Simultaneous detection of eight active components in Radix Tinosporae by ultra high performance liquid chromatography coupled with electrospray tandem mass spectrometry.

A rapid and sensitive ultra high performance liquid chromatography with electrospray ionization tandem mass spectrometry method was developed and validated for the simultaneous determination of eight major active components (magnoflorine, menisperine, 20-hydroxyecdysone, cepharanthine, columbamine, jatrorrhizine, columbin, and palmatine) in Radix Tinosporae. The separation was performed on an InterSustainSwift C18 column (1.9 µm, 2.1 id × 100 mm) at 40 °C with a gradient elution. A mixture of acetonitrile and methanol (v/v = 1:1) and ammonium acetate buffer (25 mmol/L ammonium acetate with 0.2% formic acid) were used as mobile phases, and the flow rate was set at 0.4 mL/min. The recovery was tested in real samples and calculated to be 86.97-111.28%, and all the compounds showed good linearity (r > 0.998) in relatively wide concentration ranges. The developed method was applied to the determination of eight active compounds in real herb samples, which were collected from four different places. It has been demonstrated that the proposed method has great potential for the quality control of the traditional Chinese medicine Radix Tinosporae.

Automatic on-line solid-phase extraction with ultra-high performance liquid chromatography and tandem mass spectrometry for the determination of ten antipsychotics in human plasma.

An automatic on-line solid-phase extraction with ultra-high performance liquid chromatography and tandem mass spectrometry method was developed for the simultaneous determination of ten antipsychotics in human plasma. The plasma sample after filtration was injected directly into the system without any pretreatment. A Shim-pack MAYI-C8 (G) column was used as a solid-phase extraction column, and all the analytes were separated on a Shim-pack XR-ODS III column with a mobile phase consisting of 0.1% v/v formic acid in water with 5 mM ammonium acetate and acetonitrile. The method features were systematically investigated, including extraction conditions, desorption conditions, the equilibration solution, the valve switching time, and the dilution for column-head stacking. Under the optimized conditions, the whole analysis procedure took only 10 min. The limits of quantitation were in the range of 0.00321-2.75 µg/L and the recoveries ranged from 75.9 to 122%. Compared with the off-line ultra-high performance liquid chromatography and the reported methods, this validated on-line method showed significant advantages such as minimal pretreatment, shortest analysis time, and highest sensitivity. The results indicated that this automatic on-line method was rapid, sensitive, and reliable for the determination of antipsychotics in plasma and could be extended to other target analytes in biological samples.

Determination of breath gas composition of lung cancer patients using gas chromatography/mass spectrometry with monolithic material sorptive extraction.

A gas chromatographic-mass spectrometric method with monolithic material sorptive extraction (MMSE) pretreatment was developed to determine the breath gas composition in lung cancer patients. MonoTrap silica monolithic and hybrid adsorbent was selected as the extraction medium during MMSE, given its strong capacity to extract volatile organic compounds (VOC) from exhaled gas. Under the appropriate conditions, high extraction efficiency was achieved. Using the selected ion-monitoring mode, the limit of detection (signal-to-noise ratio 3) for the benzene series was 0.012-2.172 ng L(-1) . The limit of quantitation (signal-to-noise ratio, 10) was 0.042-7.24 ng L(-1) . The linearity range of the method was 4-400 ng L(-1) . Average recovery of the benzene series at lower concentrations was 65-74% (20 ng L(-1) ). The relative standard deviation of benzene series contents determined within the linear range of detection was <10% of the mean level determined. Our proposed method is simple, rapid and sensitive, and can be competently applied to determine the breath gas composition of lung cancer patients.

Rapid determination of residual pesticides in tobacco by the quick, easy, cheap, effective, rugged, and safe sample pretreatment method coupled with LC-MS.

A quick, easy, cheap, effective, rugged, and safe (QuEChERS) sample pretreatment method coupled with LC-MS was developed for the determination of 11 pesticides in tobacco. Sample pretreatment parameters and instrumental parameters of LC-MS were investigated, and the optimal conditions were selected. Under the optimized conditions, the 11 pesticides were detected simultaneously with a good linear relationship (r(2) = 0.9993-0.9999) and high precisions (less than 5% of the RSD of peak areas). The LODs were in the range of 0.1-5.0 µg/L. Compared with SPE clean-up, QuEChERS greatly simplified the sample pretreatment with simple solvent extraction system. After QuEChERS pretreatment, no serious matrix effects were observed. Used for the analysis of real samples, metalaxyl was found in cigarette and tobacco samples at 63.47 and 132.27 ng/g, respectively. The recoveries for 11 pesticides were in the range of 70.03-118.69%, and RSDs were less than 10%. The proposed method is simple, low cost, and has good reproducibility.

