LC/MS determination of the enaminones E139, DM5 and DM27 in rat serum

Enaminones, E139, DM5 and DM27, have been recently recognized as potential anticonvulsant compounds. The molecular masses of these enarminones were proven using ion trap Finnigan mass spectrometer. For conduction of biological studies in animals, a sensitive and selective high-performance liquid chromatography-mass spectrometry (LC/MS) was developed for the determination of the selected enaminones in rat serum. A simple protein precipitation procedure was followed for cleaning up the serum samples before analysis. LC/MS determinations were performed using an APCI probe at 430 degrees C. Positive ions (M+1)(+) were acquired in MS/MS-SRM mode at m/z 308.1 (parent m/z 340.2) for E139 and m/z 262.1 (parent m/z 294.1) for DM5. On the other hand, DM27 and E118 (internal standard) were measured in SIM mode at m/z 236.5 and 222.5, respectively. Quantitation was based on measurement of the peak area ratio of enaminones (E139, DM5, DM27) and E118 as an internal standard. Calibration curves were linear (r>0.9989) over the concentration range 100-1000 ngml(-1) and were free from serum interference. Precision and accuracy studies of control samples showed intra-day and inter-day %RSD <10.1 and % deviation from nominal concentrations (%DEV) from -4.3 to +10.1. Recoveries of E139, DM5 and DM27 from quality control rat serum samples using protein precipitation method were 92.3, 89.4 and 89.6%, respectively. The reported data suggest the utility of this developed method for structural elucidation and for performing pharmacokinetics studies on the selected enaminones in rats.     

Detection of p-chloroamphetamine in urine samples with mass spectrometry

Designer drugs are introduced periodically to avoid detection and to provide new drugs with different pharmacological activities. During our routine analysis of amphetamine in urine samples, we observed one sample that reacted with immunoassay with high activity. There is one prominent peak in the gas chromatography- mass spectrometry (GC-MS) chromatogram. However, no amphetamine, methamphetamine, MDA, MDMA, MDEA, or ephedrine was detected with GC-MS. Careful examination of the mass spectrum indicated the presence of one fragment ion (m/z 140), which is similar to the base peak of trifluoroacetic anhydride derivative of amphetamine. The characteristic ion cluster representing the presence of one chlorine atom was observed. Investigation with liquid chromatography (LC)-MS detected an unknown compound with molecular ion of m/z 170. This compound was tentatively identified as chloroamphetamine. Pure standard material of p-chloroamphetamine (PCA) was purchased and analyzed with both GC-MS and LC-MS. Identical GC-MS spectra and LC-MS-MS fragmentation patterns were obtained. A GC-MS procedure was developed for the quantitation of PCA. The limits of detection and quantification were 10 μg/L. Precision was between 1.26% and 4.26%, and bias was between -0.91% and 4.27%. The prevalence PCA positive rate is 0.35% of the samples screened positive for amphetamine.     

LC/MS/MS法测定血浆中左羟丙哌嗪浓度及其药代动力学

目的建立测定血浆中左羟丙哌嗪的液相色谱-串联质谱法，考察左羟丙哌嗪在中国健康志愿者体内的药代动力学行为。方法血浆样品经液-液提取后，进行色谱分离，在三重四极杆串联质谱仪上，以多重反应离子监测(MRM)方式进行定量分析，用于监测的离子为m/z 237 → m/z 120（左羟丙哌嗪）和m/z 288 → m/z 58(佐米曲普坦，内标)。结果左羟丙哌嗪的最低定量浓度为0.25 μg·L^-1，线性范围为0.25-500.0 μg·L^-1，精密度与准确度符合生物样品分析要求。结论该法操作简便、快速、灵敏度高。可检测出健康志愿者po左羟丙哌嗪60 mg,其24 h后的血药浓度，适于临床药代动力学研究。     

Characterization of human urinary metabolites of the antimalarial piperaquine.

