Automated Olive Oil Peroxide Value Determination by Flow Injection

  • Olive oil samples are injected in 1.0% (w/w) NaI and acidified by a 43.2 % (v/v) CH3COOH stream in n-propanol. The iodine liberated by peroxides is continuously monitored.
  • The reaction mixture flows through the spectrophotometer where sample blank values are recorded. Then, it is diverted to the incubation coil selected by the stream selection valve. After loading 7 incubation coils, the pump reverses the flow direction to aspirate incubated samples for measurement. Finally by changing again the flow direction samples are driven to waste. The timing sequence and a calibration run are shown in the following figures.
  • In this way, an analysis rate of 100 samples per hour is achieved while each sample is incubated for 5 min. With the proposed analyser design, the drawback of  "one sample at a time" is overcome as 7 samples reside simultaneously in the analyser, resulting in high analysis rates.
  • In flow injection methods, the reagent(s) blank is the baseline signal. However, the sample blank value that can be quite high, is not automatically subtracted. By the proposed analyser design the analytical signal is corrected for the sample blank value.
  • Results obtained by the proposed method compare well with those obtained by the official method (0-5.6% relative difference for the analysis of 27 olive oil samples). Click to see other advantages of the method.
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Timing sequence of the analyser

(BT) back,
(LWT) load-wash,
(FT) forward and
(ST) stop time.
(SSV) Stream selection valve.
Bars indicate pump (P) and injection valve (IV) functions.
h1 is the sample blank and h2 the measured signal.

Peaks acquired during peroxide determination

Standards of
(a) 5.0, (b) 15.0,
(c) 25.0, (d) 35.0,
(e) 50.0, (f) 60.0,
(g) 70.0 and (h) 80.0
peroxide value (meq O2/kg oil).

Questions and comments to author: Dr C.A. Georgiou, cag@aua.gr
Phone: +3010-5294248, fax: +3010-5294265
Chemistry Laboratory, Agricultural University of Athens, Greece