Analytical Letters

Govindarajan, Sridhar; McNeil, Calum J.

doi: 10.1080/00032710902721972pmid: N/A

Abstract The selectivity of glutamate microdisc biosensors coated with poly(o-phenylenediamine) (PPD) as the interference-rejecting layer against ascorbic acid was observed to be very low. Enhancement in the selectivity was noticed when the electropolymerization potential for the polymerization of the o-phenylenediamine monomer was decreased from 0.65 V to 0.40 V vs. Ag/AgCl. The selectivity coefficient increased from −34.93±3.75% (n = 5) to 53.05 ± 4.33% (n = 3). Decreasing the polymerization potential decreases the rate of formation of the polymer and improves the compactness of the polymer layer formed, thereby increasing the selectivity of the electrodes.

Jing-hua, Yu; Fu-wei, Wan; Ping, Dai; Shen-guang, Ge; Bo, Li; Jia-dong, Huang

doi: 10.1080/00032710902722004pmid: N/A

Abstract Flow injection chemiluminescence (FI-CL) with molecularly imprinted polymer (MIP) was applied to determine fenfluramine. The fenfluramine-imprinted polymer was prepared with acrylamide (AM) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as cross-linker. Methyl and sulfonic group were introduced to rhodanine matrix, and a novel rhodanine ramification 3MORASP was synthesized by the author, and it was used as chemiluminescence reagent. 3-(3′-Methoxyphenyl)-5(2′-sulfonylphenylazo)-rhodanine (3MORASP), first synthesized by the authors, was used as chemiluminescence (CL) reagent. The novel flow path of FI-CL was designed, which made three merged streams of reactants injected into MIP column move through different pathways simultaneously. Fenfluramine was detected based on the reaction of fenfluramine, 3MORASP, and potassium permanganate in an acidic medium. The CL intensity was correlated linearly with the concentration of fenfluramine over the range of 1.0 × 10−7 to 5.0 × 10−6 g · mL−1, and the detection limit was 9.48 × 10−9 g · mL−1. The relative standard deviation (RSD) was 2.4% for determination of 1.0 × 10−6 g · mL−1 fenfluramine (n = 11). This method was successfully applied to the determination of fenfluramine in weight-reducing tonic.

Stefan-van Staden, Raluca-Ioana; Ozoemena, Kenneth I.

doi: 10.1080/00032710902722012pmid: N/A

Abstract An amperometric immunosensor, based on carbon paste impregnated with solubilized antidideoxyinosine (from rabbit lyophilized powder, whole antiserum) has been constructed for the assay of anti-HIV agent dideoxyinosine (didanosine, DDI). The amperometric immunosensor was reliably used for dideoxyinosine assay in the 900 pmol/L to 9 nmol/L concentration range, with a detection limit of 180 pmol/L, at E = +1.04 V vs. Ag/AgCl. The construction of the immunosensor is reproducible. Its surface can be easily renewed by simple polishing on an aluminium paper. The new amperometric immunosensor is reliable for the assay of 2′,3′-dideoxyinosine in raw material as well as in its pharmaceutical formulation (Videx tablets).

Stefan-van Staden, Raluca-Ioana; Suzan Nhlapo, Nontete; Frederick van Staden, Jacobus; Aboul-Enein, Hassan Y.

doi: 10.1080/00032710902722020pmid: N/A

Abstract Maltodextrins with different dextrose equivalent (DE) values (maltodextrin I: DE 4.0–7.0; maltodextrin II: DE 13.0–17.0; maltodextrin III: DE 16.5–19.5) were used for the design of three enantioselective, potentiometric membrane electrodes (EPMEs) for the assay of S-ketoprofen. The linear concentration ranges for the proposed electrodes were 10−10 to 10−8, 10−9 to 10−5, and 10−10 to 10−7 mol/L, with slopes of 58.0, 58.67, and 58.93 mV/decades of concentration and limits of detection of 1.49 × 10−8, 2.43 × 10−8, and 4.19 × 10−11 mol/L for EPMEs based on maltodextrin I, II, and III, respectively. The EPMEs showed high reliability and effectiveness for the enantioanalysis of S-ketoprofen raw material and its pharmaceutical formulations.

