A method is presented for the determination of trace levels of fluoride in drinking water and sea water, based on the formation of aluminium monofluoride in an electrothermal graphite furnace, followed by molecular absorption at 227.45 nm. Two linear intervals extending over wide Fconcentration ranges (0-0.2 and 0.2-0.4" pg ml-1 for the peak-height relationship and 0-1 and 1-2 pg ml-1 for the peak-area relationship) were found.The proposed method was applied to natural and artificial drinking and sea waters from a variety of sources and with different saline contents. The detection limit was 8 ng ml-1 and the determination limit 20 ng ml-1. The peak-height precision at 0.2 and 0.4 pg ml-1 of Fwas 5% and 7%, respectively.Fcontents can be measured with a simple sample dilution. The use of a deuterium lamp allows simultaneous background correction. Interferences from cations, acidic media and anions were investigated.
Investigations are described to select the most suitable drying and extraction procedures for mercury speciation in fish samples. The criteria for selection were good recovery and preservation of the original species information. Three different drying techniques were evaluated: oven-dried, microwave oven-dried and freezedried. Best results were obtained when oven-dried, but microwave dried or freeze-dried showed mercury losses. The four extraction methods investigated were: HCl leaching, alkaline-methanol extraction with tetramethylammonium hydroxide (TMAH) and with KOH, and sodium dodecyl sulfate (SDS) extraction. The extraction efficiency was determined by comparing the total amount of mercury in the samples after microwave digestion with the amount extracted by the different methods described. Mercury measurements were carried out by flow injection-cold vapour-atomic fluorescence spectrometry (FI-CV-AFS). Quantitative mercury extraction was only achieved with HCl leaching (97%). Species integrity after extraction was evaluated by investigating the extracts with capillary gas chromatography-atomic fluorescence spectrometry. Artificial formation of dimethylmercury occurs when TMAH is used as extractant. HCl leaching-GC-AFS was finally applied to methylmercury determination in tuna fish and swordfish samples, and gave results in the range 0.78-1.93 mg kg 21 . The detection limit for monomethylmercury (MMHg) was found to be 1.2 pg.
Color stabilization and modification of the visible spectrum of the p-arsonophenylazochromotropic acid (L) and Nb(V) binary complex by the addition of surfactants has been studied In the course of a search for improved spectrophotometric methods for niobium. Addition of cationic surfactants resulted in an effective means of color stabilization and brought about a drastic improvement in the intensity of the absorption band maximum (sensitized reactions). The surfactant which gave the most intense absorption band maximum was cetylpyridinium bromide (CPAB). Spectrophotometric measurements indicate the formation of two Nb-L-CPAB ion-association ternary complexes: a complex with the stoichiometry 1:2:4 was formed in approximately 1 M HCI. The other complex had the stoichiometry 1:l:Z and formed in 2-4 M HCI mediums. Both ternary complexes mentioned can be applied to the spectrophotometric determination of niobium and two different analytical methods have been established: the complex formed in a 1.0 M HCI medium provides a method less selective than the complex formed in 2-4 M HCI. The method provided by the former complex is sensitive ( t = 1.87 X lo4 L mol-' cm-I), has a working range of 0.5-5 ppm Nb, and has a relative standard deviation of 0.5 YO. The complex formed in the higher acidity range provides a less sensitive method. The working range is 1-9 ppm and t = 7.40 X lo3 L mol-' cm-I. This latter method is most adequate for a selective spectrophotometric determination of niobium (relative standard deviation being 0.5 YO).Recent research into increasing the absorptiometry sensitivity for trace metal analysis in the visible region has investigated the use of colored metal chelate systems "sensitized" by the presence of a third component (ternary systems).The use of binary metal ion complexes of organic dyestuffs such as Catechol Violet, "sensitized" by the addition of long-chain cationic surfactants such as cetyltrimethylammonium bromide (CTAB) is claimed to be a mode of analytical reaction more generally applicable to the determination of tin ( 1 ) and one of the most sensitive methods available for the absorptiometric determination of' metal ions. Although some attempts have been made to define the mechanisms and associated color changes of such reactions, much more work is needed to elucidate them.Bayley et al. ( I ) concluded from their study that ternary complexes are formed by ion association of the quaternary ammonium group with the metal dyestuff chelate. However. in aqueous solution, this occurs only when micelles are formed. It is thus necessary to form micelles t o obtain the ternary system because the critical micelle concentration (CMC) of the surfactant turned out also to be a critical reaction concentration ( I ) .The work of Ashton et al.(2) on the Sn(1V)-Catechol Violet system in the presence of surfactants of different nature confirmed that the Sn(1V)-Catechol Violet-CTAB system is a ternary ion association system which is probably formed in colloidal solution and dispersed by the excess surfact...
The sensitivity of the determination of mercury by cold vapour atomic-absorption spectrophotometry is increased by about 125% by raising the reaction vessel temperature from 20 to 75 "C. A further increase in sensitivity of about 20% was achieved by using a glass optical cell that is broad at each extreme and tapers inwards towards the centre. This cell is easy to fit to commercial instruments.
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