A microbore high performance liquid chromatography/electrospray ionization mass spectrometry method for the determination of the phytoestrogens genistein and daidzein in comminuted baby foods and soya flour

Differentiation of flavonoid glycoside isomers by using metal complexation and electrospray ionization mass spectrometry

The elucidation of flavonoid isomers is accomplished by electrospray ionization tandem mass spectrometry (ESI-MS/MS) via formation and collisional activated dissociation (CAD) of metal/flavonoid complexes containing an auxiliary ligand. Addition of a metal salt and a suitable neutral auxiliary ligand to flavonoids in solution results in the formation of [M(II) (flavonoid-H) ligand]+ complexes by ESI which, upon collisional activated dissociation, often result in more distinctive fragmentation patterns than observed for conventional protonated or deprotonated flavonoids. Previously, 2,2'-bipyridine was used as an auxiliary ligand, and now we compare and explore the use of alternative pyridyl ligands, including 4,7-diphenyl-1,10-phenanthroline. Using this technique, three groups of flavonoid glycoside isomers are differentiated, including glycosides of apigenin, quercetin, and luteolin.

Determination of daidzein and genistein in soybean foods by automated on-line in-tube solid-phase microextraction coupled to high-performance liquid chromatography

An automated on-line method for the determination of the isoflavones, daidzein and genistein, was developed using in-tube solid-phase microextraction coupled to high-performance liquid chromatography (in-tube SPME-HPLC). In-tube SPME is a new extraction technique for organic compounds in aqueous samples, in which analytes are extracted from the sample directly into an open tubular capillary by repeated draw/eject cycles of sample solution. Daidzein, genistein and their glucosides tested in this study were clearly separated within 8 min by HPLC using an XDB-C8 column with diode array detection. In order to optimize the extraction of these compounds, several in-tube SPME parameters were examined. The glucosides daidzin and genistin were analyzed as aglycones after hydrolysis because the glucosides were not concentrated by in-tube SPME. The optimum extraction conditions for daidzein and genistein were obtained with 20 draw/eject cycles of 40 microl of sample using a Supel-Q porous layer open tubular capillary column. The extracted compounds were easily desorbed from the capillary by mobile phase flow, and carryover was not observed. Using the in-tube SPME-HPLC method, the calibration curves of these compounds were linear in the range 5-200 ng/ml, with a correlation coefficient above 0.9999 (n = 18), and the detection limits (S/N = 3) were 0.4-0.5 ng/ml. This method was successfully applied to the analysis of soybean foods without interference peaks. The recoveries of aglycones and glucosides spiked into food samples were above 97%.

Review of the methods used in the determination of phytoestrogens

Interest in analytical methods for plant estrogens (phytoestrogens) has risen sharply in the past 10 years. In this review, we examine the existing analytical methods based on separations by gas-liquid chromatography, high-performance liquid chromatography and capillary electrophoresis in addition to methods of detection by ultraviolet absorption, fluorescence, electrochemical oxidation/reduction and mass spectrometry. These methods are compared with other methods of phytoestrogen analysis utilizing immunoassay approaches. The advantages and disadvantages of each of these methods are highlighted and potential areas for further development identified.

Identification and quantification of polyphenol phytoestrogens in foods and human biological fluids

We review the methods used to measure phytoestrogens (genistein, daidzein, lignans and their derivatives) in foods and biological fluids, and discuss advantages and disadvantages of each. The range of detection limits reported varies widely between individual laboratories, but generally the best reported sensitivity is as follows: immunoassay>HPLC-mass spectrometry=HPLC-multichannel electrochemical detection (coularray)>GC-single ion monitoring-mass spectrometry>HPLC-UV diode array>HPLC-single channel electrochemical detection. The best sensitivity reported so far is 0.002 pmol per assay for daidzein by radioimmunoassay. HPLC with UV diode array detection is the most commonly employed, but is the least sensitive and specific. GC and HPLC coupled with mass spectrometry or electrochemical detection are the most accurate and reproducible methods for a wide variety of analytes. Generally most methods, with the exception of immunoassay, have not been correlated with other methods. Recoveries from extraction methods, limits of detection, nature of compounds analysed and the internal standards used are summarised for more than 90 reports in the literature. From this data, it is clear that an inter-laboratory validation and correlation between a wide range of methods for phytoestrogen analysis is required. One underdeveloped area that requires particular attention is the analysis of plant lignans.

Quantitative analysis of the principle soy isoflavones genistein, daidzein and glycitein, and their primary conjugated metabolites in human plasma and urine using reversed-phase high-performance liquid chromatography with ultraviolet detection

Soy isoflavones are becoming of increasing interest as nutritional agents which can be used to combat osteoporosis and hyperlipidemia, and are also being considered as potential cancer chemopreventive compounds. However, prior to their formulation and distribution as therapeutic agents, thorough pharmacokinetic and toxicological assessment needs to be completed in men and women in a variety of health conditions in order to ensure their therapeutic efficacy and safety. At this time, studies of purified soy isoflavones are possible, and are being designed to fully evaluate the pharmacological utility of these preparations. In support of these studies, quantitative analysis of soy isoflavones in biological fluids can be accomplished with a wide variety of methods and analytical instrumentation. However, the relatively ubiquitous presence of high-performance liquid chromatography with ultraviolet detection (HPLC-UV) in most analytical laboratories, the relative ease of its operation, and the lesser expense of this instrumentation as compared to more sophisticated techniques such as liquid chromatography-mass spectrometry, offers some distinct advantages for its use in pharmacokinetic studies. In this manuscript, the development and validation of an HPLC-UV method for the quantitation of the principal soy isoflavones, genistein, daidzein, and glycitein, and their primary metabolites, in human plasma and urine is described. This analytical approach allows for pharmacologically relevant concentrations of the analytes and their principle metabolites to be detected, and has been validated in close agreement with the US Food and Drug Administration's guidelines for the validation of methods to be used in support of pharmacokinetic studies.

