J. Martínez Calatayud

Multicommutation as a powerful new analytical tool

This review presents the state of the art of the emerging continuous-flow methodology based on solenoid valves. This uses flow networks to deliver sample and reagent solutions by controlling the time of flow through the ON/OFF modes of solenoid valves and takes advantage of existing flow injection analysis (FIA) or sequential injection analysis (SIA) device or manifold configurations. It allows one to insert a single plug of sample (or reagent) into the carrier or carrier-reagent stream, mimicking the approaches of FIA or SIA. In addition to the modes used in FIA and SIA, the methodology provides a different mode, based on delivery of a series of alternating sequential insertions of very small volumes of sample and reagent. This gives rise to different hydrodynamic and chemical processes and new analytical potential. The fundamentals of the methodology are discussed together with a broad view and critical survey of the advantages and the possible trends.

Photochemical derivatization and spectrofluorimetric determination of chlorpromazine by flow injection

Abstract The flow-injection spectrofluorimetric determination of chlorpromazine was carried out by on-line photoderivatization, in which the PTFE tubing in the injection valve loop was helically coiled around the UV lamp. An aqueous solution was used as the carrier stream. The influence of foreign compounds was studied and the method was applied to the determination of chlorpromazine in pharmaceutical formulations.

Flow-injection spectrofluorimetric determination of paracetamol

Abstract A flow-injection spectrofluorimetric determination of paracetamol is reported, based on the oxidation of the analyte with potassium hexacyanoferrate(III) immobilized on an anion-exchange resin, the fluorescence being enhanced with N,N′-dimethylformamide. Concentrations of paracetamol in the range 0.04–17.60 mg l−1 are determined with a relative standard deviation of 1.5%. The injection rate is 25 samples h−1. The influence of foreign species and the determination of paracetamol in several pharamaceutical formulations are also reported.

Determination of tyrosine through a FIA-direct chemiluminescence procedure

A new FI-direct chemiluminescence method is proposed for the determination of tyrosine, based on the oxidation of the amino acid by K(3)Fe(CN)(6) in potassium hydroxide medium, at room temperature and enhanced by the presence of beta-cyclodextrin and formic acid. The dynamic range was linear over the range 1.0-10.0 mgl(-1). A large study of the influence of foreign compounds was performed, including amino acids; and, the method showed high selectivity. The reproducibility between days resulted in a rsd (in slope%) of 4.8 and the repeatability with a rsd (n=50, 10.0 mgl(-1)) of 3.1%, the LOD (s/n=3) was 50 mugl(-1) and sample throughput 98 h(-1).

Multi-insertion of small controlled volumes of solutions in a flow assembly for determination of nitrate (photoreduction) and nitrite with proflavin sulfate

A simple, maintenance-free, non-contaminating and completely automated flow system was developed for non- simultaneous determinations of nitrite and nitrate, in which spectrophotometric measurements at 328 nm were performed on the nitrite reaction with proflavin sulfate [bis(3,6-diaminoacridinium)sulfate]. The sample solutions were automatically inserted into phosphate buffer (pH 6.8) containing 10 mM EDTA by using a programmable solenoid valve; then they flowed through a 6.4 m × 0.5 mm id PTFE coil, wrapped around an 8 W low pressure mercury lamp, and finally they merged with a hydrochloric acid solution of proflavin. With the lamp off the nitrite in the sample was selectively measured with a sensitivity of 0.75 × 104 absorbance (linearity range up to 0.6 absorbance; detection limit of 1.9 × 10–7M). With the lamp on, to determine the sum of nitrite + nitrate there was a decrease in sensitivity of 41% versus that of the selective variant for nitrite determination. The sample throughput was 15 h–1 and the RSD at a 6.4 × 10–5M level of nitrate was 0.4% (n = 15). Many interferences were studied and simple methods of correcting for them were applied to analyse samples such as waters, soils, fertilisers and meat.

Flow-injection analysis-spectrophotometric determination of nitrite and nitrate in water samples by reaction with proflavin

A flow-injection manifold is proposed for determination of nitrite based on the reaction with 3,6-diamino acridine (proflavin sulfate) in hydrochloride acid medium. The assembly is adapted for nitrate determination by including a reductive column filled with copperized cadmium. The influence of foreign substances is also studied. The method gives a linear calibration graph over the range 0·06-4 mg 1−1 nitrite, with an RSD <0.5%. The method was applied to nitrite and nitrate determinations in either waste water or coastal marine water samples.

Entrapment of reagents in polymeric materials. Indirect atomic absorption spectrometric determination of isoniazid by oxidation with manganese dioxide incorporated in polyester resin beads in a flow-injection system

Abstract A method for entrapment of reagents is described. The experimental procedure is based on the dispersion of the reagent (MnO2) into an unsaturated polyester solution and grinding the product to give the required particle size (300–400 μm). The reagent is packed into a bed reactor (1.5 mm i.d.) and incorporated in a flow-injection system. The procedure was used for the indirect atomic absorption spectrometric determination of isoniazid (0.5–10 μg ml−1) in solutions of pharmaceutical products, with little interference from excipients. The measurements are based on the determination of Mn2+ released on oxidation of the isoniazid. The relative standard deviation for the determination of 5 μg ml−1 of isoniazid is 2.57% (n = 40) and the sample throughput is 43 h−1.

Indirect determination of paracetamol in pharmaceutical formulations by inhibition of the system luminol–H2O2–Fe(CN)63− chemiluminescence

After a large drug scanning, the system Luminol-H2O2-Fe(CN)6(3-) is proposed for first time for the indirect determination of paracetamol. The method is based on the oxidation of paracetamol by hexacyanoferrate (III) and the subsequent inhibitory effect on the reaction between luminol and hydrogen peroxide. The procedure resulted in a linear calibration graph over the range 2.5-12.5 microg ml(-1) of paracetamol with a sample throughput of 87 samples h(-1). The influence of foreign compounds was studied and, the method was applied to determination of the drug in three different pharmaceutical formulations.

Flow injection-spectrophotometric determination of metoclopramide hydrochloride

Abstract The determination of metoclopramide hydrochloride is spectrophotometrically determined by the Bratton-Marshall method in a flow injection assembly. The required nitrite is prepared on-line in the flow assembly by reducing a nitrate solution with the aid of a copperised cadmium solid-phase reactor. The calibration graph is linear over the range 0.5–85 mg l −1 , with a relative standard deviation (RSD) of 0.89%, and sample throughput of 51 samples h −1 . The method is easy and simple, and it is applied to determination of metoclopramide in some pharmaceutical formulations. The method eliminates the need for frequent preparation of unstable nitrite solutions.

Photochemical derivatization and fluorimetric determination of reserpine in a flow-injection assembly

Abstract The fluorimetric flow-injection determination of reserpine was achieved with the drug being derivatized on-line by photoreaction. PTFE tubing was helically coiled around a germicide lamp located between the injection valve and detector. Two analytical procedures are proposed using either dilute acetic acid or pure methanol as the carrier stream. The influence of foreign compounds was studied and the method was applied to the determination of reserpine in pharmaceutical formulations.