Sequential injection chromatographic determination of paracetamol, caffeine, and acetylsalicylic acid in pharmaceutical tablets.

In this contribution, a new separation method for simultaneous determination of paracetamol, caffeine, acetylsalicylic acid, and internal standard benzoic acid was developed based on a novel reversed-phase sequential injection chromatography (SIC) technique with UV detection. A Chromolith Flash RP-18e, 25-4.6mm column (Merck, Germany) and a FIAlab 3000 system (USA) with an 8-port selection valve and a 5 mL syringe were used for sequential injection chromatographic separations in our study. The mobile phase used was acetonitrile-(0.01 M) phosphate buffer (10:90, v/v) pH 4.05, flow rate 0.6 mL min(-1). UV detection was at 210 and 230 nm. The validation parameters showed good results: linearity (r >0.999) for all compounds, detection limits in the range 0.3-0.8 microg mL(-1), repeatability (RSD) of peak heights between runs in the range 1.10-4.30% at three concentration levels and intra-day repeatability of the retention times in the range 0.28-0.43%. The analysis time was <6 min. The method was found to be applicable for the routine analysis of the active compounds paracetamol, caffeine, and acetylsalicylic acid in pharmaceutical tablets.

Design and development of a multichannel potentiometer for monitoring an electrode array and its application in flow analysis.

A versatile potentiometer that works with electrode arrays in flow injection and/or monosegmented flow systems is described. The potentiometer is controlled by a microcomputer that allows individual, sequential multiplexed or random accesses to eight electrodes while employing only one reference electrode. The instrument was demonstrated by monitoring an array of seven flow-through ion-selective electrodes for Ag+ and for three electrodes for Cl(-), Ca2+ and K+. The figures of merit of the individual and multiplexed (summed) readings of the electrode array were compared. The absolute standard deviation of the measurements made by summing the potential of two or more electrodes was maintained constant, thus improving the precision of the measurements. This result shows that an attempt to combine the signals of the electrodes to produce a more intense signal in the Hadamard strategy is feasible and accompanied by a proportional improvement in the precision of individual measurements. The preliminary tests suggest that the system can allow for 270 determinations per hour, with a linear range from 1.0 x 10(-2) to 1.0 x 10(-4) mol l(-1) for the three different analytes. Detection limits were estimated as 3.1 x 10(-5), 3.0 x 10(-6) and 1.0 x 10(-5) mol l(-1) for Cl(-), Ca2+ and K+, respectively.

A flow system with a conventional spectrophotometer for the chemiluminescent determination of lactic acid in yoghurt.

A flow-based analytical procedure for lactate determination in yoghurt by chemiluminescence using a conventional UV-Vis spectrophotometer as detector is described. The radiation source was switched off. The flow cell was machined in acrylic with a 1 mm path length and a 80 mm(2) surface and was positioned 2 mm distal of the photodetector (100 mm(2) sensible area) in order to improve detection. The flow network computer-controlled comprised a set of three-way solenoid valves assembled to implement the multicommutation approach. The chemiluminescence was obtained by using the reaction of luminol with hydrogen peroxide, catalyzed by hexacyanoferrate (III) after enzymatic reaction with lactate. The lactate oxidase enzyme was immobilized on porous silica beads (glass aminopropyl, SIGMA). The signal generated by the spectrophotometer reaction was read by the microcomputer and stored as a function of time for further treatment. Immobilization condition, enzyme concentration, temperature, pH, stability of the enzymatic reactor, and flow rates were investigated. The feasibility of the system was ascertained by analyzing a set of yoghurt samples. Results were in agreement with those obtained by a conventional method (Boehringer UV-Kit), and no significant difference at 95% confidence level was observed. A linear response within 10-125 mg l(-1)l-lactate, a 1.9% standard deviation (n=10), and an analytical throughput of 55 determinations per hour were achieved.

Tetracycline, oxytetracycline and chlortetracycline determination by flow injection potentiometry.

