Quantitative Analysis

quantitative analysis

[′kwän·ə·tād·iv ə′nal·ə·səs] (analytical chemistry) The analysis of a gas, liquid, or solid sample or mixture to determine the precise percentage composition of the sample in terms of elements, radicals, or compounds.

Quantitative Analysis

the aggregate of chemical, physicochemical, and physical methods of determining the quantitative ratios of constituents in the substance being analyzed. Together with qualitative analysis, quantitative analysis is one of the major branches of analytical chemistry. Depending on the amount of substance taken for analysis, there are macroanalysis, semimicroanalysis, microanalysis, and ultramicroanalysis. A macroanalysis uses a sample usually greater than 100 mg and a solution volume greater than 10ml; an ultramicroanalysis uses 1–10⁻¹ mg and 10⁻³−10⁻⁶ml, respectively.

Depending on the object being studied, inorganic quantitative analysis and organic quantitative analysis are distinguished, with the latter in turn divided into elemental analysis, functional group analysis, and molecular analysis. Elemental analysis makes it possible to determine the compositions of elements (ions), and functional group analysis, the content of functional (reactive) atoms or groups in the object being analyzed. Molecular quantitative analysis entails analysis of individual chemical compounds characterized by a definite molecular mass. Phase diagram analysis is of considerable importance and constitutes an aggregate of methods for the separation and analysis of individual structural (phase) components of heterogeneous systems.

In addition to specificity and sensitivity, an important feature of quantitative analysis is accuracy, that is, the value of the relative error in the determination. Accuracy and sensitivity are expressed in percent.

The classical chemical methods of quantitative analysis include gravimetric analysis, which is based on the accurate measurement of the weight of the substance, and volumetric analysis. The latter includes titrimetric volumetric analysis, comprising methods of measuring the volume of the reagent solution expended in the reaction with the substance under analysis, and gas volumetric analysis, comprising methods of measuring the volume of the gaseous products being analyzed.

In addition to the classical chemical methods, physical and physicochemical (instrumental) methods of quantitative analysis are widespread; they are based on the measurement of optical, electrical, adsorption, catalytic, and other characteristics of the substances that are dependent on their amount (concentration). These methods are usually divided into the following groups: electrochemical methods (conductometry, polarography, potentiometry); spectral, or optical, methods (emission and absorption spectral analysis, photometric analysis, colorimetric analysis, turbidimetric analysis, luminescence analysis); chromatographic methods (liquid, gas, and gas-liquid chromatography); X-ray methods (absorption and emission X-ray analysis, X-ray phase analysis); radiometric methods (activation analysis); and massspectrometric methods.

These methods, which are inferior to chemical methods in accuracy, are significantly superior in sensitivity, selectivity, and the speed at which the analysis is performed. The accuracy of the chemical methods of quantitative analysis is usually within the limits of 0.005–0.1 percent; the error by instrumental methods is 5–10 percent and sometimes significantly greater. The sensitivity of some methods of quantitative analysis is given in Table 1.

As a rule, microscopic amounts of a substance are required in physical and physicochemical methods of quantitative analysis. The analysis can often be conducted without destroying the

Table 1. Sensitivity of some methods of quantitative analysis
(in percent)
Volumetrie	10⁻¹
Gravimetric	10⁻²
Emission spectral	10⁻⁴
Absorption x-ray spectral	10⁻⁴
Mass-spectrometric	10⁻⁴
Coulometric	10⁻⁵
Luminescence	10⁻⁶-10⁻⁵
Photometric colorimetric	10⁻⁷-10⁻⁴
Polarographic	10⁻⁸-10⁻⁶
Activation	10⁻⁹-10⁻⁸

sample; continuous and automatic recording of the results is also sometimes possible. These methods are employed for analyzing high-purity substances, evaluating product yields, and studying the properties and structures of various substances and compounds.

V. V. KRASNOSHCHEKOV

quantitative analysis

analysis

[ah-nal´ĭ-sis] (pl. anal´yses) separation into component parts.psychoanalysis. adj., adj analyt´ic.activity analysis the breaking down of an activity into its smallest components for the purpose of assessment.bivariate analysis statistical procedures that involve the comparison of summary values from two groups on the same variable or of two variables within a group.blood gas analysis see blood gas analysis.chromosome analysis see chromosome.concept analysis examination of the attributes of a concept as it occurs in ordinary usage in order to identify the meanings attached to the concept.content analysis a systematic procedure for the quantification and objective examination of qualitative data, such as written or oral messages, by the classification and evaluation of terms, themes, or ideas; for example, the measurement of frequency, order, or intensity of occurrence of the words, phrases, or sentences in a communication in order to determine their meaning or effect.correlational analysis a statistical procedure to determine the direction of a relationship (positive or negative correlation) between two variables and the strength of the relationship (ranging from perfect correlation through no correlation to perfect inverse correlation and expressed by the absolute value of the correlation coefficient).analysis of covariance (ANCOVA) a variation of analysis of variance that adjusts for confounding by continuous variables.data analysis the reduction and organization of a body of data to produce results that can be interpreted by the researcher; a variety of quantitative and qualitative methods may be used, depending upon the nature of the data to be analyzed and the design of the study.ego analysis in psychoanalytic treatment, the analysis of the strengths and weaknesses of the ego, especially its defense mechanisms against unacceptable unconscious impulses.gait analysis see gait analysis.gastric analysis see gastric analysis.multiple-locus variable number of tandem repeat analysis (MLVA) a laboratory tool designed to recognize repeats" >tandem repeats and other qualities in the genome of an individual to provide a high resolution fingerprint" >DNA fingerprint for the purpose of identification.multivariate analysis statistical techniques used to examine more than two variables at the same time.power analysis a statistical procedure that is used to determine the number of required subjects in a study in order to show a significant difference at a predetermined level of significance and size of effect; it is also used to determine the power of a test from the sample size, size of effect, and level of significance in order to determine the risk of error" >Type II error when the hypothesis" >null hypothesis is accepted.qualitative analysis the determination of the nature of the constituents of a compound or a mixture of compounds.quantitative analysis determination of the proportionate quantities of the constituents of a compound or mixture.SNP analysis analysis of polymorphisms" >single nucleotide polymorphisms to assess artificially produced genetic modifications or identify different strains of an organism.transactional analysis a type of psychotherapy based on an understanding of the interactions (transactions) between patient and therapist and between patient and others in the environment; see also transactional analysis.analysis of variance ANOVA; a statistical test used to examine differences among two or more groups by comparing the variability between the groups with the variability within the groups.variance analysis the identification of patient or family needs that are not anticipated and the actions related to these needs in a system of care" >managed care. There are four kinds of origin for the variance: patient-family origin, system-institutional origin, community origin, and clinician origin.vector analysis analysis of a moving force to determine both its magnitude and its direction, e.g., analysis of the scalar electrocardiogram to determine the magnitude and direction of the electromotive force for one complete cycle of the heart.