Wang, Yiting; Yu, Lei; Zhu, Ziqiang; Zhang, Jian; Zhu, Jianzhong

doi: 10.1080/00032710802677159pmid: N/A

Abstract In this work, we report the development of a highly sensitive and stable uric acid sensor based on the synergic action of multiwalled carbon nanotubes (MWNTs) and ZnO nanoparticles. MWNTs were first cast on pyrolytic graphite (PG) wafers. ZnO nanoparticles were then decorated onto the negatively charged MWNTs via the Vapor Liquid Solid (VLS) growth. Uricase was immobilized on the ZnO nanoparticles surface because of their large differences in the isoelectric point (IEP). Last, a cationic polydiallyldimethylammonium chloride (PDDA) layer was coated onto the uricase-contained ZnO nanoparticle layer and resulted in the PDDA/uricase/ZnO/MWNTs multilayer structure. The unique multilayer structure provides a favorable microenvironment to keep the bioactivity of uricase, which led to rapid amperometric response toward uric acid. Amperometric detection of uric acid was carried out at 320 mV (vs. SCE) in 0.05 mol/L (M) phosphate buffer solution (pH 6.8). For the sensor, a wide linear response range of 5.0 µM to 1 mM with a linear sensitivity of 393 mA cm−2M−1, a detection limit of 2.0 µM (3σ), and a long-term stability of 160 days can be obtained by using differential pulse voltammetry (DPV). Testing results in human urine obtained from the sensors were also compared with the data obtained by spectrometry. For five samples with different concentrations of urine, the relative deviations between them were smaller than 3.8%. The recovery was between 96.5 and 104.0%.

Swati, M.; Srivastava, R.

doi: 10.1080/00032710802677175pmid: N/A

Abstract A new absorbance-based enzymatic biosensor for determination of urea (in the range 0.01 to 6.7 mM) is described. Quantification using cresol red dye, immobilized in the nanofilm coatings assembled on alginate microspheres to immobilize the urease enzyme, has been accomplished using ratiometric absorbance measurements. The effect of salt concentration in polyelectrolyte nanofilms (on the stability of dye molecules) and buffer pH (on the enzyme stability) are reported. The results demonstrate excellent stability of sensing assay within alginate microspheres. Urea-sensing experiments demonstrate the potential to develop an optical urea sensor that is stable over a month.

Anfossi, Laura; Baggiani, Claudio; Baravalle, Patrizia; Giovannoli, Cristina; Guzzella, Licia; Pozzoni, Fiorenzo

doi: 10.1080/00032710802677183pmid: N/A

Abstract A molecularly imprinted polymer recognizing the fungicide carbendazim was prepared using a mimicking template approach. Methyl-3-propylcarbamoyl-1H-benzimidazol-2-ylcarbamate was synthesized and used as a mimic template for polymer preparation. Selectivity of this polymer for carbendazim and structurally related substances (the template, fluberidazole, rabenzazole, thiabendazole, and benomyl and its two degradation products) was evaluated by liquid chromatography. Results demonstrate that imprinted polymer shows significant recognition properties for carbendazim, whereas the mimic and other carbendazim-related molecules are not recognized. This peculiar selectivity pattern can be explained as an imprinting effect due to the in situ formation of carbendazim from mimic degradation during the polymerization process.

Pharr, Daniel Y.; Tomsyck, J. A.

doi: 10.1080/00032710902721923pmid: N/A

Abstract The flow injection analysis of benzoyl peroxide using N,N,N,N-tetramethyl-p-phenylenediamine (TMPDA, also known as Wurster's reagent) and a solvent system including the surfactant sodium dodecyl sulfate (SDS) and cerium(IV) as a catalyst at pH 6.0 at 612 nm was investigated. The method was applied to the analysis of acne cream and flour. The study included a 26-metal-ion search for other possible methods of catalysis and a buffer study of SDS and cetyltrimethyl ammonium bromide (CTAB).