Chemiluminometric determination of phenothiazines by means of a combined multi-commutated/multi-pumped flow assembly.

A rapid, sensitive and fully automated chemiluminometric method is described for determination of five phenothiazine derivatives, namely, trifluoperazine, fluphenazine, perphenazine, thioridazine and chlorpromazine. The method is based on the chemiluminescence (CL) induced by the oxidation of drugs with Ce(IV) in nitric acid. A flow manifold based on the association of multi-commutation and multi-pumping flow methodologies is proposed. The active operated solenoid devices consisted of a micro-pump (propelling 50µL per stroke) and a six ports solenoid valve. Reconfiguration of the flow manifold was performed by using software settings, without physical alteration of the instrument manifold. It permits the design of flexible miniaturized networks for flow analysis based on a time-pulse-counting strategy. The proposed method allows the determination of the drugs at the ngmL(-1) level with a sample throughput of 38h(-1) (chlorpromazine) and 40h(-1) (trifluoperazine, fluphenazine, perphenazine, and thioridazine). The method was successfully applied to the determination of the phenothiazine derivatives in pharmaceuticals formulations.

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.

Chemiluminescent determination of the pesticide bromoxynil by on-line photodegradation in a flow-injection system.

A new, robust and simple method is proposed for the chemiluminescent determination of the pesticide Bromoxynil. The empirical procedure is performed with the aid of a flow-injection manifold provided with an on-line photo-reactor to obtain chemiluminescent photofragments. After a period of 12 s of irradiation with an 8 W low-pressure mercury lamp, a chemiluminescent oxidation was performed with the system potassium permanganate in a polyphosphoric acid medium. The photolysis required a basic medium (KOH 0.014 mol l(-1)) with ethanol (1%) as a sensitizer. The method allowed the determination of 134 samples (h-1) of Bromoxynil in a wide interval of concentrations, over the range 5 x 10(-3) - 1 mg l(-1); the detection limit was 5 x 10(-3) mg l(-1). The RSD (n=24) at 0.25 mg l(-1) of the pesticide level was 2.3%. The method was applied to a water sample and to a formulation.

Photoinduced chemiluminescence of pharmaceuticals.

A screening test for the forward development of chemiluminescence systems able to determine pharmaceutical compounds is reported. The test is based on the on-line photodegradation of the drugs by using a photoreactor consisting of 697 cmx0.5 mm PTFE tubing helically coiled around an 8 W low-pressure mercury lamp. Photodegraded pharmaceuticals are detected by direct chemiluminescence of the resulting photofragments and their subsequent reaction with potassium permanganate in sulphuric acid medium as oxidant. The screening comprised 97 compounds with different molecular structures and relevant members of the most important families of pharmaceuticals are tested (amino acids, carboxylic acids, nitrocompounds, phenyl-alkyl and aromatic amines, sulphonic acid amides, polycarbocyclics, monocyclic N-containing heterocyclics, bicyclic N-containing heterocyclics, tricyclic N-containing heterocyclics, N-S containing heterocyclics...). Due to the relevant influence of the medium for the photodegradation a wide range of pH's and buffer solutions were studied. The proposed strategy (photoinduced chemiluminescence, Ph-CL) allows the development of systems for the determination of many pharmaceuticals which do not present "native" chemiluminescence (e.g. chloramphenicol, dextromethorpham, riboflavin, ephedrine, piperazinamide, chlotrimazole, theophylline...). Moreover, Ph-CL allows to increase the sensitivity of chemiluminescence procedures based on direct chemiluminescence detection (e.g. sulphonamides, thiazides, nicontinamide, nortryptiline, levamisole, phenylbarbituric acid...).

FI-chemiluminometric study of thiazides by on-line photochemical reaction.

The present manuscript deals with a simple and sensitive flow-injection method for the chemiluminescent determination of thiazides. The method is based on the on-line photodegradation and chemiluminescent determination of the resulting photo-fragments. The on-line photodegradation is performed in basic medium by using a photoreactor consisting of a 550cm long x 0.8mm ID piece of PTFE tubing helically coiled around an 8W low-pressure mercury lamp. The determination of the photo-irradiated thiazides is performed by a chemiluminescent oxidative reaction with Ce(IV) in sulphuric acid medium. A heterogeneous group of thiazides (indapamide, metolazone, hydroflumethiazide, chlorthalidone and bendroflumethiazide) has been studied. Hydrochlorothiazide was selected as a test substance. The "on-line" photochemical reaction approach allows the sensitive chemiluminescent determination of thiazides which do not present native chemiluminescence in the absence of sensitizers such as Rhodamine 6G. Linear calibration graphs were typically over the range 0.5-12 microgml(-1) (indapamide, metolazone, hydroflumethiazide and chlorthalidone); and over the range 0.5-5 microgml(-1) (hydrochlorothiazide). Limits of detection ranged between 0.005 microgml(-1) (hydrochlorothiazide) and 0.06 microgml(-1) (bendroflumethiazide). The relative standard deviation for the test substance was 2.0% for 2 microgl(-1) of the drug (n = 11) and the throughput was 65 h(-1) in all cases. The assessment of the photodegradation step on the molecular structure of thiazides was established by recording UV and fluorimetric spectra. The viability of the on-line photoinduced fluorescent determination of hydroflumethiazide and bendroflumethiazide was confirmed. The method was also applied to the determination of hydrochlorothiazide in commercially available formulation.

