Chemical accumulation and voltammetric determination of traces of nickel(II) at glassy carbon electrodes modified with dimethyl glyoxime containing polymer coatings.

The objective of the present study was to develop a solid mercury free electrode for the voltammetric determination of traces of nickel(II) in solution. For this purpose chemically modified electrodes (CME's) were constructed from glassy carbon coated with dimethylglyoxime-containing polymers. CME's based on a composite matrix, which contained polyvinyl chloride, polyaniline, and dimethylglyoxime were shown to possess the ability to accumulate traces of nickel(II) from ammonia buffered aquatic solutions by a purely chemical attachment. Moreover the nickel(II) contents of such solutions could be determined using voltammetric quantitation of the nickel(II) dimethylglyoximate deposits on the CME surfaces and the standard addition technique. The CME surfaces could subsequently be regenerated by acid treatment. The limit of detection for Ni(II) following a 240 s chemical deposition was estimated as 18 mug Ni l(-1), and the CME results for traces of Ni(II) in fresh water compared well with the results obtained by atomic absorption spectroscopy. Moreover the CME's retained their sensitivity for more than two days, i.e. significantly longer than the 3 h, during which analogous carbon paste electrodes completely lost their affinity to nickel(II).

Accumulation and voltammetric determination of complexed metal ions at zeolite-modified sensor electrodes.

Chemically modified electrodes based on zeolite-containing graphite pastes were constructed and evaluated as sensor electrodes for the voltammetric determination of traces of metallic species in solution. Zeolite molecular sieves with pore sizes of 3, 4, 5, and 10 A were all suitable for chemical deposition and subsequent voltammetric quantitation of traces of Cu(II), Cd(II), and Zn(II). The highest sensitivity was obtained using the zeolite with the 10 A pore size. The detection limit obtained for Cu(II) was 0.3 muM following a 2 min chemical deposition. The detection limits for Cd(II) and Zn(II) following a 4 min chemical deposition were 87 nM and 145 nM, respectively. The effects on the zinc signal of coexisting metallic species in the ammonia deposition medium were studied. While the addition of Hg(II) gave rise to increasing zinc signals, the addition of Ag(I), Cu(II), Cd(II), Ni(II), and Co(II) resulted in decreasing zinc signal amplitudes. Most notably, the magnitude of the interference from these latter metal ions correlated well with the coordination numbers of their ammonia complexes. Thus the electrode acted as a device which was sensitive to the size and shape of the interfering metal complex.

Preconcentration and determination of Bismuth (III) at a chemically modified electrode containing 1-(2-pyridylazo)-2-naphthol.

A chemically modified electrode (CME) containing 1-(2-pyridylazo-2-naphthol is evaluated for its ability to preconcentrate bismuth(III) prior to quantification by voltammetry. The CME approach is shown to be sufficiently sensitive for sub-nanomolar concentrations to be determinable after chemical deposition for 60 sec. Further, when the bismuth is deposited from iodide-containing sulphuric acid media, the discrimination against interference by copper(II) is significantly better than that obtained with conventional stripping analysis. The results obtained for Bi(III)( in an NBS reference solution agree well with the recommended value.

Evaluation of single-point calibration in flow potentiometric stripping analysis.

The use of a single-point calibration in flow potentiometric stripping analysis has been evaluated. For a number of sample matrices, the results obtained by calibration methods agree with those obtained by using standard addition. The most serious source of systematic error is inhibition in the deposition step, caused by organic surfactants and chelating agents in the sample matrix. Consequently, the use of the calibration method should be restricted to samples which have been totally mineralized. It is shown that most sources of systematic error in the calibration method will result in underestimation of the analyte concentration.

A theoretical and experimental study of the waveform in potentiometric stripping analysis with a rotating mercury-film electrode-the reversible case.

The potential-time transient in potentiometric stripping analysis with a rotating mercury-film electrode is simulated digitally by means of the finite-difference Cranck-Nicolson method. Good agreement with experimental results is obtained. The relations between peak shape and signal duration for reversible analyte systems are discussed, and it is shown that severe peak overlap gives rise to distortions of the composite signal.

Interpretation of analytical chemical information by pattern recognition methods-a survey.

Since the late sixties, pattern recognition techniques have been used by analytical chemists to facilitate the interpretation of multivariate analytical information. Most research within the field has focused on adapting pattern recognition methods to chemical data. This has been necessary since chemical data are often complicated by the fact that distributions are unknown. Through the first decade of chemical pattern recognition, promising results have been obtained even though the data sets studied have frequently been rather small for statistical analysis. The past few years have shown that an increasing number of analytical chemists are interested in the sheer utility of pattern recognition. This can be taken as a valid sign of a useful approach. The present communication surveys this development. Those methods which have proved most useful for analytical chemical data are described in some detail, and applications within the various fields of analytical chemistry are reviewed.