0000000000040245
AUTHOR
J. V. García Mateo
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 60degreesC and at flow-rate of 7.5 ml min(-1). The complete cycle lasted 35 s, which resulted in a sample flow trough of 103 h(-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 30 Rg l(-1). The dynamic int…
Selective chlorine determination by gas diffusion in a tandem flow assembly and spectrophotometric detection with o-dianisidine
Abstract A fast, selective, sensitive and automated method for determination of free chlorine in industrial formulations and water samples is proposed. The automation of the flow assembly is based on the “tandem flow” approach, which uses a set of solenoid valves acting as independent switches. The operating cycle for obtaining a typical analytical transient signal can easily be programmed by means of friendly software running in the Windows environment. The manifold is provided with a gas diffusion unit which permits the removal of interfering species as well as concentrating the chlorine. The determination of chlorine is performed on the basis of the oxidation of o-dianisidine as the colo…
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 with 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…
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 s…
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 550 cm long x 0.8 mm ID piece of PTFE tubing helically coiled around an 8 W 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 be…
Enhanced flow-injection–chemiluminometric determination of sulphonamides by on-line photochemical reaction
Abstract The viability of the tandem photochemical reaction-chemiluminescence detection has been studied for an heterogeneous group of sulphonamides (sulphamethoxazole, sulphadiazine, sulphamerazine, sulphamethoxypyridazine, sulphacetamide, sulphadimidine, sulphanilamide, sulphathiazole and sulphaguanidine) using sulphamethoxazole (whose chemiluminescent behaviour has not been previously reported) as a test substance. The ‘on-line’ photochemical-reaction of sulphonamides provides an enhancing influence on the chemiluminometric response of the drugs during their oxidation by potassium permanganate in sulphuric acid medium (sulphamethoxazole, sulphacetamide, sulphadimidine and sulphanilamide …
Study of various indicating redox systems on the indirect flow-injection biamperometric determination of pharmaceuticals
Abstract The reversible redox couples (Fe(III)/Fe(II); Ce(IV)/Ce(III); Fe(CN) 6 3– /Fe(CN) 6 4− ; I 2 /I − ; Br 2 /Br − and VO 3 − /VO 2+ ) were studied as indicating redox systems for biamperometric determination of paracetamol in a flow injection assembly. Considering the selectivity of assayed systems against excipients and antioxidants that typically are presented in pharmaceutical formulations (e.g. sucrose, glucose, ascorbic acid and hydrogen sulphite) the systems Fe(III)/Fe(II) and VO 3 − /VO 2+ were selected for the determination of the drug. The sample was injected into a carrier which merged with the oxidant stream where the drug was oxidised by excess oxidant. The observed signal…
SIGNAL PROCESSING ALGORITHM FOR SCHLIEREN EFFECT CORRECTION IN FLOW ANALYSIS
Due to the radial refractive index gradients that sometimes develop in flow cells during the travelling of the samples through them, the absorbance records obtained in such conditions have a strange shape, particularly at low analyte levels. To correct this phenomenon, called Schlieren effect, a simple and reliable signal processing algorithm is described in correlation to the detector characteristics of noise. The algorithm is illustrated in nitrite and nitrate determinations with proflavin from more real samples. It has a solid theoretical support and involves the subtraction from the sample records of a smoothed signal, acquired by working with a blank solution.
New flow-multicommutation method for the photo-chemiluminometric determination of the carbamate pesticide asulam
This paper deals with a straightforward automated method for the determination of asulam in water based on the use of a flow manifold including three computer-controlled solenoid valves. The method involves irradiating on an aqueous solution of asulam in glycine buffer at pH 8.3 with UV light during 90 s, then follows the oxidation with potassium permanganate in a sulphuric medium and chemiluminescence-based detection of the resulting photoproducts. The limit of detection thus achieved is 40 mug l(-1). The detector response is linear up to a 5 mg l(-1) asulam concentration and the throughput is 30 samples h(-1). In parallel tests, oxidation with alkaline ferricyanide was also assessed and t…
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.
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 wh…
Determination of Phenol by Preconcentration‐Direct Chemiluminescence in a FIA Assembly
Abstract The determination of phenol in water samples is proposed with the aid of a flow‐injection system. The analytical procedure is based on the direct chemiluminometric emission by oxidation of the analyte with potassium permanganate in acidic medium. The flow assembly is provided with a solid‐phase reactor filled with a resin type XAD‐4 for analyte preconcentration. A large study of potential interferences, namely, amino acids reaching water through degradation of organic matter; metals and inorganic metal ions typically present in water interfering with the CL emission of the parent compound, was performed. The calibration graph was linear over the phenol concentration range 1.0–20.0 …
Flow injection biamperometric determination of metronidazole with on-line photodegradation
Abstract The determination of metronidazole is performed in a flow injection assembly, provided with a 40 W low pressure mercury lamp and a home-made biamperometric flow-cell furnished with two platinum electrodes polarized at 100 mV. The sample solution after being irradiated is inserted into a pure water stream. It then merges with an in situ mixed solution containing potassium iodide in sulphuric acid. The calibration graph was linear over the range 0.2–8.0 mg l −1 metronidazole; the 3 σ limit of detection was 0.008 mg l −1 ; the relative standard deviation was 0.6% (for 4 mg l −1 n = 13) and the sample throughput 50 h −1 . The influence of foreign compounds is slight and the method is …
FI-on line photochemical reaction for direct chemiluminescence determination of photodegradated chloramphenicol.
