Syntheses and characterisation of mercury complexes of sulfadiazine,sulfamerazine and sulfamethazine

The triple sulfa drugs, sulfadiazine, sulfamerazine and sulfamethazine, form a large number of metal complexes in different solvent media. The present studies show the synthesis and characterization of the Hg(II) complexes of sulfadiazine 1, sulfamerazine 2 and sulfamethazine 3 in dimethylformamide solution in presence of ammonia. The compounds were characterised by spectroscopic methods and crystal structures of the complexes were determined. All the compounds, 1, 2 and 3, crystallise in monoclinic crystal systems with the space groups of C2/c, C2/c and P2₁/c, respectively. Compounds 1 and 3 have eight coordinate ‘2+6’ geometries, with two tridentate sulfonamide ions and two DMF molecules in the coordination sphere. Complex 2 has a six co-ordinate, ‘2+4’ geometry which contains a short linear N–Hg–N moiety from co-ordinated sulfonamides. The IR spectral data suggest the binding of mercury atom to the sulfonamidic nitrogen atoms in agreement with the crystal structure determination.     

Enzymatic determination of choline in milk using a FIA system with potentiometric detection

The development of a FIA system for the determination of total choline content in several types of milk is described. The samples were submitted to hydrochloric acid digestion before injection into the system and passed through an enzymatic reactor containing choline oxidase immobilised on glass beads. This enzymatic reaction releases hydrogen peroxide which then reacts with a solution of iodide. The decrease in the concentration of iodide ion is quantified using an iodide ion selective tubular electrode based on a homogeneous crystalline membrane. Validation of the results obtained with this system was performed by comparison with results from a method described in the literature and applied to the determination of total choline in milks. The relative deviation was always < 5%. The repeatability of the method developed was assessed by calculation of the relative standard deviation (RSD) for 12 consecutive injections of one sample. The RSD obtained was < 0.6%.     

Development of an FIA system with amperometric detection for determination of bentazone in estuarine waters

On the basis of its electrochemical behaviour a new flow-injection analysis (FIA) method with amperometric detection has been developed for quantification of the herbicide bentazone (BTZ) in estuarine waters. Standard solutions and samples (200 microL) were injected into a water carrier stream and both pH and ionic strength were automatically adjusted inside the manifold. Optimization of critical FIA conditions indicated that the best analytical results were obtained at an oxidation potential of 1.10 V, pH 4.5, and an overall flow-rate of 2.4 mL min(-1). Analysis of real samples was performed by means of calibration curves over the concentration range 2.5x10(-6) to 5.0x10(-5) mol L(-1), and results were compared with those obtained by use of an independent method (HPLC). The accuracy of the amperometric determinations was ascertained; errors relative to the comparison method were below 4% and sampling rates were approximately 100 samples h(-1). The repeatability of the proposed method was calculated by assessing the relative standard deviation (%) of ten consecutive determinations of one sample; the value obtained was 2.1%.     

Selective detection of metal species in HPLC and FIA by means of pulsed amperometric detection (PAD)

Triple-step pulsed amperometry is used to detect selectively metal complex species after HPLC separation in the presence of coeluting matrix compounds. Optimized pulse parameters enable accurate and selective detection of species even in the presence of electroactive compounds such as phenols or sulfurcontaining peptides. Complexes of tin(IV) with rutin and of platinum(II) with glutathione are presented as examples for these classes of compounds. It is demonstrated that by changing the pulse waveform direct and indirect detection modes can be realized. The method is applied to detect platinum species in a grass extract and iron(II)-lactate in fruit juice. Furthermore it is shown, that pulsed amperometry can be used as a detector in FIA for determining the fraction of metal complex formed after mixing of metal and excess ligand without separation.     

