Abstract: Sample-injection and reagent-injection manifolds are presented for the formation of FeSO4+ in a stream of dilute HClO4 in the presence of Al(III) and Hg(II) to mask F- and Cl-, respectively. The absorbance is measured at 355 nm; the response is rectilinear for 25 to 600 and 10 to 150 mg L-1 of SO42-, respectively, and the detection limit of the former method is 19 mg l-1. Results agreed well with those obtained gravimetrically. Organic compounds that interfere by UV absorbance can sometimes be removed on a charcoal column, but the possibility exists of loss of SO42-; a subtractive procedure with sample injections in the presence and absence of Fe(III) can alternatively be used. The sampling rate is 10 to 30 h-1.

Abstract: The literature on flow injection analysis coupled with atomic spectrometry is reviewed. Several types of closed-loop recirculating manifolds for particular applications are described, viz, for calibration, dilution, acid-leaching of Ca, and Ag matrix removal in AAS. The performance of each of the manifolds was satisfactory at recirculating flow rates up to 10 mL min-1. (75 references). Much of the recent research in analytical atomic spectrometry has been concerned with problems of a practical nature. In particular, the inaccuracies arising from a variety of matrix effects and the limitations of sample introduction systems have provided a considerable driving force for recent developments in the various techniques. The philosophy of attempting to eliminate, or compensate for, interferences by procedures implemented at the atomization stage has had success for electrothermal atomization atomic absorption spectrometry but has proved of limited utility for other techniques. Despite considerable efforts, solid-sample introduction is still best done by procedures whose initial stage is dissolution There is a steady growth in the flow injection atomic spectrometric literature and a survey of the ~50 publications in 1990 shows that much of the interest is now centered on coupling pre-concentration and matrix removal procedures with atomic spectrometry, although there is still work concerned with the basic characteristics of flow injection introduction, such as the reduction in sample loading, online dilution for calibration purposes and the ability to handle small sample volumes, being published. The role of the flow injection valve as an interface between flow systems is highlighted. This interface allows independent optimization of the various flow systems coupled in this fashion. Several possible applications of recirculating closed-loop manifolds are described. These include the serial dilution of a stock standard for calibration purposes and to establish a working detection limit. This is illustrated by the dilution of a 2.45 mg L-1 solution of magnesium by a factor of 2.20 per injection. This procedure established a detection limit for the instrument involved of between 4.2 and 5.2 ng mL-1. The online acid leaching of calcium from charcoal is shown to be sufficiently precise for the basis of a rapid screening procedure and the determination of copper in matrixes containing up to 50 g L-1 silver is made possible by the online precipitation of the matrix as the chloride in a circulating loop containing a filter column of nylon fibers. The additional possibilities afforded by these designs of manifold and the great variety of manifolds described in the literature suggest that flow injection atomic spectrometry may be emerging as an analytical methodology analogs to the variety of procedures encompassed by terms such as liquid chromatography in the vocabulary of the analytical methodology for molecular species.

Abstract: Activated charcoals, impregnated with KI or triethylenediamine, or both, are used in the nuclear industry as filter materials for the trapping of volatile radioactive compounds, especially those containing radio-iodine. The determination of iodide ion in activated charcoals impregnated with 1.5% KI is described. An aqueous extract was prepared and the iodide ion concentration. determined by injection into a water stream that is merged with a carrier solution of KIO3 and H2SO4. The FI manifold incorporated an automatic wavelength scanner and a 1-cm pathlength flow-through cell. Four different diameters of pump tubing were used to provide flow rates of 1.2, 1.5, 2.0 and 2.8 mL min-1; UV absorption was measured at 460 nm. The detection limit was 60 µM-iodide and the coefficient of variation was 1.2% (for 1 mM iodide).

Abstract: Dried plant material (400 mg; 1 mm) was mixed with activated charcoal (0.2 g) and 40 mL of 0.5% trichloroacetic acid - 0.5% Ca(H2PO4)2.2H2O buffer (pH 2.1 to 2.5). After 30 min the mixture was filtered, and 2 drops of 0.1% of phenylmercuric acetate in 4% 1,4-dioxan was added as preservative (allowing analysis up to 1 week later after storage in a refrigerator). For flow injection analysis, sample solution was mixed with the extractant plus 0.01% of Brij 35, a 70 ppm standard solution of SO42- and 11% of BaCl2.2H2O in 1% gum arabic solution or 0.5% of EDTA in 40 mM NaOH. Turbidimetry (due to formation of BaSO4) was measured at 400 nm. Recovery of 60 mg kg-1 to 13.11 g kg-1 of SO42- in various plants was 97 to 105%, with a coefficient of variation of 2.5%. Results showed good agreement with those obtained by ICP-AES. Only NO3- interfered (at 5% concentration.). The sampling rate was 120 h-1.

Abstract: Glycollate is determined by the action of L-2-hydroxyacid oxidase. The H2O2 produced is detected in the presence of peroxidase by use of an indicator reaction with 3-methyl-2-benzothiazoline hydrazine and NN-dimethylaniline. Urine samples are treated with activated charcoal before analysis to reduce interferences of reducing substances. Correction must be made for lactate in urine, which interferes. An accurate, precise and sensitive continuous-flow system, with use of enzyme immobilized on the inner surface of nylon tubing is described, but this is unsuitable for routine use because of the instability of the enzyme. A semi-automated procedure is described for the Cobas-Bio centrifugal analyzer. with use of enzyme in solution. Recovery by this method was 96% and within- and between-batch coefficient of variation were <2 and <5%, respectively. The normal reference interval for urinary excretion of glycollate is 0.13 to 1.31 mmol day-1.

Abstract: A method is proposed for the determination of nitrate using UV spectrophotometry. The use of oxidized activated charcoal minicolumn online at an elevated pH eliminates organic and inorganic interferences. The absorbance is measured at 225 nm. The procedure has a limit of detection down to 1 mg/L with a relative standard deviation less than 1.0%.