Five metabolites of the antimalarial piperaquine (PQ) (1,3-bis-[4-(7-chloroquinolyl-4)-piperazinyl-1]-propane) have been identified and their molecular structures characterized. After a p.o. dose of dihydroartemisinin-piperaquine, urine collected over 16 h from two healthy subjects was analyzed using liquid chromatography (LC)/UV, LC/tandem mass spectrometry (MS/MS), Fourier transform ion cyclotron resonance (FTICR)/MS, and H NMR. Five different peaks were recognized as possible metabolites [M1, 320 m/z; M2, M3, and M4, 551 m/z (PQ + 16 m/z); and M5, 567 m/z (PQ + 32 m/z)] using LC/MS/MS with gradient elution. The proposed carboxylic M1 has a theoretical monoisotopic molecular mass of 320.1166 m/z, which is in accordance with the FTICR/MS (320.1168 m/z) findings. The LC/MS/MS results also showed a 551 m/z metabolite (M2) with a distinct difference both in polarity and fragmentation pattern compared with PQ, 7-hydroxypiperaquine, and the other 551 m/z metabolites. We suggest that this is caused by N-oxidation of PQ. The results showed two metabolites (M3 and M4) with a molecular ion at 551 m/z and similar fragmentation pattern as both PQ and 7-hydroxypiperaquine; therefore, they are likely to be hydroxylated PQ metabolites. The molecular structures of M1 and M2 were also confirmed using H NMR. Urinary excretion rate in one subject suggested a terminal elimination half-life of about 53 days for M1. Assuming formation rate-limiting kinetics, this would support recent findings that the terminal elimination half-life of PQ has been underestimated previously.     

电喷雾离子阱质谱法直接测定几种药物的葡萄糖苷酸型代谢物

为研究药物代谢产物的质谱规律,用电喷雾离子阱质谱法对溶液中乙氧苯柳胺、SFZ-47羧基衍生物、5-羟基普罗帕酮及普罗帕酮的β-D-葡萄糖苷酸型代谢物的结构进行了测定。结果表明,它们的(-)ESI-MS均生成[M-H]^-准分子离子,(-)ESI-MS²和(-)ESI-MS³则分别生成m/z175和m/z113碎片离子。提示这些共同特征可用于LC/MS法直接分析药物的葡萄糖苷酸型代谢物。     

Therapeutic monitoring of tacrolimus concentrations in blood: semi-automated extraction and liquid chromatography-electrospray ionization mass spectrometry

The authors describe a highly selective liquid chromatographic/mass spectrometric (LC/MS) method for measurement of the immunosuppressive drug tacrolimus. A protein-free supernatant of a patient's whole-blood sample (500 microL) is applied to an Empore styrene-divinylbenzene (SDB-XC) disk cartridge (Varian Sample Preparation Products; Harbor City, CA) to isolate tacrolimus and the internal standard, ascomycin. The entire extraction is automated on the Gilson ASPEC XL4 (Gilson; Middleton, WI). Separation takes place on an octyldecyl (C18) high-performance liquid chromatographic (HPLC) column maintained at 75 degrees C with a simple mobile phase of acetonitrile/water (90/10, v/v). An atmospheric pressure ionization (API)-electrospray ionization(ESI)-mass spectrometer (MS) is used for analysis. Detection is by selected ion monitoring (SIM) of the positively charged sodium adduct of tacrolimus and ascomycin, m/z 826.5 and 814.5, respectively. Collision-induced dissociation (CID) fragment ions of tacrolimus and ascomycin (m/z 616.4 and 604.4, respectively) are also monitored to enhance overall selectivity. Total run time is 1 minute per injection. A plot of chromatographic peak height ratio of m/z 826.5 to m/z 814.5 vs tacrolimus blood concentration is linear from the lowest limit of quantitation (0.3 microg/L) to at least 120.0 microg/L. Metabolites of tacrolimus and other immunosuppressive and commonly prescribed drugs do not interfere. Analytical recovery is 94% to 113% over a range of 4.4 to 41.0 microg/L. Between-run precision coefficients of variation (CV) are 3.6% to 4.2% over a range of 8.1 to 32.4 microg/L. Comparison data (n = 156) of the LC/MS method versus a commercial immunoassay (Abbott Tacrolimus IMx MEIA II) (Abbott; Chicago, IL) demonstrated that the tacrolimus concentration as measured by LC/MS = (0.912 x MEIA concentration) - 0.049; r2 = 0.968. This validated LC/MS method demonstrates significant advantages over conventional immunoassays and improves on the lower limit of detection, sensitivity, accuracy, and range of linearity. In the authors' laboratory, this method is approximately 60% less costly to perform than the most commonly implemented immunoassay. Together, the authors' daily clinical experience during 1 year and participation in a proficiency testing program has demonstrated that the method is robust and suitable for routine therapeutic monitoring of tacrolimus.     

