Application of the H-point standard additions method by using absorbance increment values as analytical signals.

This paper demonstrates how the absorbance increment (DeltaA) between two wavelengths selected according to the fundamental criteria for application of the H-Point standard additions method (HPSAM) are only related to the analyte concentration. A procedure for calculation of the unknown analyte concentration with no bias error by applying HPSAM to DeltaA values in much the same way as the method of standard additions (MOSA), is reported. The method was also applied to a calibration with a single standard. The results obtained on 6 samples with maximal separations between 65 and 0 nm are reported. Finally, the proposed method was applied to the resolution of different phenol-o-cresol mixtures.

Atomic-absorption spectrometric determination of calcium, magnesium and potassium in leaf samples after decomposition with molten sodium hydroxide.

The decomposition of standard leaf samples of varied origin and nature by fusion with sodium hydroxide in an open system has been studied. The use of sodium nitrate as an auxiliary agent facilitated the mineralization of most of the samples. The solutions obtained were analysed for calcium, magnesium and potassium by flame atomic-absorption spectrometry. The method is fast and quite precise, with absolute standard deviations of 0.04-0.13, 0.002-0.03 and 0.04-0.12% for calcium, magnesium and potassium contents of O.8-5.0, 0.13-0.48 and 0.36-2.2% respectively. The limits of detection (mug/ml) in the determination step were 0.10 for calcium, 0.011 for magnesium, and 0.09 for potassium.

Quantitative approximation for the selectivity of analytical spectrophotometric procedures with systems which do not obey Beer's law.

A selectivity index is proposed for defining the selectivity of a spectrophotometric procedure that is subject to interference by species which do not obey Beer's law in the system. The interactions between analyte and interferents which affect the absorbance of an analytical system are studied by means of a simple mathematical model. Theoretical expressions are derived which represent the selectivity as a function of the analyte or interfering species concentration. The treatment is illustrated by a study of the Zr(IV)-chloranilic acid system in presence of thorium as interferent.

Mineralization of some organic sulphur compounds by fusion with molten alkali.

The action of molten alkali-metal hydroxides for the destruction of organic matter containing sulphur has been studied. Various procedures were developed which differed mainly in the initial phase of the process, mainly with respect to homogenization of the reaction mixture, but also with regard to addition of an auxiliary oxidant. The technique is not universally applicable to sulphur compounds, but is useful for decomposition of sulphur compounds with m.p. > 150 degrees and containing sulphonate, thiocarbonyl, phenazothionium and thio groups. The sulphur is converted into sulphate, which is then determined as barium sulphate.

Spectrophotometric determination of fluoride in fluoride-bearing minerals after decomposition by fusion with sodium hydroxide.

The decomposition of highly insoluble minerals (fluorspar and cryolite) by fusion with molten alkali-metal hydroxides is studied. The introduction of additives such as aluminium compounds or sodium peroxide to obtain total liberation of fluoride from calcium fluoride samples, is tested. The fusion is done in a silver crucible with a Bunsen burner. The cooled melt is easily soluble, giving solutions suitable for spectrophotometric fluoride determination by the Zr(IV)-fluoride-Erichrome Cyanine R method.

Spectrophotometric determination of cadmium with 1-(2-pyridylazo)-2-naphthol and non-ionic surfactants Application to acetic acid extracts of ceramic enamels.

The Cd-PAN system in the presence of non-ionic surfactants (polyoxyethylene nonylphenols), which dissolve the reagent and complex by formation of micelles, has been studied spectrophotometrically. The optimum conditions for Cd determination are pH 9 (Na(2)B(4)O(7)-HClO(4)), 2% of surfactant and measurement at 555 nm. The complex is Cd(PAN)(2) and its conditional formation constant is 3.5 x 10(11). The system obeys the Lambert-Beer law, with an error of 0.9% over the Cd concentration range 0.44-1.74 ppm; the molar absorptivity is 4.94 x 10(4)1.mole(-1).cm(-1) at 555 nm. The relative standard deviation is 0.7% and the limit of detection 0.009 mug ml . The selectivity with respect to species important in the ceramic industry is adequate for application of the method to determination of Cd in acetic acid extracts of ceramic enamels.

Determination of phosphorus in samples of vegetable origin Mineralization with molten alkali and spectrophotometric determination.

For determination of phosphorus in samples of vegetable origin (leaves and wheat flour) decomposition by means of molten alkali is proposed. Two procedures have been studied, one with dry reagents including an auxiliary oxidant, and the other with initially moist alkali with no extra oxidant. The fusion product is easily soluble and produces a solution suitable for elemental analysis. The phosphorus is determined by the molybdenum blue method. The suggested mineralization is rapid, accurate and precise.

Decomposition of organic matter with molten alkali: determination of arsenic and antimony in organic compounds.

Decomposition of organic matter with molten alkali has been examined as a method of opening out organic matrices for elemental detection and/or determination. The fusion product is readily soluble. Arsenic and antimony in organic compounds can be determined iodimetrically after mineralization by this fusion method.

A compound of iron(II), phenylbiguanide and cyanide.

A spectrophotometric investigation has been made of the red water-soluble complex of phenylbiguanide with iron(II) in cyanide medium. The complex is found to have maximum absorbance at 520 nm. Use of the extension of the Asmus method to M(s)L(m)L'(n) complexes and of Koch and Ackermann's method suggests the formula [Fc(phenylbiguanide)(CN(4))](2-) for the red compound. Anlytical procedures for the detection of iron and cyanide are proposed.