Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 310

hyaluronidase enzymatic system [229].
A method [782,818] based on mercury(II) 2-(2-pyridyl) benzimidole is very sensitive,
being capable of determining down to 0.3µg L −1 sulphate. The sample is acidified with
acetic acid and the hydrogen sulphide formed is swept into the reagent buffered to pH
6.2-7.3 The fluorescence produced due to sulphide is measured at 381nm (excitation
311nm).
A simple and sensitive fluorometric method for determining sulphide in non saline
waters is based on the blue fluorescence( 450nm) after
alkylation with methyl p-toluenesulphonate and successive condensation reactions with
taurine and o-phthalaldehyde at pH 8.0 [819]. Sulphide can be determined in the range of
0.03-5nmol/100µL with relative standard deviations (n=10) of 1.6% at 0.2nmol and 2.7%
and 3nmol. A 100-fold molar excess of each of the common anions did not interfere,
except for cyanide, thiosulphate, sulphite and carbonate, the tolerance ratios of which
were 5, 10, 30 and 50 respectively. Interferences due to metal ions such as calcium,
magnesium and zinc can be masked by addition of EDTA, copper(II) and manganese(II)
must be absent.

2.94.4 Flow injection analysis
A flow-injection method for determining sulphide has been reported by Aoki et al. [820].
A non saline water sample containing sulphide was mixed with sulphuric acid and
injected into the outer tube of a microporous Teflon membrane separator. The generated
hydrogen sulphide permeated through the membrane and gave a chemiluminescent
reaction with the flowing luminol reagent solution in the inner tube of the separator.
Chemiluminescent intensity was measured with a photomultiplier. The detection limit
was 2.6µg L −1 and the relative standard deviation was 0.7%. Cobalt, copper and
chromium ions did not interfere, and carbonate and nitrite had a negligible interference.
Milosavljevic et al. [821] have reported a preconcentrating gas diffusion flow injection
analysis method with amperometric detection for selective determination of sulphide. The
method has based on using the acceptor stream of the diffusion unit in a closed-loop,
mobile (recirculating) mode for the accumulation of the analyte. In the analysis step the
contents of the acceptor loop are injected into a sodium carbonate stream and are carried
to the amperometric detector. The various flow patterns required for this method are
regulated by a single eight-port rotary valve. The method developed has very low
detection limits of 0.15µg L −1 . The relative standard deviation for a 1µg L −1 standard is

4%, and of the potential interferences tested, only cyanide had an effect.
Sonne and Dasgupta [774] have carried out a simultaneous deter-mination of sulphide,
polysulphide, sulphate, sulphite and thiosulphate.
Kuban et al. [822] have described nitroprusside and methylene blue methods for
silicone membrane differential flow injection determination of sulphide in water and
wastewater. Hydrogen sulphide evolved from the acidified sample is collected in an
alkaline acceptor. Down to 2µg L −1 sulphide can be determined.
The application of this technique is also discussed under multianion analysis in
sections 14.4.1.1 and 14.4.1.4.