Inorganic tin(II) determination by FIA with amperometric detection of its oxinate complex

A highly selective, rapid and direct amperometric method, based on the formation of a complex between tin(II) and 8-hydroxyquinoline (oxine), has been developed for the determination of trace levels of tin(II) using flow injection analysis. Tin(II) electro-oxidation was catalyzed by oxine; its oxidation peak occurred at +0.05 V vs. Ag/AgCl at a glassy carbon electrode in 0.1 mol 1⁻¹ acetate buffer (pH 6). A linear relationship was obtained between the peak current and the tin(II) concentration in the range 0.25-20 μmol 1⁻¹. The detection limit was 0.1 μmol 1⁻¹ and the relative standard deviation calculated by the injection of a 10 μmol 1⁻¹ tin(II) solution was 5% (n = 20). Optimization of several experimental parameters has been carried out and the influence of numerous cations and possible interfering molecules encountered in radiopharmaceuticals and in dental gels has been investigated. The method was applied to the determination of tin(II) in dental gels.     

Optimization of a flow injection system with amperometric detection for arsenic determination.

A selective and sensitive analytical procedure for rapid arsenic determination by gas-diffusion flow injection analysis with amperometric detection was developed. The method is based on the arsenite reduction by NaBH(4). Derived arsine diffuses through a PTF membrane into the acceptor flow stream and is amperometrically determined on a platinum working electrode. The limit of detection (3 sigma) at room temperature was 5 microg/dm(3) of As(III). The relative standard deviation for a 1 mg/dm(3) As(III) standard was 1.96% for six repetitive injections. Arsenic(V) was determined after its prereduction with potassium iodide. Arsenic determination was not interferred with by 1 mg/dm(3) Sb(III), 5 mg/dm(3) Sn(II), 10 mg/dm(3) Se(IV), 1 mg/dm(3) As(V), 1 mg/dm(3) hydrasine, 1 mg/dm(3) Fe(II) or 0.5 mg/dm(3) Fe(III) solution. The throughput of this method was 60 analyses per hour. This method was successfully applied to arsenic determination in some power plant waste water samples.     

Preparation of superior thin-layer chromatograms for quantitative in situ densitometry by nonequilibrated development. I. Trisulfapyrimidines: sulfadiazine, sulfamerazine, and sulfamethazine.

A method of obtaining controlled nonequilibrated horizontal plate development by employing a developing system open to room atmosphere is described and compared with other plate-developing techniques. Nonequilibrated plate development produced spot configurations with the precise physical outline and densitometric distribution needed for optical scanning.     

Indirect determination of iron in a flow-injection system with amperometric detection

The change in peak current resulting from the reaction of Fe(II) with nitroso-R salt in a flow-injection system is used to quantify Fe(II) with either single- or dual-electrode amperometric detectors. The current change varies linearly with Fe(II) concentration from 0 to 200 mg 1^?1. The relative standard deviation was about 5% with the single-electrode detector and about 10% with the dual-electrode detector. The method is evaluated for the determination of iron in dietary supplements.     

Evaluation of the 'antioxidant power' of olive oils based on a FIA system with amperometric detection

A new method for the evaluation of the 'total antioxidant power' of olive oils, based on a flow injection analysis system with electrochemical detection, is described. It represents a attractive alternative to the mostly used Rancimat method since it is based on the chemical structure of antioxidants and does not require the manipulation of several parameters, such as temperature and oxygen pressure, to accelerate oil oxidation. The proposed procedure is simple, rapid, allows a throughput of 90 samples h-1 and provides a good precision: an RSD of 3.5% was obtained for caffeic acid at the concentration level of 5 mg L-1 (n = 12). A comparison of the proposed was obtained for caffeic acid at the concentration level of 5 mg L-1 (n = 12). A comparison of the proposed procedure with two other methods (Rancimat method and ABTS.+ decoloration assay) was performed to investigate the applicability and limitations of the proposed method.     

