Qualitative analysis by definition is the process of estimation or determination of the components present in given sample.
Chemical analysis has two parts as
a) qualitative aspect
b) quantitative aspect.
Qualitative aspect is the primary property determined and quantitative is the next one in most determinations.
Qualitative analysis is a quality control for many products emerging out of industry.
This quality is checked by standard institutes like “International Organization for Standardization -ISO”.
For instance if a Cop is asking a person to breathe into alcohol breath analyser or meter. The machine first detects if the breathe air contains ethanol in it. If the ethanol is present then it goes for estimating the percentage amount of ethanol in the breathe air.
So in the above instance the identification of ethanol (alcohol) is qualitative aspect. If there is ethanol, then how much of ethanol is present is quantitative aspect. If there is no ethanol (qualitative aspect) then the concept of quantitative analysis doesn’t come into the picture.
Thus qualitative analysis tells what is the substance while quantitative analysis tell how much is the substance.
Qualitative analysis methods:
Quantitative analysis is the direct estimation of component. Hence the methods focuses to estimate the presence of the components.
For example if you take a tooth paste, the components in it can be particles (to polish the teeth), foaming agents (to produce foam and dissolve fatty matter), flavoring agent (to impart good odour), sweetening agent, antiseptic (to kill microbes) etc. So to detect all the components,
we may need
- physical methods
- chemical methods
- Biological methods
- Photo-metric methods.
Physical methods in above case of tooth paste can be evaluated by particle size analysis, their shape and size by using microscope or magnifying glass. Very rough and large sized particles is not an indicator of quality tooth paste.
In other case physical methods can include, refractive index for oils, friability (for tablets) etc.
Chromatography is another type of qualitative analytical technique using physical and chemical methods combined.
Chemical methods: This is wide and largely applicable as most of the substances we use or chemicals of some sort. In the above example, sweetening agent can be determined by chemical reactions.
Chemical reaction used for qualitative analysis come mostly under either of the categories like
- Neutralization reactions
- Oxido-reductive reactions
- Complexation reaction.
- Precipitation reaction.
In the above example of tooth paste, sweetening agent can be determined by oxido-reductive reaction as most sugars have oxygen molecules in their chemistry.
Biological methods: These are used when biological agent is involved. In tooth paste, antiseptic’s ability to kill microbes can be tested by microbiological assay.
In general biological methods used are
a) Immuno assays (ELISA), b) Bio-assays using small animals (for ex: histamine shows contractions in the ileum of guinea pig as a specific reaction not shown by other bio-molecules,
c) Behavioral method using experimental animals: For example, morphine administration shows straub tail (i.e. elevation of tail specifically) in mice. Similarly, administration of D-tubocurarine to neck muscles of rabbit makes rabbits head hang without voluntary muscle control. These reactions are so specific and stand as qualitative markers for morphine & D-TC.
Photo-metric methods: These are most advanced methods for qualitative analysis and control. They are precise, super fast and easy to use than other methods.
This uses spectroscopy techniques like UV, Visible, IR, Florescent, atomic absorption spectroscopy, optical dichroism, x-ray and other electromagnetic radiations methods for detection of compounds. In the tooth paste, most substances like flavoring agent, sweetening agent, coloring agents, foaming agents, particle size, number etc. can identified precisely by photo-metric methods.
These photo-metric methods not only identify the sample but the exact internal chemistry can be known like presence of nitrogen, oxygen, sulfur or double, triple bonds etc.
Qualitative analysis is an important procedure to check the quality of any product being prepared for the market for large scale use.
Qualitative Analysis Uses:
- To test the purity of water, milk and solvents
- To identify the components withing any unknown substance.
- To check the self life and half life of drugs.
- In diagnosis of the diseases.