Stability of Hydroxytyrosol in Aqueous Solutions at Different Concentration, Temperature and with Different Ionic Content: A Study Using UPLC-MS

The work describes a stability study of hydroxytyrosol (HTyr) in aqueous solutions carried out varying the following parameters: HTyr concentration, temperature and ionic content in the aqueous solution. First, an analytical method based on the use of ultra performance liquid chromatography (UPLC-MS) as analytical technique was developed and validated. The equation of the linear model was A/AISTD = –0.0013 + 0.0117 · [HTyr], with a very good linearity, since the R-Squared was 99.9% and the P value of the lack of fit test was higher than 5%. Limits of quantification estimated, CC ( = 0.05%) and CC ( = 0.05%), were 0.2 and 0.4 g/L respectively. As well, the relative standard deviation in the intra-day precision was lower than 3%. Therefore, the method is reproducible. We have applied this methodology to study the stability of HTyr and have observed that the most critical aspect turned to be the ionic content of the aqueous solutions. A tap water with high contents of calcium and magnesium (52 and 21 mg/L) degraded HTyr up to 64% in 48 hours whereas a low mineralization water with low contents of calcium and magnesium (4 and 2 mg/L) produced only 19% degradation.