'N-in-one' strategy for metabolite identification using a liquid chromatography/hybrid triple quadrupole linear ion trap instrument using multiple dependent product ion scans triggered with full mass scan

This paper describes a new strategy that utilizes the fast trap mode scan of the hybrid triple quadrupole linear ion trap (QqQ(LIT)) for the identification of drug metabolites. The strategy uses information-dependent acquisition (IDA) where the enhanced mass scan (EMS), the trap mode full scan, was used as the survey scan to trigger multiple dependent enhanced product ion scans (EPI), the trap mode product ion scans. The single data file collected with this approach not only includes full scan data (the survey), but also product ion spectra rich in structural information. By extracting characteristic product ions from the dependent EPI chromatograms, we can provide nearly complete information for in vitro metabolites that otherwise would have to be obtained by multiple precursor ion scan (prec) and constant neutral loss (NL) analysis. This approach effectively overcomes the disadvantages of traditional prec and NL scans, namely the slow quadrupole scan speed, and possible mass shift. Using nefazodone (NEF) as the model compound, we demonstrated the effectiveness of this strategy by identifying 22 phase I metabolites in a single liquid chromatography/tandem mass spectrometry (LC/MS/MS) run. In addition to the metabolites reported previously in the literature, seven new metabolites were identified and their chemical structures are proposed. The oxidative dechlorination biotransformation was also discovered which was not reported in previous literature for NEF. The strategy was further evaluated and worked well for the fast discovery setting when a ballistic gradient elution was used, as well as for a simulated in vivo setting when the incubated sample (phase I metabolites) was spiked to control human plasma extract and control human urine.     

Development of a multi-target screening analysis for 301 drugs using a QTrap liquid chromatography/tandem mass spectrometry system and automated library searching

A new multi-target screening (MTS) procedure for drugs in blood and urine for toxicological analysis has been developed using a hybrid triple-quadrupole linear ion trap mass spectrometer (QTrap) for the fast detection and identification of 301 forensically important drugs, e.g. tranquilizers (benzodiazepines), hypnotics, drugs of abuse (opiates, cocaine, amphetamines, cannabinoids), antidepressants, neuroleptics, and some cardiac drugs, in one single liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis. Samples were extracted either with liquid-liquid extraction or solid-phase extraction. A multiple reaction monitoring (MRM) as survey scan and an enhanced product ion (EPI) scan as dependent scan were performed in an information-dependent acquisition (IDA) experiment. Finally, drug identification was carried out by library search with a newly developed MS/MS library based on EPI spectra at three different collision energies in positive mode. The advantage of this newly developed method is the possibility to detect and identify 301 drugs in one single LC/MS/MS run.     

Rapid screening and characterization of drug metabolites using a new quadrupole-linear ion trap mass spectrometer

The application of a new hybrid RF/DC quadrupole-linear ion trap mass spectrometer to support drug metabolism and pharmacokinetic studies is described. The instrument is based on a quadrupole ion path and is capable of conventional tandem mass spectrometry (MS/MS) as well as several high-sensitivity ion trap MS scans using the final quadrupole as a linear ion trap. Several pharmaceutical compounds, including trocade, remikiren and tolcapone, were used to evaluate the capabilities of the system with positive and negative turbo ionspray, using either information-dependent data acquisition (IDA) or targeted analysis for the screening, identification and quantification of metabolites. Owing to the MS/MS in-space configuration, quadrupole-like CID spectra with ion trap sensitivity can be obtained without the classical low mass cutoff of 3D ion traps. The system also has MS(3) capability which allows fragmentation cascades to be followed. The combination of constant neutral loss or precursor ion scan with the enhanced product ion scan was found to be very selective for identifying metabolites at the picogram level in very complex matrices. Owing to the very high cycle time and, depending on the mass range, up to eight different MS experiments could be performed simultaneously without compromising chromatographic performance. Targeted product ion analysis was found to be complementary to IDA, in particular for very low concentrations. Comparable sensitivity was found in enhanced product ion scan and selected reaction monitoring modes. The instrument is particularly suitable for both qualitative and quantitative analysis.     

