Optimisation of analytical methods for the characterisation of oranges, clementines and citrus hybrids cultivated in Spain on the basis of their composition in ascorbic acid, citric acid and major sugars

Three HPLC methods were optimised for the determination of citric acid, succinic acid and ascorbic acid using a photodiode array detector and fructose, glucose and sucrose using a refractive index in twenty eight citrus juices. The analysis was completed in <16 min. Two different harvests were taken into account for this study. For the season 2011, ascorbic acid content was comprised between 19.4 and 59 mg vitamin C/100 mL; meanwhile for the season 2012, the content was slightly higher for most of the samples ranging from 33.5 to 85.3 mg vitamin C/100 mL. Moreover, the citric acid content in orange juices ranged between 9.7 and 15.1 g L−1, while for clementines the content was clearly lower (i.e. from 3.5 to 8.4 g L−1). However, clementines showed the highest sucrose content with values near to 6 g/100 mL. Finally, a cluster analysis was applied to establish a classification of the citrus species.

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

In 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 nonthermal 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 that the increase in mobile phase temperature is not the only variable for improving the separation process but also other nonthermal processes must intervene. Fluorescence detection demonstrated better signal-to-noise compared to photodiode arrayed detection mainly due to the independent effect of microwave pulses on the baseline noise, but photodiode array detection was finally chosen as it allowed a simultaneous detection of nonfluorescent compounds. Finally, a determination of the content of the vitamin E homologs was carried out in different vegetable oils. Results were coherent with those found in the literature.