Chromium(III, VI) speciation analysis with preconcentration on a maleic acid-functionalized XAD sorbent

Chromium may exist in environmental waters as Cr(III) and Cr(IV), the latter being the toxic and carcinogenic form. Since atomic absorption spectrometry (AAS) and inductively coupled plasma atomic emission spectrometry can only yield information on total Cr concentration, a polymer resin bearing O,O-donor chelating groups such as the maleic acid-functionalized XAD(CO)CHCHCOOH resin was synthesized to selectively retain Cr(III) at pH 4.0-5.5. The dynamic breakthrough capacity of the resin for Cr(III) at pH 5.0 was 7.52 mg g⁻¹, and the preconcentration factor extended to 250-300. Chromium(III) in the presence of 250-fold Cr(VI)—which was not retained—could be effectively preconcentrated on the NH₄⁺-form of the resin and determined by AAS or diphenylcarbazide (DPC) spectrophotometry. When Cr(VI) was reduced to Cr(III) with Na₂SO₃ solution brought to pH 1 by the addition of 1 M H₂SO₄, and preconcentrated on the resin, total Cr could be determined. The developed method was validated with a blended coal sample CRM-1632. Since the adsorption behavior as a function of pH of possible interferent metal ions, e.g. Ni(II), Co(II), Cu(II), Cd(II), Zn(II), Pb(II) and Fe(III), was similar to that of Cr(III), selective elution of Cr(III) from the resin was realized using a mixture of 1 wt.% H₂O₂+1 M NH₃. The eluate containing Cr as chromate could be directly analyzed by diphenyl carbazide spectrophotometry without any adverse effect from the common interferents of this method, i.e. Fe(III), Cu(II) Hg(II), VO₃⁻, MoO₄²⁻ and WO₄²⁻. Various synthetic waste solutions typical of electroplating bath effluents containing Cr, Cu, Ni, Zn, Na, Ca, cyanide (and chemical oxidation demand (COD), achieved by glucose addition) were subjected to pretreatment procedures such as hypochlorite oxidation (of cyanide) and catalytic oxidation (of COD) with peroxodisulfate. Chromium determination gave satisfactory results. The combined column preconcentration—selective elution—diphenylcarbazide spectrophotometric determination was also successfully applied to the determination of Cr in artificial and real seawater.     

Über Reaktionen von Alkylbiguaniden mit Benzoin beimpH der Biguanidbasen

Summary Alkylbiguanides2 a–e react with benzoin (1) at thepH of the base in different ways.1 undergoes in presence of2 a, c oxidation to benzoic acid which reacts with the bases2 a, c to yield 4-phenyl-1,3,5-triazinamines3 c, 4 c; in presence of2 b 1 is transformed to benzil, which reacts with2 b under rearrangement to yield 1-(4-oxo-5,5-diphenyl-2-imidazolin-2-yl)-3,3-dimethylguanidine (5 b). However, the cycloalkylbiguanides2 d, e, react in presence of nitrogen as well as oxygen with1 to yield piperidine-1-[N-(4,5-diphenylimidazol-2-yl)-carboxamidine] (7 d), resp. morpholine-4-[N-(4,5-diphenylimidazol-2-yl)-carboxamidine] (7 e). The structure of7 e was established by means of an X-ray structure analysis. All proton- and carbon resonances were assigned on the basis of 2-dimensional NMR data.

     

Electroanalytical Behaviour of a Nanoarray Self-Assembled Thiocholesterol Gold Electrode

Thiocholesterol forms a self-assembled monolayer (SAM) on polycrystalline gold, offering a defect-rich hydrophobic surface. This SAM gold electrode has been exploited in batch and flow injection analysis (FIA) as it allows selective detection of hydrophobic analytes such as phenothiazines in presence of potentially interfering species such as ascorbic acid. Several phenothiazines have been investigated. Quantification has been achieved in FIA, in a broad linear concentration range: 0.5–100?μM. The stability of the modified electrode allows more than 500 sample injections in FIA.     

