Instrumental analysis
Instrumental methods
Chemists can identify substances using , which rely on machines rather than observations by eye.
Compared with chemical tests, instrumental methods are:
- accurate
- — they work with very small samples
- rapid — they give results quickly
The drawbacks are that the equipment is expensive and people need training to use it and interpret the results.
Key terms
Flame emission spectroscopy
In , a sample is put into a flame. The light it gives out passes through a spectroscope, which produces a .
- gives its own pattern of lines. Comparing the spectrum with reference spectra identifies the ions.
- The brightness of the lines shows the of the ion.
Unlike a simple flame test, it can identify the different metal ions in a , and it can measure how much of each is there.
Key terms
Calibration curves
To find a , the instrument is first tested with solutions of known concentration. The readings are plotted against concentration to make a .
The unknown sample is then tested. Its reading is found on the curve, and the concentration is read off the other axis.
Example: if a reading of 4 matches 0.02 g/dm³ on the calibration curve, an unknown sample giving a reading of 4 contains 0.02 g/dm³ of the ion.