Instrumental methods

Chemical tests are very good at identifying elements and compounds, however instrumental methods can also be used to analyse substances.

Instrumental methods advantages and disadvantages

Advantages:

• they are more sensitive - only require a very small amount of substance

• They are much quicker

• They are highly accurate

Disadvantages:

• usually very expensive

• Takes specialist training to use

• Gives results that can often be interperated only by comparison with data from known substances ( e.g say you have copper info, can find copper. Don’t have potassium info, can’t find potassium )

In summary - instrumental methods are more accurate than chemical tests but more expensive, chemical tests are less accurate but cheaper.

Uses of instrumental methods of analysis:

• Analysing blood, urine and tissue samples

• Analysing purity of medicines

• Analysing the quality of water and air

• Analysing the contents of food

Flame emission spectroscopy

As you know, when some metals ions are heated they produce distinctive colours. But, these colours are often difficult to see and it is easy to mistake the colour of one metal ion with the colour of another ( e.g lithium and calcium ions ). It is also difficult to identify a metal ion in a sample using a flame test if the sample contains more than one metal ion, producing a different flame colour (( the colours would become mixed together )

Flame emission spectroscopy is an example of an instrumental method used to analyse metal ions in solutions.

It is used for:

• identifying metal ions in solution

• Measuring the concentration of metal ions in solution

Sometimes, you may be given a graph of concentration vs absorbance. Usually you would be given one and asked to find the other, to do this simply use the one you have and follow it up/ across to where is meets the graph and then go down/ across from there top the axis and get your result.