Gold nanostars as a colloidal substrate for in-solution SERS measurements using a handheld Raman spectrometer.

The evolution of Raman spectroscopy into a useful analytical technique has been due, in part, to the development of inexpensive, compact instrumentation and advancements in methodologies that enhance Raman intensities. Surface enhanced Raman scattering (SERS) is a primary methodology for quantitative and low detection limit measurements. While a broad array of applications using solid SERS substrates have been demonstrated, in-solution SERS measurements are not as widely pursued. This work seeks to optimize the synthesis of gold nanostars (AuNS) as a colloidal SERS substrate for in-solution measurements using handheld instrumentation. The types and concentrations of two buffers typically used for AuNS synthesis are examined to optimize the SERS intensity of a chemisorbed Raman probe. The observed SERS intensity primarily depends on conditions that allow higher surface coverage of the probe. Conditions that result in AuNS aggregates are found to be most optimal for SERS, similar to other nanoparticle shapes. A method to quantitate methimazole, an anti-hormone pharmaceutical, in urine is developed and reported. The primary impact of this work is the demonstration of the combination of water dispersible substrates and handheld instrumentation for rapid and sensitive analytical measurements.

Determination of Thyreostats in Urine Using Supported Liquid Extraction and Mixed-Mode Cation-Exchange Solid-Phase Extraction: Screening and Confirmatory Methods.

The application of thyreostats in livestock has been banned in the European Union since 1981, but these drugs are currently in the focus due to the natural occurrence of thiouracil (TU). Studies have been published on TU contamination in urine samples of animal and human origins without any drug administration of it. This paper presents new analytical methods to analyze thyreostats to support the legislation on the recommended concentration (RC) levels of these drugs. Both screening and confirmatory methods are developed for analyzing thyreostats in porcine and bovine urines using a liquid chromatography-tandem mass spectrometry technique. The new methods include a chemical derivatization with 3-iodobenzyl bromide, followed by novel purification approaches using supported liquid extraction and mixed-mode cation-exchange solid-phase extraction (SPE) for screening and confirmatory purposes, respectively. The optimized derivatization in combination with the cation-exchange SPE gives high sensitivity and reducing matrix effect of the analysis. The methods are validated in accordance with the guidelines for the validation of screening methods and European Commission Decision 2002/657/EC. The confirmatory method is used in the national monitoring plan. The detected levels of TU in urine samples are below the currently applicable RC level (10 µg L-1).

Electrochemical sensor using methimazole imprinted polymer sensitized with MWCNTs and Salen-Co(III) as recognition element.

This study describes the development of a sensor with molecularly imprinted polymer (MIP) sensitized with MWCNTs and Salen-Co(III) as recognition element for methimazole (MMI) determination. This is the first report of MWCNTs and Salen-Co(III) in MIP being used to enhance its conductivity and catalytic activity in the electrochemical oxidation process. The electrocatalytic mechanism of MMI was explained in detail by evaluating the obtained voltammograms at various potential sweep rates and pH of buffer solutions. A stable, sensitive analytical method of differential pulse voltammetry (DPV) was developed using the prepared MWCNTs-Salen-Co(III)-MIP electrode for the determination of amounts of MMI, resulting in a linear range of 0.5-6.0 mg L(-1) with detection limit of 0.048 mg L(-1). It was also successfully applied for MMI determination in tablets and spiked urine sample. At three concentration levels, the recoveries for two samples were achieved to 94.0-100.1% and 87.8-101.8%, respectively. Analytical reproducibility and stability of the developed method were also evaluated by RSD, which were calculated as 4.6-6.6% and 2.0-6.1% (n=3), respectively.

Determination of methimazole in urine with the iodine-azide detection system following its separation by reversed-phase high-performance liquid chromatography.

The iodine-azide detection system to determine methimazole following its separation by RP-HPLC is described in this paper. The reaction between iodine and azide ions induced by methimazole was applied as a post-column reaction detection system. Neither extraction nor preconcentration of the sample was necessary. The methimazole standards added to normal urine show that the response of the detector, set at 350 nm (corresponding to unreacted iodine in the post-column iodine-azide reaction), was linear within the concentration range 2-10 nmol/mL of urine. The relative standard deviation values for precision and recovery within the calibration range were from 0.3 to 3.2% and from 97 to 102%, respectively. Limits of detection (LOD) and quantitation (LOQ) were 1 and 2 nmol/mL of urine, respectively. The method was applied to the separation and determination of patient urine samples and the analytical results were satisfactory.