Identification of the anti-oxidants in Flos Chrysanthemi by HPLC-DAD-ESI/MS(n) and HPLC coupled with a post-column derivatisation system.

INTRODUCTION: Flos Chrysanthemi (Jiju) is a traditional Chinese medicine (TCM) that is known to have anti-oxidant activity; in this study, on-line HPLC-DAD-ESI/MS(n) and HPLC-DAD-DPPH methods have been developed for rapidly screening and identifying free-radical scavengers in Jiju extract. OBJECTIVE: To develop an efficient method for the simultaneous identification and detection of the anti-oxidant components in Flos Chrysanthemi (Jiju). METHODOLOGY: A concentrated methanol extract of Flos Chrysanthemi from Jiaxiang County (Jiju) was first separated into phases soluble in water, petroleum ether and n-butanol. The off-line 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging method was then used to evaluate the anti-oxidant activity of each phase in vitro. The results showed that the n-butanol extract had the highest anti-oxidant activity, and its anti-oxidant compounds were analysed by HPLC-DAD-ESI/MS(n) and HPLC coupled with a post-column derivatisation (PCD) system supplied with DPPH, aluminium chloride or sodium acetate solutions. RESULTS: A total of 17 compounds were separated and identified, three of which were identified in Jiju for the first time, and seven active compounds serve as the chemical basis of the anti-oxidant efficacy of Jiju. CONCLUSION: The methods described here allow rapid separation and convenient identification of the multiple constituents in Jiju, and may be applied to other complex natural matrices.

Automated online pretreatment and cleanup recycle coupled with high-performance liquid chromatography-mass spectrometry for determination of deca-bromodiphenyl ether in human serum.

Automated online SPE-HPLC-MS was established for the determination of deca-bromodiphenyl ether in human serum. The online SPE with large volume injection was utilized to enhance the sensitivity. Online SPE with dilution line greatly decreased matrices effect, which enabled serum samples to be injected directly into pre-column. Washing line was designed for the system to solve the serious residual phenomenon and reduce the risk of sample wastage and contamination. Under the optimized conditions, the linear of the method was in the range 0.1-10 ng/mL with the LOD of 0.026 ng/mL. The recoveries of serum samples spiked with deca-bromodiphenyl ether at 0.5 ng/mL was in the range from 83.30 to 102.7% with RSD in interday less than 8.67%. The satisfactory results demonstrated that the method of online sample pretreatment and cleanup recycle were reliable for human serum analysis.

Comparison of two species of Notopterygium by high-performance liquid chromatography-photodiode array detection-electrospray ionization tandem mass spectrometry.

Notopterygium incisum Ting ex H.T. Chang (N. incisum) and Notopterygium forbesii Boiss (N. forbesii) are two medicinal species of Qianghuo (a well-known traditional herbal medicine in China) that are widely used in clinical prescriptions for the treatment of colds and rheumatism. To compare the chemical constituents of these two plant materials, the phenolic constituents and coumarins of these two species were comprehensively and systematically analyzed by high-performance liquid chromatography-photodiode array detection-electrospray ionization tandem mass spectrometry (HPLC/DAD/ESI-MS(n)) for the first time. A total of 25 compounds (nine phenolic compounds and 16 coumarins) were detected in the methanol extracts. These compounds were separated on a C18 column and identified or tentatively characterized on the basis of their UV spectra and MS fragmentation behavior. In contrast to previous reports, we found that these two plant species possess very different coumarin patterns. O-Demethylfuropinnarin (18), phenethylferulate (19), notopterol (20), and isoimperatorin (22) were the predominant constituents of N. incisum, whereas nodakenin (6), 6-O-trans-feruloylnodakenin (12), p-hydroxypenethylanisate (16) and isoimperatorin (22) were the major constituents of N. forbesii. O-Demethylfuropinnarin (18), phenethylferulate (19) and notopterol (20) were only detected in N. incisum and can be regarded as useful taxonomic markers for differentiating these two plant species. Considering the marked differences in the main chemical constituents of N. incisum and N. forbesii, the biological activities of these two species should be further investigated and compared to ensure consistency and efficacy in the pharmaceutical applications of these materials.

Determination of phthalates in fruit jellies by dispersive SPE coupled with HPLC-MS.

