Robert Zakrzewski

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.

Application of improved iodine-azide procedure for the detection of thiouracils in blood serum and urine with planar chromatography.

The application of iodine-azide reaction for the determination of thiouracils in thin-layer chromatography and high-performance thin-layer chromatography is described. The developed plates were sprayed with a freshly prepared mixture of sodium azide, adjusted to a proper pH, and starch solution, and exposed to iodine vapour for 5 s. The detection limits were established at pmol level. The factors depending on the detection limits were described. A comparison of iodine-azide tests reaction with other procedures is presented. The developed method was applied to detection of thiouracils in blood serum and urine. The possibility of detection of a thiouracils mixture was demonstrated.

Application of the iodine-azide postcolumn reaction in RP-HPLC for the determination of thioguanine in urine.

The study focuses on the analysis of a sensitive, selective, and simple postcolumn detection method for thioguanine determination, based on the sensitizing induction of thioguanine on iodine-azide reaction and the combination technique of HPLC. The analysis was accomplished in the optimum conditions for iodine-azide detection system and HPLC separation. The values for the linear range, the LOD, and DOQ amounted to 0.8-1.7, 0.4, and 0.5 nmol/mL urine, respectively.

Determination of Methimazole in Pharmaceutical Preparations using an HPLC Method Coupled with an Iodine-Azide Post-Column Reaction

Abstract A simple and reliable high performance liquid chromatographic (HPLC) method with iodine-azide post-column reaction as a detection system has been developed and validated for determination of methimazole in tablets. A chromatographic separation was achieved on a C18 column with a mobile phase consisting of acetonitrile, water, and 2.5% sodium azide solution (pH 5.5) with isocratic elution (20:30:50, v/v/v). The detection is based on spectrophotometric measurement of the residual iodine (λ = 350 nm) from the post-column iodine-azide reaction induced by methimazole, after mixing an iodine solution containing iodide ions with the column effluent containing azide ions and methimazole. Obtained chromatograms for methimazole showed negative peaks as a result of the decrease in background absorbance. The method developed for methimazole was linear over the concentration range of 0.2–2 µmol L−1. The method is accurate and precise (relative standard deviation, R.S.D. < 4%). The detection limit (defined as S/N = 3) was 0.18 µmol L−1 (3.6 pmol injected amount) for the described compound. The elaborated method was applied to determine methimazole in tablets.

Thin Layer Chromatography with Post-Chromatographic Iodine-Azide Reaction for Thiuram Analysis in Food Samples

Abstract A simple, sensitive, precise, and rapid planar chromatographic method for thiuram analysis was elaborated. Reaction between iodine and azide ions induced by thiuram was applied as a detection system. The developed plates were sprayed with freshly prepared mixtures of sodium azide and starch solution adjusted to pH 6.0, and exposed to iodine vapor. The spots became visible as white spots on a violet-grey background. The iodine-azide detection system was proved to be the most favorable and enabled detection of quantities at the level 0.5 pmol per spot. The iodine-azide test was compared with other visualizing techniques commonly used in planar chromatography: iodine vapor, UV254, Cu(II). Certain factors that influence detection with iodine-azide reaction as a detection system were checked. The developed method was linear over the concentration range of 2–9 pmol per spot. The proposed technique was applied to detect thiuram in food samples.

Application of the iodine-azide procedure for the detection of glycine, alanine, and aspartic acid in planar chromatography

ABSTRACT The application of iodine–azide reaction for the determination of non-sulphur amino acids (glycine, alanine, and aspartic acid) transformed into PTC-derivatives with phenyl isothiocyanate in TLC and HPTLC, is described. The developed plates were sprayed with a freshly prepared mixture of sodium azide, adjusted to a proper pH, and starch solution, and exposed to iodine vapour for 5 seconds. The detection limits were established at the pmole level. The factors depending on the detection limits were described. A comparison of iodine–azide test reactions with other procedures is presented. The developed method was applied to detection of aspartic acid in a drug. The possibility of detection of amino acid mixtures was demonstrated.

Iodimetric determination of 2-mercaptopyrimidines

A new method for the determination of 2-mercaptopyrimidines, using their reaction with iodine in neutral and alkaline medium, is presented. The determinability range in the volumetric titration, in phosphate buffer with starch as an indicator, was found to be equal to 40-1000 mumol for 2-mercaptopyrimidine (I) and 100-2000 mumol for 2-mercapto-4-methylpyrimidine (II), and 200-2000 mumol for 4,6-dimethyl-2-mercaptopyrimidine (III). In the volumetric titration in alkaline medium, with the potentiometric end-point detection, the determinability range is 50-250 mumol for 2-mercapto-4-methylpyrimidine (II), 50-500 mumol for 4,6-dimethyl-2-mercaptopyrimidine (III), 20-250 mumol for 4,5-diamino-2,6-dimercaptopyrimidine (IV), and 20-1000 mumol for 2-thioorotic acid (V). In the coulometric titration, using the biamperometric end-point detection, 0.1-4.0 mumol of 2-mercaptopyrimidine (I) and 0.1-5.0 mumol of 2-thioorotic acid (V) were successfully determined.

Potentiometric and coulometric titration of 6-propyl-2-thiouracil

A method for the determination of 6-propyl-2-thiouracil involving its reaction with iodine in an alkaline medium is presented. In volumetric titration with potentiometric end-point detection, the range of determination is 125-500 mumol (21-85 mg). In coulometric titration using biamperometric end-point detection, 0.5-5.0 mumol (0.085-0.85 mg) of 6-propyl-2-thiouracil was successfully determined. The RSD in all applied techniques was < 1%. The methods developed were applied to the determination of 6-propyl-2-thiouracil in tablets.

Analysis of sulfide ions by densitometric thin-layer chromatography and use of TLSee software

Simple and sensitive TLC-densitometry (method 1) and HPTLC with TLSee software (method 2) have been used for analysis of sulfide ions in water. For both methods, separations were performed on silica gel 60 with dichloromethane-methanol-diethyl ether-25% aqueous ammonia 8:1:1:0.2 (v/v) as mobile phase. Sulfide ions were detected using the ‘methylene blue method’ — production of methylene blue (MB) by oxidative coupling of sulfide with N,N-dimethyl-p-phenylenediamine (DMPD) in the presence of iron(III) ions in acidic medium. In method 1 the spots were scanned at 660 nm. In method 2 spots were converted into chromatograms by use of TLSee software. Both methods were validated. Response for both was a linear function of concentration in the range 20–100 pmol per spot. The limits of detection and quantification were 10 pmol per spot (3.2 mg L−1) and 20 pmol per spot (6.4 mg L−1), respectively.

High-performance liquid chromatographic determination of propylthiouracil in human urine by post-column iodine–azide reaction

A sensitive, selective and simple post-column detection method for the determination of propylthiouracil (PTU) based on its sensitizing induction on iodine-azide reaction and the combination technique of high-performance liquid chromatography has been presented. The analysis was conducted in the optimum conditions for iodine-azide detection system and HPLC separation. The linear range, the lower limit of detection and quantification for PTU in urine were established at the levels of 0.4-1.0 nmol/ml urine, 0.3 nmol/ml urine and 0.4 nmol/ml urine, respectively.