A tandem-flow assembly for the chemiluminometric determination of hydroquinone.

A direct chemiluminescent procedure for determination of hydroquinone based on the emergent flow methodology known as multicommutation or tandem-flow is presented for first time. The manifold was based on a set of three channels and three solenoid valves; and, the determination was performed at 60 degrees C and at flow-rate of 7.5mlmin(-1). The complete cycle lasted 35s, which resulted in a sample flow trough of 103h(-1). The chemical process was the hydroquinone oxidation with the system sulphuric acid-potassium permanganate; and the light emission was clearly enhanced by the presence of quinine sulphate and benzalkonium chloride reaching a detection limit of 30mugl(-1). The dynamic interval was over the range 0.1-15.0mgl(-1) and a large list of interferents were assayed; the chemical robustness was also tested. The method was applied to different type of samples: namely, pharmaceutical formulations, a photographic solution and irrigation and residual superficial waters.

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.

Prediction of the chemiluminescent behaviour of phenols and polyphenols.

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.

Simultaneous dissolution profiles of two drugs, sulfadiazine-trimethoprim and amitriptyline-perphenazine, in solid oral dosage forms by a FIA manifold provided with a single spectrophotometric detector.

The simultaneous determination of two dissolution profiles wih the aid of a flow injection analysis assembly has been applied to: (a) sulfadiazine-trimethoprim in tablets and (b) amitriptyline-perphenazine in sugar coated pills. The selected combinations are drugs which have overlapping UV-vis spectra. The officially proposed procedure from the pharmacopoeias has been adapted for the FIA methodology and derivative spectrophotometry and zero crossing. Preliminary experiments on the suitability of the simultaneous determination of both drugs were performed. The empirical profiles were adjusted by regression analysis using different approaches. The 3-parameter plot method was finally selected as the most suitable for the sulfadiazine-trimethoprim and the 4-parameter equation plot for amitriptyline-perphenazine.

Simultaneous dissolution profiles of two drugs in pharmaceutical formulations by an FIA manifold.

This article deals with the simultaneous determination of dissolution profiles of two drugs with overlapped spectra, present in the same pharmaceutical formulation. The official procedure for the dissolution profile is adapted to the continuous-flow methodology; the dissolution vessel is connected to an FIA manifold, in which the sample aliquots from the dissolution vessel are treated in order to adjust to the suitable pH and dilution degree to be monitored. The resulting solution is injected into the carrier stream, an acetic acid-acetate buffer at pH 4.3 and forced to the flow-cell of the spectrophotometer. The simultaneous determination of both profiles is based on the first derivative spectra and the zero-crossing mathematical procedure. The empirical profile of the curve is adjusted by regression using different approaches; the three-parameter plot method is selected. The analytical errors, when the concentration of one drug is very low or very high, are also checked. A binary mixture in commercially available formulations of solid oral administration of sulphametoxazole and trimethoprim is presented.

Determination of tannic acid by direct chemiluminescence in a FIA assembly.

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 mug 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.

Determination of nitrite by inhibition of the chemiluminescence of acriflavine in a flow-injection assembly.

The indirect determination of nitrite was performed with a flow-injection assembly on the basis of the inhibition of the analytical output obtained in a luminometer by oxidation of acriflavine. The acriflavine solution merged with the nitrite and the resulting mixture was injected into a pure water stream. This solution merged with the oxidant solution (potassium permanganate in sulfuric acid medium) and the resulting chemiluminiscence was affected (inhibited) by the presence of nitrite after reaction with the aminoacridine. The method was applicable over the range 10-800 microg l(-1) of nitrite with a correlation coefficient of 0.9960. The relative standard deviation was 1.4% and the throughput was 76 samples h(-1). The influence of foreign substances was also tested. A solid-phase reactor, filled with Amberlite IRA-900, was inserted in the assembly for the on-line preconcentration of nitrite; the analytical output resulted in an increase of up to 11.5-fold. The method was applied to the determination of nitrites in residual waters, industrial formulations and soil samples.

o-Dianisidine: a new reagent for selective spectrophotometric, flow injection determination of chlorine.

