Determination of Solanidine- and Tomatidine-Type Glycoalkaloid Aglycons by Gas Chromatography/Mass Spectrometry

Abstract

A combined derivatization method for gas chromatographic/mass spectrometric (GC/MS) analysis of steroidal glycoalkaloid (SGA) aglycons was developed using both trimethylsilylation and pentafluoropropionylation. In comparison with underivatized or only silylated aglycons, the new technique produces more specific and abundant fragmentation for compounds with a tomatidine-type structure. For example, the difference between solasodine and tomatidine, the former containing a double bond at position 5,6 in the steroidal skeleton, can be observed by their base peak fragments at m/z 417 (C(24)H(41)O(2)Si(2)) and m/z 419 (C(24)H(43)O(2)Si(2)). The method is well suited for the simultaneous determination of both solanidane- and spirosolane-type SGA aglycons from Solanum species and hybrids. The reproducibility of the method, including SGA extraction, hydrolysis, derivatization, and quantitative GC/MS analysis, was <6% (CV) for the principal aglycons determined from a hybrid between a wild potato species, Solanum brevidens Phil., and a cultivated potato, S. tuberosum L. A single ion monitoring technique using specific fragments m/z 419 and 417 could be applied for the determination of minor stereoisomers, which are often overlapped by large amounts of tomatidine.

Development of Practical HPLC Methods for the Separation and Determination of Eggplant Steroidal Glycoalkaloids and their Aglycones

“…[44] Several authors have explored novel methods for the determination of glycoalkaloids in recent years. Among these are the use of enzyme-linked immunosorbent assay (ELISA), which is useful only for the aglycone forms, [45] "fluorescence polarization immunoassay," [46] "solution phase immunoassay with capillary electrophoresis, [47] gas chromatography mass spectrometry as applied to the aglycone forms, [48] liquid chromatography mass spectrometry, [38,49] matrix-assisted laser-desorption/ ionization time-of-flight mass spectrometry (MALDI-TOF/MS), [50] "nonaqueous capillary electrophoresis with ultra violet (UV) detection (NACE-UV)" for the analysis of solasodine and solanidine aglycones, [51,52] NACE combined with ion-trap mass spectrometry, [52,53] and, lastly, derivatization of the glycoalkaloids followed by HPLC separation and chemiluminescence detection. [54] Each of these methods has its own particular merits; however, although glycoalkaloids show limited absorption of ultraviolet (UV) light, HPLC separation followed by UV detection can still be considered a viable method, due to the relative widespread availability of this instrumentation and the potential to detect not some, but all the glycoalkaloids of interest without a lengthy derivatization step.…”

Solid‐Phase Microextraction (SPME) followed by On‐Fiber Derivatization of Solasodine and Solanidine Aglycones of Steroidal Glycoalkaloids

“…3 and 4). Both solanidine and cholesterol produced mono-TMS derivatives [39] with molecular ion peaks at m/z 469 and m/z 458 (not shown), respectively.…”

“…5) and corresponding mass spectrum (Fig. 6), solasodine (from the standard solution) shows the di-TMS derivative [39] after silylation with base peak at m/z 125 and its proper molecular ion peak cluster. Unfortunately, the centroid data given by our ion trap instrument did not show the di-TMS derivative molecular ion at m/z 557.…”

“…Before the "on-fiber derivatization" scheme unique to this work was evaluated, traditional non-SPME based methods of derivatizating aglycones of glycoalkaloids [39] were carried out to gain experience in handling the derivatizing agents and to gain knowledge as a logical first step. Separate aglycone standard solutions, each containing 20 microliters, were placed in 4-mL vials, evaporated to near dryness for 30 minutes, dried at 1058C for 5 minutes, and stored in a dessicator with loose caps until they cooled to room temperature.…”

“…As a means of convenient sampling and introduction to analytical instrumentation, solid-phase microextraction (SPME) has been extensively investigated for use with gas chromatography (GC) [29 -35] and, to a lesser extent, high performance liquid chromatography (HPLC). [29,36,37] Although the fragile structures of SGAs typically preclude their analysis by GC methods, it is, however, possible to determine, by GC, the hydrolyzed aglycone forms of steroidal glycoalkaloids, either directly [38,39] or, when necessary, via derivatization of the aglycones to more volatile forms. [39] Furthermore, for studies involving the measurement of glycoalkaloids by traditional methods, researchers, for simplicity, sometimes report their results in terms of a concentration of total glycoalkaloids (TGA) or "equivalents" for a specific aglycone, referring to the combined concentrations of the SGAs under the heading of their respective aglycones, presumably when other SGAs related to that particular aglycone are deemed undetectable (e.g., [solanine SGA] þ [chaconine SGA] ¼ [solanidine SGAA]).…”