In this study, a simple, rapid and sensitive method for the determination of five phthalates including dimethyl phthalate, diethyl phthalate, dipropyl phthalate, benzyl butyl phthalate, and dicyclohexyl phthalate in fruit jellies by LC coupled with MS has been developed. Samples were pretreated by a dispersive SPE method, termed QuEChERS, which is an acronym for quick, easy, cheap, effective, rugged, and safe. The standard calibration curves were linear for all the analytes over the concentration range of 10-250 ng/mL, and the correlation coefficients ranged from 0.9976 to 0.9991. The LODs and LOQs were in the ranges of 0.09-3.68 ng/mL and 0.28-11.25 ng/mL, respectively. The accuracy of this method was evaluated by measuring the recovery from spiked samples. The recoveries of all five phthalates from samples spiked at three different concentrations (0.01, 0.03, and 0.05 mg/kg), were in the ranges of 83.5-103.9%, 86.7-95.8%, and 87.1-95.2%, respectively. The RSD values for the samples spiked at 0.01, 0.03, and 0.05 mg/kg ranged from 2.0-7.6%, 1.4-6.4%, and 1.2-3.8%, respectively. The method has been used for the analysis of real samples and BBP and DEP were found in real samples.

Differentiation of four pairs of furocoumarin isomers by electrospray ionization tandem mass spectrometry.

A mass spectrometric method based on the combined use of electrospray ionization, collision-induced dissociation (CID) and ion-trap time-of-flight (IT-ToF) tandem mass spectrometry was used to identify four pairs of furocoumarin isomers. Our results show some characteristic mass spectrometric differences in isomeric furocoumarins. In the MS(2) spectra, the relative abundance ratios of m/z 131 [M + H - 2CO](+) to m/z 143 [M + H - CO(2)](+) and m/z 115 [M + H - CO-CO(2)](+) of psoralen are less than one, but both ratios are greater than one in the case of isopsoralen. The relative abundance of m/z 159 [M + H - CO(2)](+) is much higher than that of m/z 175 [M + H - CO](+) in the case of bergaptol, but this trend is reversed in xanthotoxol. Moreover, three diagnostic ions of m/z 189 [M + H - CO](+), m/z 185 [M + H - CH4O](+) and m/z 161 [M + H - 2CO](+) are observed in the MS(2) spectrum of xanthotoxin but not in that of bergapten. Further, two diagnostic ions of m/z 226 [M - H - CH(3) - CO](-) and m/z 210 [M - H - CH(3) - CO(2)](-) are observed in the MS(2) spectrum of isoimperatorin but not in that of imperatorin. The relative abundance of product ions associated with some diagnostic ions can be used to characterize furocoumarin isomers.

Determination of vitamin D3 in daily oily supplements by a two-dimensional supercritical fluid chromatography-liquid chromatography-mass spectrometry system.

A two-dimensional system composed of supercritical fluid chromatography (SFC) and reverse phase liquid chromatography (RPLC) coupled a tandem mass spectrometry (MS) was developed for the quantitative analysis of vitamin D in daily oily supplements. Two six-port switching valves are configured, allowing four different valve positions. When the valve positions were fixed at Position A, this system worked at SFC-MS mode. When the valve positions switched between Position B and C, this system worked at a SFC-LC-MS switching mode. Vitamin D3 in two kinds of oily drops, Baby Ddrops and Vitamin AD drops, was determined at both SFC-MS and SFC-LC-MS switching modes by using the same system. The linearity, repeatability and recovery were investigated using the internal and external standard methods for the two modes. The results obtained from the internal standard method are better than those of the external standard method at either mode. The coefficient of determination (r2) for the internal standard method is more than 0.999, with a linear range of 20-1000 µg/L. Both Baby Ddrops and Vitamin AD drops were analyzed with good repeatability (<3.21%) and recovery (94.1%-116.1%) using internal standard method. When calculated by the external standard method, as compared to SFC-MS mode, SFC-LC-MS switching mode has better linearity (r2>0.999), repeatability (Baby Ddrops: 4.45%, Vitamin AD drops: 1.12%) and recovery (86.3%-107.1%). The results indicate that the two-dimensional SFC-MS/SFC-LC-MS system is useful for determination of vitamin D in oily drops. If it works at SFC-MS mode, the internal standard is required. When SFC-LC-MS switching mode is used, external standard method can also obtain the accurate results with good precision.

Fast determination of isomeric triterpenic acids in Osmanthus fragrans (Thunb.) Lour. fruits by UHPLC coupled with triple quadrupole mass spectrometry.

