Instrumental methods do the same job with a machine

1. Chemical tests rely on an observation made by a person.
2. An instrumental method takes the same measurement with a machine.
3. Machines improve the sensitivity, so a far smaller amount can be detected.
4. They improve the accuracy, so the result is closer to the true value.
5. They improve the speed, so many samples can be analysed in the time one test takes.

Why those three advantages matter

1. A trace of an ion too small to colour a flame can still be detected by an instrument.
2. A judgement between lilac and red depends on the observer, while a machine reads a number.
3. A laboratory testing hundreds of samples needs the throughput a machine gives.
4. An instrument also gives a numerical result, which a colour never does.
5. Against that, instruments are expensive and need trained operators.

A flame photometer measures the light from a flame

1. The sample is put into a flame, as in a flame test.
2. The instrument measures the light the flame gives out.
3. The pattern of light is compared with reference data to identify the metal ion.
4. The intensity of the light depends on how much of the ion is present.
5. No knowledge of how the instrument works is needed to use its output.

Using a calibration curve

1. Solutions of known concentration are measured first.
2. Their readings are plotted against concentration to give a curve.
3. The unknown solution is then measured in the same instrument.
4. Its reading is found on the vertical axis and traced across to the curve, then down to the concentration.
5. A reading beyond the range of the curve cannot be read off, so the sample is diluted first.