Determination of serotonin and its precursors in chocolate samples by capillary liquid chromatography with mass spectrometry detection.

A method for the analysis of serotonin (5-HT) and its precursors, 5-hydroxytryptophan (5-HTP) and l-tryptophan (TP) in chocolate samples by capillary liquid chromatography-mass spectrometry (cLC-MS) has been developed. Optimum chromatographic conditions were established by using a personalized multifactorial experimental design. Finally the cLC separation was achieved through a mixture of acetonitrile and 5mM ammonium formate at pH 4 (3:97, v/v) as mobile phase in gradient elution, setting the injection volume at 10 µL and using pure water as injection solvent for focusing purposes on the head of the capillary column. For extraction of targets in chocolate samples a new, fast and simple procedure based on the use of acidic extraction medium and sonication was developed. Working in selected ion mode (m/z 177 for 5-HT, m/z 205 for l-tryptophan and m/z 221 for 5-HTP) detection limits were between 0.01 and 0.11 µg g(-1) and linearity was in the concentration range of 0.5-25 µg g(-1). Recoveries higher than 76% with RSDs lower than 8% were obtained from spiked samples for all analytes, showing the effectiveness of the proposed method. Serotonin and its precursors were determined in 5 kinds of commonly consumed chocolates with different cocoa contents (70-100%). The highest serotonin content was found in chocolate with a cocoa content of 85% (2.93 µg g(-1)). Regarding l-tryptophan, the highest content of this amino acid (13.27-13.34 µg g(-1)) was found in chocolate samples with the lowest cocoa content (70-85%). 5-Hydroxytryptophan was not detected in any chocolate samples.

Direct chiral liquid chromatography determination of aryloxyphenoxypropionic herbicides in soil: deconvolution tools for peak processing.

In this paper, the enantiomeric separation of two aryloxyphenoxypropionic esters (fluazifop-butyl and quizalofop-ethyl) and a safener herbicide (mefenpyr-diethyl), which is widely used for protecting crop plants, has been studied by direct liquid chromatography (LC) with UV detection on an α(1)-acid glycoprotein as chiral stationary phase. Optimization of separation conditions was done by factorial experimental design. Experimental factors and ranges selected were propanol (5-10%), phosphate buffer pH (6.5-7.0), and column temperature (15-25 °C). Responses were expressed in terms of enantioresolution (R(s)) and adjusted retention time of the second eluted enantiomer (t(r2)'). The chemometric method used to explore data was response surface analysis. Multiple response analyses were carried out to determine the combination of experimental factors which simultaneously optimize experimental responses. Under optimum conditions for enantioseparation of each herbicide, partially overlapped or fully resolved enantiomers were obtained. Deconvolution tools were employed as an integration method to fit chromatographic data and to achieve a more precise enantiomeric ratio (ER) and enantiomeric fraction (EF) values. Applicability of both direct chiral LC and peak deconvolution methods was evaluated in spiked soil samples at different R/S enantiomeric ratios. Acceptable and reproducible recoveries between 71% and 96% with precision in the range 1-6% were achieved for herbicide-spiked levels from 0.50 to 9.0 µg g(-1). In addition, parameters such as R(s), ER, and EF were calculated and compared with values obtained using the common valley drop integration method.