Orawan Chailapakul

A flow injection method for the analysis of tetracycline antibiotics in pharmaceutical formulations using electrochemical detection at anodized boron-doped diamond thin film electrode

A method using flow injection (FI) with amperometric detection at anodized boron-doped diamond (BDD) thin films has been developed and applied for the determination of tetracycline antibiotics (tetracycline, chlortetracycline, oxytetracycline and doxycycline). The electrochemical oxidation of the tetracycline antibiotics was studied at various carbon electrodes including glassy carbon (GC), as-deposited BDD and anodized BDD electrodes using cyclic voltammetry. The anodized BDD electrode exhibited well-defined irreversible cyclic voltammograms for the oxidation of tetracycline antibiotics with the highest current signals compared to the as-deposited BDD and glassy carbon electrodes. Low detection limit of 10nM (signal-to-noise ratio = 3) was achieved for each drug when using flow injection analysis with amperometric detection at anodized BDD electrodes. Linear calibrations were obtained from 0.1 to 50mM for tetracycline and 0.5-50mM for chlortetracycline, oxytetracycline and doxycycline. The proposed method has been successfully applied to determine the tetracycline antibiotics in some drug formulations. The results obtained in percent found (99.50-103.01%) were comparable to dose labeled.

Flow-injection determination of iodide ion in nuclear emergency tablets, using boron-doped diamond thin film electrode.

The electrochemical determination of iodide was studied at boron-doped diamond thin film electrodes (BDD) using cyclic voltammetry (CV) and flow-injection (FI) analysis, with amperometric detection. Cyclic voltammetry of iodide was conducted in a phosphate buffer pH 5. Experiments were performed using glassy carbon (GC) electrode as a comparison. Well-defined oxidation waves of the quasi-reversible cyclic voltammograms were observed at both electrodes. Voltammetric signal-to-background ratios (S/B) were comparable. However, the GC electrode gives much greater in the background current as usual. The potential sweep rate dependence exhibited that the peak current of iodide oxidation at 1mM varied linearly (r(2) = 0.998) with the square root of the scan rate, from 0.01 to 0.30Vs(-1). This result indicates that the reaction is a diffusion-controlled process with negligible adsorption on BDD surface, at this iodide concentration. Results of the flow-injection analysis show a highly reproducible amperometric response. The linear working range was observed up to 200muM (r(2) = 0.999). The detection limit, as low as 0.01muM (3sigma of blank), was obtained. This method was successfully applied for quantification of iodide contents in nuclear emergency tablets.

The electrochemical oxidation of homocysteine at boron-doped diamond electrodes with application to HPLC amperometric detection

The electrochemical oxidation of homocysteine was studied at as-deposited and anodized (oxidized) boron-doped diamond (BDD) thin film electrodes with cyclic voltammetry, flow injection analysis and high-pressure liquid chromatography with amperometric detection. At anodized boron-doped diamond electrodes, highly reproducible, well-defined cyclic voltammograms for homocysteine oxidation were obtained in acidic media, while as-deposited diamond did not provide a detectable signal. In alkaline media, however, the oxidation response was obtained both at as-deposited and anodized diamond electrodes. The potential sweep rate dependence of homocysteine oxidation (peak currents for 1 mM homocysteine linearly proportional to v(1/2), within the range of 0.01 to 0.3 V s(-1)) indicates that the oxidation involves a diffusing species, with negligible adsorption on the BDD surface at this concentration. In the flow system, BDD exhibited a highly reproducible amperometric response, with a peak variation less than 2%. An extremely low detection limit (1 nM) was obtained at 1.6 V vs. Ag/AgCl. In addition, the determination of homocysteine in a standard mixture with aminothiols and disulfide compounds by means of isocratic reverse-phase HPLC with amperometric detection at diamond electrodes has been investigated. The results showed excellent separation, with a detection limit of 1 pmol and a linear range of three orders of magnitude.

Simple and fast colorimetric detection of inorganic arsenic selectively adsorbed onto ferrihydrite-coated silica gel using silver nanoplates.

The optical detection for inorganic arsenic (As) semi-quantitative determination is presented by using silver nanoplates (AgNPls). The color of AgNPs is immediately changed in the presence of As(III) and As(V) with the same sensitivity. To improve the selectivity of AgNPls for As detection, ferrihydrite-coated silica gel (SiO2-Fh) was specifically exploited as adsorbent for arsenic prior to As detection by AgNPls. The developed method provides the detection limit of 0.5ppm with the detection range between 0.5ppm and 30.0ppm for As determination observed with naked eye, and allows to determine total inorganic arsenic. This is the first report of As detection approach combining As removal technology together with nanotechnology. This combined technique provides a rapid, sensitive and selective method for monitoring As levels in aqueous samples, and can be employed as a testing field kit to screen arsenic contamination outside of a laboratory.

