Analysis seawater

Anodic-stripping voltaimnetry (ASV) is used for the analysis of cations in solution, particularly to detemiine trace heavy metals. It involves pre-concentrating the metals at the electrode surface by reducmg the dissolved metal species in the sample to the zero oxidation state, where they tend to fomi amalgams with Hg. Subsequently, the potential is swept anodically resulting in the dissolution of tire metal species back into solution at their respective fomial potential values. The detemiination step often utilizes a square-wave scan (SWASV), since it increases the rapidity of tlie analysis, avoiding interference from oxygen in solution, and improves the sensitivity. This teclmique has been shown to enable the simultaneous detemiination of four to six trace metals at concentrations down to fractional parts per billion and has found widespread use in seawater analysis. 

Chapter 1 discusses a very important aspect of seawater analysis, namely sampling. If the sample is not taken correctly, the final result is invalidated, no matter how sophisticated the final analytical procedure. Recent important work on sampling is discussed in detail. 

Strickland JDH, Parsons TR (1968) A Practical Handbook of Seawater Analysis, Fisheries Research Board of Canada Bulletin 167... 

Very limited work has been published on the determination of anions in estuary and coastal waters. However, there is no doubt that the open seawater analysis methods discussed in Chap. 2 would in many instances be applicable to estuary and coastal waters. 

Determination of trace metals in seawater represents one of the most challenging tasks in chemical analysis because the parts per billion (ppb) or sub-ppb levels of analyte are very susceptible to matrix interference from alkali or alkaline-earth metals and their associated counterions. For instance, the alkali metals tend to affect the atomisation and the ionisation equilibrium process in atomic spectroscopy, and the associated counterions such as the chloride ions might be preferentially adsorbed onto the electrode surface to give some undesirable electrochemical side reactions in voltammetric analysis. Thus, most current methods for seawater analysis employ some kind of analyte preconcentration along with matrix rejection techniques. These preconcentration techniques include coprecipitation, solvent extraction, column adsorption, electrodeposition, and Donnan dialysis. 

The preponderance of work on multielement analysis in seawaters has been carried out using the graphite furnace technique, as this has the additional sensitivity over the direct technique that is required in seawater analysis. 

Montgomery and Peterson [675] showed that ammonium nitrate used as a matrix modifier in seawater analysis to eliminate the interference of sodium chloride degrades the pyrolytic coating on graphite-furnace tubes. The initially enhanced sensitivities for copper, manganese, and iron are maintained for up to 15 atomisations. There is then a rapid decline to a constant lower sensitivity. The characteristics depend strongly on the particular lot of furnace tubes. To... 

The extension of inductively coupled plasma (ICP) atomic emission spectrometry to seawater analysis has been slow for two major reasons. The first is that the concentrations of almost all trace metals of interest are 1 xg/l or less, below detection limits attainable with conventional pneumatic nebulisation. The second is that the seawater matrix, with some 3.5% dissolved solids, is not compatible with most of the sample introduction systems used with ICP. Thus direct multielemental trace analysis of seawater by ICP-AES is impractical, at least with pneumatic nebulisation. In view of this, a number of alternative strategies can be considered ... 

The relative advantages and disadvantages ofvoltammetric and atomic absorption methodologies are listed below. It is concluded that for laboratories concerned with aquatic chemistry of metals (which includes seawater analysis), instrumentation for both AAS (including potentialities for graphite furnace AAS as well as hydride and cold vapour techniques) and voltammetry should be available. This offers a much better basis for a problem-orientated application of both methods, and provides the important potentiality to compare the data obtained by one method with that obtained in an independent manner by the other, an approach that is now common for the establishment of accuracy in high-quality trace analysis. 

Some applications of neutron activation analysis to seawater analysis are summarised in Table 5.11. 

This technique has been applied to the concentration of organochlorine and organophosphorus insecticide [7,8] and various ethers, glycols amines, nitriles, hydrocarbons, and chlorinated hydrocarbons. Although this work was concerned with drinking water, it is a useful technique which may have application in seawater analysis. Cellulose acetate [9], ethyl cellulose acetate [6], and crosslinked polyethyleneinine [8] have been used as semi-permeable membranes. 

