Determination of phosphate using a highly sensitive paired emitter-detector diode photometric flow detector

Martina O'Toole, King Tong Lau, Roderick Shepherd, Conor Slater, Dermot Diamond*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

67 Citations (Scopus)


The use of a novel inexpensive photometric device, a paired emitter-detector diode (PEDD) has been applied to the colorimetric determination of phosphate using the malachite green spectrophotometric method. The novel miniaturized flow detector applied within this manifold is a highly sensitive, low cost, miniaturized light emitting diode (LED) based detector. The optical flow cell was constructed from two LEDs, whereby one is the light source and the second is the light detector, with the LED light source forward biased and the LED detector reversed biased. The photocurrent generated by the LED light source discharges the junction capacitance of the detector diode from 5 V (logic 1) to 1.7 V (logic 0) and the time taken for this process to occur is measured using a simple timer circuit. The malachite green (MG) method employed for phosphate determination is based on the formation of a green molybdophosphoric acid complex, the intensity of which is directly related to phosphate concentration. Optimum analytical parameters such as reaction kinetics, reagent to sample concentration ratio and emitter wavelength intensity were investigated for the spectrophotometric method. Linear calibration plots that obeyed the Beer-Lambert law were obtained for phosphate in the range of 0.02-2 μM. The dynamic range, sensitivity and limits of detection are reported.

Original languageEnglish
Pages (from-to)290-294
Number of pages5
JournalAnalytica Chimica Acta
Issue number2
Publication statusPublished - 10 Aug 2007
Externally publishedYes


  • Colorimetric flow analysis
  • Light emitting diode detector
  • Malachite green
  • Phosphate


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