Rapid detection and identification of <Emphasis Type="Italic">N</Emphasis>-acetyl-<Emphasis Type="Italic">L</Emphasis>-cysteine thioethers using constant neutral loss and theoretical multiple reaction monitoring combined with enhanced product-ion scans on a linear ion trap mass spectrometer

A sensitive and specific liquid chromatography-mass spectrometry (LC-MS) method based on the combination of constant neutral loss scans (CNL) with product ion scans was developed on a linear ion trap. The method is applicable for the detection and identification of analytes with identical chemical substructures (such as conjugates of xenobiotics formed in biological systems) which give common CNLs. A specific CNL was observed for thioethers of N-acetyl-L-cysteine (mercapturic acids, MA) by LC-MS/MS. MS and HPLC parameters were optimized with 16 MAs available as reference compounds. All of these provided a CNL of 129 Da in the negative-ion mode. To assess sensitivity, a multiple reaction monitoring (MRM) mode with 251 theoretical transitions using the CNL of 129 Da combined with a product ion scan (IDA thMRM) was compared with CNL combined with a product ion scan (IDA CNL). An information-dependent acquisition (IDA) uses a survey scan such as MRM (multiple reaction monitoring) to generate "informations" and starting a second acquisition experiment such as a product ion scan using these "informations." Th-MRM means calculated transitions and not transitions generated from an available standard in the tuning mode. The product ion spectra provide additional information on the chemical structure of the unknown analytes. All MA standards were spiked in low concentrations to rat urines and were detected with both methods with LODs ranging from 60 pmol/mL to 1.63 nmol/mL with IDA thMRM. The expected product ion spectra were observed in urine. Application of this screening method to biological samples indicated the presence of a number of MAs in urine of unexposed rats, and resulted in the identification of 1,4-dihydroxynonene mercapturic acid as one of these MAs by negative and positive product ion spectra. These results show that the developed methods have a high potential to serve as both a prescreen to detect unknown MAs and to identify these analytes in complex matrix.     

Predictive Multi Experiment Approach for the Determination of Conjugated Phenolic Compounds in Vegetal Matrices by Means of LC-MS/MS

Polyphenols (PCs) are a numerous class of bioactive molecules and are known for their antioxidant activity. In this work, the potential of the quadrupole/linear ion trap hybrid mass spectrometer (LIT-QqQ) was exploited to develop a semi-untargeted method for the identification of polyphenols in different food matrices: green coffee, Crocus sativus L. (saffron) and Humulus lupulus L. (hop). Several conjugate forms of flavonoids and hydroxycinnamic acid were detected using neutral loss (NL) as a survey scan coupled with dependent scans with enhanced product ion (EPI) based on information-dependent acquisition (IDA) criteria. The presented approach is focused on a specific class of molecules and provides comprehensive information on the different conjugation models that are related to specific base molecules, thus allowing a quick and effective identification of all possible combinations, such as mono-, di-, or tri-glycosylation or another type of conjugation such as quinic acid esters.     

Fast atom bombardment tandem mass spectrometry employing ion-molecule reactions for the differentiation of phospholipid classes

Fast atom bombardment tandem mass spectrometry, employing ion-molecule reactions with ethyl vinyl ether in a triple-quadrupole mass spectrometer, is used to differentiate classes of phospholipids. The phospholipids are desorbed and ionized by fast atom bombardment, mass-selected by the first quadrupole, and reacted with ethyl vinyl ether in the second quadrupole; the resulting product ions are analyzed by the third quadrupole. The protonated molecules and reaction product ions observed permit the differentiation of various phospholipid classes. The pattern of addition reaction products formed is shown to depend solely on the functionality of the lipid polar head group and not on the fatty acyl constituents. Neutral gain scans that are specific for each phospholipid class are performed. Ion dissociation products are observed in the same scan as the ion reaction products to provide data on the fatty acyl composition and position on the glycerophosphate core along with the phospholipid class. Although this method is less sensitive than neutral loss scanning for most phospholipid classes, it can (1) identify phospholipids that do not readily lose their head group as a neutral fragment and (2) detect phospholipids in mixtures containing species that give interfering neutral losses.     

