J. Gené

Diode-array detectors in flow-injection analysis Mixture resolution by multi-wavelength analysis

The application of diode-array spectrophotometers to multi-component analysis by flow-injection analysis is reported. Two different aspects are considered: (a) the obtainment of a reproducible spectrum corresponding to the maximum of the FIA peak, and (b) the mathematical treatment involved in determining the mixture of components. The spectrum is recorded by two different procedures according to the type of injection system used. The mixtures are resolved with the aid of three different treatments: (a) a linear equation system, (b) a multi-component analysis program (Hewlett-Packard) and (c) a graphical method (multi-wavelength linear regression analysis). All three procedures have been applied to the determination of Fe(II) and Fe(III) with a mixture of 1,10-phenanthroline and sulphosalicylic acid.

Use of diode-array detectors for the simultaneous spectrophotometric determination of calcium and magnesium by flow injection

Abstract A method for the simultaneous flow injection spectrophotometric determination of calcium and magnesium with Arsenazo III based on the use of diode-array detector and merging zones is described. The method is applicable to the resolution of mixtures in which the chromogenic reagent has a high absorbance and its spectrum strongly overlaps those of its complexes. In resolving the mixtures, the excess reagent is considered as another component. Quantitation is based on the normal absorbance and first-derivative absorbance spectra. The method is applied to 0.2–1.5 μg ml −1 Ca and 0.1–1.0 μg ml −1 Mg. The analysis rate is 50 h −1 .

Analysis of Multicomponent Spectra by the Simplex Method

Abstract The Simplex method to simultaneously identify and quantify the components of complex mixtures from their UV-visible spectra is used. Calibration was performed by using a data base containi...

Application of the Davidon-Fletcher-Powell algorithm to the resolution of multicomponent mixtures using UV-vis spectrophotometry

The Davidon-Fletcher-Powell (DFP) iterative algorithm was used for the simultaneous quantitation of the components of complex mixtures from their UV-vis spectra. First, the effect of noise, overlap between standard spectra and the starting point for resolving numerically generated spectra were investigated. Then, spectra for the pure solutions of the mixture components were used to apply the method to the resolution of ternary and quaternary mixtures of active principles and pharmaceutical preparations. Samples were also quantified by using a set of standard spectra which included not only those of the pure components, but also some for other substances. The proposed method effectively quantifies the actual mixture components.

Diode array detectors in flow injection analysis. Simultaneous determination of rare earth metals with Arsenazo III

SummaryA flow injection spectrophotometric procedure for the simultaneous determination of rare earths with Arsenazo III is reported. The spectrum of the sample is recorded by using a diode array detector and the mixed spectra are resolved with the aid of a multicomponent analysis program based on a least-squares fitting algorithm. Binary mixtures of tervalent cations at concentrations between 0.5 and 2.5 μg/g and uranyl in the range 1.4–4.3 μg/g were accurately resolved by univariate calibration. The presence of thorium (2.8–7.0 μ/g) required the use of multivariate calibration in order to obtain accurate results. Tervalent cations were globally determined as lanthanum. The sampling rate was about 60 samples/h. The results obtained in the analysis of U and Th in a pitchblende agree well with the certified values.

Atomic absorption determination of indium after extraction with di-(2-ethylhexyl) phosphoric acid

The equilibrium data show that indium can be quickly extracted from acidic aqueous solutions by di-(2-ethylhexyl)phosphoric acid in methyl isobutyl ketone. In this polar solvent the species ML3·HL is extracted. The overall extraction constant is higher than that for other tervalent metals. The extraction process can be combined with AAS determination of the indium. The method is fast because stripping is not necessary, and the organic phase can be analysed directly by AAS. Use of a 5∶1 v/v aqueous: organic phase ratio increases the sensitivity. In the pH-range used the method has good selectivity.

Spectrofluorimetric Identification of Polycyclic Aromatic Hydrocarbons at PPB Level

Abstract This paper reports a method for the spectrofluorimetric identification of fourteen polycyclic aromatic hydrocarbons (PAHs) at the nanogram per mililitre level in pure samples. The total fluorescence spectrum is scanned asynchronously to record the fluorescence intensity at 15 preset excitation—emission wavelength pairs. By calculating a match index between the unknown sample and a library of standard samples, the fourteen PAHs can be correctly identified. The match index obtained was always greater than 0.95.