What instrument is used to measure the concentration?

Question

In a chemical reaction I need to know the instrument you use to measure concentration.

Answer 1

It depends on the state and type of reactants and products.

Could use a spectrometer, gas chromatograph, flame atomic absorption, pH meter or titrations.

Answer 2

Depending on the reactants and products, you could use a variety of devices: spectrometer (color change), pH meter, Oxygen or CO2 sensor. If you just want to know a final concentration and don't need to worry about changes of concentration with time, then redox or acid/base titration are common tools used in order to calculate a concentration.