Novel colorimetric assay for paraquat detection on-silica bead using negatively charged silver nanoparticles

A simple, rapid, sensitive, and economical method based on colorimetry for the determination of paraquat, a widely used herbicide, was developed. Citrate-coated silver nanoparticles (AgNPs) were synthesized as the colorimetric probe. The mechanism of the assay is related to the aggregation of negatively charged AgNPs as induced by positively-charged paraquat resulting from coulombic attraction which causes the color to change from a deep greenish yellow to pale yellow in accordance with the concentrations of paraquat. Silica gel was exploited as the paraquat adsorbent for purification and pre-concentration prior to the direct determination with negatively charged AgNPs without the requirement of the elution step. The validity of the proposed approach was evaluated by spiking standard paraquat in water and plant samples. Recoveries of paraquat in water samples were 93.6% and 95.4% for groundwater and canal water, respectively, while those in plant samples were 89.5% and 86.6% for Chinese cabbage and green apple, respectively,after using the optimized extraction procedure. The absorbance of AgNPs at 400nm was linearly related to the concentration of paraquat over the range of 0.05-50mgL-1, with detection limits of 0.05mgL-1 for water samples, and 0.10mgL-1 for plant samples by naked eye determination.

Paper-based thioglycolic acid (TGA)-capped CdTe QD device for rapid screening of organophosphorus and carbamate insecticides

A paper-based device, based on the fluorescence switching of water-soluble thioglycolic acid (TGA)-capped CdTe QDs, was developed for the simple, rapid and sensitive detection of organophosphorus (OP) and carbamate (CM) insecticides. A new design platform for the developed device was created, comprising a foldable sheet with a detection zone and a buffer solution loading channel, to simplify the multi-step reaction of a bi-enzyme assay with a signal enhancement system. This device was very useful for fast screening and on-site detection, without requiring many reagents. The bi-enzyme includes acetylcholinesterase (AChE), choline oxidase (ChOx) and TGA-capped CdTe QDs, which were coated on the paper-based device at the detection zone in a separated sheet, starting with an acetylcholine (ACh) substrate coating. After incubation of the sample at the detection zone, the device was closed to initiate enzyme catalyzed hydrolysis of the pre-spotted ACh. Subsequently, the buffer solution was applied to the device, allowing for the pre-spotted chemicals to mix well and importantly, result in signal enhancement. The hydrolysis of ACh was catalyzed by AChE followed by ChOx to yield H2O2, which can quench the fluorescence of the TGA-capped CdTe QDs. In the presence of OP and CM insecticides, the AChE activity was inhibited, resulting in decreased quenching of the TGA-capped CdTe QDs. The change in the fluorescence intensity of the TGA-capped CdTe QDs can be observed using the naked eye under UV-black light. Under optimized conditions, the limit of detection for pirimicarb, dichlorvos and carbaryl were found to be 0.05, 0.01 and 0.01 ppm, respectively, using visual measurements. This developed device was successfully applied to the detection of OP and CM insecticide residues in agricultural products. The data correlated well with the data obtained using gas chromatography-tandem mass spectrometry (GC-MS/MS). This developed device shows good selectivity and sensitivity for the rapid screening of insecticides and could be useful for on-site applications.

Electrospinning: a carbonized gold/graphene/PAN nanofiber for high performance biosensing

In this study, a novel biosensor was produced from a carbonized gold (Au)/graphene (G) hybrid nanowire fabricated on a disposable screen-printed carbon electrode (SPCE) in order to amplify signals. The processes of carbonization and electrospinning were merged in order to determine dopamine (DA) in a selective and sensitive manner when it is present in uric acid (UA) or ascorbic acid (AA). In order to assess the nature of the surface morphology and the physical product properties, transmission electron microscopy, scanning electron microscopy, and X-ray diffraction were employed prior to and following the carbonization step. The modified electrode (CPAN-Au/G) in [Fe(CN)6]3−/4− and DA was examined using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in order to establish the electrochemical behavior. The findings from this test revealed that the modified electrode was capable of selectively identifying DA in 0.1 M PBS at pH 7.4 when other substances were present to provide interference. This process did not require the use of an anionic surfactant to serve as the discriminating agent. From the analysis of the DPV current, a linear dependence upon DA concentrations became apparent, in the range of 0.001–60 μM when the detection limit was 0.8 nM (S/N = 3) and sensitivity was 1.4351 μA cm−2. DA quantities in human serum could be effectively detected using the CPAN-Au/G electrode, and the modified electrode raises considerable expectations for application as a high-potential electrode. This would permit the determination of DA in a selective and sensitive manner while achieving sensor stability over the long term.