Pilar Campíns Falcó

H-point standard additions method. Part 1. Fundamentals and application to analytical spectroscopy

A modification of the standard additions method called the “H-point standard additions method” is proposed in order to obtain an unbiased analyte concentration when both analyte and interferents are present in a sample. It also permits the determination of an interferent known to be present. The method uses the analytical signal data at two selected wavelengths, giving two straight lines that have a common point with coordinates H (–CH, AH), where –CH is the unknown analyte concentration and AH the analytical signal due to an interferent. Examples of the application of the proposed method are given.

Spectrophotometric analysis of mixtures of two components with extensively or completely overlapping spectra by the H-point standard additions method

SummaryThis paper discusses the requirements and scope of application of the H-Point Standard Additions Method (HPSAM) for resolving binary mixtures. Various mixtures of dyes with extensively or completely overlapping spectra were assayed with accurate, precise results. The method thus developed was also applied to the spectrophotometric resolution of binary mixtures of phenol and o-cresol, the absorption bands of which lie in similar positions and feature similar absorptivities.

Comparison of several methods used for the determination of cephalosporins. Analysis of cephalexin in pharmaceutical samples.

The precision of UV absorbance of intac and acid degraded cephalosporins, ninhydrin, high performance liquid chromatography and iodometric methods used for analysis of cefoxitin, cefotaxime, cephazolin and cephalexin were compared. To obtain the calibration graphs the analytical signal used were: absorbance, first derivative absorbance, second derivative absorbance and H-point Standard Additions Method by using absorbance values at two selected wavelengths as analytical signal. These methods and calibration graphs were also used for the determination of cephalexin in pharmaceutical samples.

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.

Extractive-spectrophotometric determination of amphetamine in urine samples with sodium 1,2-naphthoquinone 4-sulphonate

Abstract Sodium 1,2-naphthoquinone 4-sulphonate (NQS) was tested as a reagent for amphetamine in order to develop an extractive-spectrophotometric method for the drug in urine samples. The standard additions method showed the absence of proportional bias error whereas the Youden method and the two standard addition plots method showed the presence of a constant bias error [total Youden blank (TYB)]. Acceptable results were obtained by evaluating the TYB error or by using a placebo (urine sample from a normal subject). The dynamic range of concentrations was 1.4–50 mg 1−1 in urine samples and the detection limit was 0.6 mg 1−1 when 10 ml of urine sample were taken.

Determination of amphetamine and methamphetamine in urine with sodium 1,2-naphthoquinone 4-sulphonate using the H-point standard addition method

Abstract The determination of amphetamine and methamphetamine in urine by the H-point standard additions method (HPSAM) is described. An extraction-spectrophotometric method for the determination of these drugs with sodium 1,2-naphthoquinone 4-sulphonate using n-hexane-ethyl acetate (1:1) as the extraction solvent is proposed. The analytes are previously extracted into n-hexane. Although their spectra are very similar and overlap, the H-point standard additions method provides good results for both amines. The applicability of the method when the total Youden blank is present is demonstrated. The relative errors found were less than 10%.

Derivatization of amphetamine and methamphetamine with 1,2-naphthoquinone 4-sulfonic acid into solid-phase extraction cartridges. Determination of amphetamine in pharmaceutical and urine samples.

The derivatization of amphetamine and methamphetamine with 1,2-naphthoquinone-4-sulfonate (NQS) into solid-phase extraction cartridges (C 18 ) is described. Optimum conditions were the use of carbonate–hydrogencarbonate buffer of pH 10, a 10 min reaction time at 25 °C and an NQS concentration of 9.6 × 10 - 3 M. The accuracy and the precision of the method were tested. The results obtained with the proposed liquid–solid procedure were compared with those obtained with a traditional liquid–liquid extraction with hexane–ethyl acetate. The procedure was used to measure amphetamine in pharmaceutical and urine samples

Interpretation and Chemometric Evaluation of the Bilirubin Interference in the Kinetic Spectrophotometry Determination of Creatinine in Serum by Use of the Jaffe Reaction

Abstract SUMMARY In an alkaline picrate medium we demonstrated the occurrence of isosbestic points over the range 520–550 nm, the position depending on the bilirubin content and less on the albumin content. Bilirubin does not markedly modify the ratt constant of the reaction between creatinine and picrate, however, it does modify the intercept of the Ln ΔA vs t, plots. The absolute value of Ln ΔA varies with the concentration, though not with time, which indicates that bilirubin acts by consuming part of the initially present creatinine irrespective of its owr concentration at the wavelengths typically used in the creatinine determination. The Ln ΔA values at the isosbestic points coincide with those obtained in its absence. From the results obtained by applying the Youden and Standard-Addition methods we can conclude that bilirubin gives rise to systematic errors in the creatinine determination. The magnitude of interference depends on its concentration, changing the intercept of the plots. The results o...