112
Estuarine Sediments
5.1.3
Selenium
Itoh et al. [330] have developed an automated flow system to eliminate interferences
from transition metal ions during the hydride generation I atomic absorption spectrometric determination of selenium in estuarine sediments. Experimental conditions
were adjusted to minimize interferences. Low concentrations of tetrahydroborate in 6
mol 1-1 hydrochloric acid were preferred. Iron(III), added as chloride at a concentration of 2 mmoll- 1 , removed the depression of selenium signals by ions such as copper
(II) and bismuth(III).
5.1.4
Multielements
Atomic Absorption Spectrometry. Sinex et al. [331] have evaluated the accuracy and
precision of a method for the determination of chromium, manganese, iron, cobalt,
nickel, copper, zinc, cadmium, and lead in estuarine sediments. This method involved
a 4 h hot digestion of 5 g of dried (at 105°C) sample with 100 ml 9:1 v Iv nitric
acid-hydrochloric acid followed by atomic absorption spectrometry of the 25 ml of
concentrated extract. High recoveries and good reproducibility were obtained with
coefficients of variation being 10 % or less. They compared results obtained by this
procedure with those obtained by a lithium metaborate fusion-d.c. plasma emission
spectroscopic method [332, 333], NBS SRM-1645 river sediment and on an estuarine
sediment (US Geological Survey Marine mud sample MAG-I). In the lithium metaborate fusion method, 100 mg of the dried sediments were fused with 0.5 g of lithium
metaborate in a graphite crucible at 900°C for approximately 15 min. The molten
lithium borate glass bead was poured into a 150-ml Teflon FEP beaker containing
100 ml of 4 % nitric acid. The beaker was placed on a magnetic stirrer, and the
contents were stirred for approximately 10 min. The solution was then transferred to
a 125-ml polyethylene bottle. Considerably higher and more reproducible recoveries
were obtained by fusion than by acid digestion. When the acid extraction method was
applied to estuarine acids (MAG-I), the resulting trace metal concentrations, although
reproducible, were usually substantially lower than total concentrations determined
by lithium metaborate fusion-d.c. plasma emission spectroscopy. Excellent recoveries
were obtained when the test was applied to the NBS SRM 1645 reference river
sediment; chromium, manganese, nickel, copper, zinc, and lead recovery was complete, while for iron, cobalt, and cadmium, modest under recovery (13-25 %) was observed.
Sturgeon et al. [334] demonstrated quantitative recovery of cadmium, lead, copper,
nickel, cobalt, beryllium, and chromium from estuarine sediments using a digestiongraphite furnace atomic absorption spectrometric with a L'vov platform method.
In general, it is agreed that there is a lack of well characterized and representative
standard reference estuarine sediments for the evaluation of methods of analysis. The
National Research Council of Canada Marine Analytical Standards Programme has
prepared two near-shore marine sediment reference materials, MESS-l and BCSS-l,
for which reliable results are available for 12 major and minor constituents and 13
trace metals. Sturgeon et al. [334] used these standards to evaluate their method.
Estuarine Sediments
5.1.3
Selenium
Itoh et al. [330] have developed an automated flow system to eliminate interferences
from transition metal ions during the hydride generation I atomic absorption spectrometric determination of selenium in estuarine sediments. Experimental conditions
were adjusted to minimize interferences. Low concentrations of tetrahydroborate in 6
mol 1-1 hydrochloric acid were preferred. Iron(III), added as chloride at a concentration of 2 mmoll- 1 , removed the depression of selenium signals by ions such as copper
(II) and bismuth(III).
5.1.4
Multielements
Atomic Absorption Spectrometry. Sinex et al. [331] have evaluated the accuracy and
precision of a method for the determination of chromium, manganese, iron, cobalt,
nickel, copper, zinc, cadmium, and lead in estuarine sediments. This method involved
a 4 h hot digestion of 5 g of dried (at 105°C) sample with 100 ml 9:1 v Iv nitric
acid-hydrochloric acid followed by atomic absorption spectrometry of the 25 ml of
concentrated extract. High recoveries and good reproducibility were obtained with
coefficients of variation being 10 % or less. They compared results obtained by this
procedure with those obtained by a lithium metaborate fusion-d.c. plasma emission
spectroscopic method [332, 333], NBS SRM-1645 river sediment and on an estuarine
sediment (US Geological Survey Marine mud sample MAG-I). In the lithium metaborate fusion method, 100 mg of the dried sediments were fused with 0.5 g of lithium
metaborate in a graphite crucible at 900°C for approximately 15 min. The molten
lithium borate glass bead was poured into a 150-ml Teflon FEP beaker containing
100 ml of 4 % nitric acid. The beaker was placed on a magnetic stirrer, and the
contents were stirred for approximately 10 min. The solution was then transferred to
a 125-ml polyethylene bottle. Considerably higher and more reproducible recoveries
were obtained by fusion than by acid digestion. When the acid extraction method was
applied to estuarine acids (MAG-I), the resulting trace metal concentrations, although
reproducible, were usually substantially lower than total concentrations determined
by lithium metaborate fusion-d.c. plasma emission spectroscopy. Excellent recoveries
were obtained when the test was applied to the NBS SRM 1645 reference river
sediment; chromium, manganese, nickel, copper, zinc, and lead recovery was complete, while for iron, cobalt, and cadmium, modest under recovery (13-25 %) was observed.
Sturgeon et al. [334] demonstrated quantitative recovery of cadmium, lead, copper,
nickel, cobalt, beryllium, and chromium from estuarine sediments using a digestiongraphite furnace atomic absorption spectrometric with a L'vov platform method.
In general, it is agreed that there is a lack of well characterized and representative
standard reference estuarine sediments for the evaluation of methods of analysis. The
National Research Council of Canada Marine Analytical Standards Programme has
prepared two near-shore marine sediment reference materials, MESS-l and BCSS-l,
for which reliable results are available for 12 major and minor constituents and 13
trace metals. Sturgeon et al. [334] used these standards to evaluate their method.