Triterpenic acids possess rich biological activity. Due to slight differences in structure and polarity, the simultaneous determination of isomeric triterpenic acids is challenging. In the present work, a simple and effective approach to chromatographic separation of such compounds based on conventional C18 stationary phase with gradient elution was developed, which allowed the simultaneous separation of eleven analytes including euscaphic, arjunic, tormentic, arjunolic, asiatic, pomolic, maslinic, corosolic, oleanolic, ursolic and 2-Epi tormentic acid (internal standard). This approach with mass spectrometric detection and ultrasonic extraction was fast, sensitive and accurate for analyzing isomeric triterpenic acids in O. fragrans fruits with a toal duration of the analytical cycle (including pretreatment) within one hour. The LODs lie in ranges of 0.8-12 ng/mL (30 ng/mL for asiatic and corosolic acid). The developed method was validated and successfully applied in ten batches of O. fragrans fruits, which could reflect the detail content difference of triterpenic acid components.

Profiling the metabolites of astrapterocarpan in rat hepatic 9000g supernatant.

Astrapterocarpan (AP) is a bioactive constituent of Astragali Radix and was selected as a model compound for investigating the in vitro metabolism of pterocarpans in this study. Its in vitro metabolism was conducted by incubation with rat hepatic 9000g supernatant (S9) in the presence of an NADPH-generating system. At first, four compounds were isolated and their structures were elucidated as 6a-hydroxy-AP (M1), astrametabolin I [M2, 1a-hydroxy-9, 10-dimethoxy-pterocarp-1(2), 4-diene-3-one], 9-demethyl-AP (M3, nissolin) and 4-methoxy-astraisoflavan (M4, 7, 2'dihydroxy-4, 3', 4'-trimethoxy-isoflavan) on the basis of NMR data, respectively. Among them, M1, M2 and M4 were new compounds. Next, the metabolite profile of AP in rat hepatic S9 was obtained via HPLC-DAD-ESI-IT-TOF-MSn, and 40 new metabolites were tentatively identified. These newly identified metabolites included 9 monohydroxylated metabolites, 1 demethylated metabolite, 7 demethylated and monohydroxylated metabolites, 4 dihydroxylated metabolites, 1 hydration metabolite, 1 didemethylated metabolite, 2 glucosylated metabolites, 1 monohydroxylated and dehydrogenated metabolite, 2 monohydroxylated and demethylated and dehydrogenated metabolites, 2 dimerized metabolites, 3 dimerized and monohydroxylated metabolites, 2 dimerized and didemethylated metabolites, and 5 dimerized and demethylated metabolites. Finally, the major metabolic reactions of AP in rat hepatic S9 were summarized and found to be hydroxylation, demethylation, dimerization, hydration, and dehydrogenation. More importantly, the biotransformation from AP to M2 and the dimerization of AP by incubation with hepatic S9 were reported for the first time. In conclusion, this is the first report on the metabolism of a pure pterocarpan in animal tissues, and these findings will provide a solid basis for further studies on the metabolism of other pterocarpans.

On-line liquid chromatography-mass spectrometry with dilution line to achieve large volume urine injection for the improvement of sensitivity.

A unique automated on-line high-performance liquid chromatography-mass spectrometry (LC-MS) method was developed allowing injection of a large volume of urine for the improvement of sensitivity using estrogens as analytes. The urine sample was precipitated by acetonitrile (sample:acetonitrile, 1:2, v/v) to remove most proteins. Then the supernatant was directly delivered at 0.3 mL/min by a pump, which broke through the limit of autosampler with fixed loop. Then the sample was loaded onto a restricted access media (RAM) pre-column after on-line dilution with NH(4)Ac solution which was delivered by another pump under high flow-rate. After the addition of on-line dilution line, the content of organic solvent in the sample aliquot was sharply decreased so that the analytes were effectively trapped by pre-column. In addition, another 6-port valve was added to selectively deliver the effluent containing analytes into MS, which minimized the pollution of the MS and matrix effect. After optimization of the condition of extraction method, 3 mL sample (containing 1 mL urine) could be successfully enriched. The injection volume increased 10 times compared with conventional on-line LC-MS methods for biofluid analysis, significantly improving sensitivity. Moreover, no obvious increase of column pressure was observed after 300 injections. The method was validated by spiking urine. Linearity was determined by sample which was in the range of 1-500 ng/mL. The process efficiency ranged from 70.2 to 106% with RSDs less than 15% with the exception of a few analytes. The limit of detection (LOD) and quantification (LOQ) ranged from 0.3 to 2 ng/mL and 1 to 8 ng/mL, respectively, corresponding a decrease of 1-2 orders of magnitude compared with those of off-line and on-line methods.