Separation/preconcentration of trace heavy metals in urine, sediment and dialysis concentrates by coprecipitation with samarium hydroxide for atomic absorption spectrometry

Multi-element determination of trace elements in urine and dialysis solutions by atomic absorption spectrometry has been investigated. Coprecipitation with samarium hydroxide was used for preconcentration of trace elements and elimination of matrix elements. To 10 ml of each sample was added 500 μl of 2 mg ml⁻¹ samarium solutions; the pH was then adjusted to 12.2 in order to collect trace heavy metals on samarium hydroxide. The precipitate was separated by centrifugation and dissolved in 1 ml of 1 mol l⁻¹ HNO₃. Coprecipitation parameters and matrix effects are discussed. The precision, based on replicate analysis, is around 5% for the analytes, and recovery is quantitative, based on analysis of spiked samples and solutions including matrix components. The time required for the coprecipitation and determination was about 30 min.     

Determination of pK a Values of Cefdinir and Cefixime by LC and Spectrophotometric Methods and Their Analysis in Pharmaceutical Dosage Forms

The pK _a values of cefdinir and cefixime, which are used in the treatment of bacterial infections, have been determined precisely in water and methanol?Cwater binary mixtures (20% v/v) using spectrophotometric titration and LC, respectively. A simple, fast and precise isocratic high-performance liquid chromatographic (LC) procedure has been developed for the determination of cefdinir and cefixime in drug formulations. This method was validated successfully for specificity, precision, linearity, range, accuracy, limit of detection, and limit of quantitation as per the ICH guidelines. The proposed method can be used for routine analysis of studied cephalosporin compounds and as an alternative tool for drug quality control laboratories.     

Simultaneous determination of amlodipine besylate and rosuvastatin calcium in binary mixtures by voltammetric and chromatographic techniques

Voltammetric and liquid chromatographic (LC) methods have been developed for the simultaneous determination of amlodipine besylate (AML) and rosuvastatin calcium (ROS) for the first time. Detailed electrochemical behavior and simultaneous voltammetric determination of AML and ROS were investigated in detail using glassy carbon electrode (GCE). High-performance liquid chromatography (HPLC) and ultra-performance liquid chromatography (UPLC) were also developed for the comparison. Voltammetric method exhibited linear dynamic responses for the simultaneous assay of AML and ROS in the concentration range between 0.006 and 2.85 μg/mL and between 0.01 and 5.00 μg/mL, with detection limits of 0.001 and 0.003 μg/mL, respectively. On the other hand, LC methods presented a wider linearity range than that of the SWV method between 0.5 and 100 μg/mL with the detection limits of 0.011 and 0.027 μg/mL for AML and 0.034 and 0.042 μg/mL for ROS by UPLC and HPLC techniques, respectively.     

Spectrophotometric determination of various polyanions with polymeric film optodes using microtiter plate reader

Polycation-sensitive membrane optodes based on the chromoionophore 2′,7′-dichlorofluorescein octadecylester (DCFOE) have previously been developed and used for determination of heparin via a titrimetric method. In this study, it is shown that some other important polyanions such as PPS (pentosan polysulfate), DNA, xanthan, Na-alginate, and carrageenan (food additive) can also be readily determined by using DCFOE-based microtiter plate-format optodes (MPOs) and polycationic titrants that bind these polyanionic species. The optical sensors are prepared with poly(vinyl chloride) (PVC), polyurethane (PU), bis(2-ethylhexyl)sebacate (DOS), and 2′,7′-dichlorofluorescein octadecylester (DCFOE) and exhibit reproducible and sensitive absorbance changes in response to the varying polycationic titrant concentrations. Three different polycations; protamine, poly-l-lysine and poly-l-arginine, are employed as titrants. The method has a detection limit of 1 μg mL⁻¹, and a dynamic range of 1–40 μg mL⁻¹. After the quantitative determinations are successfully demonstrated in buffered solutions, similar titrations are also performed in real samples. The method is validated by recovery studies in these samples. The average polyanion recoveries were quantitative [99.7(±1.3) % for pastry cream with vanillin (protamine titrant); 100.4 (±3.3) % for pastry gel with strawberry(PLA titrant), and 102.9(±2.0) % for pastry gel with strawberry (PLL titrant)].