R. M. Soto-Ferreiro

Palladium–magnesium nitrate as a chemical modifier for the determination of lead in mussel slurries by electrothermal atomic absorption spectrometry

A method for the determination of lead in mussel slurries by atomic absorption spectrometry with electrothermal atomization using Pd–Mg(NO3)2 as a chemical modifier is proposed. The drying, ashing and atomization temperatures were optimized. Calibration and standard additions graphs, sensitivity, precision, accuracy and the effects of different slurry stabilization agents were also studied. The method was applied to the determination of lead in mussel samples from the Galician coast and the results obtained were compared with those achieved by means of a wet digestion procedure.

Direct determination of tin in tap waters by electrothermal atomization atomic absorption spectroscopy

SummaryA method is described for the direct determination of tin in tap waters by electrothermal atomization atomic absorption spectroscopy (ETA-AAS), using magnesium-nitric acid and palladium-magnesium as chemical modifiers. The charring and atomization temperatures and times, and the amount of modifier were optimized. The calibration and addition graphs, detection limit, quantitation limit, precision, accuracy, interferences and characteristic mass were also investigated. The method was applied to the determination of tin in tap water samples.

Interpolation in the standard additions method

The standard additions method (SAM) has traditionally been performed by using extrapolation. This practice is suboptimal because predictions are affected by even slight departures of calibration points from a straight line. Despite this, most textbooks and papers in analytical chemistry still refer exclusively to extrapolation. In contrast, the use of interpolation is recommended in this paper as a way to get predictions on the central part of the regression line and thus minimize the bias in the prediction and the variance associated with the analytical result. Several scenarios were studied, with concentration errors simulated in different calibration solutions. It was found that translational effects due to variations at the central part of the calibration caused the lowest disturbances on the predicted concentrations. The differences between the interpolated and extrapolated predictions can be as large as ±30%. The confidence interval associated with the extrapolation result is wider than that due to interpolation by as much as 100%. It is shown that commonly used equations underestimate the correct confidence intervals. Both, absence of bias and improved precision, are of relevance in quality assurance, method validation and error propagation.

Comparative Study of Sample Preparation Methods for Zn, Fe and Cu Determination in Mussels by Flame Atomic Absorption Spectrometry

Abstract Sample preparation is a very important stage in the determination of heavy metals. In this paper a comparison was made of three digestion procedures: conventional acid digestion, calcination and microwave acid digestion. Conventional procedures (acid digestion and calcination) are very tedious and take a lot of time, while microwave acid digestion is a very rapid procedure and the results obtained in Zn, Fe and Cu determinations are comparable with those obtained with the conventional methods.

Pressurized liquid extraction to determine Mg, Al, Ti, Cu, Sn and Pb in lubricating oils by inductively coupled plasma mass spectrometry

A method to determine metals in lubricating oils was developed using pressurized solvent extraction (PLE) with a semi-automatic extractor ASE 200 (Dionex, USA) by inductively coupled plasma mass spectrometry (ICP-MS). The special nature of the sample made it necessary to adsorb it on a “drying” agent, which allowed us to handle it as a solid, and to use a cleaning agent in the extraction cell. A Plackett–Burman experimental design was used to study the variables determining the extraction conditions of Mg, Al, Ti, Cu, Ag, Sn and Pb: pH of the aqueous phase used as the extractant, mass of the dispersing agent, mass of the cleaner agent, temperature, time of the extraction cycle and number of cycles. The pH was revealed as the critical variable (optimum pH = 0.5, adjusted with concentrated HCl). Good recoveries (80–118%) were obtained when a certified lubricating oil (SRM 1084a) was analysed, but only low recoveries were obtained for Ag. The procedure was applied to analyse crankcase oils. The method proposed here has important advantages over the conventional procedures employed to analyse lubricating oils as it provides aqueous sample extracts which reduce instrumental interferences, enable the use of aqueous standards and, hence, avoid the use of organic solvents. Thus, it is environmentally friendly, following the green analytical chemistry guidelines.

A simple procedure to select a model for mass discrimination correction in isotope dilution inductively coupled plasma mass spectrometry

A fast, simple and straightforward procedure to decide on the best model to calculate the mass discrimination factor in Isotope Dilution Inductively Coupled Plasma Mass Spectrometry (ID-ICP-MS) is proposed. It is based on the study of the residuals of the different models that are proposed commonly, viz., the linear, the exponential, the power and Russells models. However, it can be generalized to evaluate any model proposed to linearize the relationship between the theoretical/measured isotope ratios and the mass. The procedure does not involve laboratory extra work, it is rooted on basic statistics associated with the least squares fit, and can be applied easily by the analysts so that decision making is fast and reliable. The procedure was exemplified with four different examples where Cd, Cr, Nd and Sm were determined by ID-ICP-MS.

Evaluation of analytical figures of merit when multivariate calibration is employed in atomic spectrometry

Electrothermal atomic absorption spectrometry (ETAAS) is a common choice to measure trace metals in complex materials. However, its combination with experimental design and multivariate calibration to exploit all the information contained within atomic spectra present is uncommon. A reason may be that it was not straightforward to evaluate the corresponding figures of merit of the resulting methodology. In this work, multivariate figures of merit which consider the risk of false negatives and false positives are calculated for the first time in the atomic spectrometry field following the latest ISO and European guidelines: critical level, minimum detectable value, trueness and precision, multivariate analytical sensitivity (or multivariate capability of discrimination) and sample-specific confidence intervals. The practical case study is about quantifying Cu in lubricating oils (a complex problem although relevant to trace machinery wearing) using partial least squares (PLS).

Multivariate calibration to implement green ETAAS methods when analysing Cu in lubricating oils

The quantification of metals in lubricating oils is relevant to trace machinery wearing and to evaluate potential environmental effects related to their disposal. Electrothermal atomic absorption spectrometry (ETAAS) is a common choice to measure metal content and despite efforts being made to reduce the amount of organic materials in the measurement aliquot (e.g., using emulsions), potential interferents still remain there. Therefore, quantification of the analyte is a highly difficult task. In this work a general-purpose methodology based on multivariate partial least squares regression (PLS) is presented to address interferences when difficult organic materials are analysed by ETAAS. It is shown that such a methodology yields powerful quantification models and requires less staff dedication, shorter turnaround times and lower expenses than traditional approaches. Besides, it is totally compatible with green analytical chemistry principles. Further, figures of merit which consider the risk of false negatives and false positives were calculated following the latest ISO and European guidelines: critical level (decision limit), minimum detectable value (detection capability), trueness and precision, multivariate sensitivity and sample-specific confidence interval. They have not been used in the atomic spectrometry field. The case study is about quantifying Cu in lubricating oils as a tracer of machine weathering.