Determination of zinc in pharmaceutical products by use of a sequential injection analysis system.

A sequential injection analysis (SIA) system is proposed for the determination of zinc in pharmaceutical samples. The method is based on the spectrophotometric detection of zinc using xylenol orange as a colour reagent at 568 nm. The system can be used to monitor zinc at a frequency of 30 samples h(-1) with an average recovery of +/-98.5% and a relative standard deviation of less than 1%. A linear relationship between peak height and zinc concentration is obtained between 10 and 60 mg L(-1). The results obtained are in good agreement with those obtained by use of a standard method.

Amperometric biosensors/sequential injection analysis system for simultaneous determination of S- and R-captopril.

Two amperometric biosensors based on L- and D-amino acid oxidase, respectively, are proposed for the simultaneous detection of S- and R-captopril in a sequential injection analysis system (SIA). The linear concentration ranges are: 0.4-1.6 micromol/l (S-captopril) and 120-950 nmol/l (R-captopril) with detection limits of 0.2 and 15 nmol/l, respectively. The biosensors/SIA system can be used reliably on-line in synthesis process control, for the simultaneous assay of S- and R-captopril with a frequency of 34 samples/h.

Determination of zinc in pharmaceutical products using an electrodialyser incorporated into a flow system.

An electrodialyser unit has been designed, incorporated into the conduits of a flow injection (FI) system, and employed for the removal of interferences in the determination of zinc(II) in multivitamin tablets. The proposed system is fully computerised and is able to determine zinc(II) at a frequency of 18 samples/h with a sample interaction of 0.0015%. The calibration graph is linear between 1 and 20 mg/L. The detection limit is 0.998 mg/L. The results obtained for zinc(II) in multivitamin tablets with the proposed system compared favourably with those obtained with the standard manual AAS method.

Simultaneous detection of S and R captopril using sequential injection analysis.

A simultaneous detection sequential injection analysis (SIA) system is proposed for the determination of S and R captopril using a potentiometric, enantioselective membrane electrode based on maltodextrin (DE=14-17) for the assay of S-captopril and an amperometric biosensor for the assay of R-captopril. The proposed SIA system can be utilized reliably for the on-line simultaneous detection of the enantiomers in the synthesis process at a rate of 38 samples per hour in the following linear concentration ranges: 100-1000 nmol/l (R-captopril) and 1-1000 mumol/l (S-captopril) with a RSD better than 0.009% (n=10).

Evaluation of different SIA sample-buffer configurations using a fluoride-selective membrane electrode as detector.

The peak profiles of four different buffer-sample SIA configurations, e.g. buffer-sample; sample-buffer; buffer-sample-buffer and sample-buffer-sample with the last two in the sandwich mode were evaluated with a fluoride-selective membrane electrode as detector. The best response characteristics and peak shapes as well as recovery and precision values were obtained for the buffer-sample configuration. For low concentration levels, sandwich SIA configurations are more suitable, when optimum buffer and pH are used. The utilisation of a cheap electrolyte with a minimum consumption of buffer and a cheap, robust instrumentation made the SIA system suitable for on-line determination of fluoride.

S-perindopril assay using a potentiometric, enantioselective membrane electrode.

A potentiometric, enantioselective membrane electrode based on graphite paste (graphite powder and paraffin oil) has been constructed. The graphite paste is impregnated with a 10(-3) mol/L 2-hydroxy-3-trimethylammoniopropyl-beta-cyclodextrin (as chloride salt) solution. The potentiometric, enantioselective membrane electrode can be used reliably for enantiopurity tests of S-perindopril using a chronopotentiometric (zero current) technique, in the 10(-5)-10(-2) mol/L concentration range (detection limit 5 x 10(-6) mol/L), with an average recovery of 99.58% (RSD = 0.33%). The enantioselectivity was determined over R-perindopril and D-proline. The response characteristics of the enantioselective, potentiometric membrane electrode were also determined for R-perindopril. It was shown that L-proline is the main interfering compound. The surface of the electrode can be regenerated simply by polishing, obtaining a fresh surface ready to be used in a new assay.

A new construction for a potentiometric, enantioselective membrane electrode--its utilization to the S-captopril assay.

A novel potentiometric, enantioselective membrane electrode based on graphite paste (graphite powder and paraffin oil) has been constructed. The graphite paste is impregnated with 2-hydroxy-3-trimethylammoniopropyl-beta-cyclodextrin (as chloride salt) solution, 10(-3) mol l(-1). The potentiometric, enantioselective membrane electrode can be used reliable for S-captopril assay as raw material and from Novocaptopril tablets, using a chronopotentiometry (zero current) technique, in the 10(-6)-10(-2) mol l(-1) concentration range (detection limit 2 x 10(-7) mol l(-1)), with an average recovery of 99.99% (RSD=0.05%). The enantioselectivity was determined over R-captopril and D-proline. The response characteristics of the enantioselective, potentiometric membrane electrode were determined also for R-captopril. It was shown that only L-proline is the main interfering compound. The surface of the electrode can be regenerated by simply polishing, obtaining fresh surface ready to be used in a new assay.