A flow injection analysis (FIA) procedure for the determination of free chlorine in industrial formulations and water samples is proposed. The manifold is provided with a gas-diffusion unit which permits the removal of interfering species and also the preconcentration of chlorine. The determination of chlorine is performed on the basis of the oxidation by o-dianisidine as a chromogenic reagent to a coloured product which can be monitored at 445 nm. The method (for a preconcentration step of 60 s) is linear over the range 0.04-1.00 mg l(-1) of chlorine, the limit of detection is 0.04 mg l(-1), the reproducibility of the procedure (as RSD of the slope) is 3.7% for a series of four independent calibrations, the precision (as RSD of a series of 30 continuous FIA peaks of 0.56 mg l(-1) of chlorine) is 1.4% and the sample throughput is 40 h(-1). A detailed comparative study of the analytical characteristics of a single mono-channel reverse FIA assembly and the same system but provided with a Fluoropore membrane filter of 0.5 microm pore size was performed to check the advantages of the new approach in terms of sensitivity, selectivity and limit of detection.

Enhanced chemiluminescent determination of chloramphenicol and related nitro compounds by 'on-line' photochemical reaction.

The viability of tandem photochemical reaction-chemiluminescence detection was studied for a heterogeneous family of nitro compounds using chloramphenicol as a test substance. The 'on-line' chemical photodegradation of chloramphenicol was performed in a flow injection assembly by using a photoreactor consisting of a 725 cm x 0.5 mm id piece of PTFE tubing coiled around an 8 W low-pressure mercury lamp. Photodegraded chloramphenicol was detected by oxidizing photo-fragments from the parent compound and their subsequent reaction with a luminol-Co(II) system. The calibration graph was linear up to 3 x 10(-5) mol l-1 chloramphenicol, the limit of detection was 3 x 10(-9) mol l-1, the relative standard deviation was 1.8% for 2 x 10(-6) mol l-1 of the drug and the sample throughput was 60 h-1. The proposed method was used to determine chloramphenicol in pharmaceutical formulations and its application to other related nitro compounds was studied.

Flow-injection biamperometric determination of epinephrine.

A flow-injection manifold is proposed for the determination of epinephrine. The experimental procedure is based on the indirect biamperometric detection of the drug by using Fe(III)-Fe(II) as an indicating redox system and a flow-through detector with two polarized Pt wire electrodes. The calibration graph is linear over the range 0.3-20 micrograms ml-1 of epinephrine. The relative standard deviation for the determination of 10 micrograms ml-1 of epinephrine is 1.5% (n = 25) and the sample throughput is 153 h-1. The method was applied to the determination of epinephrine in two commercially available pharmaceutical preparations.

Spectrofluorimetric determination of vitamin K3 by a solid-phase zinc reactor immobilized in a flow injection assembly.

The spectrofluorimetric determination of vitamin K3 (menadione) using a flow injection (FI) assembly provided with a solid-phase reactor with immobilized zinc is described. The naphthohydroquinone was produced by means of two coupled steps in the FI system: hydrolysis of the sodium sulfite derivative of the menadione in a basic medium and reduction of the generated menadione in the zinc reactor in an acidic medium. The fluorescent product was monitored spectrofluorimetrically (lambda ex 325 nm; lambda em 425 nm). The calibration graph was linear over the range 0.1-18 micrograms ml-1 with a reproducibility of 1.6%; the limit of detection was 0.005 microgram ml-1 and the sample throughput was 70 h-1. The influence of foreign compounds was studied and the procedure was applied to the determination of vitamin K3 in three different pharmaceutical formulations.

High-pressure flow-injection assembly. Indirect determination of glycine by atomic absorption spectrometry.

A procedure for the determination of glycine is described. The method is based on the reaction of the analyte with finely powdered, solid copper(II) carbonate in a continuous-flow assembly. The optimum experimental conditions of pH, temperature, sample volume, flow-rate, column length and internal diameter, and the linear range of calibration, were studied. Interference from foreign substances that accompany this amino acid in pharmaceutical formulations was studied, and the method was applied to the determination of glycine.

FIA determination of chlorhexidine by means of the precipitation with Cu(II).

The determination of chlorhexidine in pharmaceutical formulations is carried out using flow injection analysis (FIA) with measurement by atomic absorption spectrometry (AAS). The method is based on the formation of a copper-biguanide complex precipitate when the sample is injected into an ammoniacal copper solution. The precipitate is retained on a plastic or paper filtering device. A nitric acid stream dissolves the precipitate and carried the Cu(II) to the AAS detector. The chlorhexidine is determined over the range 5-20 ppm. The influence of interfering substances is investigated.