异钩藤碱代谢产物的质谱鉴定及药理活性的探讨

目的研究异钩藤碱(Isorhy)在猫体内的代谢并同步观察其可能的药理活性。方法麻醉猫静脉注射异钩藤碱5 mg/kg后,观察家猫血压的变化,收集0～3 h的血浆样品,用氢氧化钠—乙醚(1∶5)提取异钩藤碱及其代谢物,高效液相色谱法(HPLC)分离收集色谱峰流分,以液相色谱/质谱(LC/MS)测定异钩藤碱代谢物1(metabolite 1)分子离子峰的质荷比(m/z);代谢物1以60 ℃减压蒸馏24 h,同法测定代谢物1裂解物(metabolite 2)的分子离子峰m/z,根据m/z推测二者的化学结构。结果异钩藤碱代谢物1的相对分子质量为386,其热裂解化合物(metabolite2)相对分子质量为300,代谢产物在降压方面的药理作用贡献不大。结论①异钩藤碱代谢物的相对分子质量为386,为异钩藤碱的加氢还原产物;②代谢物不稳定,加热易裂解,其相对分子质量为300;③代谢物没有表现出心血管药理活性。     

LC/MS/MS法测定人血浆中愈创木酚甘油醚浓度及药动学研究

目的:建立以高效液相色谱-质谱联用法测定人血浆中愈创木酚甘油醚浓度的方法,并研究愈创木酚甘油醚片的人体药动学。方法:碱化的血浆药品经乙酸乙酯萃取后,以甲醇-1%甲酸(70:30)为流动相,对乙酰氨基酚为内标,采用Aquasil C18柱分离。通过液相色谱-串联质谱联用仪,以选择反应监测方式进行检测,定量分析的离子反应分别为m/z199→m/z125(愈创木酚甘油醚)和m/z152→m/z110(对乙酰氨基酚)。结果:愈创木酚甘油醚检测浓度在5·0～2500ng·mL-1范围内线性关系良好(r=0·9953),定量下限为5·0ng·mL-1。20名受试者口服愈创木酚甘油醚片0·2g后的主要药动学参数Cmax为(754·6±190·5)ng·mL-1、t1/2为(0·97±0·12)h、tmax为(0·63±0·22)h、AUC0～t为(1435·8±441·9)ng·h·mL-1、AUC0～∞为(1444·9±449·3)ng·h·mL-1。结论:本方法简便、快速、灵敏,可用于愈创木酚甘油醚的临床药动学研究。     

Determination and pharmacokinetics of danshensu in rat plasma after oral administration of danshen extract using liquid chromatography/tandem mass spectrometry.

A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed and validated for the determination and pharmacokinetics of danshensu in rat plasma samples using ferulic acid as internal standard (IS). The plasma samples were treated by liquid-liquid extraction, and the analyses were determined using electrospray negative ionization mass spectrometry in selected reaction monitoring (SRM) mode. The signal intensity of the m/z 196.8 --> 134.8 transition of danshensu was found to relate linearly to danshensu concentrations in the plasma from 5-500 ng/mL. The lower limit of quantification (LLOQ) as determined by the LC/MS/MS method amounted to 5 ng/mL. The intra- and inter-day precision was below 10.82%, and the accuracy was between -3.51% and +11.92%. The validated LC/MS/MS method was applied to a pharmacokinetic study in which danshen extract (containing 40 mg/g danshensu) was administered orally to rats at a single dose of 200 mg/kg in 2% water.     

