Magnetic Solid-Phase Extraction Based on Poly 4-Vinyl Pyridine for HPLC-FLD Analysis of Naproxen in Urine Samples.

A magnetic solid phase extraction technique followed by liquid chromatography with a fluorescence detector for naproxen analysis in human urine samples was developed. The method includes the extraction of naproxen with a magnetic solid synthetized with magnetite and poly 4-vinylpriridine, followed by the magnetic separation of the solid phase and desorption of the analyte with methanol. Under optimal conditions, the linear range of the calibration curve was 0.05-0.60 µg L-1, with a limit of detection of 0.02 µg L-1. In all cases values of repeatability were lower than 5.0% with recoveries of 99.4 ± 1.3%. Precision and accuracy values are adequate for naproxen (Npx) analysis in urine samples.

Effects of Zinc Supplementation on Nutritional Status in Children with Chronic Kidney Disease: A Randomized Trial.

BACKGROUND: Zinc is an essential micronutrient for human beings and its deficiency affects their normal growth and development. OBJECTIVE: The main aim was to evaluate the effect of two doses of zinc supplementation (ZS) on the nutritional status in chronic kidney disease (CKD) children. METHODS: A randomized-trial multicentric study was conducted in 48 CKD (23 females) patients under 18-years-old, for a year. At random, participants took 30 or 15 mg/day of ZS, respectively. Anthropometric measurements and biochemical analysis were performed. Hypozincemia was determined by serum zinc concentration (SZC) using atomic absorption spectrophotometry. The positive or negative change in patients' body mass index (BMI) Z-score, serum albumin, zinc and C-reactive protein (CRP) levels were used to evaluate the effect of ZS. RESULTS: Mean SZC was normal before and after ZS. Despite ZS, there were no significant changes in serum albumin, zinc and CRP levels. A positive and significant association was observed between SZC and serum albumin before (p = 0.000) and after (p = 0.007) ZS. In both groups of ZS, there was a small but positive and significant change in body mass and normalization in BMI Z-score, hypoalbuminemia, hypozincemia and high CRP, especially with 30 mg/day of ZS. CONCLUSIONS: Zinc supplementation may be beneficial for nutritional status in children and adolescents with CKD.

Flow based determination of Cr(VI) by adsorptive cathodic stripping voltammetry on an immobilized magnetic poly(ionic liquid) modified electrode.

In this work an electrochemical procedure for Cr(VI) flow based determination in tap water is presented. An AdCSV method was developed using a screen printed electrode modified with magnetic poly(1-allyl-3-methylimidazolium) chloride and the procedure does not require the addition of complexing agents in the solution unlike the methodologies reported so far for Cr(VI) determination. The flow based system is described and the control variables were studied in detail and optimized using a Taguchi parameters design. Under optimal conditions, the electrochemical sensor offered an excellent response to Cr(VI) and the limit of detection estimated from 3σ was 0.5 µg L-1 (n = 3) allowing the analysis of tap water samples. The effect of interfering ions was also investigated below the maximum permissible limits for tap water according to Mexican standards. The presence of the magnetic particles on the sorbent allowed its easy modification on the electrode surface between each determination when removing the magnetic field placed in the wall-jet cell. Finally, the precision of the method was tested with tap water samples using standard addition method for Cr(VI) quantification and the accuracy was evaluated comparing the results with the dyphenylcarbazide method and by analyzing a certified water sample. The method shows good repeatability and reproducibility (%RSD less than 5%) making it feasible for Cr(VI) flow based determination and no significant difference is observed in the results obtained by both methods.

Chromium(VI) Removal from Aqueous Solution by Magnetite Coated by a Polymeric Ionic Liquid-Based Adsorbent.

An evaluation of the chromium(VI) adsorption capacity of four magnetite sorbents coated with a polymer phase containing polymethacrylic acid or polyallyl-3-methylimidazolium is presented. Factors that influence the chromium(VI) removal such as solution pH and contact time were investigated in batch experiments and in stirred tank reactor mode. Affinity and rate constants increased with the molar ratio of the imidazolium. The highest adsorption was obtained at pH 2.0 due to the contribution of electrostatic interactions.

Amperometric flow system for blood glucose determination using an immobilized enzyme magnetic reactor.

An amperometric flow system for glucose determination in blood serum samples after enzymatic reaction with glucose oxidase immobilized on magnetite covered with silica gel modified propylamine is described. The solid was magnetically retained on a mini-column and placed into the flow injection system preceding the amperometric detector using a modified screen printed electrode with [Fe(tris(3,5-dimetyl-1-pyrazolyl)borate)(2)](+)[FeCl(4)](-). The variables involved in the system such as flow rate, enzyme concentration, injection volume and reaction coil length were evaluated using a Taguchi parameter design. Under optimal conditions, the calibration curve of glucose sample was linear between 0.24 and 6.00 mM, and with a limit of detection of 0.08 mM. The repeatability for a 4.0mM glucose solution was 1.0%.The method was validated by comparing the obtained results to those provided by the enzymatic spectrophotometric method; no significant differences were observed.

Amperometric biosensor for oxalate determination in urine using sequential injection analysis.

An amperometric flow biosensor for oxalate determination in urine samples after enzymatic reaction with oxalate oxidase immobilized on a modified magnetic solid is described. The solid was magnetically retained on the electrode surface of an electrode modified with Fe (III)-tris-(2-thiopyridone) borate placed into a sequential injection system preceding the amperometric detector. The variables involved in the system such as flow rate, aspired volumes (modified magnetic suspension and sample) and reaction coil length were evaluated using a Taguchi parameter design. Under optimal conditions, the calibration curve of oxalate was linear between 3.0-50.0 mg·L⁻¹, with a limit of detection of 1.0 mg·L⁻¹. The repeatability for a 30.0 mg·L⁻¹ oxalate solution was 0.7%. The method was validated by comparing the obtained results to those provided by the spectrophotometric method; no significant differences were observed.

Magnetic solid phase extraction based on phenyl silica adsorbent for the determination of tetracyclines in milk samples by capillary electrophoresis.

A magnetic solid phase extraction method coupled to capillary electrophoresis is proposed for the determination of tetracycline, oxytetracycline, chlortetracycline and doxycycline in milk samples. Five different magnetic phenyl silica adsorbents covered with magnetite were synthesized by varying the molar ratio of phenyltrimethylsilane and tetramethylorthosilicate; these adsorbents were evaluated in terms of their pH and degree of hydrophobicity for tetracycline retention. The optimal, selected combination of conditions was a pH of 10.0 and a magnetic sorbent ratio of 4:1; under these conditions, the retention capacity ranged from 99.7% to 101.2% for the four tetracyclines analyzed. The elution conditions and initial sample volume of the proposed extraction method were also optimized, and the best results were obtained with 1×10(-3) M acetic acid in methanol as eluent and a 200 ml of sample volume. Under optimal conditions, average recoveries ranged from 94.2% to 99.8% and the limits of detection ranged from 2 to 9 µg l(-1) for the four tetracyclines. After the proposed method was optimized and validated, 25 milk samples of different brands were analyzed, oxytetracycline residues were detected in five samples, in concentrations ranging from 98 to 213 µg l(-1). Subsequent analysis of positive samples by SPE-CE and magnetic solid phase extraction-HPLC revealed than no significant differences were found from results obtained by the proposed methodology. Thus, the developed magnetic extraction is a robust pre-concentration technique that can be coupled to other analytical methods for the quantitative determination of tetracyclines.