This paper describes tetracycline (TCH), oxytetracycline (OTCH) and chlortetracycline (CTCH) determination by flow injection potentiometry. In the flow system proposed TC samples are inserted in a carrier solution and converged with a Cu(II) solution of known concentration; the Cu(II) decrease due to its complexation with tetracyclines (TC) was monitored. The detector used was a homogeneous crystalline CuS/Ag2S double membrane tubular electrode with increased sensitivity. The present system allows tetracyclines determinations within a 48.1-4.8 x 10(3) ppm for TCH, 49.1-4.9 x 10(3) ppm for OTCH and 51.5-5.1 x 10(3) ppm for CTCH and a precision better than 0.4% for the three TC species. This procedure accomplishes 150-200 samples h(-1) with a Cu(II) consumption of about 13 microg determination(-1).

Development of a tubular periodate electrode for flow-injection determination of glycerol.

Periodate electrodes without inner reference solution based on tetraoctylammonium periodate plus solvent mediator (dibutyl phthalate or 2-nitrophenyl octylether) were constructed. Linear dynamic range, practical detection limit, slope, stability, selectivity coefficients, pH dependence, response time and lifetime were evaluated. A tubular version was further developed and coupled to a flow-injection system for glycerol determination in samples relevant to the industrial production of soaps, detergents and similar. The method involves glycerol oxidation by periodate with potentiometric evaluation of its consumption. The influence of oxidizing agent concentration (10(-5)-10(-2)M NalO(4)), ionic strength (0.0-1.0M Na(2)SO(4)) and mean resident time were investigated and the feasibility of using a single-fine manifold was discussed. The proposed system handles about 40 samples/hr, is very stable and suitable to industrial control. Results within the 1000 and 5000 mg/l range glycerol are precise (r.s.d. <0.005) and in fair agreement with conventional procedures. Baseline drift or noise is not observed and a thermostat water bath is not required. A noteworthy feature is the almost linear relationship between glycerol concentration and recorded peak height which is a consequence of combined effects of reaction kinetics and electrode Nernstian response.

[Benzoate determination in medicinal syrups with a PVC membrane ion selective electrode without inner reference solution]. / Dosage de benzoate dans des sirops médicamenteux à l'aide d'électrodes sélectives à membrane de PVC sans solution de référence interne.

Two electrodes sensitives to benzoate ion, without inner reference solution, in which tetraoctylammonium benzoate in dibutylphtalate (type A) or 2-nitrophenyloctylether (type B) immobilized in PVC are used in membranes, applied on a conductive support, were prepared. The response characteristics and behaviour of this low-cost electrodes are presented. The analytical application possibilities are discussed and shown as practical examples on analyses of the ion in medicals syrups.

Vitamins B1 and B6 tubular electrodes as FIA detectors; their use in the analysis of pharmaceutical products.

Ion-selective electrodes without an inner reference solution and tubular potentiometric detectors for the determination of vitamins B1 and B6 in pharmaceutical preparations by flow injection analysis (FIA) are reported. The membranes were prepared with the vitamin tetra(2-chlorophenyl)borate (TCPB) dissolved in o-nitrophenyloctyl ether (o-NPOE) and immobilized on PVC. Intrinsic behaviour of the tubular detectors was assessed using a low-dispersion single-channel FIA manifold and was compared with conventionally-shaped electrodes using the same membrane. Data obtained in the determination of vitamins B1 and B6 in pharmaceutical preparations with a double channel flow injection manifold incorporating the tubular detectors are presented and compared with those obtained by the U.S. Pharmacopeia method and by direct potentiometry with conventionally-shaped electrodes.

Solid-state PVC flow-through benzoate electrode.

A general construction procedure for conventional shape ion-selective electrodes based on a conductive support prepared with a mixture of a non-conductive epoxy and graphite was used in the preparation of a flow-through benzoate electrode to be used as potentiometric detector in flow injection analysis manifolds. The membranes were prepared from tetraoctylammonium benzoate in o-nitrophenyloctylether immobilized on PVC. The results of the assessment of the tubular electrodes behaviour in low dispersion manifolds against that of conventional electrodes with the same membrane are reported. Data obtained with a double-channel flow injection manifold incorporating these tubular detectors for benzoate determinations in several commercially available pharmaceutical preparations are also presented.