Ilya Kuselman

Simultaneous voltammetric determination of uric and ascorbic acids in urine.

Anodic voltammetric method for simultaneous determination of uric acid (UA) and ascorbic acid (AA) in urine has been developed with the use of a commercial working rotating glassy carbon electrode. UA may be determined in a sample diluted by the buffer supporting electrolyte (HOAc+NH(4)OH; pH 5.1-5.2) approximately 100 times, and AA-in a sample diluted approximately 20 times. Before obtaining the analytical signal the electrode should be maintained in the diluted sample during 3 min at potential 0 V and the working electrode rotating 100 rpm, for achievement of the adsorption equilibrium of inhibitors from the urine matrix. For UA the electron transfer is close to reversible, for AA it is an irreversible one. Optimal voltammetric techniques are the square-wave for UA and the differential pulse for AA. Calibration curves, detection limits and recoveries for both determinations were evaluated as satisfactory.

pH-metric determination of acid values in vegetable oils without titration

A new method for determining acid values in vegetable oils has been developed for a nontitration pH-metric technique with a reagent consisting of 0.20 M triethanolamine in a 1∶1 solution of water and isopropanol. The emulsive properties of this reagent provide rapid (within a minute) and quantitative extraction of free fatty acids from an oil into the solvent phase. Acid values were determined by measuring conditional pH of the emulsified reagent in a pH-meter with an aqueous reference electrode. Three different applications of this technique are discussed.

Human errors and reliability of test results in analytical chemistry

The present paper is a review of the main theoretical and technical aspects of human error treatment (error modelling, reduction and quantification) as applied in aviation, engineering, medicine and other fields. The aim of the review is to attract the attention of analysts and specialists in metrology and quality in chemistry to the human error problem and its influence on the reliability of test results of chemical composition and associated measurement uncertainty. Therefore, the subject of human error is interpreted in the review in application to the conditions of a chemical analytical laboratory.

Traceable property values of in-house reference materials

Abstract The traceability of in-house reference materials (IHRM) is discussed. It is shown that a systematic error in results of a measured value, specific to a measurement method or to a laboratory developing an IHRM, can be overcome if a comparative approach to IHRM characterization is used. A traceability chain of the value carried by the IHRM to the value carried by the reference material with higher metrological status and sufficiently similar matrix (for example, a certified reference material – CRM according to ISO Guide 30) is helpful in such a case. The chain is realized when the IHRM samples are analysed simultaneously with the CRM samples under the same conditions. This and other traceability chains necessary for the IHRM development are examined as the measurement information sources.

Redox-potentiometric determination of peroxide value in edible oils without titration

Standard methods for peroxide value determination in edible oils, which are based on KI oxidation by the hydroperoxides and volumetric titration of the liberated iodine, have been improved using redox-potentiometric iodine determination without titration. Stages of the KI oxidation and redox-potentiometric measurements were combined in the same electrochemical cell. The limit of quantitation of the new method is 0.16 meq kg(-1), which allows the analysis of fresh refined oils. The method is simple, not time and labor consuming, and suitable for automation.

IUPAC/CITAC Guide: Selection and use of proficiency testing schemes for a limited number of participants—chemical analytical laboratories (IUPAC Technical Report)

A metrological background for implementation of proficiency testing (PT) schemes for a limited number of participating laboratories (fewer than 30) is discussed. Such schemes should be based on the use of certified reference materials (CRMs) with traceable property values to serve as PT items whose composition is unknown to the participants. It is shown that achieving quality of PT results in the framework of the concept “tested once, accepted everywhere” requires both metrological comparability and compatibility of these results. The possibility of assessing collective/group performance of PT participants by comparison of the PT consensus value (mean or median of the PT results) with the certified value of the test items is analyzed. Tabulated criteria for this assessment are proposed. Practical examples are described for illustration of the issues discussed.

Interlaboratory comparison of test results of an ordinal or nominal binary property: analysis of variation

Applications of a new statistical method Ordinal Analysis of Variance (ORDANOVA) for interlaboratory comparisons of measurement or test results of semi-quantitative (ordinal) and qualitative (binary) properties are discussed. ORDANOVA can be helpful for validation of measurement or test methods, proficiency testing of laboratories, development of reference materials with certified semi-quantitative and qualitative properties, that is, probably in every field where ANOVA is applied for quantitative properties. A statistics and criteria are proposed for performance assessment of laboratories active in semi-quantitative and qualitative testing and for other purposes of statistical analysis of such test results.

Alternative methods for titratable acidity determination

Methods for determination of titratable acidity, other than traditional titration, i.e. methods without titration, are considered. A number of them use analytical acid-base reagents which quickly convert a mixture of strong and weak acids into a new system. This conversion makes it possible to obtain directly the analytical signal (pH, optical density, etc.) for titratable acidity calculation. These methods in stationary conditions and in flow injection analysis are discussed. Methods not using acid-base reagent (iodide-iodate, chromatographic, spectroscopic and others) are also described. The advantages of the alternative methods such as the decrease labour-consumption and analysis time, simplicity of automation and others are shown.

House-of-security approach to measurement in analytical chemistry: quantification of human error using expert judgments

A new technique for quantification of human errors in chemical analysis using expert judgments is described. This technique is based on the house-of-security approach developed recently in the field of safety and security for prevention of terrorist and criminal attacks against an organization. The following relative quantification parameters (expressed in %) are proposed in the technique: (a) likelihood score of human error in a chemical analytical measurement/testing method, (b) severity score of human error for reliability of the test results, (c) importance score of a component of a laboratory quality system, and (d) effectiveness score of the quality system as a whole in preventing/blocking human error. As an example, 34 scenarios of human error in pH measurement of groundwater are discussed and quantified.

Assessment of limits of detection and quantitation using calculation of uncertainty in a new method for water determination

Abstract An approach to the assessment of the limit of detection and the limit of quantitation using uncertainty calculation is discussed. The approach is based on the known evaluation of the limits of detection and quantitation as concentrations of the analyte equal to three and ten standard deviations of the blank response, respectively. It is shown that these values can be calculated as the analyte concentrations, for which relative expanded uncertainty achieves 66% and 20% of possible results of the analyte determination, correspondingly. For example, the calculation is performed for the validation of a new method for water determination in the presence of ene-diols or thiols, developed for analysis of chemical products, drugs or other materials which are unsuitable for direct Karl Fischer titration. A good conformity between calculated values and experimental validation data is observed.