Current Analytical Chemistry - Volume 11, Issue 2, 2015

This paper focuses the separation and voltammetric quantification of five significant compounds, such as tryptophan (Trp), paracetamol (APAP), uric acid (UAC), dopamine (DA) and ascorbic acid (AA), which may coexist in urine samples. The poly (Rhodamine B) / MWCNTs composite film was created on glassy carbon electrode by cyclic voltammetric technique. Electroanalytical behaviors of analytes at poly (Rhodamine B)/ MWCNTs/GC electrode were examined using both cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Electrochemical impedance (EIS) and scanning electron microscopy (SEM) were employed to characterize the dielectric properties and morphology of the composites. The linear working ranges for simultaneous estimation of Trp, APAP, UAC, DA and AA were 2.0–100 μM, 3.0–70 μM, 2.0–100 μM, 0.5–20 μM, and 200–5000 μM, respectively and the detection limits were 0.25 μM, 0.65 μM, 0.54 μM, 0.05 μM, and 20 μM, respectively. The developed sensor was set up to be suitable for the routine analysis of the Trp, APAP, UAC, DA and AA in the urine and pharmaceutical samples and satisfactory results were received. Moreover, the sensor was applied for the quantification of p-aminophenol (PAP) in the presence of Trp, APAP, UAC, DA and AA. Well-separated oxidation peak currents were observed in phosphate buffer solution at pH 7.0.

A sensitive square wave voltammetric sensor for the quantification of bilirubin (BR) at the Nafion-electrochemically reduced graphene oxide (NF/ER-GO) hybrid composite modified conventional glassy carbon electrode was offered. The voltammetric oxidation conducts of bilirubin at the NF/ER-GO modified GC electrode were examined in acetone containing H&2SO4 as the supporting electrolyte. The electrochemical conduct of BR on NF/ER-GO hybrid modified GC electrodes was explored by electrochemical impedance spectroscopy, cyclic voltammetry and square-wave voltammetry (SWV). The oxidation peak current response of BR achieved at the NF/ER-GO modified GC electrode was 3 times higher than that of the unmodified GC electrode. At specified conditions, the linear calibration curve for BR showed two good linear segments: the first linear segment increased from 2.0 μM to 20 μM and second linear segment increased up to 70 μM. The limit of detection was calculated as 0.84 μM using SWV. The results showed that the NF/ER-GO modified electrode can be applied to determine BR without interference from ascorbic acid and uric acid, while ensuring good sensitivity, selectivity, and reproducibility. Finally, the proposed sensor was successfully employed to detect bilirubin in human serum samples.

A new polyvinyl chloride (PVC) membrane Fe3+ ion selective electrode was constructed as a detector for the analysis Fe3+ using a home-made low-volume flow through cell. Optimum working conditions for the flow injection analysis (FIA) measurements were examined. In addition, under optimum conditions, potentiometric performance characteristics of the Fe3+ ion-selective electrode were investigated. Electrode had a linear response in the concentration range of 1.0 x 10-3-1.0 x 10-6 M (R2=0.9961, y=24.7+772.0). Reproducibility of the electrode responses was very satisfied. The potential of Fe3+ ion selective electrode was decreased intra and inter day 0.9 % and 3.7% respectively. The designed flowthrough cell system as Fe3+ detector revealed sampling rates of approximately 50 injections per hour. The obtained results in FIA were in a good agreement with AAs results at %95 confidence level for each syrups.

Inhibition of corrosion of mild steel material in sulphuric acid medium has been tried with many synthetic and green inhibitors. Each inhibitor has its own merits and limitations. The present study aims at the synthesis of 8-Hydroxy Quinoline (8HQ) and Pyridine N-Oxide (PyNO) and the study of their inhibition behaviour on the corrosion of mild steel in 2 N sulphuric acid. The inhibition behaviour of the synthesised compounds was studied by subjecting to weight loss measurements, polarisation studies and electrochemical impedance spectra (EIS) for the assessment of their performance. The studies were made with 2 N sulphuric acid as the corroding medium, but with the inhibitor concentration in the range of 50 -350 ppm. The results revealed that the inhibitors studied perform better in the medium and function by the mechanism of adsorption onto the metal surface.

