S. Sagrado Vives

Fluorimetric determination of captopril by flow injection analysis

A flow injection analysis procedure is proposed for the determination of captopril. The sample solution was directly injected into the carrier-reagent stream which was prepared by a solution of ceric ions in 0.25 M sulfuric acid. The procedure is based on the fluorimetric monitoring of the formed Ce(III). Chemical, FIA, and instrumental parameters were optimized and the procedure is applied to the captopril determination in pharmaceutical formulations with competitive precision and adequate accuracy.

An oxidative column for the flow injection analysis—spectrophotometric determination of paracetamol

Abstract A flow injection—spectrophotometric determination of paracetamol is reported. The procedure is based on the oxidation of the analyte with potassium hexacyanoferrate(III) previously retained in an anionic exchange column and the reaction of the N -(hydroxyphenyl)- p -benzoquinonimine so produced with phenol. The oxidation is carried out at room temperature and in aqueous ammoniacal solution. Concentrations of paracetamol in the 0.20–20 ppm range are determined with relative standard deviations (RSD) of 0.6% ( n = 40) at an injection rate of 42 samples h −1 . The influence of foreign species on the assay and its application to the determination of paracetamol in several pharmaceutical formulations are reported.

Determination of Paracetamol by a Flow Injection-Spectrophotometric Method

Abstract A flow injection-spectrophotometric determination of paracetamol is reported. The procedure is based on the oxidation of the analyte with potassium hexacyanoferrate (III) and reaction of the N-(hydroxyphenyl)-p-benzoquinonimine produced with phenol; both reactions are carried out at 80 × 1°C and in aqueous ammoniacal solution. Concentrations of paracetamol in 0.25-30 ppm range are determined; relative standard deviations are 0.4% (n=40).Injection rate 26 samples/h.The influence of foreign species and the determination of paracetamol in several pharmaceutical formulations are also reported.

Screened indicators for the direct chelometric titration of lead(II)

Two screened indicators, Eriochrome Black T-Methyl Red (7.4 + 1)-NaCl (1 + 100, m/m) and Bromopyrogallol Red-Naphthol Green B-Thymol Blue (2.5 + 21 + 1)-NaCl (1 + 100, m/m), are proposed for the titration of lead against Na2EDTA. Clarity and accuracy of titration are improved.

Fluorometric determination of diphenhydramine by flow-injection analysis

A sensitive, rapid and simple flow injection procedure for the determination of diphenhydramine has been designed based on a fluorometric approach. An aqueous solution of diphenhydramine is injected into a carrierreagent stream containing Ce(IV) in dilute sulphuric acid and the fluorescence intensity of the Ce(III) produced is monitored. Chemical, FIA and instrumental variables were optimized. Analytical features of the method are: linear range 0.2–2 ppm, precision 0.7%, sample throughput 80/h. The influence of some foreign substances which can be found in typical pharmaceutical samples containing diphenhydramine was also investigated. The diphenhydramine content of a pharmaceutical preparation was determined.

Some observations on the automation by flow injection analysis of the spectrophotometric determination of amino acids and proteins witho-phthalaldehyde

Automation by flow injection analysis with Spectrophotometric detection of the determination of total amino acids and proteins witho-phthalaldehyde is not straightforward. The use of spectrophotometry, instead of spectrofluorimetry, and of N-acetyl-L-cysteine, instead of the conventional mercaptoethanol is advantageous because of the lower variability of absorptivities with respect to fluorescence yields, and the larger stability of the derivatives. Under adequate working conditions and with leucine as reference, the procedure can be used for the evaluation of total amino acids. A similar procedure is proposed for the analysis of proteins in a sample. Limits of detection are ≈ 1 × 10−5M for amino acids, and ≈ 1 × 10−6M for proteins, respectively.

Spectrophotometric measurement of pH gradients in continuous-flow systems

Abstract In the presence of an acid-base indicator and using fast diode-array spectrophotometric scans, pH gradients in the spectrophotometric cell can be measured at the same time as any other colorimetric flow-injection (FI) determination is performed. The effects of refractive index changes, adsorption-desorption processes at the tube walls and association of the indicator species with the system to be investigated are considered. Effective correction for the first two effects is demonstrated. Indicators with different molecular structures and polarities gave similar pH gradients, suggesting adequate accuracy for most potential applications. Application to the detection and correction of systematic and random errors in pH-sensitive FI procedures is demonstrated using the o -phthalaldehyde- N -acetyl- l -cysteine method for bovine serum albumin.

Device for data-acquisition from transient signals: kinetic considerations.

This paper reports on the evaluation and testing of a home-made device. Data-acquisition, treatment of transient signals and the hardware and software involved are discussed. Some practical aspects are developed in order to power the autonomy of procedures using the device. Kinetic and multi-signal calculations are considered in order to cover the actual tendencies in continuous-flow analysis. Somepractical advantages versus the use of classical chart recorders or commercial computerized-instrument devices are pointed out.

Continuous-flow tristimulus colorimetry: a new approach for gradient scanning techniques

Abstract A flow-injection gradient scanning technique for colour evaluation by means of tristimulus colorimetry is described. Equipment and data acquisition requirements are discussed. The program CHROMA.FIA data the treatment and comparative chromatic analysis is presented. The chemical and flow conditions were optimized. Comparative studies using metallochromic indicators with both the flow-injection and the conventional batch procedures were made. The continuous-flow procedure provides good results and is more than fifteen times faster than the manual titrimetric procedure.