Evaluation of various liquid chromatography-quadrupole-linear ion trap-mass spectrometry operation modes applied to the analysis of organic pollutants in wastewaters

The LC-MS/MS analysis of a group of 14 organic pollutants in wastewater – including pharmaceuticals (analgesics/anti-inflammatories, lipid regulators and diuretics), pesticides (diuron) and disinfectants (chlorophene) – has been carried out using a hybrid triple quadrupole-linear ion trap-mass spectrometer (QqLIT). In order to take advantage of the capabilities of the QqLIT system, two methods have been developed and compared, based on the application of different operation modes. One of them uses selected reaction monitoring (SRM), which is the standard mode for quantitative LC-MS/MS analysis. The other is based on the use of an information dependent acquisition scan function (IDA), which allows the combination of a SRM acting as the survey scan and an enhanced product ion scan (EPI) as dependent scan within the same analysis. Performance of both methods was compared, especially in terms of their limits of detection and identification capability. The advantages and limitations of both techniques are discussed. Finally, the two methodologies developed were applied to real samples for evaluation of effluent wastewater in a treatment plant on the south-eastern Mediterranean coast of Spain. The presence of most of the target compounds was detected at mean concentrations ranging from 50 ng/L (mefenamic acid) to 3373 ng/L (hydrochlorothiazide).     

Use of a quadrupole linear ion trap mass spectrometer in metabolite identification and bioanalysis

A new type of quadrupole linear ion trap mass spectrometer, Q TRAP trade mark LC/MS/MS system (Q TRAP trade mark ), was evaluated for its performance in two studies: firstly, the in vitro metabolism of gemfibrozil in human liver microsomes, and, secondly, the quantification of propranolol in rat plasma. With the built-in information-dependent-acquisition (IDA) software, the instrument utilizes full scan MS in the ion trap mode and/or constant neutral loss scans as survey scans to trigger product ion scan (MS(2)) and MS(3) experiments to obtain structural information of drug metabolites 'on-the-fly'. Using this approach, five metabolites of gemfibrozil were detected in a single injection. This instrument combines some of the unique features of a triple quadrupole mass spectrometer, such as constant neutral loss scan, precursor ion scan and multiple reaction monitoring (MRM), together with the capability of a three-dimensional ion trap. Therefore, it becomes a powerful instrument for metabolite identification. The fast duty cycle in the ion trap mode allows the use of full product ion scan for quantification. For the quantification of propranolol, both MRM mode and full product ion scan in the ion trap mode were employed. Similar sensitivity, reproducibility and linearity values were established using these two approaches. The use of the product ion scan mode for quantification provided a convenient tool in selecting transitions for improving selectivity during the method development stage.     

液相色谱-串联质谱结合谱库检索测定猪组织中的9种β-兴奋剂残留量

建立了猪组织中9种β-兴奋剂(克伦特罗、莱克多巴胺、沙丁胺醇、利托君、特布他林、班布特罗、妥布特罗、西马特罗和异舒普林)多残留的液相色谱-四极杆/线性离子阱串联质谱(QTrap LC-MS/MS)检测方法。样品经β-葡萄糖醛苷酶/芳基硫酸酯酶酶解提取,液液萃取净化,以乙腈-甲酸水溶液为流动相,经C18柱分离后用QTrap LC-MS/MS进行多反应监测(MRM)、信息相关采集(IDA)、增强子离子扫描(EPI)和谱库检索分析。9种β-兴奋剂的线性范围为0.1～50.0 μg/L,线性关系良好(r＞0.99);样品中9种目标物在0.5、1.0和5.0 μg/kg添加水平下的回收率为72.0%～95.1%,相对标准偏差为3.1%～12.1%;方法检出限为0.1～0.2 μg/kg。实际样品检测结果表明,本方法可实现猪组织样本中β-兴奋剂残留量的灵敏、准确的定性和定量分析。     

液相色谱-四极杆/离子阱质谱快速测定蜂蜜中痕量硝基咪唑类药物及其代谢物残留

采用液相色谱-四极杆/离子阱串联质谱(LC-QTRAP)建立了蜂蜜中痕量硝基咪唑类药物(甲硝哒唑、咯硝哒唑、二甲硝咪唑、异丙硝唑)及其羟基代谢物(2-羟甲基-1-甲基-5-硝基咪唑、羟基甲硝唑和羟基异丙硝唑)残留的快速测定方法。样品经磷酸盐缓冲液(0.5 mol/L,pH 8.8)/乙酸乙酯提取,高速冷冻离心净化;C18柱色谱分离,流动相为0.1%甲酸水溶液-甲醇,梯度洗脱;质谱采集使用预设定多反应监测(sMRM)-信息依赖性采集(IDA)-增强子离子扫描(EPI)模式;目标分析物使用同位素内标定量,在线EPI谱库辅助定性。7种目标分析物在0.125～50.0μg/L范围内线性关系良好(r>0.999);定量下限(LLD)均达到0.1μg/kg;1LLD、2LLD和4LLD 3个加标水平的回收率为94%～108%;相对标准偏差(RSD)均不大于11.4%。     

