Selectivity and specificity in analytical chemistry. General considerations and attempt of a definition and quantification

Selectivity and specificity are performance characteristics of analytical methods which are frequently used in analytical literature. In general, the terms are applied verbally and a quantification of selectivity and specificity is given rarely. Excepted are methods like chromatography and ISE sensoring which use individual quantities such as selectivity coefficients, indices and other parameters to characterize analytical procedures and systems. Here a proposal is given to characterize selectivity and specificity quantitatively by relative values in a range of 0 to 1 expressing so a certain degree of selectivity and specificity. By examples it will be shown that the derived quantities characterize analytical methods and problems in a plausible way.     

Selectivity versus specificity in chromatographic analytical methods

  Analytical chemists should be aware of the differences between selectivity and specificity. Few analytical methods, including the chromatographic analytical methods, are truly specific. The International Union of Pure and Applied Chemistry (IUPAC) recommends that specificity is the ultimate of selectivity, therefore, analysts should promote this concept and aim to achieve highly selective analytical methods. Received: 30 September 1999 / Accepted: 17 January 2000     

A closer look at analytical signals

Analytical chemistry will be considered here as the measurement science of chemistry that generates, treats, and evaluates signals which contain information about the composition and structure of samples. Analytical information is always obtained from signals. Characteristics and peculiarities of analytical signals will be considered from a very general point of view. A mathematical model of the influencing of signals will be given from which essential performance characteristics of analytical methods can be derived, e.g. sensitivity, cross-sensitivity, specificity, selectivity, and ruggedness (robustness).     

Some remarks on the quantitative expression of the selectivity of an analytical procedure

The selectivity of an analytical method may be defined as expressing the degree to which a component can be determined in the presence of other but similarly behaving components without interference. The method itself will usually serve for determination of the other components, under slightly different conditions. The selectivity is closely related to the resolution of the method and also to the resolution of the instrument used for obtaining the signals. A simple formula is suggested for expressing the percentual degree of selectivity of an analytical procedure, on the basis of signal overlap caused by the interfering components, and can be used quite generally. A distinction is made between the terms analytical selectivity and selectivity of an analytical procedure, and between selectivity and specificity.     

Assessing and Advancing Technology for the Noninvasive Measurement of Clinical Glucose

Abstract

Noninvasive glucose sensing is an active area of research and development with many different approaches being explored since the 1980s. The promise of this approach is to provide a measure of the blood glucose concentration in a rapid, painless, and cost-effective manner so that people with diabetes can better maintain tight glycemic control, thereby reducing the complications of diabetes. This mini-review covers the major approaches to noninvasive glucose sensing and focuses on issues that must be resolved before a clinically useful device can be developed. A strong emphasis is placed on measurement selectivity, and methods to examine and characterize the selectivity of such a complex analytical problem are discussed.     

Problems and Possibilities of Modern Trace Analysis

As a result of the development of measuring techniques, analytical chemists can now determine very small quantities as well as trace concentrations of the order of 10^?8% with good accuracy. In exceptional cases it is even possible to detect 10⁵ atoms of an element. In this review, definitions of important analytical terms are outlined and a critical appraisal of the principal methods of trace analysis is given.     

Detection methods and performance criteria for genetically modified organisms

Detection methods for genetically modified organisms (GMOs) are necessary for many applications, from seed purity assessment to compliance of food labeling in several countries. Numerous analytical methods are currently used or under development to support these needs. The currently used methods are bioassays and protein- and DNA-based detection protocols. To avoid discrepancy of results between such largely different methods and, for instance, the potential resulting legal actions, compatibility of the methods is urgently needed. Performance criteria of methods allow evaluation against a common standard. The more-common performance criteria for detection methods are precision, accuracy, sensitivity, and specificity, which together specifically address other terms used to describe the performance of a method, such as applicability, selectivity, calibration, trueness, precision, recovery, operating range, limit of quantitation, limit of detection, and ruggedness. Performance criteria should provide objective tools to accept or reject specific methods, to validate them, to ensure compatibility between validated methods, and be used on a routine basis to reject data outside an acceptable range of variability. When selecting a method of detection, it is also important to consider its applicability, its field of applications, and its limitations, by including factors such as its ability to detect the target analyte in a given matrix, the duration of the analyses, its cost effectiveness, and the necessary sample sizes for testing. Thus, the current GMO detection methods should be evaluated against a common set of performance criteria.     

