Determination of sulphate ion

This can be done gravimetrically or volumetrically. In either case it is necessary to do a parallel determination on a sample that has not been hydrolysed, unless the hydrolysed sample had been rendered free of sulphate before hydrolysis, e.g. by extraction with dry ethanol or propan-2-ol. 

Transfer the hydrolysed solution after extraction of the fatty alcohol or ethoxylate to a 500 ml volumetric flask, dilute to volume and mix. Use water for this dilution if the gravimetric procedure is to be followed, or acetone for the volumetric procedure. Continue as follows. The volumetric procedure is preferred if other surfactants are present. 

If the hydrolysed solution has been neutralised, add 10 ml 1.0 M hydrochloric acid. 

Cover with a watch glass and leave on a steam bath for 2 h. 

Filter through a dry tared sintered silica crucible, ensuring that the precipitate is quantitatively transferred. 

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Discussion. Dead-stop end point titrimetry may be applied to the determination of nitrate ion by titration with ammonium iron( II) sulphate solution in a strong sulphuric acid medium ... 

Determine the sulphate-ion content of an unknown solution, say ca 0.3 mg mL"1, using the calibration curve. 

Nephelometric assay may be employed for the determination of sulphate (S042-) and phosphate (P 04 ) ions quite efficiently. These two estimations shall be discussed below in an elaborated manner ... 

A radioisotope can be used as a tracer instead of the enzyme used in immunochemical tests. This method, introduced in 1960 for the measurement of insulin in serum, is called radio-immunology. It is the transposition in immuno-chemistry of the same principle as that used to determine the sulphate ion (cf. 17.5). Radioimmunoassays are similar to ELISA assays in the way in which the analysis is... 

Stainton [31] has described an automated method for the determination of sulphate and chloride in non saline waters. An ion exchange resin is used to convert the sulphates and chlorides to their free acids. Detection is achieved by electrical conductance. The use of silver-saturated cation exchange resin to precipitate chloride permits distinction between chloride and sulphate. High levels of nitrate, orthophosphate and fluoride give positive interference for sulphate bromide and iodide similarly interfere with chloride estimates. 

Finally, the UV determination of sulphate, the knowledge of which is very important for natural water quality, is not yet possible, as this ion in not absorbing, and no simple and robust colorimetric method is available. 

In the case of moss samples exposed in the Mansfelder Land area, inductively coupled plasma atomic emission spectrometry (ICP-AES) was used for the determination of As, Cu, Fe, Mn, Ni, Pb, Zn in both aqueous and acidic solutions by standard addition technique. Atomic absorption techniques were applied for the determination of arsenic (hydride generation coupled with graphite furnace atomization), cadmium and lead (both by Zeeman-corrected graphite furnace AAS) (Krauss et al., 1998, 2000). Ion chromatography was used for the determination of sulphate. 

The volume of the water sample to be employed for gravimetric determination of sulphate must be measured so that it contains between 10 and 500 mg sulphate ions. Where necessary, a larger volume of water must be reduced to 400 ml, and/or in the case of lower concentrations of sulphate ions to 100 ml. 

Izatt, R.M. D. Eatough, J.J. Christensen, C.H. Bartholomew, "Calorime-trically determined log K, delta H and delta S values for the interaction of sulphate ion with several hi and ter-valent metal ions", J. Chem. Soc (A), PP47-53 (1969)... 

Coetzee, J.F. and Gardner, C.W., Determination of sulphate, ortho-phosphate, and triphosphate ions by flow injection analysis with the lead ion selective electrode as detector. Analytical Chemistry 58, 608,1986. 

Lee Y-K, Kim C-K, Park J-T, Kim K-S, Whang K-J (1985) Potentiometry with carbon paste-based ion-selective electrode for the determination of sulphate. J Korean Air Pollut Res Assoc 1 99-103... 

Izatt RM, Eatough D, Christensen JJ, Bartholomew CH. (1969) Calorimetri-cally determined log K delta H degree and delta S degree values for interaction of sulphate ion with several Bi- and Ter-valent metal ions. J Chem Soc A 47-53. 

Regarding nitrates and phosphates or sulphates, their main users are agriculture (mainly as fertilisers) and water-treatment stations. Sulphite is of interest mainly in food analysis. Nitrite, iodide, and fluoride are also more typical for the food and pharmaceutical industry but, in some extent, they are monitored in the environment (e.g. nitrite is used in syntheses of explosives, together with nitrates, azides, and perchlorates). A severe industrial pollutant is undoubtedly cyanide, mainly for its extreme toxicity and well-known ability to participate in numerous complexforming reactions. Hydroxide is needed in many industrial processes as being involved in various pH-dependent reactions, unless of quoting that pH measurement itself—i.e., the determination of H" ions— represents a routine laboratory operation needed almost anywhere. 

Note. Lead or barium can be determined by precipitating the sparingly soluble chromate, dissolving the washed precipitate in dilute sulphuric acid, adding a known excess of ammonium iron(II) sulphate solution, and titrating the excess of Fe2 + ion with 0.02M potassium dichromate in the usual way. 

Determination of barium as sulphate Discussion. This method is most widely employed. The effect of various interfering ions (e.g. calcium, strontium, lead, nitrate, etc., which contaminate the precipitate) is dealt with in Section 11.72 The solubility of barium sulphate in cold water is about 2.5 mg L"1 it is, however, greater in hot water or in dilute hydrochloric or nitric acid, and less in solutions containing a common ion. 

The effect of different ions upon the titration is similar to that given under iron(III) (Section 17.57). Iron(III) interferes (small amounts may be precipitated with sodium fluoride solution) tin(IV) should be masked with 20 per cent aqueous tartaric acid solution. The procedure may be employed for the determination of copper in brass, bronze, and bell metal without any previous separations except the removal of insoluble lead sulphate when present. 

A determination of dimethyl sulphoxide by Dizdar and Idjakovic" is based on the fact that it can cause changes in the visible absorption spectra of some metal compounds, especially transition metals, in aqueous solution. In these solutions water and sulphoxide evidently compete for places in the coordination sphere of the metal ions. The authors found the effect to be largest with ammonium ferric sulphate, (NH4)2S04 Fe2(S04)3T2H20, in dilute acid and related the observed increase in absorption at 410 nm with the concentration of dimethyl sulphoxide. Neither sulphide nor sulphone interfered. Toma and coworkers described a method, which may bear a relation to this group displacement in a sphere of coordination. They reacted sulphoxides (also cyanides and carbon monoxide) with excess sodium aquapentacyanoferrate" (the corresponding amminopentacyanoferrate complex was used) with which a 1 1 complex is formed. In the sulphoxide determination they then titrated spectrophotometrically with methylpyrazinium iodide, the cation of which reacts with the unused ferrate" complex to give a deep blue ion combination product (absorption maximum at 658 nm). 

Y. Mourzina, Y. Ermolenko, T. Yoshinobu, Y. Vlasov, H. lwasaki, and MJ. Schoning, Anion-selective light-addressable potentiometric sensors (LAPS) for the determination of nitrate and sulphate ions. Sens Actuators, B 91, 32—38 (2003). 

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