Quantitative analysis

Introduction

Quantitative analysis is the set of experimental methods allowed to determine the quantitative content (concentration) of individual components and impurities in the sample of the material to be examined. 

The aim of quantitative analysis is the determination of quantitative ratios of chemical compounds, ions and elements, which are the part of substances to be examined.

Quantitative analysis is used to solve various questions of modern science & production. With the help of quantitative analysis, optimal conditions accomplish various chemical and technological processes are determined, the quality of raw materials, the purity degree of manufactured products like medicines are controlled, the content of components in mixtures, the relation between the chemical composition and physical properties of substances are obtained.

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Quantitative analysis

Quantitative analysis meaning is all about analyzing number based data which is used in various statistical techniques. Quantitative analysis methods are classified into three groups:

chemical methods

physical methods

physical and chemical methods.

Chemical methods are those which are based on using the various types of chemical reactions proceeding quantitatively in solutions, melts, solids or gasses. These methods are divided into: 

gravimetric (weight) methods of analysis are based on the exact mass measurement of the component to be analyzed in the substance to be researched;

titrimetric (volumetric) methods of analysis are those in which the quantitative composition of the sample to be researched is determined by the exact volume measurement of a reagent solution with the known concentration (titrant), which interacts with the substance to be determined in the equivalent quantities;

Gas analysis is based on the measurement of the gas volume, which is obtained due to a chemical reaction. 

Chemical methods of quantitative analysis chemistry are also called classical methods. These are the most advanced methods of analysis, which continue to be developed. They are exact, simple in performance, and do not require special equipment. But their application is bound up with some difficulties and a comparatively low limit of sensitivity.

Physical methods of quantitative analysis chemistry are based on size measurement of physical parameters of substances to be analyzed or their solutions, on conditions that physical parameters are the function of substances quantitative composition. These methods are based on the size of measurement of refractive index, the optical rotation (polarimetry), the fluorescence intensity (fluorimetry), etc., belonging to them. Physical methods are defined by rapidity, low limit of detection, the objectivity of results, the possibility of process automation. But they are not always clearly defined or identified., because physical size is influenced not only by the concentration of the substance to be examined, but is also influenced by the presence of other substances and impurities. Their use frequently requires the application of complex equipment.

Physical & chemical methods of Quantitative analysis chemistry are based on the size measurement of physical parameters of the system to be examined, appearing or changing as a result of carrying out chemical reactions. These methods are characterized by low limits of detection and quickness of their performance.

Physical and chemical methods of quantitative analysis are called instrumental methods because they require application of definite devices. 

GRAVIMETRIC METHODS OF ANALYSIS

The gravimetric method of quantitative data analysis is based on the exact mass measurement of the substance which is to be researched or the mixture component, which are separated in the chemically pure substances or in the form of chemical compounds with the known composition.  Gravimetric analysis is conditionally classified into three groups of methods: precipitation, volatilization and particulate methods.

PRECIPITATION METHODS

In precipitation methods, the component to be determined is quantitatively precipitated in chemical ways in the form of a slightly soluble chemical compound with a constant composition. The sample of the substance to be investigated is dissolved in a suitable solvent, and then the certain component is quantitatively precipitated in the form of a slightly soluble compound. A precipitate is called the precipitated form. It is uncovered to the analytical processing, which is separated by filtering, washed out, dried, ignited and then it is weighed with the help of the analytical balance. These precipitates are called the gravimetric or the weighted form. 

VOLATILIZATION METHODS

In volatilization gravimetric methods of quantitative analysis, the components to be examined are separated from the sample to be examined and quantitatively volatilized as a volatile compound. A Volatilization method is called a direct one if the mass of the volatilized product is measured directly. In the cases when the mass is calculated by the difference of the sample masses before and after volatilization, it is called the indirect method.

PARTICULATE METHODS

In gravimetric particulate methods, the components to be examined or the mixture components are quantitatively isolated in a free state and weighed with the help of the analytical balance.

The particulate method is applied, supposedly, for quality evaluation of medicines by obtaining the substance contained in them. The total ash is obtained by ignition of a weighted medicine already weighed with the help of the analytical balance in a platinum or porcelain crucible. After analyzing the residue by hydrochloric acid the ash, which is not soluble in hydrochloric acid, is obtained. Besides, the sulphated ash determined after heating and ignition of the analyte sample processed preliminary by concentrated sulphuric acid is also determined.

The gravimetric & precipitated forms must satisfy a number of requirements: the precipitated form should be slightly soluble (in case of binary electrolytes precipitation completeness is reached at KS0 = 10–8); the precipitate should be macrocrystalline; the precipitated form should quantitatively transfer in the gravimetric one; the composition of the gravimetric form should correspond exactly to its chemical formula; the gravimetric form should be chemically stable, and the content of the component to be examined in it must be as small

as possible to reduce the error of determination. Therefore, the molecular mass of the gravimetric form should be as large as possible. Precipitation gravimetric methods allow to determine quantitatively almost all of the most important cations and anions of the inorganic nature, as well as a number of organic compounds, including medicinal ones. So, lactose present in dairy products, salicylates present in medicinal substances, nicotine present in insecticides, cholesterol present in blood serum, etc., are determined by the precipitation gravimetric method. 

BALANCE AND WEIGHING TECHNIQUE

Balance is a device that is used in the gravimetric method of analysis. Weighing with the accuracy of ± 0.01 g is adept with the help of the pharmacy or the techno chemical balance. Weighing with the accuracy of ± 0.0001 – 0.0002 g is carried out with the help of the analytical balance. When weighing by the help of the techno chemical or the technical balance the subject to be examined is placed on the left-hand pan of the arrested balance, and counterpoise weights are placed on the right-hand pan. Weighing process is finished when the balance pointer is in the middle position after free damping the balance beam oscillation. 

When weighing by the help of the pharmacy balance, a central ring is held by the thumb & forefinger of the left hand leaning by elbow against the laboratory bench. The place of things to be weighed on this or that pan of the balance is strictly analysed. Damping the balanced beam oscillation can be accelerated by a light beam of the balance pans bottom to the surface of the laboratory bench. The analytical balance is put in specially intended laboratory premises (weighing rooms) on special monolithic tables-supports.

When working with the analytical balance it becomes necessary to follow these requirements and rules: the balance state is tested & the zero point is set before each weighing; substances to be weighed are placed into a special container, the temperature of the substances to be weighed is adjusted to the balance temperature in the weighing room for 20 minutes; the balance must not to be loaded over the fixed limit load.

The analytical balance possesses a high degree of sensitivity in order to give the true weight of samples (weight in this context being synonymous with mass). Factors affecting these requirements are: the length of the balance arms; coplanarity of the knife edges; the weight of the beam; the position of the gravity center of the beam related to the central knife edge or pivot.

Conclusion 

Hence Quantitative analysis chemistry is a very important branch of chemistry as it enables chemists to calculate the known quantities of the materials. e.g. , how much product can be made from known starting material or how much of a given component is available in a sample. An acid-base titration is a famous example of quantitative analysis. Qualitative research in healthcare refers to the methods which are used to collect & analyze textual or image-based data in order to make sense of behavioral issues in the clinical setting.