Determination of short-chain chlorinated paraffins using comprehensive two-dimensional gas chromatography coupled with low resolution mass spectrometry.

Short-chain chlorinated paraffins (SCCPs), recently listed as Persistent Organic Pollutants (POPs) under the Stockholm Convention, are contained in commercial chlorinated paraffin (CP) products, which are used in industries such as metalworking fluids, sealants, and textiles. A novel method to determine SCCPs by comprehensive two-dimensional gas chromatography coupled with low resolution mass spectrometry was developed. Calibration curves of response factor versus chlorine content in two chlorine content ranges (R2 were 0.9544 and 0.9736, respectively) were used for quantification of SCCP total concentration. Moreover, relative concentrations of 24 congener groups were also theoretically calculated. Results showed that this method was able to detect SCCP concentration in commercial CP products and urban air samples. SCCP contribution varied largely among different CP products, which is highly determined by carbon chain distribution in paraffins. SCCP concentration in urban air ranged between 12.8-49.1 ng m-3 during nine-month sampling period. The highest SCCP concentration appeared in summer, and the lowest concentration occurred in winter. Gas phase was dominantly occupied by lighter congeners such as C10 group and Cl6 group, while heavier congeners such as C13 group and Cl7 and Cl8 groups contributed more in particle phase.

Determination of vitamin D in oily drops using a column-switching system with an on-line clean-up by supercritical fluid chromatography.

A column-switching system, composed of supercritical fluid chromatography (SFC) and reverse phase liquid chromatography/mass spectrometry (RPLC/MS) was developed for the analysis of vitamin D in oily and fatty matrices. The SFC with the similar retention behavior as normal-phase liquid chromatography (NPLC), was applied for an on-line clean-up of oily and fatty samples, then followed by separation and detection using a reverse-phase LC-MS/MS. Three SFC columns packed with materials of different functional groups (Silica, NH2, Diol) were compared and the column with diol groups, on which the retention time of vitamin D was the longest, was finally selected for purification of the samples. 100% methanol was chosen to carry vitamin D from the clean-up column to the pre-treatment column. It was also used as the mobile phase for the separation of vitamin D on a reverse phase C18 column. Vitamin D2 and D3 were baseline separated by using this system. The linearity was calculated with a value of coefficient of determination (r2) ≥ 0.998. The linear range is from 20 ng/mL to 200 ng/mL. Two kinds of liquid vitamin D3 supplements (Baby Ddrops and Vitamin AD drops) were directly analyzed using this system without any fussy preparation procedure. The limit of detection (LOD) for vitamin D3 in the two oily samples was estimated to be 10 ng/mL. The relative standard deviations (RSD) of intra- and inter-day precision, repeatability were 1.47%, 2.43% and 1.59% for Baby Ddrops and 5.76%, 8.24% and 5.86% for Vitamin AD drops. The recoveries vary between 84.3% and 102.8% with 7.1% RSD for Baby Ddrops and 90.8-109.6% with 5.83% RSD for Vitamin AD drops, respectively. These results suggest that the method based on the SFC-RPLC/MS column-switching system is simple and suitable for analysis of vitamin D in oily and fatty samples.

Solid-phase extraction with C30 bonded silica for analysis of polycyclic aromatic hydrocarbons in airborne particulate matters by gas chromatography-mass spectrometry.

A solid-phase extraction (SPE) method using triacontyl bonded silica (C30) as sorbent was developed for the determination of 16 US Environmental Protection Agency polycyclic aromatic hydrocarbons (PAHs) in airborne particulate matters quantitatively by gas chromatography-mass spectrometry (GC-MS). Optimization experiments were conducted using spiked standard aqueous solution of PAHs and real airborne particulates samples aiming to obtain highest SPE recoveries and extraction efficiency. Factors were studied in SPE procedures including the concentration of organic modifier, flow rate of sample loading and elution solvents. The ultrasonication time and solvents were also investigated. Recoveries were in the range of 68-107% for standard PAHs aqueous solution and 61-116% for real spiked sample. Limits of detection (LODs) and limits of quantification (LOQs) with standard solution were in the range of 0.0070-0.21 microgL(-1) and 0.022-0.67 microgL(-1), respectively. The optimized method was successfully applied to the determination of 16 PAHs in real airborne particulate matters.