This is another technique which has applications in seawater analysis. Approximately 100% recovery of glucose and lindane at the 0.1 and 0.15mg/l level have been obtained from water by this technique. 

Ahnoff and Josefsson [18] built a solvent extraction apparatus for river work which was later modified into their in situ extractor [ 17]. The unit as described in the earlier work could easily be adapted for seawater analysis. A unit based on a Teflon helix liquid-liquid extractor, some 332 feet (101.5 metres) in length, was constructed by Wu and Suffet [19]. The extractor was optimized for the removal of organophosphorus compounds, specifically pesticides, with an efficiency of around 80%. For some compounds, these continuous extraction methods should be the methods of choice and should be explored. 

Another fresh-water method which holds some promise for seawater analysis is twin cell potential sweep voltammetry, as proposed Afghan et al. [138]. In this method, semicarbazones are formed by reaction with semicarbazide... 

Some comparative studies of these methods have been made anthrone and N-ethylcarbazole were compared by Lewis and Rakestraw [153] and by Collier [155], and anthrone, phenol, orcinol and N-ethylcarbazole and L-tryp-tophan were examined by Josefsson et al. [156]. In general, the comparative studies show anthrone to be more reliable than N-clhylcarbazole, although somewhat less sensitive. However, Josefsson and co-workers [154] found that of the five methods, the tryptophan method gave the best results when adapted to automatic analysis, and was capable of analysis at concentrations of interest in seawater analysis, i.e., xg/l levels. 

Josefsson B, KoroleffF (1976) Polyphenolic substances. In Grasshoff K (ed) Methods of seawater analysis. Verlag Chemie, New York, p 220-227... 

Ultraviolet photo-oxidation techniques can be used as a method for organic nitrogen. The organic nitrogen compounds are oxidised to nitrate and nitrite then determined by the standard seawater analysis methods [17,18,23]. 

The merits and limitations of wet chemical oxidation, high-temperature combustion, and photo-oxidation methods for seawater analysis were summarised by Gershey et al. [58]. 

The versions of the persulfate oxidation methods used at present yield results that are lower than those obtained using the dry combustion or photooxidation techniques (Table 11.2). Close agreement between the persulfate and other methods is obtained when the analyses are carried out on freshwater rather than seawater samples. If the persulfate oxidation procedure is to be retained as a method for seawater analysis, serious consideration should be given to abandoning the present batchwise procedure in favour of an automated procedure. 

Strickland JDH, Parsons TR (1972) A practical handbook of seawater analysis. Bulletin 167. Fisheries Research Board, Canada, p 310... 

Koroleff, F. (1976) Total and organic nitrogen. In Methods of Seawater Analysis, Grasshoff, K., ed., Verlag Chemistry, Weinheim, pp. 167-181. 

Grasshoff, K., M. Ehrhardt, and K. Kremling. 1983. Methods of Seawater Analysis, 2nd edition. Weinheim Verlag Chemie. 

Sector-based ICP-MS instruments have recently been used for seawater analysis. These instruments can provide high resolution to minimize spectral overlaps or high sensitivity when used in a low-resolution mode. The sample can be diluted to reduce sample-dependent variations in sensitivity while maintaining sufficient detection limits. Diluted seawater was introduced into the ICP without further sample preparation in one recent report [324]. Nonspectral matrix effects due to seawater for quadrupole and sector-based ICP-MS instruments have been compared [325]. 

Grashoff K, Kremling K, Ehrhard M (1999) Methods of seawater analysis. Wiley, Weinheim, p 600... 

Strickland JDH, Parsons TR (1972) A practical handbook of seawater analysis. Bull Fish Res Bd Canada 167 1-311 Suzuki R, Ishimaru T (1990) An improved method for the determination of phytoplankton chlorophyll using N, N-Dimethylformamide. J Oceanogr Soc Japan 46 190-194 Tiselius P (1992) Behavior of Acartia tonsa in patchy food environments. Limnol Oceanogr 8 1640-1651 Thingstad TF, Billen G (1994) Microbial degradation of Phaeocystis material in the water column. J Mar Syst 5 55-65... 

Parsons T, Maita Y, Lalli C (1984) A manual of chemical and biological methods for seawater analysis. Perg-amon Press, Oxford, UK, 173 pp... 

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