LC/MS/MS法同时测定细胞孵化液中6种雌激素类化合物的含量

目的建立同时测定细胞孵化液中6种雌激素类化合物含量的LC/MS/MS法,并用该法研究E1S在乳腺癌细胞中的代谢行为。方法细胞孵化样品经处理后,采用Diamonsil C18柱分离,流动相为乙腈和5 mmol.L-1醋酸铵(pH 7.8),梯度洗脱,采用电喷雾电离(electrospray ionization,ESI)源,以多反应监测(multiple reaction monitoring,MRM)方式进行检测,用于定量分析的离子反应分别为m/z 269.3→m/z 145.2(雌酮,estrone,E1),m/z 271.1→m/z 145.2(雌二醇,estradiol,E2),m/z349.2→m/z 269.2(硫酸雌酮e,strone-3-sulfate,E1S),m/z 351.1→m/z 271.3(硫酸雌二醇,estradiol-3sulfate,E2S),m/z 445.5→m/z 269.3(β-D-葡萄糖醛酸雌酮,estrone-3-glucuronide,E1G),m/z 447.4→m/z 271.0(葡萄糖醛酸雌二醇,estradiol-3-glucuronide,E2G)和m/z 253.4→m/z 223.0(大豆苷元,内标)。结果该方法中E1、E2、E1S、E2S的线性分别为9.8～5 000.0 nmol.L-1,E1G、E2G的线性为0.98～500.00 nmol.L-1;日内和日间精密度均小于10.8%,相对误差在±11.7%以内。结论该法适用于细胞孵化液中6种雌激素类化合物的同时测定。     

Isolation, purification, and characterization of two new chemical decomposition products of methylazoxyprocarbazine.

We have previously reported that the antineoplastic agent, procarbazine, in aqueous solutions was chemically oxidized to its azoxy metabolites (methylazoxy and benzylazoxy). To determine if there was additional metabolism of the most active metabolite, methylazoxyprocarbazine, it was incubated in the presence and absence of CCRF-CEM human leukemia cells. Incubations were extracted, and potential metabolites were detected by HPLC with UV detection and by combined HPLC and thermospray mass spectrometric analysis. The major metabolite identified by HPLC with UV detection of the extracts was N-isopropyl-p-formylbenzamide; this was identified by comparison of its retention time with that of a synthesized standard. This identification was further corroborated by HPLC/thermospray mass spectrometry (LC/MS). Analysis of the extracts by LC/MS also showed the presence of a closely eluting peak that had a protonated molecular ion at m/z 207. This new metabolite was identified as N-isopropyl-(benzene-1,4-bis-carboxamide) by 1H NMR and gas chromatography/ion trap mass spectrometry. This metabolite is postulated to arise from breakage of the N-N bond in the hydrazine portion of the molecule. Reconstructed ion (m/z 236) current profiles from the analysis of the cell extracts indicated that there was only a trace amount of methylazoxyprocarbazine left after a 72-hr incubation. Interestingly, a peak with the same molecular weight as the parent compound (methylazoxyprocarbazine) was observed in the cellular incubations and also in extracts of control incubations in which methylazoxyprocarbazine was incubated in medium without cells. This unknown was silylated and identified as a hydroxyazo compound by an ion trap mass spectrometer operated under both single and multiple-stage mass analysis. Formation of this decomposition product appears to involve a novel intramolecular rearrangement of methylazoxyprocarbazine in solution. This pathway may be responsible for the formation of the ultimate cytotoxic species by chemical decomposition of procarbazine.     