In this study, a capillary electrophoresis-mass spectrometry method was applied to the determination of isoflavones in samples with low content in these analytes, such as legumes. Sample stacking was used to enhance the sensitivity of the technique. Extraction of the analytes was carried out by a modified approach of QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) methodology, in which the extracts were injected directly into electrophoretic system coupled with mass spectrometry detector. The developed method was validated and applied for the determination of isoflavone aglycones and glycosides in legume samples. The values of the validation parameters and the isoflavone contents found were compared with those obtained by LC-MS/MS. Both methods provided similar results and were comparable in terms of recovery (in the 80-120% range), precision (lower than 10 %) and limits of detection (ranging from 0.20 to 1.8 μg L-1).

Sensitive, fast, and precise UPLC-MS/MS analytical method was validated for the identification and quantification of the anticoagulant rivaroxaban (RIV) in pharmaceutical dosage form, using a full factorial design for robustness assessment. Chromatographic separation was achieved in 3.5 min on a C18 Zorbax Eclipse Plus (rapid resolution HD) Agilent® column at isocratic elution mode. Ultra pure water adjusted to pH 4.0 with ammonium hydroxide and ACN (63:37), both phases containing 0.1 % formic acid, was used at a flow rate of 0.2 mL/min. Detection of RIV was carried out with a quadrupole time of flight mass spectrometer detector equipped with an electrospray ionization source which was applied on positive mode. Internal standard substance was used to ensure small variations between analyses. Validation parameters were evaluated and the results found within acceptable ranges. Linearity was evaluated from 1.0 – 50.0 μg/mL, presenting a mean of 0.9970 (r2). Relative standard deviation was within 2.57 % to intra and inter-day, and relative error for accuracy ranged from -0.16 % to 1.85 %. The four factors selected to evaluate method robustness by a full factorial design were flow rate, injection volume, column temperature, and ACN concentration; the responses were found to be not significant for RIV quantification. The proposed UPLC-MS/MS method was successfully validated regarding linearity, specificity, sensitivity, precision, accuracy and robustness, allowing fast and reliable analysis of RIV along with multiple compounds (impurities and degradation products) simultaneously, affording the use of a hyphenated technique in quality control studies.

Obesity, impaired glucose tolerance, and hypertension are often related and represent a major health burden in modern societies. Telmisartan (TEL) and Metformin HCl (MET) are widely used for the management of these commonly associated diseases. Few attempts have been made for the determination of TEL and MET in human plasma by liquid chromatography tandem mass spectrometry. This study describes the first chromatographic method for the simultaneous quantitation of TEL and MET in human plasma by ultra-performance liquid chromatography coupled to quadruple tandem mass spectrometry (UPLC–MS/MS). Chromatography was performed on aC18 column with isocratic elution using a mobile phase consisting of acetonitrile, water and formic acid (88.2 11.7: 0.1), at a flow rate of 250 μL/min for a total run time of 2 min. Losartan (LOS) was used as the internal standard. Mass spectrometric analysis was carried out by a TSQ Quantum Access MAX triple quadruple system coupled with electro spray ionization (ESI) source in the positive ion mode. The assay was validated over a concentration range of 10–100 ng/ml for both drugs. The precision and accuracy for both intra- and inter-day determination of all analytes were acceptable (<15%). Stability of the compounds was established for short term bench and auto sampler storage as well as freeze/thaw cycles. Moreover, the method was successfully applied to a pharmacokinetic study in six healthy volunteers who had been given a single oral dose of metformin HCl and telmisartan, 500 mg and 40 mg, respectively.

A high throughput and sensitive analytical method for the comprehensive determination of 31 environmental contaminants (10 pharmaceuticals and personal care products, PPCPs; 8 benzotriazole UV stabilizers, BUVSs; and 13 organophosphorus flame retardants and plasticizers, PFRs) in aqueous sample using solid phase extraction (SPE) followed by ultra-high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UHPLC-ESI-MS/MS) was developed. The optimized method was applied to aqueous samples and the limits of quantification (LOQs) ranged from 1.9 to 16 ng L-1 and from 2.3 to 45 ng L-1 in river water and effluent of sewage treatment plant (STP), respectively. All the correlation coefficients of the calibration curves were equal or greater than 0.99 in the range of 0.01-10 μg L-1. Oasis HLB (60 mg) cartridge showed the highest recoveries for all the analytes in river water (71- 115%) as well as in wastewater (71-117%) except for dibenzyl phosphate (DBzP) (58%). The intra- and inter-day repeatabilities were less than 14% at the two spiked levels (100 and 500 ng L-1). The developed method was applied for the determination of these target compounds in river water and STP effluent collected from Kumamoto, Suya and Matsuyama, Japan. Of the thirty-one compounds monitored, seventeen were found in one or more samples, especially diclofenac (DF) and carbamazepine (CBZ) were detected in all the water samples.