A. Lopez Molinero

Silicon determination by inductively coupled plasma atomic emission spectrometry after generation of volatile silicon tetrafluoride.

A method for the determination of silicon by inductively coupled plasma atomic emission spectrometry (ICP-AES) is described. The procedure is based on a discontinuous generation of volatile silicon tetrafluoride in concentrated sulphuric acid medium after injecting 125 mul of 0.1%, w/v sodium fluoride solution into 100 mul of the sample. The gaseous silicon tetrafluoride is fed directly into the ICP torch by a flow of 250 ml min(-1) Ar carrier gas. The calibration curve was linear up to at least 100 mug ml(-1) of Si(IV) and the absolute detection limit was 9.8 ng working with a solution volume of 100 mul. The relative standard deviation for six measurements of 10 mug ml(-1) of Si(IV) was 2.32%. The method was applied to the determination of silicon in water and iron ores.

Volatilization of methyl borate in iron matrix. Determination of boron in steel by ICP atomic emission spectrometry.

A rapid and reliable method for the determination of boron by ICP-AES in steels is described. The procedure is based on a discontinuous generation of methyl borate, in concentrated sulphuric acid and phosphoric acid medium, after injecting 45 microl of methanol in 20 microl of sample. The gaseous methyl borate and excess methanol are fed into the ICP torch via the intermediate tube by a flow of 430 ml/min Ar carrier gas, without disturbing the discharge. This work simplifies drastically the existing methodology of boron analysis in steels. Acid-soluble boron has been determined, but acid-insoluble boron can also be determined. The determination is carried out without iron interferences, with a reproducibility of 1.90% r.s.d. for a concentration of 20 microg/ml, and an absolute detection limit of 20 ng of total boron, working with a solution volume of 20 microl.

Determination of Nickel and Vanadium in Oil By Inductively Coupled Plasma-Atomic Emission Spectrometry With Microemulsion Sample Introduction.

Abstract The introduction of oils into an inductively coupled plasma spectrometer is carried out after the formation of oil-in-water microemulsions. These organic-aqueous solutions are tolerated by the spectrometer while working at 1 Kw of power and with 20 1.min−1 Ar plasma gas flow. In these conditions the emission intensity of emulsions of nickel and vanadium at 221.64 nm and 292.40 nm, respectively, can be interpolated in aqueous calibration graphs of the elements. The method has been evaluated using three synthetic samples prepared from base oil spiked with Ni and V. Detection limits of Ni and V in oils of 1.25 and 0.94 μg.−1, respectively, are found.

Multivariate statistical characterization of the tolerance of argon inductively coupled plasmas to organic solvents

Abstract The tolerance of Argon-inductively coupled plasmas to the introduction of organic solvents, defined by Matsunagas parameter and by “limiting aspiration rate”, has been correlated with their nature by statistical methods. The main physical variables of solvents obtained from the technical literature were used as independent variables to perform principal component analysis (PCA) and factorial discriminant analysis (FDA). Thus the variables which had the greatest influence on heat exchange nebulization and transport processes were determined. Organic solvents were classified into different groups characterized by their tolerance in plasma operation. In the PCA study, the second principal component was the most significative to differentiate between the tolerance of solvents and it showed a high correlation with surface tension, viscosity and heat of vaporization. Scores of the organic solvents belonging to the same class can be adjusted to straight lines and their positions in the plane (expressed as ordinates in the origin) as well as the slope values are characteristics of organic solvent groups. The results of FDA confirms those obtained with PCA. Multivariable regression was applied to obtain predictive equations of the limiting aspiration rate for organic solvents, in terms of their main physical variables.

Determination of ytterbium by AES-ICP. Application to samples of biological origin

SummaryYtterbium is used as a marker in studies of digestion physiology in ruminants; its determination has been accomplished by Inductively Coupled Plasma — Atomic Emission Spectroscopy (ICP-AES). An analytical study has been carried out, which includes the evaluation of various emission lines (atomic, ionic). The line at 328.937 nm is proposed for determining Yb, with a limit of detection of 1.68 ×10−3μg ml−1. The analytical procedure has been applied to the determination of this element in samples of animal fodder, rumen contents and feces.

Possibilities for graphic representation of multifactor simplex optimisation

Abstract The progress of a multifactor simplex optimisation algorithm has been plotted in a visual mode, after a reduction in the number of factors using the statistic principal component analysis method. The effectiveness of the proposed graphic representation has been evaluated when applied to simplex previously published optimisation methods such as: colorimetric determination of cholesterol, flow-injection spectrophotometric determination of promethazine and synthesis of an industrial pyrazolone. The procedure has also been applied to develop new experimental analytical methods like the determination of arsenic trichloride by inductively coupled plasma atomic emission spectrometry.

Sulphate determination after its reduction to hydrogen sulphide and volatile separation by molecular absorption spectrometry

A rapid spectrophotometric method for sulphate determination in a discontinuous mode is described. The method is based on sulphate reduction to hydrogen sulphide followed by its volatilization and absorption in an alkaline solution. The reduction is obtained when a sulphate sample is heated to 287 degrees C for 15 min, with a mixture of Fe(o)/KI and phosphoric acid. The resulting gas is swept by nitrogen flow into a 0.1 M sodium hydroxide solution and the absorbance of the sulphide ions is measured directly at 230 nm. The proposed method enabled us to determine 50-700 mug of total sulphate with a relative standard deviation of the order of 5%. The method has been applied for the determination of sulphates in liquid (mineral waters) and solid (gypsiferous soils) samples.

Arsenazo, 2-(4-arsonophenyl(azo-7-(4-antipyril)azo-1,8-dihydroxy-3,6-naphtalene disulphonic acid as reagent for calcium ions. New parameters for metallochromic indicator characterization

Ca(II) ions react with arsenazo, 2-(4-arsonophenyl)-azo-7-(4-antipyril)azo-l,8-dihydroxy-3,5-naphtalene disulphonic acid, at pH 10.0 to produce a blue complex, with stoichiometry 1∶1, and stability constant of 6.64×105. Its molar absorptivity is 3.78×1041·mol−1 cm−1. This reagent has been used as metallochromic indicator in the complexometric titration of Ca. Its colour transition has been specified by tristimulus colourimetry. New parameters are defined and compared to Ringboms parameters.

Multielement analysis of gypsiferous soils using a sequential inductively coupled plasma-atomic emission spectrometric method

Abstract The amount of major, minor, and trace elements (Ca, Mg, Fe, Na, Sr, Mn, Cu, Cr, V, Mo, B, Ni, Li, and Ba) in gypsiferous soils formed by evaporitic processes was determined. A sequential analysis method by atomic emission spectroscopy with an inductively coupled plasma was used, working with partial matrix matching between the reference standards and the real samples. Furthermore, a simplified method, based on two calibration graphs (Fe and Li), was developed for calibrating the analysis procedure.