Determination of Pb and Cu by Anodic Stripping Voltammetry Using Glassy Carbon Electrodes Modified with Mercury or Mercury-Nafion Films

 Two different approaches for the modification of glassy carbon electrodes using a mercury film and mercury-nafion are compared. The mixture of mercury(II) chloride solution with a nafion solution diluted in ethanol is used to coat the polished glassy carbon surface. The modified working electrodes are compared when measuring Pb and Cu in real seawater samples. An optimisation of the parameters during the formation of the films was done to obtain well-defined stripping peaks. The type of inert supporting electrolyte and the pH play an important role on the sensitivity of the measurement. Results for Pb and Cu determinations show the advantages of Hg-nafion modification as an alternative method. These advantages include a shorter modification time, the avoidance of Hg solutions during the formation of the Hg film and an improved sensitivity for Pb determination. Received March 16, 1999. Revision April 24, 2000.     

Development of a capillary electrophoretic method for the analysis of low-molecular-weight amines from metal working fluid aerosols and ambient air

A method for the determination of low-molecular-weight amines from indoor and ambient air was developed using a concentration device followed by CE coupled with indirect spectrophotometric and mass spectrometric detection that enables a reliable, rapid-response and easy-to-operate method. In indirect detection method, the selected amines were separated from interfering metal ions and amino alcohols present in the samples with an imidazole-based buffer with ethanol and EDTA as modifier. By replacing imidazole with ammonium, the final buffer was applicable for MS detection for the analytes with m/z higher than 50. A novel monolithic polymer material based on poly(methacrylate-acrylate) copolymer was developed for sampling short-chain amines from the gaseous phase. The selected analysis conditions were applied to quantify the selected short-chain amines with detection limits for the whole procedure determined between 1 and 2 microg/filter when 40 L air was sampled with 1 L/min velocity. Improved linearity and precision were obtained when the raw, time-scaled electropherogram data were transformed into mobility-scale applied for the determination of the performance characteristics of the methods. The applicability of the process of data transformation into the mobility scale was demonstrated by studying the matrix effect of water-miscible metal working fluid (stable water-oil emulsion) and of ambient air as real samples. CE-indirect UV and CE-MS, combined with the possibility of rapid air sampling, can be useful for the estimation of short-term exposure of the selected biogenic amines.     

Calibrated nanoinjections of mercury vapor

A simple technique for the calibration of mercury vapor chemosensors is described. It is based on a reductive deposition of a well-defined quantity of mercury (0) onto gold wire followed by thermal evaporation of the mercury into the sensor cell. The quantity of mercury on the gold wire was measured electrochemically by oxidation before and after heating, as well as after storage under different conditions. It is shown that the technique can be used for calibrated injections of nanogram quantities of mercury. The approach was applied to test the performance of ultrasensitive mercury chemoresistors.     

Development of a capillary electrophoresis-mass spectrometry method for the determination of formaldehyde releasers as their hydrolysis products and amino alcohols from metal working fluids

Metal working fluids (MWFs) are widely used as lubricants and coolants for different industrial operations. Biocides are ingredients of MWFs to control the microbial growth; derivatives of hexahydrotriazines and oxazolidines are generally used. Because of the lack of appropriate characterization, an existing capillary electrophoretic method for their quantification was improved. During the process of optimization, it became clear that hydrolysis products, derivatives of amino alcohols, severely interfere with the separation procedure. Since indirect-UV detection lacked the required selectivity, mass-selective detection was employed. NMR and MS established the absence of amino alcohols in the original educts. The aqueous solutions of the biocides stored for extended time remained amino alcohol-free, suggesting that these amino alcohols are formed from the biocides during the capillary electrophoretic separation. The observation of narrow and symmetric peaks indicated hydrolysis, and the polarity of the products implied favorable conditions for capillary electrophoretic separation. Methods were optimized for the analysis of the amino alcohols, the hydrolytic products of the formaldehyde releasers, using indirect-UV and MS detection. This method was extended to other likely solutes used as alkaline-reserve ingredients. The analytes were separated within 9 min with a high precision of migration times (the RSDs were below 1.5%). When quantifying from mobility scale, the calibration curves produced linearity with regression coefficients in the range of 0.990-0.999. The detection limit was lower than 1 mg/L in the case of MS detection. The influence of water-based MWF was also investigated, and no matrix effect on the migration of the analytes and on the peak areas was observed.     

Calibrated nanoinjections of mercury vapor

A simple technique for the calibration of mercury vapor chemosensors is described. It is based on a reductive deposition of a well-defined quantity of mercury (0) onto gold wire followed by thermal evaporation of the mercury into the sensor cell. The quantity of mercury on the gold wire was measured electrochemically by oxidation before and after heating, as well as after storage under different conditions. It is shown that the technique can be used for calibrated injections of nanogram quantities of mercury. The approach was applied to test the performance of ultrasensitive mercury chemoresistors.     

Preparation of a high-performance multi-lectin affinity chromatography (HP-M-LAC) adsorbent for the analysis of human plasma glycoproteins

We report on the preparation of an improved multi-lectin affinity support for HPLC separations. We combined the selectivity of three different lectins: concanavalin A (ConA), wheat germ agglutinin (WGA), and jacalin (JAC). Each lectin was first covalently immobilized onto a polymeric matrix and then the three lectin media were combined in equal ratios. The beads were packed into a column to produce a mixed-bed multi-lectin HPLC column (high-performance multi-lectin affinity chromatography (HP-M-LAC)) for fast chromatographic affinity separations. The support was characterized with respect to kinetics of immobilization, ligand density, and binding capacity for human plasma glycoproteins. A high lectin density (15 mg/mL of beads) was found to be optimal for the binding of glycoproteins from human plasma. A single clinical sample can be fractionated in less than 10 min per run, making this a useful sample preparation tool for proteomics/glycoproteomics studies associated with disease abnormalities.     

Amino Acid Determination Using Screen-Printed Electrochemical Sensors

The use of a screen-printed electrochemical sensor (SPES) strip, consisting of a two-electrode system (a carbon working electrode and Ag/AgCl reference electrode), for amino acid determination is reported.The behaviour of the SPES toward cysteine and tyrosine is investigated using linear sweep and hydrodynamic voltammetries. The SPES operate at a lower oxidation potential (vs. Ag/AgCl) compared with traditional carbon and platinum electrodes, in a buffer solution (pH = 7) prepared using 0.1 M phosphates and 0.1 M KCl. The linear response lies between 5 * 10⁻⁵ M and 5 * 10⁻⁴ M for both amino acids while the sensitivity is 2.95±0.03 µA mM⁻¹ for cysteine and 8.00±0.01 µA mM ⁻¹for tyrosine; the correlation coefficient is higher than 0.9980. The sensors were applied to the analysis of some commercial pharmaceutical samples, and the results suggested that the devices hold promise in this application area.