volume is then made up to 50 mi and the mouthsof the tubes covered with Parawax.Previous practice was to ash all samples at 600°C prior to digestion. However,it was realized that there could be serious losses of volatile metals such as lead andcadmium. Low temperature ashing (LTA) was evaluated as a means of removingorganic matter, obtaining an ash which could be readily extracted with cold nitric acidwith minimum loss of volatile metals. The method worked very satisfactorily forbiomaterials such as fish but was unsuccessful for sediment, principally because ofincomplete ashing, small sample size (0.1 gm) and the long time required. It wasplanned to obtain an LTA with a vibrator system. **It is recognized that these extractions are not complete (van Loon and Lichwa,1973) as metals bound in minerals are not measured (Anderson, 1974). Lithiumtetraborate fusion was previously practiced in this laboratory but has the disadvantageof small sample size and hence low sensitivity, high reagent blank contribution andhigh salt content interferences in AAS._______________* Recently found unnecessary following adoption of washing in a Mielé washer** Obtained since meeting and currently being evaluated.35