The kudzu vine (Pueraria sp.) is a rich source of isoflavones. Dietary supplements based on kudzu have become commercially available. In the present study, liquid chromatography coupled with negative and positive electrospray ionization tandem mass spectrometry (MS/MS) and diode array detection (DAD) has been used for the detection and characterization of isoflavonoids in kudzu dietary supplements (KDS). The MS/MS spectrum of the protonated ion of puerarin showed characteristic product ions of the C-glycoside unit itself, whereas daidzin generated an abundant Y(0)(+) aglycon ion in its product ion spectrum. A base peak due to the loss of 120 Da [M + H - 120](+) is the diagnostic ion for C-glycosides. Neutral loss scans allowed for the detection of other C- and O-glycosides in the methanolic extract of KDS, and their structures have been proposed. The concentration of isoflavonoids in the methanolic extract of commercially available KDS was quantified by using DAD-HPLC. Puerarin, rather than daidzin, was the most abundant component (8.44-30.60 mg/capsule) in commercially available KDS.

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High-performance liquid chromatography (HPLC) or capillary electrophoresis (CE) is particularly suited to the separation and analysis of a wide range of biological compounds. When investigating such compounds in complex matrices (e.g., blood, tissue, urine, foods), specificity of the detection method becomes an important issue. This can be overcome by extensive purification procedures before HPLC or CE analysis, but at the cost of a lot of effort and often unknown losses during the extraction and purification procedures. Such losses can be overcome by the addition of isotopically labeled internal standards, subject to their availability. The coupling of HPLC or CE with mass spectrometry provides a very specific method of detection. Compounds are transferred as ions to the gas phase by two types of spraying technologies, electrospray ionization (ESI) and heated nebulizer-atmospheric pressure chemical ionization. Although the mass-to-charge ratios of the molecular ions can be used to provisionally identify a compound, full confirmation of structure requires collision-induced dissociation and analysis of the resulting fragment ions. Combination of specific parent ion-daughter ion pairs allows for the quantitative measurement of isoflavones in the 1-5 pmol range with coefficients of variation for duplicate samples in the range of 5-9%. CE places greater demands on the mass spectrometer than does HPLC, because it generates narrow peak widths. A mass spectrometer with a scanning quadrupole analyzer does not enable full exploitation of the power of CE; in this context, an instrument with an ESI interface and a time-of-flight analyzer is ideal.