Analytical Method Validation and Determination of Iron and Phosphorus in Vegetable Oil by Inductively Coupled Plasma–Mass Spectrometry with Microwave Assisted Digestion

ABSTRACT

Inductively coupled plasma–mass spectrometric determination of iron and phosphorus in three vegetable oils (soybean, coconut, and sunflower) was validated for the intermediate precision, trueness, linearity, and quantitation limit. The overall precision (n = 5) for the analytes, which were above the method’s practical limit of quantification, were less than 2% relative standard deviation and the same as the laboratory control, NIST-SRM-1849a. Trueness was demonstrated with spike recoveries of the analytes in all vegetable oils at limit of quantification-level spiking. Although good linearity (regression coefficient greater than 0.9990) obtained, the recovery of phosphorus (156–189%) was high, possibly due to oil matrix enhancement, compared to the recovery of iron (91–106%). For soybean oil, sunflower oil, coconut oil, and medium chain triglycerides, the concentrations (mg/kg) of iron were in the range of 0.10–1.47, 0.09–1.51, 0.20–0.35, and 0.09–0.13, respectively. Similarly, phosphorus concentrations (mg/kg) were in the range of 0.77–124.56, 0.49–125.57, 0.52–9.72, and 0.85–11.90, respectively. The study achieved considerably low instrument-based practical limits of quantification for iron (0.005 mg/kg) and phosphorus (0.05 mg/kg), which are fivefold lower than the AOAC Official Method 2015.06. The high instrument sensitivity and selectivity of the method allow the determination of trace levels of iron and phosphorus in vegetable oils with good precision and trueness.

KEYWORDS:

• Inductively coupled plasma–mass spectrometry (ICP-MS)
• iron
• microwave digestion
• phosphorus
• vegetable oils

Acknowledgment

Anjaneyulu Pendem, Research Scientist, Syngene Regional Lab, Bangalore, India is greatly acknowledged for reviewing the manuscript before submission to publisher.

Declaration of conflict of interest

We wish to confirm that there are no known conflicts of interest associated with this publication. We confirm that the manuscript has been read and approved by all named authors. We further confirm that the order of authors listed in the manuscript has been approved by all of us.