Sensitivity equation for quantitative analysis with multivariate curve resolution-alternating least-squares: theoretical and experimental approach.

A new equation is derived for estimating the sensitivity when the multivariate curve resolution-alternating least-squares (MCR-ALS) method is applied to second-order multivariate calibration data. The validity of the expression is substantiated by extensive Monte Carlo noise addition simulations. The multivariate selectivity can be derived from the new sensitivity expression. Other important figures of merit, such as limit of detection, limit of quantitation, and concentration uncertainty of MCR-ALS quantitative estimations can be easily estimated from the proposed sensitivity expression and the instrumental noise. An experimental example involving the determination of an analyte in the presence of uncalibrated interfering agents is described in detail, involving second-order time-decaying sensitized lanthanide luminescence excitation spectra. The estimated figures of merit are reasonably correlated with the analytical features of the analyzed experimental system.

Lanthanides determination in red wine using ultrasound assisted extraction, flow injection, aerosol desolvation and ICP-MS.

This paper deals with the determination of the fourteen naturally occurring elements of the lanthanide series in red wine. Ultrasound (US) was used for sample preparation prior lanthanides determination using ICP-MS. Flow injection (FI) and pneumatic nebulization/aerosol desolvation were used for nebulization of aliquots of 50 µL of sample and its subsequent transportation to plasma. Sample preparation procedures, matrix interference and time of sonication were evaluated. Better results for lanthanides in red wine were obtained by sonication with US probe for 90 s and sample 10-fold diluted. The limits of detection of La, Ce, Nd, Sm, Gd, Pr, Eu, Tb, Dy, Ho, Er, Tm, Lu and Yb were 6.57, 10.8, 9.97, 9.38, 2.71, 1.29, 1.22, 0.52, 2.35, 0.96, 2.30, 0.45, 0.24 and 1.35 ng L(-1), respectively. Red wines of different varieties from three countries of South America were discriminated according to the country of origin by means of multivariate analysis of lanthanides concentration.

Determination of lanthanides in international geochemical reference materials by reversed-phase high-performance liquid chromatography using error propagation theory to estimate total analysis uncertainties.

The weighted least-squares (WLS) regression method was successfully applied to establish calibration curves with variable amounts of lanthanides ranging from 0.002 to 0.430 microg. These curves were employed for the analysis of 13 lanthanides (La-Nd, Sm-Tb, and Ho-Lu) in 12 international geochemical reference materials (IGRM). The separation of the lanthanide group was achieved in approximately 15 min. Dysprosium could not be determined in IGRM because of its co-elution with Yttrium. A linear gradient program of alpha-HIBA eluent with a concentration ranging from 0.05 to 0.5 M (0.1 M OS, pH 3.8 with NH(4)OH, and a flow-rate of 1.0 ml/min) was employed. The detection was performed with a UV-vis system at 658 nm using a post-column reagent of Arsenazo III (0.5 ml/min). With this set of RP-HPLC conditions together with the use of both the ordinary least-squares (OLS) and the WLS regressions, we report the results of the measurements along with the total propagated uncertainties in individual concentration values. The uncertainties were obtained by combining standard errors in both regression parameters (slope and intercept) with those related to the chromatographic peak areas. The straight-line slopes and intercepts calculated by the WLS method provided not only considerably smaller errors than the conventional OLS method but also a much better estimation of the limits of detection. The concentrations calculated were compared with the "most probable" concentration values of these reference materials reported in the literature. Statistically significant agreement was consistently observed between the HPLC data and the literature values. The total uncertainties in estimated concentration values for the WLS were consistently smaller than the respective errors for the OLS.

Determination of lanthanides in synthetic standards by reversed-phase high-performance liquid chromatography with the aid of a weighted least-squares regression model estimation of method sensitivities and detection limits.

A reversed-phase liquid chromatography method was used for determining lanthanides in synthetic standards. The separation of lanthanide group was achieved in less than 15 min using a linear gradient program of alpha-hydroxyisobutyricacid eluent from 0.05 to 0.5 M (pH 3.8) with a UV-Vis detection system at 658 nm. A post-column reagent of Arsenazo III was employed for improving the sensitivity and selectivity of the method as well as for lowering the limits of detection (LODs). Linear calibration curves for all lanthanides were constructed using an ordinary least-squares (OLS) regression as well as a weighted least-squares (WLS) regression model for taking into account the heteroscedastic errors. The WLS model was successfully used for a better estimation of the sensitivities and the LODs of the RP-HPLC method than the conventional OLS model. The lanthanide sensitivity obtained from the slope of each calibration curve seems to be better for a lanthanide with an odd-atomic number compared to its neighboring element with an even-atomic number, as if nature is helping us to quantify the concentrations of the less abundant lanthanides. This observation was also confirmed when the LODs computed for all lanthanides were examined. The LODs observed for all lanthanides depicted a clear systematic "zigzag" pattern. This is actually the first time that the lanthanide detection limits determined by a HPLC method are shown to mimic the zigzag patterns for the concentration data in geological and cosmological materials. Such a "zigzag" pattern should be used as a standard criterion for evaluating the quality of detection limit data.