An inexpensive, portable and microcontrolled near infrared LED-photometer for screening analysis of gasoline

A microcontrolled, portable and inexpensive photometer is proposed. It uses a near infrared light emitting diode (NIR LED) as radiation source, a PbSe photoresistor as infrared detector and a programmable interrupt controller (PIC) microcontroller as control unit. The detector system presents a thermoresistor and a thermoelectric cooling to control the detector temperature and keep the noise at low levels. The microcontroller incorporated total autonomy on the proposed photometer. As its components are inexpensive and of easy acquisition, the proposed NIR LED-photometer is an economical alternative for chemical analyses in small routine, research and/or teaching laboratories. By being portable and microcontrolled, it also allows carrying out field chemical analyses. The instrument was successfully applied on the screening analysis to verify adulteration in gasoline samples.