Simultaneous determination of sulfite and phosphate in wine by means of immobilized enzyme reactions and amperometric detection in a flow-injection system

A flow-injection system is proposed for the simultaneous determination of sulfite and phosphate in wine. A sulfite oxidase immobilized reactor and purine nucleoside phosphorylase-xanthine oxidase co-immobilized reactor are incorporated at fixed positions (parallel configuration) in the flow line, which is based on the splitting of the flow after sample injection and subsequent confluence. A poly(1,2-diaminobenzene)-coated platinum electrode is used as an amperometric detector to detect selectively hydrogen peroxide generated enzymatically in the enzyme reactors, without any interference from oxidizable species and proteins present in wine. Because each channel has a different residence time, two peaks are obtained. The first peak corresponds to sulfite and the second peak to phosphate. The peak current is linearly related to the concentrations of sulfite between 1 × 10⁻⁵ and 2 × 10⁻³M and phosphate between 2 × 10⁻⁵ and 5 × 10⁻³M. The simultaneous determination of sulfite and phosphate in wine can be performed at a rate of 30 samples/hr with satisfactory precision (less than 1.2% RSD) and no pretreatment except for the sample dilution.     

Optimization of analytical conditions and validation of a fluorescence method for the determination of sulfadiazine in milk

This paper describes optimization and validation of a method for sulfadiazine determination in milk samples based on sulfadiazine derivatization with fluorescamine followed by excitation–emission (fluorescence) measurement. For both the optimization and the validation, a comparison between zero-order and first-order signals has been made, showing the advantages of using first-order signals. In the optimization the effects of the temperature of the derivatization reaction, the amount of fluorescamine and the derivatization time on the instrumental signal (maximum intensity or the net analyte signal) are studied by a factorial experimental design, with the optimal values of these factors which give the highest signal being 22 °C for the reaction temperature, 50 μl fluorescamine and 20 min of derivatization time. The validation of the method under the optimal experimental conditions shows that the analytical method is fit-for-purpose, with values of the capability of detection (CCβ) of 4.3 μg l⁻¹ at a sulfadiazine concentration of zero and with probabilities of a false positive and a false negative of 5%. Around the permitted limit (established for the sulfonamides at 100 μg l⁻¹), CCβ is 112 μg l⁻¹. The precision, as the intermediate reproducibility, was established as 1.2 and 3.3 μg l⁻¹ around 0 and 100 μg l⁻¹, respectively. In the application to milk samples spiked with sulfadiazine a mean recovery of around 90% was obtained with a standard deviation of about 8% (14 samples of different concentrations).     

Determination of mono- and disaccharides in milk and milk products by high-performance anion-exchange chromatography with pulsed amperometric detection

A simple and sensitive liquid chromatographic method for the separation and quantification of mono- and disaccharides in raw- and processed-milk is described. Samples of cows’, buffalos’, sheeps’ and goats’ milk were analyzed upon clarification and appropriate dilution for the quantification of lactose, galactose, glucose and N-acetylglucosamine (GlcNAc). The separation was accomplished by high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD), using a gold working electrode and dilute alkaline eluents modified by a millimolar concentration of barium acetate. The eluent composition employed was designed to provide optimum separation with respect to the selected sample, without interference from the matrix components. The analytical method was successfully employed for the determination of mono- and disaccharides naturally occurring in dairy milk, mozzarella cheese and whey samples, with high sensitivity and accuracy.     

HPLC determination of sulfamethazine in milk using surface-imprinted silica synthesized with iniferter technique

A new method for the synthesis of sulfamethazine-imprinted polymer on the surface of silica via quasi-living radical polymerization and the application of the resulting polymer in determination of the SMZ in milk is developed. In the synthesis, initiator-transfer agent-terminator (iniferter) was immobilized on the silica surface using chemical reagents with good availability. The imprinting polymerization was initialized by the silica-supported iniferter under the UV radiation. The molecularly imprinted polymer (MIP) layer grafted on the silica surface was constructed by using sulfamethazine (SMZ) as the template, methacrylic acid (MAA) as the functional monomer and ethylene dimethacrylate (EDMA) as cross-linker. The resulting MIP-silica has good selectivity for SMZ and high column efficiency in the HPLC analysis. The result demonstrated that the SMZ-imprinted polymer was grafted on the silica surface successfully. Under the optimized HPLC condition, the MIP-silica has been used for the determination of SMZ in milk. The method was linear over the concentration range of 0.1-50 microgmL(-1) with correlation coefficient R>0.999. The detection limit for SMZ was 25 ngmL(-1). The recoveries were above 78% at the spiked concentration of 0.024, 0.24 and 0.48 microgmL(-1).     