Quantification of hyaluronic acid fragments in pharmaceutical formulations using LC-ESI-MS

Three different hyaluronic acid fragment preparations (HAF) derived from hyaluronic acid (HA) by hyaluronate lyase digestion have been investigated. The amount of these fragment mixtures in pharmaceutical formulations was determined by liquid chromatography-electrospray tandem mass spectrometry (LC/MS/MS). HAF analysis was performed in less than 8 min using a Nucleosil 100-7 C2 column. Based on the assumption that the mass distribution is kept constant, which is confirmed by the calibration results, quantification can be carried out relating to the most intense fragments. For that purpose, the ratios of the peak areas of product ions of m/z=378 (tetramer, hexamer, octamer) to the peak area of m/z=83 ([2xmaltose-H(+)], internal standard) were calculated. Calibration was done for each HAF and good linearity from 5 to 80 microg/ml has been shown. To evaluate the molecular weight distribution of the fragment preparations used in this approach MALDI-TOF, mass spectra have been collected.     

Identification of a novel glutathione adduct of diclofenac, 4'-hydroxy-2'-glutathion-deschloro-diclofenac, upon incubation with human liver microsomes.

Clinical use of the nonsteroidal anti-inflammatory drug diclofenac (DF) is associated with an incidence of idiosyncratic hepatoxicity. The formation of reactive metabolites of DF in vivo has been proposed to be responsible for such toxicity. One type of reactive metabolite, a benzoquinone imine of DF formed through oxidation by cytochromes P450, can be trapped by glutathione in vitro in liver microsomes to form glutathione (GS) adducts. Three GS adducts from DF were reported in the literature, namely, 5-hydroxy (OH)-4-glutathione-DF, 4'-OH-3'-glutathione-DF and 5-OH-6-glutathione-DF, and they all have the same molecular weight of 616. Recently, we developed a sensitive and high throughput method for the detection of GS adducts from liver microsome incubation. This method uses a constant neutral loss scan of m/z 129, a "structure-characteristic" fragment for GS adduct, on an automated chip-based nanoelectrospray (Advion NanoMate 100) attached to a tandem mass spectrometer (Sciex API 3000). The analysis of GS adducts from human liver microsome incubation with DF by the NanoMate 100-API 3000 method unambiguously revealed a new adduct ion with m/z 583 (MH+), in addition to the known adduct peak with m/z 617 (MH+). This new adduct was further confirmed to be 4'-OH-2'-glutathion-deschloro-diclofenac by liquid chromatography (LC) tandem mass spectrometry (MS), LC/MS-NMR, and comparison to a synthetic standard.     

A simple and sensitive LC/MS/MS assay for 7-ethyl-10-hydroxycamptothecin (SN-38) in mouse plasma and tissues: application to pharmacokinetic study of liposome entrapped SN-38 (LE-SN38)

An LC/MS/MS method to quantify SN-38 in mouse plasma and tissue homogenates containing liposome entrapped SN-38 (LE-SN38) was developed. Camptothecin (CPT) was used as the internal standard (IS). Sample preparation consisted of simple protein precipitation by acetonitrile containing 0.5% acetic acid. SN-38 and IS were separated by a C18 HPLC column and detected using a mass spectrometer operating in the multiple reaction monitoring (MRM) mode. The peak area of the m/z 393.3-->349.1 transition of SN-38 and that of the m/z 349.1-->305.2 transition of the IS were measured and a standard curve was generated from their ratios. The method had a LLOQ of 0.5 ng/mL in mouse plasma, which corresponds to 2.5 pg for the 5 microL injection volume. The linear range was 0.5-1000 ng/mL of SN-38 in plasma sample spiked with LE-SN38. The LLOQ in tissue homogenates (5%, w/v) quantitation was 1 ng/mL (20 ng/g tissue) of SN-38 in kidney, liver, lung, and spleen homogenates, and 2 ng/mL (40 ng/g tissue) in heart homogenate containing LE-SN38. The assay was linear up to 400 ng/mL of SN-38 in tissue homogenates, and may be extended to 120 microg/mL by proper dilution of samples over the upper limit of quantitation. Acceptable precision and accuracy were obtained for concentrations over the entire standard curve range, both between-run and within-run for plasma and tissue homogenates. The method was successfully used to quantify SN-38 in plasma and tissues samples for pharmacokinetic and tissue distribution studies of LE-SN38 in mice.     

Identification of phase I and phase II metabolites of Guanfu base A hydrochloride in human urine.

