Determination of squalene and oxidized squalene in edible oil by gas chromatography-tandem mass spectrometry and evaluation of the thermal stability of squalene

The quality and safety of edible oils have frequently been compromised in recent years， seriously threatening consumer's legitimate rights and health. Hence， establishing methods for determining the quality of edible oils based on their endogenous components is greatly significant. Squalene is widely present in various oils； hence， studying the thermal stability of squalene in edible oils is expected to provide a new storage-management model and a method for rapidly determining oil quality. A method for determining squalene and oxidized squalene in edible oils was established based on QuEChERS-gas chromatography-tandem mass spectrometry. Edible oil samples were extracted by <i>n</i>-hexane and purified using a mixed adsorbent consisting of ethylenediamine-<i>n</i>-propyl silanized silica gel （PSA） and silica gel （CNW BOND Si）. Separation was used a TG-5ms column （30 m×0.25 mm×0.25 μm） and the squalene was used as an internal standard for quantitative analysis in selective reaction monitoring （SRM） mode. The chromatography column and adsorbent were judiciously optimized. Methodological verification revealed good linear relationships for squalene and oxidized squalene in the ranges of 0.03-0.4 and 0.29-3.80 mg/L， respectively， with correlation coefficients （<i>r</i>）≥0.992 under the optimized experimental conditions. Limits of detection （LODs， <i>S/N</i>=3） of 0.4 and 4.0 mg/kg were obtained for squalene and oxidized squalene， respectively， with corresponding limits of quantification （LOQs， <i>S/N</i>=10） of 1.2 and 12 mg/kg， respectively. Spiked recovery experiments were conducted at low， medium， and high spiked levels using three different oils， the average recoveries of squalene and oxidized squalene were 81.9%‒102.5% and 89.4%‒116.1%， respectively， with relative standard deviations （RSDs， <i>n</i>=6） of 3.5%‒6.8% and 3.2%‒7.4%， respectively. The developed method has the advantages of operational simplicity， stability， reliability， low LODs， and is suitable for detecting squalene and oxidized squalene in edible oils. The developed method was used to evaluate the thermal stability of squalene in peanut oil. The results showed that when the temperature was lower than 120 ℃， squalene did not undergo the phenomenon of conversion to oxidized squalene. However， when the temperature exceeds 120 ℃， the peak area of squalene shows a cliff-like decline， and the formation of oxidized squalene can be clearly detected. This method was used to test rapeseed oil， peanut oil， soybean oil and corn oil. The results showed that squalene was detected in all samples， while oxidized squalene was not detected in any samples. This method aims to provide new ideas for the storage management and rapid quality identification of edible oil.