Complete profiling and characterization of in vitro nefazodone metabolites using two different tandem mass spectrometric platforms

This paper describes the complete profiling and characterization of in vitro metabolites of the antidepressant agent nefazodone (NEF) generated by human liver microsome (HLM). Two new metabolic pathways (biotransformation) for NEF have been discovered by the characterization of three new metabolites, including two new metabolites (M24, M25) formed due to the N-dealkylation reaction that occurred between the triazolone and propyl units, and one new metabolite (M26) formed due to the O-dearylation reaction that occurred on the phenoxyethyl unit. These metabolites were initially detected by a 4000 Q-Trap instrument and then confirmed by exact mass measurement using an LTQ-Orbitrap. Both instruments proved to be capable of providing complete in vitro metabolite information in a single liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis, although each had its advantages and disadvantages. One noticeable disadvantage of the 4000 Q-Trap was the reduced quality of isotopic pattern in the enhanced mass scan (EMS) spectrum when it was used as survey scan to trigger multiple dependent product ion scans. The problem was especially exacerbated for minor metabolites with low signal intensity. On the other hand, the LTQ-Orbitrap maintained excellent isotopic pattern when used as a full scan survey scan. Twenty-six metabolites were detected and identified. The formation of these new metabolites was also confirmed by analyzing duplicate incubations at different time points.     

基质分散固相萃取-液相色谱-离子阱质谱法检测罐头食品中双酚类化合物残留

建立了采用基质分散固相萃取-液相色谱四级杆串联线性离子阱质谱分析罐头食品中双酚类化合物残留的方法.样品中的双酚类化合物残留经0.1％甲酸乙腈提取,基质分散固相萃取净化,外标法定量,液相色谱-质谱测定.使用数据相关采集扫描功能(IDA)结合增强离子产物(EPI)模式对样品中的双酚类进行定性分析,并建立双酚类的二级子离子谱库.通过MRM模式对双酚类进行定量分析,双酚类化合物在4种罐头食品中的平均回收率为49.3％～128.4％(n=6);相对标准偏差在3.2％～14.4％(n-6)之间,可以满足对罐头食品中的双酚类残留的快速同时定性与定量检测的要求.     

Different electrospray tandem mass spectrometric approaches for rapid characterization of phospholipid classes of Curosurf,a natural pulmonary surfactant

Curosurf is a pulmonary surfactant used in the treatment or prophylaxis of neonatal respiratory distress syndrome. It contains low molecular weight hydrophobic apoproteins and a series of lipids including phosphatidylcholines, lisophosphatidylcholines, phosphatidylethanolamines, sphingomyelins, phosphatidylinositols, phosphatidylglycerols and phosphatidylserines. In the present work, a rapid method to qualitatively map the Curosurf phospholipid classes without prior derivatization or chromatographic separations is described. In particular, a series of specific electrospray tandem mass spectrometric (ES-MS/MS) experiments, i.e. product ion, precursor ion and neutral loss scans, were chosen on the basis of the chemical nature of each phospholipid class and then used to identify single components of the commercial suspension, directly infused into the ion source of the mass spectrometer.     

液相色谱-四极杆/离子阱质谱同时确证和测定肌肉中16种同化甾体激素残留

采用液相色谱-四极杆/离子阱质谱(LC-Q/Trap-MS)建立了肌肉中16种同化甾体激素类物质(ASs)残留的同时确证及测定方法。肌肉中的ASs采用乙腈超声辅助提取,正己烷脱脂,氨基固相萃取柱净化,CAPCELL PAK C18 MGIII柱(150 mm×2.0 mm, 5.0 μm)分离,0.1%(v/v)甲酸-乙腈溶液和0.1%(v/v)甲酸-5 mmol/L甲酸铵水溶液为流动相梯度洗脱;预设定多反应监测(sMRM)-信息依赖性采集(IDA)-增强子离子扫描(EPI)模式检测,在线EPI谱库确证,内标法定量。结果表明,16种ASs在线性范围内线性关系良好(r≥0.999);定量限(LOQ, S/N≥10)为0.029～0.36 μg/kg; 3个添加水平(0.5、2.0和20 μg/kg)下的回收率为89.9%～118%;相对标准偏差(RSD)为6.3%～16.2%。该方法准确灵敏,一次性完成16种ASs的确证和测定,可有效用于肌肉组织中ASs残留的监测分析。     

