Non saline waters

The technique has since 1975 progressed rapidly and in 1978 a book was published on Ion Chromatographic Analysis of Environmental Pollutants. Other early papers on the application of ion chromatography include the determination of selected ions in geothermal well water [7,8], the determination of anions in potable water [9] and the separation of metal ions and anions [10] and anions and cations [11]. 

While atomic absorption spectroscopy and inductively coupled plasma techniques will continue to be the workhorse instrument in the metals analytical laboratory, an ever-growing need exists for the complementary 

Cr(Vl), M xW Naturally occurring oxides CrOn , Mo04, W04 Conductivity 

Ni Cr(IM) Prederivatised EDTA complexes Pb(EDTA) , Cu(EDTA). Zn(EDTA) -. Ni(EDTA) Cr(EDTA) Conductivity 

Au Chloro-completes formed in situ in the column eluent PdC PtCV , PbCl4, AuCU UV or pulsed amperometric 

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Despite its potential importance, formic acid has proven difficult to quantify at submicromolar levels in non-saline water samples. Formidable analytical difficulties are associated with its detection in highly saline samples. Ion exclusion, anion exchange, and reversed-phase high performance liquid chromatography techniques based on the direct detection of formic acid in aqueous samples are prone to interferences (especially from inorganic salts) that ultimately limit the sensitivity of these methods. 

A potentially more sensitive and selective approach involves reaction of formic acid with a reagent to form a chromophore or fluorophore, followed by chromatographic analysis. A wide variety of alkylating and silylating reagents have been used for this purpose. Two serious drawbacks to this approach are that inorganic salts and/or water interfere with the derivatisation reaction, and these reactions are generally not specific for formic acid or other carboxylic acids. These techniques are prone to errors from adsorption losses, contamination, and decomposition of the components of interest. Enzymic techniques, in contrast, are ideal for the analysis of non-saline water samples, since they are compatible with aqueous media and involve little or no chemical or physical alterations of the sample (e.g., pH, temperature). 

As a consequence of the previous considerations Kieber et al. [75] have developed an enzymic method to quantify formic acid in non-saline water samples at sub-micromolar concentrations. The method is based on the oxidation of formate by formate dehydrogenase with corresponding reduction of /3-nicotinamide adenine dinucleotide (j6-NAD+) to reduced -NAD+(/3-NADH) jS-NADH is quantified by reversed-phase high performance liquid chromatography with fluorimetric detection. An important feature of this method is that the enzymic reaction occurs directly in aqueous media, even seawater, and does not require sample pre-treatment other than simple filtration. The reaction proceeds at room temperature at a slightly alkaline pH (7.5-8.5), and is specific for formate with a detection limit of 0.5 im (SIN = 4) for a 200 xl injection. The precision of the method was 4.6% relative standard deviation (n = 6) for a 0.6 xM standard addition of formate to Sargasso seawater. Average re-... 

Williams and Robertson [76] have described a simple inexpensive method for determining reactive chlorine in non-saline waters. It involves addition of bromine, which is oxidised by the reactive chlorine in the sample, and which in turn brominates fluorescein to give a pink derivative this can be measured visually or spectophotometrically, or the decrease in fluorescein can be measured fluorimetrically. Potential applications of the method are indicated. 

Isaeva [181] described a phosphomolybdate method for the determination of phosphate in turbid seawater. Molybdenum titration methods are subject to extensive interferences and are not considered to be reliable when compared with more recently developed methods based on solvent extraction [182-187], such as solvent-extraction spectrophotometric determination of phosphate using molybdate and malachite green [188]. In this method the ion pair formed between malachite green and phosphomolybdate is extracted from the seawater sample with an organic solvent. This extraction achieves a useful 20-fold increase in the concentration of the phosphate in the extract. The detection limit is about 0.1 ig/l, standard deviation 0.05 ng-1 (4.3 xg/l in tap water), and relative standard deviation 1.1%. Most cations and anions found in non-saline waters do not interfere, but arsenic (V) causes large positive errors. 

Inductively coupled plasma atomic emission spectrometry has also been used to determine sulfate directly in non-saline waters [225]. 

Non-saline water samples are normally acidified to stabilise them during storage. There is an effect due to hydrochloric acid concentration on the sulfur emission signal. This effect is conveniently overcome by making the acid content of samples and standards identical at, for example, 1 vol%. 

The recovery of selenium was satisfactory. The forms of selenium in waters are known to be selenite and selenate [7]. Selenium occurs in non-saline water at concentrations ranging from less than 0.0002 xg/l to greater than 50 xg/l. Therefore, a large sample size is necessary for analysis at lower concentration levels. 

The determination of ammonia in non-saline waters does not present any analytical problems and, as seen above, reliable methods are now available for the determination of ammonia in seawaters. In the case of estuarine waters, however, new problems present themselves. This is because the chloride content of such waters can vary over a wide range from almost nil in rivers entering the estuary to about 18 g/1 in the edges of the estuary where the water is virtually pure seawater. 

Whilst much of the literature on this subject is concerned with non-saline water samples, it is believed that many of these procedures will also work satisfactorily with seawater indeed, the presence of salts in the sample may assist in the removal of volatiles. 

Leoni [366] observed that in the extraction preconcentration of organochlo-rine insecticides and PCB s from surface and coastal waters in the presence of other pollutants such as oil, surface active substances, etc., the results obtained with an absorption column of Tenax-Celite are equivalent to those obtained with the continuous liquid-liquid extraction technique. For non-saline waters that contain solids in suspension that absorb pesticides, it may be necessary to filter the water before extraction with Tenax and then to extract the suspended solids separately. Analyses of river and estuarine sea waters, filtered before extraction, showed the effectiveness of Tenax, and the extracts obtained for pesticide analysis prove to be much less contaminated by interfering substances than corresponding extracts obtained by the liquid-liquid technique. Leoni et al. [365] showed that for the extraction of organic micro pollutants such as pesticides and aromatic polycyclic hydrocarbons from waters, the recoveries of these substances from unpolluted waters (mineral and potable waters) when added at the level of 1 xg/l averaged 90%. 

