Microwave high performance liquid chromatography with UV-visible detection. Application to vitamins determination

Abstract

The present work describes the first attempt to use microwave reversed phase high performance liquid chromatography (MW-HPLC) to carry out the separation of organic compounds. Biotin and riboflavin were selected for the characterization of the new separation technique. Additional vitamins (nicotinamide, pyridoxine and thiamine) were used as reference compounds. In order to perform the separation, a chromatographic column was placed inside a domestic microwave oven in a hanging position. The column particular location was an extremely critical point, since it precluded the actual power absorbed by the sample. In order to avoid magnetron damage, a heat well (i.e., water vessels) was used. Vitamins were detected using a UV-VIS detector. Results obtained showed that the application of microwave radiation, even at low power levels, gave rise to a significant modification in the characteristics of the chromatograms. It was found that retention times for biotin and riboflavin shortened as the power increased. Furthermore, the peak shape also changed, with the modification being more significant for the former vitamin than for the latter one. Furthermore, sensitivity also increased as the column was exposed to the action of microwave. Comparatively speaking, MW-HPLC was more efficient in terms of compound separation than when performed at room temperature or thermostatted at 45 °C HPLC. This was likely due to the combined action of a moderate and quick heating of the mobile phase with an increase in the analytes diffusivity caused by the radiation.

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.…”

“…This significant heating was due to the composition of the mobile phase. Additionally, a 40 and % reduction in peak width was registered for riboflavin and biotin, respectively (Terol et al, 2012) (Terol et al, 2012a). 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.…”

“…For conventional heating, an HPLC column oven from Gecko-2000 (CIL Cluzeau Info Labo, Sainte-Foy-La-Grande, France) was employed. Meanwhile, for MW-HPLC assisted with microwaves, the column was placed inside a microwave oven in a hanging position in the same way as in previous work (Terol et al, 2012) (Terol, Maestre, Prats, & Todolí, 2012a). The heating system consisted of a conventional LG microwave oven (LG MB4047C) at the standard 2450 MHz frequency)(see Supplementary Figure 1).…”

“…So far, microwave assisted HPLC has been successfully applied for vitamin separation using a polar mobile phase containing water (Terol et al, 2012), (Silvia Carballo et al, 2015). Once the detection conditions and the column were selected, experiments were done in the presence of a microwave field for a fully organic mobile phase.…”

“…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).…”