Determination of Aldehydes and Ketones Pollutants in Ambient and Polluted Air by HPLC with Precolumn Chemical Derivatization

In the last years, aldehydes and ketones have been the pollutants constantly in air with the development of the chemical industry. Most of aldehydes and ketones are toxic or carcinogenic. There are six carbonyl compounds in the pollutants with the maximum permission concentration, which limited by our state standard in residential area, workshop air and surface water formulated in 1979. In New Clean Air Act of America, there are 189 toxic and harmful pollutants including nine carbonyl compounds.Therefore, it is extremely necessary to study the sampling process and analytical method of aldehydes and ketones. At present, the main domestic analytical methods are colorimetric method and titrimetric method. In addition, ion chromatography and gas chromatography are also adopted. These methods can only be used for the analysis of one or two kinds of aldehydes and ketones. The absorbent solutions in these methods includes acidic sulfate, potassium hydroxide,water and weak acid. Because the reaction of these absorbent solutions and carbonyl compounds has no specificity, the selectivity and sensitivity of these methods are often low. Thus, the application of these methods in analysis of actual samples are limited greatly.     

Quality criteria for residue analysis and reference materials. Relationship between legal procedures and materials

Summary For qualitative results objective reliability checks are often not present at all or applicable. Interlaboratory ring testing of methods, as sometimes required, showed often not to be applicable simply because enough adequate laboratories are not available. For instance this situation applied to the large number of methods of unclear reliability status, to be used for residue monitoring of hormonal growth promotors (anabolic agents), which are completely banned within the European Communities since January 1988. This impasse was circumvented in 1987 with the formulation by an international group of analytical experts of a set of quality criteria for common analytical techniques like TLC, GC and HPLC (separation), UV, MS and IR spectrometry (detection) and immunoassays (separation and detection). These criteria, now published, are overviewed, as well as the availability of the control and reference materials belonging to them for actual analytical quality control and for validation of laboratories. Although developed for anabolic agents this new approach is applicable in practice for nearly all organic analytes and since very recently also for heavy metals. This approach has clear consequences for the mandatory quality of legislative residue analyses of food stuffs. As based on, amongst others, the combined experience of regulatory residue chemists within the EC, a collection of experimental selectivity indices is presented to rank the required specificity of regulatory residue methods (ranging from within laboratory orientation to international forensic purposes) in an objective way. Finally an estimate is summarized of the financial consequences of the applicable analytical techniques.     

Applications of on-line weak affinity interactions in free solution capillary electrophoresis

The impressive selectivity offered by capillary electrophoresis can in some cases be further increased when ligands or additives that engage in weak affinity interactions with one or more of the separated analytes are added to the electrophoresis buffer. This on-line affinity capillary electrophoresis approach is feasible when the migration of complexed molecules is different from the migration of free molecules and when separation conditions are nondenaturing. In this review, we focus on applying weak interactions as tools to enhance the separation of closely related molecules, e.g., drug enantiomers and on using capillary electrophoresis to characterize such interactions quantitatively. We describe the equations for binding isotherms, illustrate how selectivity can be manipulated by varying the additive concentrations, and show how the methods may be used to estimate binding constants. On-line affinity capillary electrophoresis methods are especially valuable for enantiomeric separations and for functional characterization of the contents of biological samples that are only available in minute quantities.     

Bioelectrocatalytic Synthesis: Concepts and Applications

Bioelectrocatalytic synthesis is the conversion of electrical energy into value-added products using biocatalysts. These methods merge the specificity and selectivity of biocatalysis and energy-related electrocatalysis to address challenges in the sustainable synthesis of pharmaceuticals, commodity chemicals, fuels, feedstocks and fertilizers. However, the specialized experimental setups and domain knowledge for bioelectrocatalysis pose a significant barrier to adoption. This review introduces key concepts of bioelectrosynthetic systems. We provide a tutorial on the methods of biocatalyst utilization, the setup of bioelectrosynthetic cells, and the analytical methods for assessing bioelectrocatalysts. Key applications of bioelectrosynthesis in ammonia production and small-molecule synthesis are outlined for both enzymatic and microbial systems. This review serves as a necessary introduction and resource for the non-specialist interested in bioelectrosynthetic research.     

生物样品中硒的测定方法研究进展

硒是生物体必需的微量元素,硒的毒性和营养功能与其总量有关,硒的测定具有重要意义。综述了生物样品中硒的测定分析方法研究进展,包括：样品预处理方法,荧光法,原子吸收光谱法,原子荧光光谱法,电感耦合等离子体发射光谱法,吸光光度法,化学发光法,电分析法,中子活化分析法,色谱法等。     

Some remarks on the information power and selectivity of analytical processes

The consistency of the equation given by Shannon for the transfer of maximum amount of information in one channel, and the equation deduced by Kaiser for the expression of the information power of analytical methods is shown. The fundamental difference between the maximum amount of information obtainable by an instrument and that by an analytical procedure is reported. In the second case the selectivity of the analytical procedure also has to be taken into consideration.     

