Instrumental methods of analysis
Instrumental methods of analysis are faster, more accurate and more sensitive than simple chemical tests. There are several different types of instrumental analysis. Some are suitable for detecting and identifying A substance made of one type of atom only., while others are better suited to A substance formed by the chemical union of two or more elements..
Compared to simple laboratory tests, instrumental methods of analysis may give improved:
- speed (they are quick)
- accuracy (they reliably identify elements and compounds)
- sensitivity (they can detect very small amounts of a substance in a small amount of sample)
The flame photometer
The flame photometer is a scientific instrument based on flame testing. Data from a flame photometer can be used to:
- identify metal Electrically charged particle, formed when an atom or molecule gains or loses electrons. in a sample
- determine the The concentration of a solution tells us how much of a substance is dissolved in water. The higher the concentration, the more particles of the substance are present. of metal ions in dilute Mixture formed by a solute and a solvent.
Identifying metal ions
In the flame photometer, the coloured light from a vaporised sample can be split to produce an Light given off by a substance, split into its component colours or wavelengths.. The different lines in an emission spectrum look like a coloured barcode. Each metal ion produces a unique emission spectrum.
The metal present in a sample is identified by comparing its A series of similar waves arranged in order of wavelength or frequency. with reference spectra. These are emission spectra from known metal ions. If two spectra match, they must be from the same metal ion.
Determining concentrations
A reading is taken from the flame photometer for different concentrations of a metal ion in solution. These readings are used to plot a Graph with the readings from a machine plotted against known amounts of a substance..
Example
A solution containing sodium ions gives a reading of 4 units on the flame photometer. Use the calibration curve above to determine the concentration of sodium ions in this solution.
The concentration is 0.02 g dm-3.
Question
A solution containing sodium ions gives a reading of 9 units on the flame photometer. Use the calibration curve above to determine the concentration of sodium ions in this solution.
The concentration is 0.045 g dm-3 .