J.V Garcı́a Mateo

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.

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.

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.

FI-on line photochemical reaction for direct chemiluminescence determination of photodegradated chloramphenicol

A new, simple, clean and selective flow injection strategy based on the tandem photochemical reaction-chemiluminescence detection was applied to the determination of chloramphenicol. The determination is based on the on-line photodegradation of the drug in a glycine buffer at pH 8.8 by using a photoreactor consisting of 697 cmx0.5 mm PTFE tubing helically coiled around an 8 W low-pressure mercury lamp. Photodegradated chloramphenicol is detected by direct chemiluminescence of resulting photo-fragments and their subsequent reaction with potassium permanganate in sulfuric acid medium as oxidant. The method allows the chemiluminescence determination of compounds which do not exhibit native chemiluminescence. The calibration graph was linear up to 14 mug ml(-1) chloramphenicol, the limit of detection was 30 ng ml(-1), the relative standard deviation was 2.4% for 7 mug ml(-1) of the drug and the sample throughput was 60 h(-1). Taking into account the importance of the medium of photodegradation on the mechanism of photodegradation a comparative study in terms of selective was performed for different chemical media employed in the procedure of photodegradation. The proposed method was applied to the determination of chloramphenicol in commercially available pharmaceutical formulations.

On-line solid-phase reactors for unsegmented continuous-flow drug analysis

Abstract The use of solid-phase reactors in unsegmented continuous-flow methodologies as applied to the determination of pharmaceuticals is critically reviewed. The types of reagents, immobilization strategies, and the function of the bed-reactor are discussed. The review is confined to the analysis of pharmaceuticals in formulations and in biological samples.

Prediction of the chemiluminescent behaviour of phenols and polyphenols

Abstract A paper from this laboratory ‘J. Anal. Chem. 73 (2001) 4301’ was recently published and dealing with the first attempt to apply molecular connectivity calculations to predict a chemical property with analytical usefulness; namely, the chemiluminescent behaviour of substances when react with common strong oxidants in liquid phase. In the present work, the usefulness of molecular topology on the search for new chemiluminescent compounds is clearly demonstrated. The proposed discriminant equation, represented a success of 92.7% in the prediction. The present paper is the further step from the cited paper; it is dealing on the application of molecular connectivity calculations (former discriminant equation ‘J. Anal. Chem. 73 (2001) 4301’) to predict the chemiluminescent behaviour of phenols and polyphenols when they react with common oxidants in liquid phase. A number of phenols and polyphenols (close to 100) were theoretically studied by means of the discriminant equation ‘J. Anal. Chem. 73 (2001) 4301’, being some of them predicted as chemiluminescent with a high probability. These theoretical predictions have been empirically checked through a continuous flow manifold. A number of 33 compounds, selected between those which chemiluminescent behaviour was predicted, were assayed. A success of 100% over the theoretical predictions was obtained.

Theoretical prediction of the photoinduced chemiluminescence of pesticides

Although it is relatively easy to find chemiluminescent (CL) molecules working on the field of direct liquid phase (especially employing strong oxidants), the molecules found as chemiluminescent are normally very weak CL compounds for developing suitable analytical CL-procedures. Therefore, it is mandatory to develop new strategies to enhance in a simple way the native chemiluminescence of such a compounds, and even to increase the number of compounds to be determined by direct chemiluminescence. Photoinduced chemiluminescence (Ph-CL) results in a simple and easily on-line accessible strategy to solve these disadvantages. In the present paper, molecular connectivity, a topological method which allows an unique mathematical characterization of molecular structures by the so-named topological descriptors and their correlation with physical, chemical and biological properties of molecules was applied to predict the Ph-CL in liquid phase. Molecular connectivity calculations and discriminant analysis was applied to 72 pesticides for which either a Ph-CL or non Ph-CL behaviour was observed in an experimental screening. The screening test is based on the on-line photodegradation of pesticides by using an automated multicommutation based flow asssembly provided with a photoreactor consisting of 150 cm x 0.8mm PTFE tubing helically coiled around a 20 W low-pressure mercury lamp. Photodegraded pesticides are detected by direct chemiluminescence of the resulting photo-fragments and their subsequent reaction with potassium permanganate in sulfuric acid medium as oxidant. The screening comprised pesticides with different molecular structures and relevant members of the most important families of pesticides were tested (oxime carbamates, sulfonylcarbamates, thiocarbamates, 1,3,5-triazines, organophosphorous, hydroxybenzonitrile, sulfonylureas, phosphonic acid derivatives, imidazolinones, carboxamides, aryloxyalkanoic acids, 1,2,4-triazinones, etc.). The theoretical predictions agree with the empirical results obtained by means of the screening test performed in the multicommutation flow-assembly.

Entrapped copper(II) carbonate for indirect determination of glycine by flow injection atomic absorption spectrometry

Abstract Copper(II) carbonate was physically entrapped in a polyester during polymerization. The resulting solid resin was used as a rector for glycine determination by means of a flow injection manifold and applied to pharmaceutical formulations; the glycine complexed with and thus dissolved some of the immobilized Cu(II), which was monitored by an atomic absorption spectrometer. The calibration graph is linear in the range 1.2–35 μg ml −1 glycine, the detection limits is 1.2 μg ml −1 , the relative standard deviation at 20 μg ml −1 is 1.1% ( n = 20) and the sample throughput is 180 h −1 .

Determination of tannic acid by direct chemiluminescence in a FIA assembly

Abstract The determination of tannic acid is performed in a FIA assembly on the basis of the analytical output obtained by oxidation of the acid. The analyte solution was daily prepared in a mixture of quinine as sensitiser and perchloric acid and it was injected into a pure water stream acting as a carrier. This solution merges with the mixture potassium permanganate in perchloric medium and the resulting chemiluminescence is monitored. The method was applied over the range 0.5–20 mg l −1 of tannic acid with a LOD 100 μg l −1 . The reproducibility was 2.1% and the sample throughput 54 h −1 . The influence of foreign substances was studied and the new method is applied to the determination of tannic acid in pharmaceutical and galenic formulations in human urine and surface waters.

Spectrofluorimetric Determination of Iproniazid and Isoniazid in a FIA System Provided with a Solid-Phase Reactor

Abstract A FIA assembly is proposed for the fluorimetric determination of iproniazid and isoniazid. The oxidation of both drugs is carried out by H2O2. The excess of reagent is destroyed and removed from the flow-injection manifold by means of a metallic copper reactor which acts as catalyst in the decomposition of H2O2 and a home made debubbler. The calibration graphs were linear up to 14 μg ml−1 and 10 μg ml−1 (n=6) for iproniazid and isoniazid, respectively, with limits of detection of 0.008 μg ml−1 and 0.005 μg ml−1. The sample throughput was 24 h−1 for both drugs. The influence of foreign compounds was studied and the procedure was applied to determination of iproniazid and isoniazid in pharmaceutical formulations.