Basics

BASIC PRINCIPLES OF ANALYTICAL CHEMISTRY

Analytical Chemistry

       It is a branch of chemistry that deals with the determination of the composition of the materials in terms of elements or compounds present in them. It is used to identify the substance which is present in a material and to determine the exact amount of the identified substance.

 1. Divisions of Analytical Chemistry

  a. Based on the nature / proportion of constituents to be analyzed

(i). Qualitative analysis

            The process of detecting the nature of constituents in a given substance (i.e.)., the nature of chemical elements, simple ions, groups of atoms and molecules present in the substance being analyzed. Ex. Presence of Fe & S in Ferrous sulphide

(ii). Quantitative analysis

            The process of determining the proportions of various constituents in a substance. The results are expressed as parts of analyte per million (ppm), parts of analyte per hundred (%) and in terms of weight or volume of the analyte per unit volume of the sample. Ex. Proportion of Fe and S in Ferrous Sulphide

b. Based on the quantity of sample required for analysis

    Macro analysis     : > 0.1 g

            Semi micro analysis  : 0.01 – 0.1 g

            Micro analysis             : 0.001 – 0.01 g

            Sub micro /ultra micro : < 1 mg

c. Based on no. of constituents to be analyzed

  (i) Complete analysis: If a compound is to be analyzed for all its   constituents, it is called         complete analysis.

Ex. Estimation of Na and Cl in NaCl

(ii)  Partial analysis: If a compound is to be analyzed for one or more of  its  constituents, it is called partial analysis

Ex. Estimation of Na alone in NaCl

d. Based on the nature of constituents to be analyzed

  (i) Proximate analysis: The analysis of one or more constituents in the sample which behave alike and extracted by the same treatment.Ex. Fe & Al (Sequioxides) in HCl extracts.

(ii) Ultimate analysis: The percent of each element is determined separately for establishing the formula of the compounds.

e. Classification of the size of the constituent present in the sample

  (i) Major constituent                               : > 1%

            (ii) Minor constituent                        : Less than 1 %

            (iii) Trace                                                    : 1- 100 ppm

            (iv) Ultra trace                                     : sub ppm

   2. Common analytical methods

Neutralization reactions are the types of analytical methods where reactions between the acids and bases are involved. The determination of bases using a standard acid is acidimetry. If a standard base is utilized for the determination of an unknown acid, the method is called alkalimetry.

Precipitation methods are volumetric methods which result in formation of insoluble precipitates. Eg. Argentimetry

Complex formation reactions employ chelating or complex forming agents which form bigger molecular weight complexes around the element or ion to be determined

Gravimetry is the branch of analytical chemistry that takes into account of the quantity of products of a reaction employed

Conductometry deals with the measurement of electrical conductivity and resistance of a substance

Voltametry involves measurement of potential at micro electrode at a specific voltage

Coulometry is the measurement of current and time required for a chemical reaction

Potentiometry is the measurement of potential at an electrode, equilibrium with an ion to be determined

Turbidimetry and Nephelometry deal with the measurement of light stopped or scattered by the precipitates

Colorimetry is an analytical method based on comparison of colour intensities

In Emission spectroscopy, the sample is subjected to an electric arc and the light emitted is measured

In Flame Photometry, the sample is injected as a fine spray into the flame and the light emitted is measured

In Fluorometry, commonly a metal fluorescent agent is excited by irradiation with visible or UV radiation and the characteristic emitted radiation is measured.