Enhanced detection of flavonoids by metal complexation and electrospray ionization mass spectrometry

Metal complexation with the use of an auxiliary ligand is explored as an alternative to conventional protonation or deprotonation for analysis of a series of flavonoids by electrospray ionization mass spectrometry. Use of a neutral auxiliary ligand, 2,2'-bipyridine, results in formation of [MII(flavonoid - H)bpy]+, ternary complexes with intensities that are 2 orders of magnitude greater than the corresponding protonated flavonoids and up to 1.5 orders of magnitude greater than the deprotonated flavonoids, based on confirmation by collisionally activated dissociation patterns. The formation of ternary complexes with six divalent transition metals, Co2+, Ni2+, Cu2+, Zn2+, Mn2+, and Fe2+ were compared. Cu2+ resulted in the most intense complexes and simplest mass spectra, while Co2+ gave the second most intense spectra and also produced two key products that could be useful for a selected ion monitoring strategy. Complexation with iron(III) bromide is also investigated to explore the feasibility of using triply charged metals.

Fast liquid chromatographic-mass spectrometric determination of pharmaceutical compounds

We present fast LC-MS-MS analyses of multicomponent mixtures containing flavones, sulfonamides, benzodiazepines and tricyclic amines. Using a short microbore HPLC column with small particle size, five to eight compounds were partially resolved within 15 to 30 s. TurboIonSpray and atmospheric pressure chemical ionization interfaces were well suited to tolerate the higher eluent flow-rates of 1.2 to 2 ml/min. The methods were applied to biological sample matrices after clean-up using solid-phase or liquid-liquid extraction. Good precision and accuracy (average 8.9 and 97.7%, respectively) were achieved for the determination of tricyclic amines in human plasma. Benzodiazepines were determined in human urine with average precision of 9% and average accuracy of 95% for intra- and inter-assay. Detection limits in the low ng/ml range were obtained. An example for 240 injections per hour of demonstrated the feasibility of rapid LC-MS-MS analysis.

Biotransformation of genistein in the rat: elucidation of metabolite structure by product ion mass fragmentology

Biotransformation of the phytoestrogen [14C]genistein was investigated in male and female rats by application of narrow-bore radio-HPLC-MSn (LCQ, Finnigan) to determine intermediates in metabolism. Urine contained five metabolites, Gm1-Gm5, 24 h after dosing by gavage with [14C]genistein (4 mg kg(-1)). Structural analysis following ESI revealed molecular ions [M+H]+ of m/z 447, 449, 273, and 271 for metabolites Gm2, Gm3, Gm5 and genistein, respectively and an [M-H]- of m/z 349 for Gm4. Metabolite structure was deduced by evaluation of product ion spectra derived from unlabelled and [14C]-labelled ions and sensitivity to treatment with beta-glucuronidase. These studies indicated identity of metabolites with genistein glucuronide (Gm2), dihydrogenistein glucuronide (Gm3), genistein sulphate (Gm4) and dihydrogenistein (Gm5). Detection of the beta-glucuronidase resistant major metabolite Gm1 by ESI was poor and so was analysed by negative ion APCI; this revealed a deprotonated molecular ion of m/z 165 which had chromatographic and mass spectral properties consistent with authentic 4-hydroxyphenyl-2-propionic acid, a novel metabolite of genistein. In vitro metabolism studies with anaerobic caecal cultures derived from male and female rats revealed metabolism of genistein to Gm1 via Gm5 and an additional metabolite (Gm6) which was identified from product ion spectra as 6'-hydroxy-O-desmethylangolensin. Biotransformation of genistein by both isolated hepatocytes and precision-cut liver slices was limited to glucuronidation of parent compound. Commonality of genistein metabolites found in rats with those reported in man suggest similar pathways of biotransformation, primarily involving gut micro-flora.

Quantitative analysis of xanthohumol and related prenylflavonoids in hops and beer by liquid chromatography-tandem mass spectrometry

A method for quantitation of six prenylflavonoids (xanthohumol, isoxanthohumol, desmethylxanthohumol, 6- and 8-prenylnaringenins and 6-geranylnaringenin) in hops and beer by HPLC-tandem mass spectrometry has been developed. The method allows direct analysis of beer and crude methanolic extracts of hops. After HPLC separation, prenylflavonoids were detected by positive ion multiple-reaction monitoring using a triple-quadrupole mass spectrometer equipped with a heated nebulizer--atmospheric pressure chemical ionization interface. The accuracy and precision were evaluated by replicate analyses of (spiked) samples. Thirteen commercial beers were analysed with the method. Isoxanthohumol, formed by isomerization of xanthohumol during the brewing process, was the most abundant flavonoid in hopped beers, ranging from 0.04 to 3.44 mg/l.