Metals
33
Malo [38] evaluated four procedures employing 0.3 N hydrochloric acid, citratedithionite pH3, nitrate-dithionite pH7, acetic acid-hydroxylamine, and nitric acidhydrogen peroxide-hydrochloric acid for their potential for removing surface metals
from river sediments.
Prior to application of the partial extraction procedures, the samples were treated
with 30 % hydrogen peroxide on a steam bath to destroy organic matter.
The following are brief descriptions of the four partial extraction procedures and
the nitric acid dry ashing treatment.
Hydrochloric Acid. The sediment (5-10 g) water mixture, following hydrogen peroxide treatment, is diluted to 200 ml with deionized water. Then 10 ml of 6 mol 1-1
hydrochloric acid is added, and the suspension is mixed and heated to just below
boiling on a hot plate. Heating at this temperature is continued for 30 min. The hot
mixture is filtered through a Whatman No. 42 filter paper, or equivalent, and the
filtrate is collected in a 250-ml volumetric flask. The residue on the filter is washed at
least three times with hot, dilute 5 vol. % hydrochloric acid and the fIltrate is cooled
and brought to volume with 5 vol. % hydrochloric acid.
pH Buffered Citrate-Dithionite. Add 40 ml of pH 3 citrate buffer (160.0 g citric acid
and 71.3 g sodium citrate dissolved in deionized water to give a final volume of
1 000 ml) to 5-10 g of peroxide treated sample and heat with occasional swirling for
1 h at 80°C in an oven. Add 80 ml of purified dithionite-citrate solution (95.6 g
sodium citrate and 36.8 g citric acid dissolved in 11 of deionized water, extracted by
shaking with 1 g ammonium pyrrolidone diethyldithiocarbamate, 100 ml ethyl propionate, and 50 g sodium dithionite, and re-extracted using only 100 ml of solvent)
and hold at 80°C with occasional swirling for 3 h. If the solution temperature exceeds
80°C, insoluble sulfides will form. Remove from oven and flocculate the sediment
with saturated sodium nitrate solution, centrifuge, and decant into a 250 ml volumetric flask. Wash the sediment twice with 10 ml citrate buffer, combine washings and
extract, and adjust to volume with deionized water.
pH 7 Buffered Citrate-Dithionite. Add 50 ml of 0.3 mol 1-1 sodium citrate (88 g I-I
Na 3 C 6 H s 0 7 2HP) and 5 ml 1 mol 1-1 sodium bicarbonate (84 g I-I NaHC0 3 ) to the
peroxide treated sample (5-10 g). Heat to 80°C in an oven, remove and quickly add
10 ml of sodium dithionite solution (100 g I-I Na 2 Sp4). Heat to 80°C in an oven and
continue heating for 15 min. If the solution temperature exceeds 80 °c, insoluble
sulfides will form. Cool and flocculate sediment with saturated sodium chloride
solution, centrifuge, and decant the clear supernate into a 250-ml volumetric flask.
Wash residue twice with lO-ml portions of 0.3 mol 1-1 sodium citrate and combine
washings with the extract. Adjust to volume with deionized water.
1 mol I-I Hydroxylamine Hydrochloride in 25 vol. % Acetic Acid. Add 50 ml of mixed
acid-reducing reagent [mix 150 ml of 25 % (w Iv) hydroxylamine hydrochloride and
350 ml of 35 vol. % acetic acid] to the peroxide treated sample (5-10 g) in a 250-ml
conical flask. Place on a mechanical shaker and shake at room temperature for 4 h.
Filter through a No. 42 Whatman paper into a 250-ml volumetric flask. Wash the
residue on the paper several times with deionized water, combine washings and
filtrate, and adjust to volume with deionized water.
33
Malo [38] evaluated four procedures employing 0.3 N hydrochloric acid, citratedithionite pH3, nitrate-dithionite pH7, acetic acid-hydroxylamine, and nitric acidhydrogen peroxide-hydrochloric acid for their potential for removing surface metals
from river sediments.
Prior to application of the partial extraction procedures, the samples were treated
with 30 % hydrogen peroxide on a steam bath to destroy organic matter.
The following are brief descriptions of the four partial extraction procedures and
the nitric acid dry ashing treatment.
Hydrochloric Acid. The sediment (5-10 g) water mixture, following hydrogen peroxide treatment, is diluted to 200 ml with deionized water. Then 10 ml of 6 mol 1-1
hydrochloric acid is added, and the suspension is mixed and heated to just below
boiling on a hot plate. Heating at this temperature is continued for 30 min. The hot
mixture is filtered through a Whatman No. 42 filter paper, or equivalent, and the
filtrate is collected in a 250-ml volumetric flask. The residue on the filter is washed at
least three times with hot, dilute 5 vol. % hydrochloric acid and the fIltrate is cooled
and brought to volume with 5 vol. % hydrochloric acid.
pH Buffered Citrate-Dithionite. Add 40 ml of pH 3 citrate buffer (160.0 g citric acid
and 71.3 g sodium citrate dissolved in deionized water to give a final volume of
1 000 ml) to 5-10 g of peroxide treated sample and heat with occasional swirling for
1 h at 80°C in an oven. Add 80 ml of purified dithionite-citrate solution (95.6 g
sodium citrate and 36.8 g citric acid dissolved in 11 of deionized water, extracted by
shaking with 1 g ammonium pyrrolidone diethyldithiocarbamate, 100 ml ethyl propionate, and 50 g sodium dithionite, and re-extracted using only 100 ml of solvent)
and hold at 80°C with occasional swirling for 3 h. If the solution temperature exceeds
80°C, insoluble sulfides will form. Remove from oven and flocculate the sediment
with saturated sodium nitrate solution, centrifuge, and decant into a 250 ml volumetric flask. Wash the sediment twice with 10 ml citrate buffer, combine washings and
extract, and adjust to volume with deionized water.
pH 7 Buffered Citrate-Dithionite. Add 50 ml of 0.3 mol 1-1 sodium citrate (88 g I-I
Na 3 C 6 H s 0 7 2HP) and 5 ml 1 mol 1-1 sodium bicarbonate (84 g I-I NaHC0 3 ) to the
peroxide treated sample (5-10 g). Heat to 80°C in an oven, remove and quickly add
10 ml of sodium dithionite solution (100 g I-I Na 2 Sp4). Heat to 80°C in an oven and
continue heating for 15 min. If the solution temperature exceeds 80 °c, insoluble
sulfides will form. Cool and flocculate sediment with saturated sodium chloride
solution, centrifuge, and decant the clear supernate into a 250-ml volumetric flask.
Wash residue twice with lO-ml portions of 0.3 mol 1-1 sodium citrate and combine
washings with the extract. Adjust to volume with deionized water.
1 mol I-I Hydroxylamine Hydrochloride in 25 vol. % Acetic Acid. Add 50 ml of mixed
acid-reducing reagent [mix 150 ml of 25 % (w Iv) hydroxylamine hydrochloride and
350 ml of 35 vol. % acetic acid] to the peroxide treated sample (5-10 g) in a 250-ml
conical flask. Place on a mechanical shaker and shake at room temperature for 4 h.
Filter through a No. 42 Whatman paper into a 250-ml volumetric flask. Wash the
residue on the paper several times with deionized water, combine washings and
filtrate, and adjust to volume with deionized water.