CHEMICAL ANALYSES, Qualitative Analysis, Semiquantitative Analysis, Quantitative analysis, Titrimetric analysis

 CHEMICAL ANALYSES

• Qualitative Analysis
• Semi quantitative Analysis
• Quantitative analysis
• Titrimetric analysis

CHEMICAL ANALYSES

A chemical analysis can be performed in three ways:

1. Qualitative

2. Semi quantitative or

3. Quantitative.

1. Qualitative Analysis

A qualitative analysis is a test in which the presence or absence of a substance analyte) in a mixture is detected by chemical means. The analysis can be a simple test to identify certain chemical substances. The method is particularly useful in the analysis or examination of certain body fluids. For example, bile pigments in urine can be detected qualitatively by Fouchet's test. The result is expressed as positive or negative.

2. Semiquantitative Analysis

This is basically a qualitative estimation where the degree of positivity of a test roughly indicates the quantity of substance being analysed. For example, the presence of reducing substances in urine can be expressed roughly as trace, +, ++, +++, or ++++

3. Quantitative analysis

A quantitative analysis is one in which exact quantity of an analyte is measured. This method is extensively utilised in measuring the constituents of body fluids. The two methods most commonly used for quantitative analysis in clinical chemistry are:

Spectrophotometric analyses is Spectrophotometry is described in the Clinical Chemistry section.

Titrimetric analysis in this method, the volume of a solution of accurately known concentration is made to react with a solution of the substance to be measured. This solution of known concentration is the standard solution. The titration is done by adding the standard solution to the unknown substance until an end point is reached. The end point may be indicated by: 

(i) a colour change due to the standard solution, 

(ii) a colour change due to an indicator used inthe titration, or 

(iii) the appearance of precipitate.

Titration may be a neutralisation reaction, oxidation-reduction reaction or a precipitationreaction. 

Note Titrimetric methods are less commonly used in Clinical Chemistry.