Separation and determination of enkephalin-related peptides by capillary electrophoresis with amperometric detection

A simple, reliable, and reproducible method for separation and determination of five enkephalin-related peptides based on CE with amperometric detection (AD) is described in this paper. A potential of 1.0 V was applied to the carbon disk electrode, which was used as a working electrode in this system. At 15 kV of applied voltage, the five compounds were separated within 18 min in a 20 mmol/L phosphate buffer solution (PBS, pH 7.6) including 2.5% methanol v/v. LOD for five enkephalins were ranged from 6.31 to 54.3 nmol/L. The method was applied successfully to determine the five compounds added in the human cerebrospinal fluid (CSF) and the recoveries were in the range of 95.8-98.2%.     

Total determination of metal-binding carbohydrates in plant extracts by using FIA with electrochemical detection

FIA with pulsed amperometric detection (PAD) is used for the determination of metal-binding carbohydrates in plant extracts. Results of direct FIA measurements agree very well with those of corresponding HPLC-PAD analyses. The proposed method is used to determine total carbohydrates in isolated low-molecular-weight fractions of plant roots, which have been obtained after extraction at different pH values. The results are compared with those obtained by corresponding metal determinations (Ca, Mg, Zn, Mn) by AAS and also with constant potential amperometric detection at a copper working electrode. The latter detection mode is more sensitive, but less selective for carbohydrates. Received: 12 January 2000 / Revised: 2 March 2000 / Accepted: 4 March 2000     

Total determination of metal-binding carbohydrates in plant extracts by using FIA with electrochemical detection

FIA with pulsed amperometric detection (PAD) is used for the determination of metal-binding carbohydrates in plant extracts. Results of direct FIA measurements agree very well with those of corresponding HPLC-PAD analyses. The proposed method is used to determine total carbohydrates in isolated low-molecular-weight fractions of plant roots, which have been obtained after extraction at different pH values. The results are compared with those obtained by corresponding metal determinations (Ca, Mg, Zn, Mn) by AAS and also with constant potential amperometric detection at a copper working electrode. The latter detection mode is more sensitive, but less selective for carbohydrates.     

Enhanced determination of glucose by microchip electrophoresis with pulsed amperometric detection

The present report describes a new analysis strategy for microchip capillary electrophoresis with pulsed amperometric detection and its application to the determination of glucose. The addition of sodium dodecyl sulfate (SDS) to the mobile phase and detection reservoir stabilized flow rates and enhanced the detection signal for glucose. A higher pH (compared to the running buffer) was used at the waste reservoir in order to improve the detection performance while maintaining good separations. To our knowledge, this is the first report describing the use of post-column pH modification using microchip electrophoresis. Under optimum conditions, a linear relationship between the peak current and the concentration of glucose was found between 10⁻²-10⁻⁵ M, with a limit-of-detection of 1.2 μM. In addition, the separation of glucosamine and glucose was performed at pH 7.1 while the detection was performed at pH 11 to demonstrate the ability to use post-column pH modification.     

A flow-injection system with amperometric detection for selective determination of antioxidants in foodstuffs and drinks

Amperometric detection in flow-injection systems intended for total determination of antioxidants (flavonoids, oxyaromatic acids, etc.) in various foodstuffs (berries, fruit, vegetables) and drinks (wine, tea, coffee, cognac, beer, etc.) was described and discussed. Advantages of this method were demonstrated. These measurements can underlie building of a bank of data on the content of antioxidants in foodstuffs and drinks.