Determination of fat‐soluble vitamins in vegetable oils through microwave‐assisted high‐performance liquid chromatography

Abstract

This article is protected by copyright. All rights reserved. AbstractIn this manuscript, a study of the effect of microwave radiation on the high-performance liquid chromatography separation of tocopherols and vitamin K1 was conducted. The novelty of the application was the use of a relatively low polarity mobile phase in which the dielectric heating effect was minimized to evaluate the non-thermal effect of the microwave radiation over the separation process. Results obtained show that microwave-assisted high-performance liquid chromatography had a shorter analysis time from 31.5 to 13.3 min when the lowest microwave power was used.Moreover, narrower peaks were obtained; hence the separation was more efficient maintaining or even increasing the resolution between the peaks. This result confirms the fact that the increase in mobile phase temperature is not the only variable for improving the separation process but also other non-thermal processes must intervene. Fluorescence detection demonstrated better signal-to-noise compared to photodiode arrayed detector mainly due to the independent effect of microwave pulses on the baseline noise, but photodiode array detector was finally chosen as it allowed a simultaneous detection of non-fluorescent compounds. Finally a determination of the content of the vitamin E homologues was carried out in different vegetable oils. Results were coherent with those found in the literature.

Microwave assisted high performance liquid chromatography for the separation of triacylglycerols in vegetable oils using an evaporative light scattering detector

“…This fact indicates that equilibrium conditions should have been reached inside of the HPLC column. Previous studies using microwave radiation to assist an HPLC separation also showed a similarthis trend (Carballo et al, 2015;Terol et al, 2012). It should be mentioned that, although the MW radiation was quickly absorbed by the mobile phase, moderate heating inside of the column was produced in this application.…”

“…170 W. However, the column did not wholly absorb the radiation. Therefore, to avoid magnetron damage, a water container (2100 mL total volume) at a temperature of 20 ºC was placed inside the oven as a radiation well (Carballo et al, 2015) (Carballo, Prats, Maestre, & Todolí, 2015). Furthermore, an optimisation study was performed to select both the 300 S ELSD spray chamber and drift tube temperatures.…”

“…In a different application involving separation of fat-soluble vitamins, the application of MW radiation at 170 W resulted in a 36 % shortening in analysis time with respect to conventional HPLC. Furthermore, peak height increased by nearly 100 % and band broadening decreased by 51 % for tocopherol homologues (Carballo et al, 2015). In thatis application, the mobile phase consisted of an acetonitrile/tetrahydrofuran/water (87.5/ 5 /7.5 v/v/v) mixture.…”

“…Nonetheless, iIt was not until 2012 when microwave radiation was applied for the first time to assist the separation of water-soluble vitamins (Terol, Maestre, Prats, & Todolí, 2012). Later, the set up was employed for fat-soluble vitamins using a less polar mobile phase (Carballo, Prats, Maestre, & Todolí, 2015) (Carballo, Prats, Maestre, & Todolí, 2015). In both cases, a general shortening in retention times and more efficient separations were observed.…”

A convenient ultrasound‐assisted saponification for the simultaneous determination of vitamin E isomers in vegetable oil by HPLC with fluorescence detection

“… made a 20‐fold dilution of 40 mg oils in tetrahydrofuran/acetonitrile (4:6, v/v), Carballo et al. made a 1:10 v/v dilution with propan‐1‐ol. Moreover, QuEChERS was also applied for VE extraction.…”