This analytical method is a validated measurement procedure for the determination of indium [7440-74-6] and its compounds in workplace air in an concentration range of one tenth up to twice the currently valid German OEL of 0.0001 mg/m³ R (respirable fraction). For sampling a defined volume of air is drawn through a membrane filter (cellulose nitrate). The flow rate is set to 10 l/min and sampling is performed over 2 hours (which correspond to a sampling volume of 1200 l). Indium and its compounds deposited as dust on the filter is treated with acid and afterwards analysed using inductively coupled plasma mass spectrometry (ICP-MS). The quantitative determination is based on a calibration function, whereby the indium concentration of the calibration standard is plotted against the intensities, calculated over the internal lutetium standard. The limit of quantification is 0.0000022 mg/m³ based on an air sample volume of 1200 l. The mean recovery is 105% and the expanded uncertainty for the validation range of 0.00001 to 0.0002 mg/m³ is 26.5 to 26.9%.