Abstract 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 cm×0.5 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 n…
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 …
Photochemical-chemiliminometric determination of aldicarb in a fully automated multicommutation based flow-assembly
[EN] A sensitive and fully automated method for determination of aldicarb in technical formulations (Temik) and mineral waters is proposed. The automation of the flow-assembly is based on the multicommutation approach, which uses a set of solenoid valves acting as independent switchers. The operating cycle for obtaining a typical analytical transient signal can be easily programmed by means of a home-made software running in the Windows environment. The manifold is provided with a photoreactor consisting of a 150 cm long x 0.8 mm i.d. piece of PTFE tubing coiled around a 20 W low-pressure mercury lamp. The determination of aldicarb is performed on the basis of the iron(III) catalytic minera…
Flow‐Injection Chemiluminescent Determination of Thiamine in Pharmaceutical Samples by On‐line Photodegradation
Abstract A simple, sensitive, and precise method for the determination of thiamine hydrochloride in a flow‐injection system is described. The method is based on the UV irradiation of thiamine in acid medium. Then, the photo‐fragments are oxidized by permanganate in acid medium, and the resultant chemiluminescent intensity is measured. The optimum conditions for the photoreaction and for the chemiluminescence emission were investigated. The method allows the determination of thiamine, over the range 0.05(LOD)–84 mg · l−1, with a throughput of 30 h−1, and a RSD (n, 20) at 20 and 0.5 mg · l−1 of the thiamine level of 2.5 and 1.3%, respectively. The method was applied to pharmaceutical preparat…
Selective flow-injection biamperometric determination of sulfur-containing amino acids and structurally related compounds
Abstract A simple and selective flow-injection method for the determination of cysteine and methionine is proposed. The method is based on the reaction of the amino acid with chloramine-T and the subsequent reaction of the excess of chloramine-T with an acidic solution of iodide producing a stoichiometric amount of tri-iodide (diminution of the flow-injection analysis (FIA) peak) which is determined biamperometrically using two platinum electrodes polarized at 100 mV. The calibration graph is linear up to 10 μg ml−1 of cysteine and 30 μg ml−1 of methionine; the limit of detection is 0.06 and 0.1 μg ml−1; the repeatability (also as percent of a series of 70 continuous FIA peaks of 5 μg ml−1 …
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 μg l−1 of nitrite with a correlation coefficient of 0.9960. The relative standard deviation was 1.4% and the throughput …
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 i…
Indirect Catalytic Spectrophotometric Determination of Metamizol Following Oxidation by Lead Dioxide Immobilized in A Polyester Resin Bed
Abstract A spectrophotometric-indirect procedure for the determination of metamizol is described. The method is based on the reaction of the drug in a solid-phase (lead dioxide immobilized in a polyester resin bed) in acidic media (perchloric acid 0.01 M as carrier). The lead dioxide reactor provides simultaneously an effective oxidation of the drug and a controlled liberation of Pb(II) which acts as catalyst on the reaction pyrogallol red-potassium persulphate; the oxidation of the red pyrogallol results in a less coloured solution. The decreased red colour (negative FIA peaks) is monitored at 520 nm. The calibration graph is linear in the interval 2–16 ppm in metamizol. The relative stand…
Flow injection biamperometric determination of chloramine-T in environmental, pharmaceutical and veterinary samples
Abstract A flow injection assembly for the determination of chloramine-T is proposed. The sample (213 μl) is inserted into the carrier, de-ionized water flowing at 4.1 ml min−1. This carrier merges with a mixture of potassium iodide and sulphuric acid, and the resulting solution flows to the flow cell through a reactor 66 cm long. The chloramine-T oxidises the iodide to tri-iodide. The resulting iodide/iodine ratio is biamperometrically tested. The calibration graph is linear up to 65 μg ml−1 chloramine-T; the limit of detection is 0.5 μg ml−1; the relative standard deviation (r.s.d) of the calibration slope is 2.8% for a series of eight independent calibrations. The r.s.d. of a series of 7…
Photoinduced chemiluminescence of pharmaceuticals
Abstract 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 cm × 0.5 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, carbox…
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 tann…
Flow-injection analysis study of the chemiluminescent behaviour of proflavine and acriflavine
Abstract The chemiluminescent behaviour of the amino acridines like acriflavine, and proflavin is reported. Different strong oxidants (potassium permanganate, cerium(IV), hexacyanoferrate(III), hydrogen peroxide in different media) were tested, and potassium permanganate in sulphuric acid medium was selected. The study of the experimental parameters affecting the oxidation and detection was performed with the aid of a FIA assembly. The calibration graph was applied over the range 0.05–12.0 μg ml −1 of acriflavine (regression coefficient 0.9957, and the calculated relative standard deviation (R.S.D., %) was 0.9; LOD 10 ng ml −1 and the sample throughput 48 h −1 . The study of interfering com…
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 sm…
Flow injection biamperometric determination of chloramphenicol and related nitro compounds by on-line chemical photodegradation
Abstract An unsegmented continuous-flow assembly for the determination of chloramphenicol is proposed. The determination is based on the on-line photodegradation of the drug in an NH4+/NH3 buffer at pH 10.4 by using a photoreactor consisting of a 697 cm long × 0.8 mm ID piece of PTFE tubing coiled around an 8 W low-pressure mercury lamp. Photodegraded chloramphenicol is detected by photolytic cleavage of nitrite from the parent compound as well as by organic oxidizing photofragments, and their subsequent reaction with iodide ion, which is monitored biamperometrically. Triiodide thus formed is detected in excess iodide solution by polarizing two platinum electrodes at 100 mV. The calibration…
Simultaneous dissolution profiles of two drugs in pharmaceutical formulations by an FIA manifold
Abstract 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 der…