Guanfu base A is a novel arrhythmic drug candidate isolated from the tuber of a traditional Chinese herb. Phase I and Phase II metabolites of Guanfu base A (GFA) Hydrochloride were studied in human urine by means of liquid chromatography mass spectrometry (LC/MSD) and tandem mass spectrometry (MS/MS). For phase I metabolites, Guanfu base I (GFI) was separated by HPLC and identified by comparison with authentic reference for their retention times, molecular ion peaks, fragment ions, and UV spectra. GFA oxide was also indicated to exist in human urine. For phase II metabolites, after human urine was treated either with glucuronidase or sulfatase, GFA occured in the chromatograms. It was suggested that there were GFA glucuronide and GFA sulfate in human urine. Further more, positive molecular ions, m/z 606 and m/z 510, of the two conjugates were detected in human urine by LC/MSD. In addition, characteristic ion of m/z 606 was identified as the precursor ion of m/z 177 [Glucuronic acid+H]+ by using MS/MS. Characteristic ion of m/z 430 [GFA+H]+ was also identified as a product ion of m/z 606 [GFA glucuronide+H]+. It was concluded that there were GFI. GFA oxide, GFA glucuronide and GFA sulfate in human urine.     

Establishment of a liquid chromatographic/mass spectrometry method for quantification of tetrandrine in rat plasma and its application to pharmacokinetic study

A rapid and sensitive liquid chromatography-tandem mass spectrometric method (LC/MS/MS) for the determination of tetrandrine in rat plasma has been developed, fully validated and successfully applied to pharmacokinetic study in Sprague-Dawley (SD) rats after a single oral administration. Sample preparation involves a liquid-liquid extraction with n-hexane-dichlormethane (65:35, containing 1% 2-propanol isopropyl alcohol, v/v). Tetrandrine and brodimoprim (internal standard) were well separated by LC with a Dikma C(18) column using acetonitrile-methanol-ammonium formate aqueous solution (20mM) containing 0.3% formic acid (20:30:50, v/v/v) as mobile phase. Detection was performed on a triple quadrupole mass spectrometer in multiple reaction monitoring mode. The ionization was optimized using ESI(+) and selectivity was achieved using MS/MS analysis, m/z 623.0-->381.0 and m/z 339.0-->281.0 for tetrandrine and I.S., respectively. The present method exhibited good linearity over the concentration range of 5-2,000 ng/mL for tetrandrine in rat plasma with a lower limit of quantification of 5 ng/mL. The intra- and inter-day precision were 2.0-9.2% and 4.5-9.4%, and the intra- and inter-day accuracy ranged from -7.6 to 10.3% and -6.0 to 5.3%, respectively. No endogenous compounds were found to interfere with the analysis, and tetrandrine was stable during the whole assay period. The method was successfully applied to a pharmacokinetic study after an intragastric administration (i.g.) of tetrandrine to SD rats with a single dose of 50mg/kg. The results confirm that the assay is suitable for the pharmacokinetic study of tetrandrine.     

UFLC-MS／MS法快速测定酚酞片中的酚酞

目的建立超快速液相色谱-质谱／质谱联用（UFLC—MS／MS）法测定酚酞片中酚酞的量。方法样品以乙醇提取、微孔滤膜滤过、离心后,通过电喷雾离子化（ESI）,采用多反应检测（MRM）方式进行正离子检测,用于定量分析的检测离子为m／z319．0→225-2。采用Shim-packXR-ODS色谱柱（75mm~3．0mm,2．0μm）分离,以乙腈-水．甲酸（55：45：0．1）为流动相,体积流量为0．40mL／min,在3min内完成酚酞定量分析。结果线性范围为2．5～1000．0ng／mL,最低检测限为2．5ng／mL;日内RSD小于1．85％,日问RSD小于2．56％。结论本方法灵敏度高,分析速度快,操作简单,可作为酚酞片中酚酞质量控制方法。     