Development of automated online gel permeation chromatography-gas chromatograph mass spectrometry for measuring multiresidual pesticides in agricultural products.

An automated online gel permeation chromatography-gas chromatograph mass spectrometer (GPC-GC/MS) was developed for the rapid determination of residual pesticides in agricultural products. Pesticides were extracted from homogenized food samples with acetonitrile and decontaminated via the matrix solid-phase dispersion (MSPD) technique, using a primary secondary amine as sorbent prior to GPC-GC/MS analysis. A slightly modified preparation method and automated GPC step proved useful in minimizing matrix interference. To evaluate the performance of the system, 97 target pesticides were spiked at a concentration of 0.1mg/kg into a range of food types, including potato, cabbage, carrot, apple, orange, cucumber, and rice. A low flow rate of 0.1 mL/min in GPC resulted in a 40-fold reduction in solvent consumption compared with conventional GPC column applications. The combination of MSPD technique and GPC-GC/MS for the analysis of the 97 pesticides can be accomplished within 90 min. Most pesticides were recovered in the range of 70-120%, with relative standard deviation generally less than 10%. The results demonstrate that the method can be successfully applied with acceptable recoveries to a broad range of target pesticides within a diverse range of food types.

Determination of particle-associated polycyclic aromatic hydrocarbons in urban air of Beijing by GC/MS.

Particle-associated polycyclic aromatic hydrocarbons (PAHs) collected in urban air of Beijing were studied using a gas chromatograph mass spectrometer (GC/MS). The average concentration of particle-associated PAHs measured in this work was in the range from 28.53 to 362.15 ng/m3, which suggested a serious pollution level of PAHs in Beijing. The results also showed that the concentration of PAHs in the winter was distinctly higher than that in summer and spring. Benzo(a)pyrene (BaP) and benzo(a)pyrene-equivalent carcinogenic power (BaPE) were adopted to evaluate the PAHs pollution state at the sampling site. Through some diagnostic ratios, it can be concluded that traffic exhaust, especially vehicles with diesel engines, and domestic coal-burning heaters might have a prominent contribution to the PAHs concentration.

On-line enrichment and determination of polycyclic aromatic hydrocarbons in atmospheric particulates using high performance liquid chromatography with fluorescence as detector.

Seven polycyclic aromatic hydrocarbons (PAHs) in atmospheric particulates were determinated by high performance liquid chromatography (HPLC) with fluorescence detector using direction injection and an on-line enrichment trap column. The method simplified the sample pretreatment, saved time and increased the efficiency. With the on-line trap column, PAHs were separated availably even underground injecting 1.0 ml sample with relatively high column efficiency. The recoveries of the seven PAHs were from 85% to 120% for spiked atmospheric particulate sample. The limit of detection was 15.3-39.6 ng/L (S/N=3.3). There were good linear correlations between the peak areas and concentrations of the seven kinds of PAHs in the range of 1-50 ng/ml with the correlation coefficients over 0.9970. Furthermore, it also indicated that the method is available to determine PAHs in atmospheric particulates well.

Automated on-line liquid chromatography-photodiode array-mass spectrometry method with dilution line for the determination of bisphenol A and 4-octylphenol in serum.

A novel on-line liquid chromatography-photodiode array detection-mass spectrometry (LC-DAD-MS) system was established with restricted-access media (RAM) pre-column and dilution line combined with a column-switching valve. The serum samples were injected directly onto pre-column under diluted condition by dilution line. After elution of proteins in the serum, the analytes were backflushed onto an ODS analytical column using a six-port column-switching device. The influence of the composition of the mobile phase, for instance, organic modifer, ionic strength, pH, dilution times and the rotation time of the switching valve have been investigated using bisphenol A (BPA) and 4-octyphenol (4-OP) as analytes. The evaluations for peak responses and sensitivity were conducted by MS, and proteins were removed by RAM-column with DAD monitoring at 280 nm. The peak shape was improved by adding a dilution line, especially in the case of large volume injection (LVI), which increased the sensitivity of the analysis. The selective and sensitive quantification of BPA and 4-OP in serum sample could be finished within 25 min. The method had linearity in the range 0.1-500 ng/mL with a limit of quantification for BPA and 4-OP of 0.1 and 0.5 ng/mL, respectively. The recoveries were in the range of 80-101% with less than 9.0% RSDs. This on-line LC-MS method demonstrates potential application to evaluating the exposure and risk of BPA and 4-OP in human.