Anions in seawater - Determination of Anions in Natural and Treated Waters - page 365

Total 0.46

Source: Reproduced with permission from Elsevier Science [38]

Murray [35] agrees quite well with the value for chromium(VI) reported by them
although the value for chromium(III) is lower. The results obtained by Grimaud and
Michard [40] for chromium(III) differ considerably but the discrepancies cannot be
discussed because details of the analytical procedure were not given. It seems reasonable
to conclude that the inconsistency of past results concerning the dominant chromium
species and the total chromium concentration in seawater can be attributed, at least partly,
to the fact that the presence of organic chromium species was not considered properly.
Mullins [37] has described a procedure for determining the concentrations of dissolved
chromium species in seawater. Chromium(III) and chromium(VI) separated by co-
precipitation with hydrated iron(III) oxide and total dissolved chromium are determined
separately by conversion to chromium(VI), extraction with ammonium pyrrolidine
diethyl dithiocarbamate into methyl isobutyl ketone and determination by atomic
absorption spectrometry. The detection limit is 40ng L −1 chromium. The dissolved
chromium not amenable to separation and direct extraction is calculated by difference. In
the waters

Table 3.5 Determination of dissolved chromium species in some seawaters

Chromium found a (µg L −1 )

Location Cr(III) Cr(VI) Cr bound Cr total

Port Hacking 0.27±0.02 0.49±0.03 0.56±0.07 1.32±0.05

Georges River 0.42±0.04 0.89±0.04 0.42±0.08 1.72±0.06

Drummoyne Bay 0.32±0.03 0.95±0.04 0.69±0.10 1.96±0.07

Botany Bay 0.45± 0.04 1.26±0.06 0.71±0.04 2.41±0.09

Cooks River 0.51±0.04 2.98±0.11 0.88±0.10 4.37± 0.06

Parramatta River 0.88 ± 0.02 3.1 7 ±0.06 0.82 ± 0.09 4.87 ±0.11

a All results are the mean (±s.d.) of three measurements; s.d. calculated as in Table 3.3
Source: Reproduced with permission from Elsevier Science [37]

investigated, total concentrations were relatively high (1-5µg L −1 ) with chromium(VI)
the predominant species in all areas sampled with one exception, where organically
bound chromium was the major species.
A standard contact time of 4h found to be necessary for the quantitative co-
precipitation of chromium on ferric oxide. The results of triplicate determinations of
samples taken from six locations in the Sydney area are listed in Table 3.5. The rsd
values for the determinations of chromium(III), chromium(VI) and total dissolved