Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 303

measure a volume, dilute with an equal volume of 1, 4-dioxan and titrate with, eg 5mmol
L −1 lead nitrate, using the lead-selective electrode to indicate the end-point. Down to
10mg L −1 sulphate could be determined in the presence of up to a 10-fold excess of
chloride. Phosphate interferes in the procedure.
Lukianets et al. [793] described a rapid method for the determination of sulphate in
river water by potentiometry with a lead selective electrode using a hard membrane of
lead sulphide and silver sulphide. The titrant was lead(II) perchlorate. Acetone was the
most effective solvent for accelerating the precipitation process. Adsorption of sulphate
ions on to the precipitant was prevented by addition of crystal violet solution. The
method was unaffected by pH in the range 2-8. Calcium, magnesium, sodium and
chloride did not interfere with sulphate determination. Carbonate interference was
eliminated by adding acetic, perchloric and nitric acid. Analysis of river water using the
method compared well with analysis by high frequency titration with barium acetate.
Workers at Orion Research Inc US [794] have described an ion selective electrode
method using their Orion 960 lead electrode and Autochemistry system. This system
determines the end-point of a lead perchlorate titration and calculates the concentration of
sulphate in the sample. The standard deviation of this procedure is 0.87% at the 59mg L −1
sulphate level.
2.93.11 Ion chromatography
Singh et al. [795] determined sulphate in deep sub surface waters by suppressed ion
chromatography.
Conboy et al. [796] employed ion chromatography mass spectrometry to determine
sulphate and ammonium compounds in non saline waters.
The ion spray liquid chromatography/mass spectrometry interface is coupled via a
post-suppressor split with an ion chromatography system. The micromembrane
suppressor selectively removes over 99.9% of the ion-pair agents required for ion
chromatography from the eluent. The resulting solution consists of analyte, organic
modifier, and water, which is compatible with ion evaporation mass spectrometry. A flow
rate of 0.8 or 1.0mL/min from the column was split after suppression such that
approximately 10-20µL/min was directed to the ion spray liquid chromatography/mass
spectrometry interface, which was coupled to an atmospheric pressure ionisation mass
spectrometer. This system provided a convenient way to effect isocratic and gradient
separations of organic ions under chromatographic conditions incompatible with most
forms of mass spectrometric ionisation. This work describes the separation and positive
ion detection of quaternary ammonium drugs and tetraalkylammonium compounds of
industrial importance using both single and tandem mass spectrometric detection (eg ion
chromatography/mass spectrometry and ion chromatography/mass spectrometry/mass
spectrometry). The former easily provided the molecular weights of these compounds
while the latter gave some structural information. The limit of detection of 40pg injected
on-column for tetra-propylammonium cation is a factor of 10 better than that obtained
with the conventional ion chromatography detector. The separation, detection, and
identification of some alkyl sulphates and sulphonates are also shown with negative ion