Lars Kryger

Multiple-scanning potentiometric stripping analysis

Abstract A computerized data acquisition technique— multichannel potentiometric monitoring—is used in conjunction with potentiometric stripping analysis. Multiple-scanning stripping potentiograms can be recorded so that the analytical signals are enhanced. A minicomputer with an internal store of4K 16-bit words suffices for experimental control and data treatment. The technique is suitable for stripping analysis with preconcentration times of 60–90 s at a mercury film electrode with linear response ranges of 1–100 μg l -1 for cadmium(II) and lead(II). For preconcentration times of 30 min, the limit of detection is about 5 ng l -1 . Preliminary tests on continuous flow analysis are reported.

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.

Differential potentiometric stripping analysis

Abstract Differential potentiometric stripping analysis, a sensitive instrumental modification of potentiometric stripping analysis, is described. For trace elements like cadmium and lead, which exhibit transport-controlled potentiometric stripping, signal enhancement is possible by employing a scheme involving multiple stripping and re-reduction of the preconcentrated analytes. For such elements the detection limit is below 5 × 10-10 M with 60-s plating. The accuracy of the technique is tested on a biological reference material. Like potentiometric stripping analysis, the technique presented is not sensitive to reversible redox couples in solution.

A versatile computerized system for the development and comparison of electroanalytical procedures

Abstract The computerized system reported is suitable for potentiometric and voltammetric techniques. All instrumental settings are fully automated and new analytical schemes can be implemented simply by software modifications. A dedicated 4K, 16-bit microcomputer allows rapid real-time data acquisition and processing. By application of a data acquisition scheme simulating a multichannel analyser, stripping potentiograms and chronopotentiograms can be conveniently represented in digital form as time vs. potential relationships. Procedures developed on the system can be transferred to microprocessorcontrolled equipment as the software for complete analytical procedures, including device handlers, data storage buffers and graphic output, occupies 3–4K words. Flexibility in program editing and assembling is obtained with an optional data link to a medium-sized, time-shared computer with extensive software packages. The link described is of simple construction and can be readily established between computers with standard teletype terminals. The performance of the system is illustrated by comparing the selectivities of two established voltammetric stripping techniques with the selectivity of a new potentiometric technique developed on the system.

The determination of traces of cadmium, lead and thallium in fly ash by potentiometric stripping analysis

Abstract The suitability of potentiometric stripping analysis for the determination of cadmium, lead and thallium in fly ash and in waters polluted by leaching of fly ash is assessed. By an appropriate choice of medium and of electrolysis potential and by employing a rotating working electrode, it is possible to eliminate interferences from electroactive species often found in fly ash in high concentrations. The accuracy obtained in a study of a certified coal fly ash (SRM 1633a) is satisfactory.

Computerized electroanalysis: Part I. Instrumentation and programming

Abstract The electronic circuit of a computerized electroanalytical instrument is described. The computer is programmed in a high-level language. The instrument can generate linear potential scans of any conceivable form within a wide range of scan rates. Pulses of varying height and duration can be superimposed on the linear scans. Stirrer motors, inert gas flow and addition of standard reagent are under computer control, thus permitting completely automatic analytical procedures. Data are displayed on a graphical screen. Results from anodic stripping experiments are given.

Computerized electroanalysis : Multiple scanning anodic stripping and its application to sea water

Abstract the determination of copper, lead, zinc, cadmium and bismuth in standard sea water samples by multiple scanning anodic stripping has been investigated. The influence of plating potential and sample pH has been studied.

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.

Reductive potentiometric stripping analysis for elements forming sparingly soluble mercury compounds with amalgamated metal as the reducing agent

Abstract The suitability of amalgamated metals as reducing agents in reductive potentiometric stripping analysis is demonstrated. The amalgams are generated in a mercury pool by electrolysis of dissolved metals. During the stripping process, the reducing agent, which is stored inside the working electrode, reacts with sparingly soluble mercury compounds of the analytes preconcentrated on the electrode surface. The importance of the timing of the processes involving amalgam formation and analyte preconcentration is discussed. With amalgamated sodium, the technique is suitable for the determination of selenium and sulphur at the 10 -7 M level with 1–2 min preconcentration. Halides may be determined at the 10 -6 M level with a few seconds of preconcentration; a less powerful reducing agent such as amalgamated zinc is then suitable.

Reductive potentiometric stripping analysis

Abstract The feasibility of determining trace elements by anodic preconcentration and subsequent reductive potentiometric stripping analysis is demonstrated. The determination of manganese is chosen as an example. The interferences of various anodic films formed on the platinum working electrode are discussed. Certain interferences may be minimized by a careful choice of electrolysis potential and pH. The technique is suitable for the determination of manganese in the μg l -1 range. The accuracy of the technique, tested on standard biological materials, is satisfactory.