Rapid and high-performance analysis of thyreostatic drug residues in urine using gas chromatography-mass spectrometry.

A more sensitive method was developed using the hyphenated technique of gas chromatography-mass spectrometry (GC-MS) supplementary to the official high-performance thin-layer chromatography (HPTLC) method. Even combined with less efficient extraction and clean-up methods, GC-MS is able to lower the detection limit to less than 50 ppb. The powerful technique of GC-MS-MS is tried out to reduce the detection limit even more, in combination with simplified extraction methods. This time-saving approach combined with the increase in sensitivity is of great importance for a routine technique.

Screening and confirmation of thyreostatics in urine by gas chromatography with nitrogen-phosphorus detection and gas chromatography-mass spectrometry after sample clean-up with a mercurated affinity column.

Methods are described for the screening and confirmation of residues of the thyreostatics thiouracil, methylthiouracil and propylthiouracil in urine samples of cattle at levels down to 25 micrograms/l. After a selective preconcentration of the thiol-containing thyreostatics on a mercurated affinity column, the analytes are derivatized by extractive alkylation and analysed by gas chromatography with nitrogen-phosphorus or mass spectrometric detection.

Pharmacokinetics of methimazole in normal subjects and hyperthyroid patients.

Serum and urinary concentrations of methimazole (MMI) were measured by high-performance liquid chromatography (HPLC) with an electrochemical detector (ECD) in 10 normal subjects and 43 hyperthyroid patients after intravenous and oral administration of the drug. The pharmacokinetic parameters of MMI were estimated in 5 normal subjects and 15 hyperthyroid patients according to a two-compartment model after intravenous injection of a 10 mg dose. The mean half-life of the distribution phase (T1/2 alpha) was 2.7 +/- 1.0 h (mean +/- SD) and 3.1 +/- 1.4 h and that of the slower-phase (T1/2 beta) was 20.7 +/- 9.6 h and 18.5 +/- 12.9 h in normal subjects and hyperthyroid patients, respectively. There were no significant differences between pharmacokinetic parameters of normal subjects and those of hyperthyroid patients. No correlations between free T4 index (FT4I) and pharmacokinetic parameters were observed. Maximum serum MMI concentrations (Cmax) (213 +/- 84 and 299 +/- 92 ng/ml) were attained 1.8 +/- 1.4 h and 2.3 +/- 0.8 h after a single dose of 10 mg in 5 normal subjects and in 15 hyperthyroid patients, respectively. In hyperthyroid patients the time taken to reach the peak concentration (Tmax) after a single dose of 10 mg was similar to that after a single 15 mg and 30 mg dose. The pharmacokinetic parameters, except Cmax and the area under the curve (AUC), were not affected by the administered dose and those, except Cmax, were not affected by the thyroid function. All urine was collected at intervals of 3 h for the first 12 h and then at 24 h and 48 h after intravenous and oral administration of MMI. In all subjects, MMI rapidly appeared in the urine and the rate of excretion was highest in the first 3 h. The cumulative urinary excretion of MMI was 5.5-8.5% of administered doses in normal subjects and hyperthyroid patients. These findings in the present study are compatible with the assumption that the extent of absorption of MMI is high, if not complete, and hyperthyroidism does not affect the kinetics of MMI, and that interindividual variation is observed in the time taken to reach the peak concentration after oral administration.

2-Mercapto-1-methyl-5-methylmercapto-imidazole: a new metabolite of thiamazole.

2-Mercapto-1-methyl-5-methylmercapto-imidazole (13) was found in urine samples of man and rat after intake of thiamazole (1). It is assumed that the metabolite is produced via a N-oxidation intermediate enabling a nucleophilic attack at carbon-5 in the thiazole ring.

The metabolism of [2-14C]methimazole in the rat.

1. The metabolism of [2-14C]methimazole was studied in Sprague-Dawley rats after a daily intraperitoneal dose of 17.6 mg/kg for three days. 2. 78.4% of the administered 14C was excreted in the urine; only 6.7% dose as methimazole. After extraction of the urine with chloroform and n-butanol, 47.5% of administered 14C remained in the urine. 3. Six solvent-extractable metabolites were isolated and characterized by t.l.c. and high-resolution mass spectrometry, as N-methylimidazole, S-methylmethimazole, 3-methyl-2-thiohydantoin, 1-methyl-2-thiohydantoic acid, N-methylthiourea and a methylhydantoin.