Rahel Girmai Bokretsion

Simultaneous determination of creatine and creatinine using amperometric biosensors.

In order to determine creatine and creatinine amperometric biosensors were proposed. A bienzymatic biosensor based on creatinase (CI) and sarcosine oxidase (SO) was used for the assay of creatine and a trienzymatic biosensor based on CI, SO and creatininase (CA) for the assay of creatinine. The linear concentration ranges are of pmol l(-1) to nmol l(-1) magnitude order, with very low limits of detection. The biosensors proved high reliability for determination of creatine and creatinine as raw material, and in the pharmaceutical formulation.

Simultaneous determination of L- and D-methotrexate using a sequential injection analysis/amperometric biosensors system.

A sequential injection analysis (SIA) is proposed for the simultaneous determination of L- and D-methotrexate (Mtx) using amperometric biosensors as detectors. A SIA system is proposed due to the highest precision and accuracy and lower consumption of sample and buffer. The amperometric biosensors used as detectors in SIA system were based on L-amino acid oxidase (L-AAOD) or/and L-glutamate oxidase (L-Glox) and horseradish peroxidase (HRP) for the assay of L-Mtx and D-amino acid oxidase (D-AAOD) and HRP for the assay of D-Mtx were selected. The linear concentration ranges are of pmol/l to nmol/l magnitude order, with very low limits of detection. The SIA/biosensors system can be used reliably on-line in synthesis process control, for the simultaneous assay of L- and D-Mtx with a frequency of 34 samples per hour.

Simultaneous determination of l- and d-carnitine using a sequential injection analysis/amperometric biosensors system

A sequential injection analysis (SIA) system is described for the simultaneous determination of L-and D-carnitine using amperometric biosensors as detectors. The SIA system was used, because of its high precision, accuracy and low sample and buffer consumption. The biosensors were designed using physical and chemical immobilization of L-amino acid oxidase and horseradish peroxidase (HRP) for the assay of L- carnitine, and D-amino acid oxidase and HRP for the assay of D-carnitine. The linear concentration ranges are in the pmol/l to nmol/l magnitude order, with very low limits of detection. The biosensors/SIA system was used reliably for on-line process control of the enantiopurity of carnitine with a frequency of 34 samples per hour.

Immunosensor for the determination of azidothymidine: its utilization as detector in a sequential injection analysis system.

An amperometric immunosensor based on graphite paste (graphite powder and paraffin oil) has been constructed for the assay of azidothymidine (AZT). The graphite paste is impregnated with anti-AZT. The immunosensor can be reliably used for the assay of AZT in its pharmaceutical formulation. The potential used for AZT assay was 435 mV vs Ag/AgCl electrode. The surface of the immunosensor can be regenerated by simply polishing, obtaining fresh immunocomposite ready to be used in a new assay. Due to its reliability, the immunosensor was successfully used as a detector in a sequential injection analysis system, and gave reliable results for on-line assay of AZT purity in raw material and AZT contents in pharmaceutical formulations.

Diamond Paste Based Immunosensor for the Determination of Azidothymidine

Abstract An amperometric immunosensor, based on diamond paste (diamond powder and paraffin oil), has been constructed for the assay of azidothymidine (AZT). The diamond paste is impregnated with anti-AZT. The immunosensor can be used reliably for the assay of azidothymidine in its pharmaceutical formulations. The potential used for azidothymidine assay was + 240 mV vs. Ag/AgCl electrode. The surface of the immunosensor can be regenerated by simply polishing, thereby obtaining fresh immunocomposite ready to be used in a new assay. The new amperometric immunosensor, based on diamond paste, gives reliable results for the assay of AZT as raw material and from its pharmaceutical formulation.

Simultaneous Determination of Creatine and Creatinine using Monocrystalline Diamond Paste–Based Amperometric Biosensors

Abstract In order to determine creatine and creatinine, amperometric diamond paste biosensors were proposed. A bienzymatic biosensor based on creatinase and sarcosine oxidase was used for the assay of creatine and a trienzymatic biosensor based on creatinase, sarcosine oxidase, and creatininase was proposed for the assay of creatinine. The linear concentration ranges are of fmol/L magnitude order, with very low limits of detection. The biosensors proved to be highly reliable for determination of creatine and creatinine as raw materials in pharmaceutical formulations as well as in serum samples.

Determination of l- and d-enantiomers of methotrexate using amperometric biosensors

In order to determine the enantiopurity of methotrexate (Mtx), seven biosensors were proposed for the assay of L-Mtx and three biosensors for the assay of D-Mtx. The biosensors were designed using physical and chemical immobilization of glutamate oxidase and/or L-amino acid oxidase (L-AAOD) and/or horseradish peroxidase (HRP) for the assay of L-methotherexate, and D-amino acid oxidase (D-AAOD) and HRP for the assay of D-Mtx. Electrode characteristics were obtained and compared for the different carbon paste based biosensors. The linear concentration ranges for the proposed biosensors were in the ranges of fmol l(-1) to pmol l(-1), magnitude order with limits of detection in the fmol l(-1) to nmol l(-1) concentration range. All biosensors were successful for the determination of the enantiopurity of Mtx as raw material, and in its pharmaceutical formulations (tablets and injections).

Determination of Creatine and Creatinine Using a Diamond Paste Based Electrode

Abstract A diamond paste based electrode is proposed for the simultaneous assay of creatine and creatinine. Natural diamond is used for the construction of the electrode. The electrode can be reliably used for creatine and creatinine assay in pharmaceutical formulations and serum samples. The potentials used for the assay of creatine and creatinine were 580 mV and 500 mV vs. Ag/AgCl electrode, respectively. The linear concentration ranges for the proposed electrode were in the ranges of 1–500 pmol/L (creatine) and 0.01–100 nmol/L (creatinine) with low limits of detection and RSD values better than 0.21% (n = 10).

Utilization of maltodextrin-based enantioselective, potentiometric membrane electrodes for the enantioselective assay of S-flurbiprofen

Abstract Three enantioselective, potentiometric membrane electrodes (EPMEs) based on carbon paste impregnated with different maltodextrins [dextrose equivalent (DE) (DE 4.0–7.0 (I), 13–17 (II), 16.5–19.5 (III)], were proposed as chiral selectors for the assay of S‐flurbiprofen raw materials and from its pharmaceutical formulation, Froben 100® tablets. The best response and enantioselectivity were obtained when maltodextrin with lower DE was used for the electrode design. The three EPMEs showed very low detection limits. The surfaces of the electrodes are easily renewable by simply polishing on an alumina paper.

Determination of l- and d-Enantiomers of Carnitine Using Amperometric Biosensors

Abstract In order to determine the enantiopurity of carnitine, three biosensors were proposed for the assay of l-carnitine and three biosensors for the assay of d-carnitine. The biosensors were designed using physical and chemical immobilization of l-amino acid oxidase and/or horseradish peroxidase for the assay of l-carnitine, and d-amino acid oxidase and horseradish peroxidase for the assay of d-carnitine. Electrode characteristics were obtained and compared for the different carbon paste biosensors. The linear concentration ranges for the proposed biosensors were in the fmol/L to nmol/L magnitude order. The biosensors proved high reliability for the determination of the enantiopurity of carnitine as raw material, and in its pharmaceutical formulations.