液相色谱-质谱-质谱联用法测定人血浆中氨氯地平

目的　建立测定人血浆中氨氯地平的液相色谱-质谱-质谱联用法。方法　血浆样品经液-液萃取后,以乙腈-水-甲酸(75∶35∶1)为流动相,采用ZorbaxC₈柱分离,通过电喷雾离子化四极串联质谱,以选择离子反应监测(SRM)方式进行检测。用于定量分析的二级碎片离子分别为m/z238(氨氯地平)和m/z116(内标4′-羟基普罗帕酮)。结果　线性范围为0.4-16.0ng·mL^-1,最低定量浓度为0.4ng·mL^-1,每个样品测试时间仅3.7min。在氨氯地平临床药物动力学研究项目中,应用此法可在两周内测试1500多个血浆样品。结论　该法灵敏度高,操作简便,快速、准确,适用于临床药物动力学研究。     

Determination of a beta(3)-agonist in human plasma by LC/MS/MS with semi-automated 48-well diatomaceous earth plate

Methods for the determination of a beta(3)-agonist (A) in human plasma were developed and compared based on high-performance liquid chromatography (HPLC) with tandem mass spectrometric (MS/MS) detection using a turbo ion spray (TIS) interface. Drug and internal standard were isolated from plasma by three sample preparation methods, liquid-liquid extraction, Chem Elut cartridges and 48-well diatomaceous earth plates, that successively improved sample throughput for LC/MS/MS. MS/MS detection was performed on a PE Sciex API 365 tandem mass spectrometer operated in positive ion mode and using multiple reaction monitoring (MRM). The precursor/product ion combinations of m/z 625/607 and 653/515 were used to quantify A and internal standard, respectively, after chromatographic separation of the analytes. Using liquid-liquid extraction and Chem Elut cartridges, the assay concentration range was 0.5-100 ng/ml. Using diatomaceous earth plates, the concentration range of the assay was extended to 0.5-200 ng/ml. For all three assays, the statistics for precision and accuracy is comparable. The assay accuracy ranged from 91-107% and intraday precision as measured by the coefficient of variation (CV) ranged 2-10%. The sample throughput was tripled when the diatomaceous earth plate method was compared with the original liquid-liquid extraction method.     

Potent estrogenic metabolites of bisphenol A and bisphenol B formed by rat liver S9 fraction: their structures and estrogenic potency.

We previously demonstrated that the estrogenicity of either bisphenol A [BPA; 2,2-bis(4-hydroxyphenyl)propane] or bisphenol B [BPB; 2,2-bis(4-hydroxyphenyl)butane] was increased several times after incubation with rat liver S9 fraction (Yoshihara et al., 2001). This metabolic activation, requiring both microsomal and cytosolic fractions, was observed with not only rat liver, but also human, monkey, and mouse liver S9 fractions. To characterize the active metabolites of BPA and BPB, we investigated the structures of the isolated active metabolites by negative mode LC/MS/MS and GC/MS. The active metabolite of BPA gave a negative mass peak at [M-H](-) 267 on LC/MS and a single daughter ion at m/z 133 on MS/MS analysis, suggesting an isopropenylphenol dimer structure. Finally, this active metabolite was confirmed to be identical with authentic 4-methyl-2,4-bis(p-hydroxyphenyl)pent-1-ene (MBP) by means of various instrumental analyses. The corresponding peaks of the BPB metabolite were [M-H](-) 295 and m/z 147, respectively, suggesting an isobutenylphenol dimer structure. Further, coincubation of BPA and BPB with rat liver S9 afforded an additional active metabolite(s), which gave a negative mass peak at [M-H](-) 281 and two daughter ion peaks at m/z 133 and m/z 147 on MS/MS analysis. These results strongly suggest that the active metabolite of either BPA or BPB might be formed by recombination of a radical fragment, a one-electron oxidation product of carbon-phenyl bond cleavage. It is noteworthy that the estrogenic activity of MBP, the active metabolite of BPA, is much more potent than that of the parent BPA in several assays, including two reporter assays using a recombinant yeast expressing human estrogen receptor alpha and an MCF-7-transfected firefly luciferase plasmid.