Chiral HPLC-MS/MS determination of hyoscyamine enantiomers in baby herbal infusions after preconcentration with sulfonic HMS mesostructured silica synthesized by co-condensation

Abstract

Tropane alkaloids are considered a major food safety issue in recent years, due to their worrying appearance in many foods, such as herbal infusions, usually due to cross-contamination with weeds during harvest. (−)-Hyoscyamine is synthesized by tropane alkaloids-producing plants and its ingestion can cause all types of disorders in humans. Its enantiomerization occurs easily over time, so the inactive (+)-hyoscyamine can be found in foods in variable proportions. Therefore, the goal of the current work was to develop a chiral high performance liquid chromatography tandem mass spectrometry method for the enantiomeric determination of (−)- and (+)-hyoscyamine. Chromatographic separation was optimized, and the best chiral resolution (Rs = 1.59) was achieved in 6.5 min with a Chiralpak® AY-3 polysaccharide-based stationary phase column using ethanol with 0.05 % diethylamine as mobile phase. For the preconcentration of the sample, two types of mesostructured silicas with sulfonic groups were synthesized, by grafting and co-condensation methods, and characterized. The materials were evaluated as sorbents for strong-cation exchange solid-phase extraction of hyoscyamine in baby herbal infusions. Based on the findings gathered, silica denoted as HMS-SO3−(co) was the best sorbent due to the high number of functional groups attached to silica (2.63 mmol/g) and its textural properties. Under optimal conditions, the preconcentration factor obtained was 167, using only 50 mg of the material, and a very low racemization of the (−)-hyoscyamine to the (+) enantiomer was found (<20 %). The method was validated with recoveries of 94–99 %, good linearity (R2 > 0.99), precision (RSD < 20 %), no matrix effect for both analytes and low method quantification limit (0.089 µg/L and 0.092 µg/L for (+)-hyoscyamine and (−)-hyoscyamine, respectively) to meet its applicability in monitoring real samples. Two types of herbal teas for babies (instant and teabags) were analyzed with the developed methodology. Two of the instantaneous infusions analysed were contaminated, one of them with 0.21 µg/L of (−)-hyoscyamine and 0.09 µg/L of (+)-hyoscyamine (ratio 70(−)/30(+)) and the other with 0.075 µg/L of (−)-hyoscyamine (the (+)- enantiomer was below the limit of quantification of the method). Taking these results into account, it is important to evaluate the content of hyoscyamine enantiomers in the infusions to avoid overestimation of (−)-hyoscyamine exposure.