Determination of microcystins in water using integrated solid-phase microextraction with microbore high-performance liquid chromatography-electrospray quadruple time-of-flight mass spectrometry

The development of a technique combining solid-phase microextraction (SPME) with microbore high-performance liquid chromatography (micro-HPLC)-tandem quadrupole time-of-flight (QTOF) mass spectrometry (MS) for determination of dissolved microcystins in water is reported. Several important parameters affecting the efficiency of SPME extraction of microcystins are investigated. A microbore C18 column HPLC coupled with tandem QTOF-MS with information-dependent acquisition (IDA) is developed to effectively analyze microcystins in microliter volumes of SPME extracts. The micro-HPLC-QTOF-MS with IDA technique provides comprehensive information, including a survey chromatogram (total ion chromatogram), full scan mass spectrum, and product ion scan mass spectra at different collision energies for individual analytes, which allows for both identification and quantitation in the same run. Linear calibration curves of microcystin standard [microcystin (MC)-arginine (R)R] 1-100 microg/L and of microcystin standard [MC-leucine (L)R] 1-250 microg/L are obtained with a correlation coefficient of 0.996. The combination of SPME with HPLC-QTOF-MS and IDA offers limits of detection of 0.6 pg for MC-RR and 1.6 pg for MC-LR. Analysis of spiked lake-water samples shows a recovery of > 86% for MC-RR and > 70% for MC-LR. This technique requires small sample volumes, minimizes the use of organic solvents, and provides sensitive and information-rich analysis of unknown samples.     

Mass spectral characterization of ergot alkaloids by electrospray ionization, hydrogen/deuterium exchange, and multiple stage mass spectrometry: Usefulness of precursor ion scan experiments

Six ergot alkaloids belonging to the lysergic acid derivatives (ergonovine (EGN) and methysergide hydrogen maleinate (MHM)) and peptide-type derivatives (ergocristine (EGR), ergotamine (EGT), ergocornine (EGC) and alpha-ergokryptine (EGK)) were studied by positive electrospray tandem mass spectrometry. The fragmentation mechanisms of these compounds were studied by collision-induced dissociation (CID) using triple quadrupole and ion trap mass spectrometers, and the nature of the major product ions further confirmed by hydrogen/deuterium (H/D) exchange experiments. A common abundant product ion at m/z 223 was characteristic of the two classes of ergot alkaloids. Therefore, a precursor ion scan of m/z 223 that triggers information data acquisition (IDA) in combination with CID experiments was used to identify other potential ergot alkaloids. Using this approach, it was possible to confirm the presence of ergosine, another peptide-type ergot alkaloid, in a rye flour extract at trace levels.     

The Q-trap mass spectrometer,a novel tool in the study of protein glycosylation

The use of the recently introduced Q-Trap mass spectrometer in the study of protein glycosylation is described. The combined ion trap and triple quadrupole scan functions make it a powerful system in both oligosaccharide and glycopeptide analysis. Several oligosaccharides, both linear and branched, were analyzed to obtain information on sequence, linkage, and branching. Quadrupole like MS/MS spectra with ion trap sensitivity but without the typical ion trap low mass cut-off were obtained. To determine the origin of fragments and to reveal the existence of new ions, the MS(3) capabilities of the system proved to be useful. Glycopeptides were selectively detected in peptide mixtures using the triple quadrupole precursor ion scan function, either in off-line experiments or during LC/MS using information dependent acquisition (IDA).     