Radioimmunoassay

Biologically active substances are often effective in nanogram or even smaller quantities. Investigations of their mode of action therefore require highly sensitive microanalytical methods of detection. Chemical, chromatographic or spectrometric methods frequently lack the required sensitivity; it was only after the discovery of the radioimmunoassay (RIA) that quantitative determination of minute amounts of substances in the presence of a millionfold excess of other compounds became possible. The radioimmunoassay combines the extreme sensitivity of detection of radioactively labeled substances with the high specificity of immunological reactions. The superiority of radioimmunological methods over other analytical techniques rests upon their sensitivity, specificity, facile application, and especially their broad general scope.     

Photopolymerization and photostructuring of molecularly imprinted polymers for sensor applications—A review

Biosensors are already well established in modern analytical chemistry, and have become important tools for clinical diagnostics, environmental analysis, production monitoring, drug detection or screening. They are based on the specific molecular recognition of a target molecule by a biological receptor such as an antibody or an enzyme. Synthetic biomimetic receptors like molecularly imprinted polymers (MIPs) have been shown to be a potential alternative to biomolecules as recognition element for biosensing. Produced by a templating process at the molecular level, MIPs are capable of recognizing and binding target molecules with similar specificity and selectivity to their natural analogues. One of the main challenges in MIP sensor development is the miniaturization of MIP structures and their interfacing with the transducer or with a microchip. Photostructuring appears thereby as one of the most suitable methods for patterning MIPs at the micro and nano scale, directly on the transducer surface. In the present review, a general overview on MIPs in biosensing applications is given, and the photopolymerization and photopatterning of MIPs are particularly described.     

Patents and literature

Protein engineering and site-directed mutagenesis is becoming immensely important in both fundamental studies and commercial applications involving proteins and enzymes in biocatalysis. Protein engineering has become a powerful tool to help biochemists and molecular enzymologists elucidate structure-function relationships in enzymic active sites, to understand the intricacies of protein folding and denaturation, and to alter the selectivity of enzymatic catalysis. Commercial applications of engineered enzymes are being developed to increase protein stability, widen or narrow substrate specificity, and to develop novel approaches for use of enzymes in organic synthesis, drug design, and clinical applications. In addition to protein engineering, novel expression systems have been designed to prepare large quantities of genetically engineered proteins. Recent US patents and scientific literature on protein engineering, site-directed mutagenesis, and protein expression systems related to protein engineering are surveyed. Patent abstracts are summarized individually and a list of literature references are given.     

Monitoring and characterization of polyaromatic compounds in the environment

This paper provides an overview of analytical techniques and instruments used to monitor and characterize polycyclic aromatic compounds (PACs) in the environment. The basic operating principles of various analytical approaches and systems are presented. The review deals specifically with spectroscopic methods, chromatographic and hyphenated techniques, and field monitoring devices. Emphasis is given to portable devices that can be used under field conditions. Specific examples of analytical techniques and instruments developed in the authors's laboratories will be discussed to illustrate the usefulness and potential of these approaches for environmental monitoring and characterization of PACs.     

Liquid chromatography-inductively coupled plasma mass spectrometry.

The technique of coupling liquid chromatography to inductively plasma mass spectrometry (ICP-MS) is reviewed. A brief introduction to the ICP-MS instrument is given as well as methods to couple the two analytical instruments together. The various types of LC that have been used with ICP-MS detection are discussed and advantages over traditional methods of detection are highlighted, such as the improvements in sensitivity and selectivity. Several applications that have been described in the literature are reviewed. An outlook for the future of LC-ICP-MS, particularly with regard to elemental speciation is given.     

How Far the Ion-Selectivity Should be Improved; a Task Oriented Limit of Ion-Selective Electrode Design

Abstract

A simple formula is proposed for the definition and the calculation of the highest acceptable selectivity coefficient values of ion-selective electrodes. On the basis of the formula which is based on the consideration of the precision of the direct potentiometric measuring techniques one can easily decide whether the selectivity of an electrode is sufficient or not for solving a well defined analytical task correctly. On the other, hand it indicates clearly for ion-selective electrode developing teams or manufacturers how far the ion-selectivity of an electrode should be improved for a certain type of analytical application.

Characteristic selectivity values for a few concrete analytical sample types are given in table together with the selectivity coefficients of the corresponding, existing ion-selective electrodes.     

Validation and qualification: the fitness for purpose of mass spectrometry-based analytical methods and analytical systems

The context of validation for mass spectrometry (MS)-based methods is critically analysed. The focus is on the fitness for purpose depending on the task of the method. Information is given on commonly accepted procedures for the implementation and acceptance of analytical methods as ‘confirmatory methods’ according to EU criteria, and strategies for measurement. Attention is paid to the problem of matrix effects in the case of liquid chromatography-mass spectrometry-based procedures, since according to recent guidelines for bioanalytical method validations, there is a need to evaluate matrix effects during development and validation of LC-MS methods “to ensure that precision, selectivity and sensitivity will not be compromised”. Beneficial aspects of the qualification process to ensure the suitability of the MS analytical system are also evaluated and discussed.