Use of a certified reference material for extractable trace metals to assess sources of uncertainty in the BCR three-stage sequential extraction procedure
A. Sahuquillo et al., Use of a certified reference material for extractable trace metals to assess sources of uncertainty in the BCR three-stage sequential extraction procedure, ANALYT CHIM, 382(3), 1999, pp. 317-327
Various potential sources of irreproducibility in the BCR three-stage seque
ntial extraction procedure have been investigated using the lake sediment C
RM 601. Of the variables considered, the pH of the hydroxylamine hydrochlor
ide in Step 2 proved most important. Factors such as the type of acid used
in pH adjustment, the temperature and duration of extraction, and working u
nder nitrogen did not affect precision, although they did alter the amounts
of metals extracted. Improved precision was obtained when the hydroxylamin
e hydrochloride concentration was increased from 0.1 to 0.5 mol l(-1) and w
hen the speed of the centrifugation was increased from 1500 to 3000 x g. Th
e addition of a MgCl2 wash between the steps of the extraction procedure ga
ve rise to increased uncertainty. Although it did not adversely affect repr
oducibility, the use of filtration to separate solid and liquid phases was
not recommended since it promoted dissolution of non-target phases. Neither
ammonium hydrogen oxalate nor oxalic acid proved suitable alternatives in
Step 2 owing to precipitation of insoluble lead salts, particularly in the
presence of calcium. (C) 1999 Elsevier Science B.V. All rights reserved.