The chemical method for the determination of the chemical oxygen demand of non-saline waters involves oxidation of the organic matter with an excess of standard acidic potassium dichromate in the presence of silver sulfate catalyst followed by estimation of unused dichromate by titration with ferrous ammonium sulfate. Unfortunately, in this method, the high concentrations of sodium chloride present in sea water react with potassium dichromate producing chlorine ... 

Chau et al. [19] have described the optimum conditions for extraction of alkyllead compounds from sediments originating in non-saline waters and in saline waters [16]. Analyses of some environmental samples revealed for the... 

The data suggests that organotin compounds may not be as strongly adsorbed on to sediment in saline water, i.e. coastal and seawaters as they are in non-saline waters. 

In a review of available data relating to the physico-chemical speciation of plutonium in the Irish Sea and western Mediterranean, Mitchell et ai. (1995) concluded that a high percentage of the plutonium is present as Puv and not retained by a 1 kD filter, thus demonstrating that plutonium in the oxidised state is in true solution. The data also indicate that a significant proportion of plutonium in the reduced state is associated with colloids and that the size of the colloidal particles or aggregates involved (<10kD) is considerably smaller than those observed in non-saline waters. 

This technique has found limitations in the determination of bromide mixed halides, iodide, iodate, nitrite, nitrate, sulphide, sulphite, thiocyanate, thiosulphate and isobutyrate in non saline waters. 

Rubin and Heberling [12] have reviewed the applications of ion chromatography in the analyses of cations in non saline waters. Elements discussed include sodium, lithium,... 

Basta and Tabakabi [13] used a Dionex Model 10 ion chromatograph for the simultaneous determination of potassium and sodium or of calcium and magnesium in different types of non saline waters, including soil extracts. The pH and specific conductance of the water samples are tabulated. Tabulated data are included comparing the results obtained by ion chromatography with those obtained by atomic absorption... 

Further applications of the determination of cations in non saline waters are reviewed in Table 2.2. 

An ultraviolet detector used in series with a conductivity detector is the basis for a method [39] for the determination of anions in non saline waters. This combination of detectors greatly increases the amount of information that can be collected on a given sample. The application of ultraviolet detection has the following advantages ... 

Smee et al. [40] used ion chromatography has been used for the measurement of background concentrations of fluoride, chloride, nitrate and sulphate in non saline waters. 

Table 2.4 Dionex replicate samples, measurements of precision non saline waters...

Tong and Shi [44] used ion chromatography with an electrical conductivity detector to determine fluoride, chloride, nitrate, sulphate and hydrogen phosphate (HP042 ) in non saline water with detection limits of 0.8, 1.0, 8.0, 10.0 and 12.5pgL 1 respectively. 

Conboy el al. [47] employed ion chromatography mass spectrometry to determine sulphate and ammonium compounds in non saline waters. 

Dionex Corporation [86] have issued a technical note covering the application of anion exchange chromatography to the determination of the very wide range of anions, quoted above, in non saline waters. 

Further applications of ion chromatography to the determination of anions in non saline waters are summarised in Table 2.7. 

When using conventional ion chromatographic separation techniques, it is possible that other matrix anions also common to non saline waters may coelute with bromide. For example, bromide and nitrate elute simultaneously using a standard anion separator column (Dionex No. 30065), standard anion suppressor (Dionex No. 30366) and standard eluant (0.003M sodium bicarbonate/0.0024M sodium carbonate). 

The Rocklin and Johnson [48] procedure described in Section 2.3.2.3 (non saline waters) has been applied to the determination of cyanide and sulphide in trade effluents. 

Kieber et al. [12] determined formate in non saline waters by a coupled enzymatic/high performance liquid chromatographic techinique. The precision is approximately 5% relative standard deviation. Inter-calibration with an anion chromatographic technique showed an agreement of 98%. Down to 0.5pmol L 1 absolute of formate could be determined. Kieber et al. [12] found 0.2-0.8mol IT1 formate in seawater and 0.4-10pmol in rainwater. 

Crathome [16] reported a method for the determination of Pyrazon (5-amino-4-chloro-2-phenyl-3-pyridazone) in non saline waters. Pyrazon was isolated from water samples (500mL) by rotary evaporation to dryness in vacuo, extraction of the solid residue with methanol (2><25mL) and further evaporation of the methanol extract (to approx. 2mL). Final concentration (to 0.5mL) was achieved by removal under a stream of nitrogen. 

Nygren el al. [260] interfaced on-line a liquid chromatograph to a continuously heated graphite furnace atomic absorption spectrometer to determine di- and tributyltin species in non saline waters with a detection limit of 0.5pg tin absolute. 

Wang and Yang [261] used liquid chromatography with indirect photometric detection to determine down to 0.8pg triorganotin compounds in non saline waters. 

High performance liquid chromatography coupled with hydride generation-atomic absorption spectrometry has been used for the determination of arsenic species in non saline water samples [265],... 

Blais et al. [268] determined arsenobetaine, arsenocholine and tetramethyl arsonium ion in non saline waters in amounts, respectively, down to 13.3, 14.5 and 7.8pg by a procedure based on liquid chromatography-thermochemical hydride generation atomic absorption spectrometiy. 

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