High-resolution mass spectrometry for integrated qualitative and quantitative analysis of pharmaceuticals in biological matrices

Quantitative and qualitative high-resolution (HR) dependent and independent acquisition schemes on a QqTOF MS (with resolving power 20,000–40,000) were investigated for the analysis of pharmaceutical compounds in biological fluids. High-resolution selected reaction monitoring (HR-SRM) was found to be linear over three orders of magnitude for quantitative analysis of paracetamol in human plasma, offering a real alternative to triple quadrupole LC–SRM/MS. Metabolic stability of talinolol in microsomes was characterized by use of three different acquisition schemes: (i) information-dependent acquisition (IDA) with a TOF MS experiment as survey scan and product-ion scan as dependent scan; (ii) MS^ALL by collecting TOF mass spectra with and without fragmentation by alternating the collision energy of the collision cell between a low (i.e., 10 eV) and high setting (i.e., 40 eV); and (iii) a novel independent acquisition mode referred to as “sequential window acquisition of all theoretical fragment-ion spectra” (SWATH) or “global precursor ions scan mode” (GPS) in which sequential precursor ions windows (typically 20 u) are used to collect the same spectrum precursor and fragment ions using a collision energy range. SWATH or GPS was found to be superior to IDA or MS^ALL in combination with UHPLC for qualitative analysis but requires a rapidly acquiring mass spectrometer. Finally, the GPS concept was used for QUAL/QUAN analysis (i.e. integration of qualitative and quantitative analysis) of bosentan and its metabolites in urine over a concentration range from 5 to 2,500 ng mL⁻¹.     

Triterpenoid saponins profiling by adducts-targeted neutral loss triggered enhanced resolution and product ion scanning using triple quadrupole linear ion trap mass spectrometry

Triterpenoid saponins (TSs) are a unique class of high molecular weight glycosides and have been frequently used in cosmetic and phytotherapy industry. There is a great need to comprehensively profile these plant metabolites for studying their functions. In the present study, a novel adducts targeted neutral loss (NL), triggered enhanced resolution (ER) and enhanced product ion (EPI) scanning approach were described for TSs profiling using a triple quadrupole linear ion trap mass spectrometry. This approach circumvented the disadvantages of poor glycosidic bond cleavage of TSs by monitoring the NH₃ (NL17) and HCOOH (NL46) loss of their abundant ammonium and formate adducts, respectively. The sugar-loss independent NL scanning served as a sensitive survey scan and triggered information-dependent ER and EPI scans to increase peak assignment confidence. NL17 was superior to NL46 for TSs characterization due to the better fragmentation of ammonium adducts than formate adducts. For those TSs undetectable by NL17, precursor ion (PI) scan for sapogenin fragments could be used to screen out non-adducted TSs. The NL/PI-ER-EPI approach was applied for TSs profiling in Astragali Radix, a famous medicinal and nutritional plant widely used in Asian countries and United States. In total, 136 TSs were detected while previous research using high resolution mass spectrometry based full scan only detected 22 TSs in this herb.     

Method for rapid metabolite profiling of drug candidates in fresh hepatocytes using liquid chromatography coupled with a hybrid quadrupole linear ion trap

Rapid information on metabolic profiling is required to evaluate the structural liabilities of drug candidates in early drug discovery. In this study, a sensitive and rapid semi-quantitative method was developed to simultaneously monitor the drug candidate and metabolites as well as collect tandem mass (MS/MS) spectra for subsequent metabolite identification. The simultaneous semi-quantitation and identification of metabolites in fresh hepatocytes is achieved using high-performance liquid chromatography (HPLC) coupled with a hybrid quadrupole linear ion trap. The survey experiment consists of monitoring multiple-reaction monitoring (MRM) transitions for the internal standard, the parent, and 48 MRM transitions designed to cover the most common phase I and II biotransformations. An information-dependent acquisition (IDA) method was employed to trigger product ion scans above the MRM signal threshold. Three biotransformations of a lead compound have been identified through enhanced product ion scans and the respective MRM transitions of those metabolites were selected for semi-quantitation. Parent disappearance and formation of the metabolites as a function of incubation time in five different species were monitored by their respective MRM responses. The method provides the necessary sensitivity to detect minor metabolites in a relevant therapeutic concentration range. Enzymatic turnover of the parent and the metabolites in different species are revealed based on the different initial concentrations of the parent. This methodology integrates the parent disappearance, metabolite identification, and the formation of the metabolites along the time course using a single rapid LC/MS/MS analysis. This method can be used as a complementary tool to the conventional method of metabolic profiling. It provides a rapid and sensitive initial profile of the metabolism of potential structural series at the lead selection stage. The method can also be incorporated into the overall metabolite profiling scheme to evaluate the drug candidates in drug discovery.