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Topological insulators (TIs) are novel materials that manifest spin-polarizedDirac states on their surfaces or at interfaces made with conventional matter.We have measured the electron kinetics of bulk doped TI Bi$_2$Se$_3$ with angleresolved photoemission spectroscopy while depositing cathodic and anodicadatoms on the TI surfaces to add charge carriers of the opposite sign frombulk dopants. These P-N overlayer interfaces create Dirac point transportregimes and larger interface potentials than previous N-N type surfacedeposition studies, revealing unconventional Rashba-like and surface-bulkelectron interactions, and an unusual characteristic distribution of spectralweight near the Dirac point in TI Dirac point interfaces. The electronicstructures of P-N doped topological interfaces observed in these experimentsare an important step towards the understanding of solid interfaces withtopological materials.

High-quality MnxTi1-xN thin films were grown on MgO(001) substrates using plasma-assisted molecular beam epitaxy. Magnetic measurements evidence the presence of ferromagnetism with Curie temperature exceeding 380 K. X-ray photoelectron spectroscopy indicates that the Mn ions are in a divalent state and uniformly substitute on Ti cation sites, consistent with the ferromagnetism that correlates with Mn substitution on Ti sites. The origin of the ferromagnetism might be attributed to itinerant-carrier mediated Rudermann-Kittel-Kasuya-Yosida (RKKY)-type long-range coupling which allows for arbitrary itinerant-carrier spin polarization and dynamic correlations. [ABSTRACT FROM AUTHOR]

Based on the processes and characteristics of secondary electron emission and the formula for the yield due to primary electrons hitting on semiconductors and insulators, the universal formula for maximum yield due to primary electrons hitting on semiconductors and insulators was deduced, where is the maximum ratio of the number of secondary electrons produced by primary electrons to the number of primary electrons. On the basis of the formulae for primary range in different energy ranges of , characteristics of secondary electron emission and the deduced universal formula for , the formulae for in different energy ranges of were deduced, where is the primary incident energy at which secondary electron yields from semiconductors and insulators, , are maximized to maximum secondary electron yields from semiconductors and insulators, ; and is the maximum ratio of the number of total secondary electrons produced by primary electrons and backscattered electrons to the number of primary electrons. According to the deduced formulae for , the relationship among , and high-energy back-scattering coefficient , the formulae for parameters of and the experimental data as well as the formulae for in different energy ranges of as a function of , , and were deduced, where and are the original electron affinity and the width of forbidden band, respectively. The scattering of was analyzed, and calculated values were compared with the values measured experimentally. It was concluded that the deduced formulae for were found to be universal for . [ABSTRACT FROM AUTHOR]

MK-0524 is a potent, selective and orally active Prosglandin D2 Receptor 1 (DP1) antagonist currently under clinical development for the treatment of niacin-induced flushing. Experiments to study the pharmacokinetics, metabolism and excretion of MK-0524 were conducted in rats, dogs and monkeys. MK-0524 displayed linear kinetics and rapid absorption following an oral dose. Following intravenous (i.v.) administration of MK-0524 to rats and dogs (1 and 5 mg/kg), the mean Clp was ∼2 and ∼6 ml/min/kg, the T1/2 was ∼7 and ∼13 h and the Vdss was ∼1 and ∼5 L/kg, respectively. In monkeys dosed i.v. at 3 mg/kg, the corresponding values were 8 ml/min/kg, 3 h and 1 L/kg, respectively. Following oral dosing of MK-0524 to rats (5, 25 and 100 mg/kg), dogs (5 mg/kg) and monkeys (3 mg/kg), the absorption was rapid with the mean Cmax occurring between 1 and 4 h. Absolute oral bioavailability values in rats, dogs and monkeys were 50, 70 and 8%, respectively. The major circulating metabolite was the acyl glucuronide of MK-0524 (M2), with ratios of glucuronide to the parent aglycone being highest in the monkey followed by dog and rat. In bile duct-cannulated rats and dogs, MK-0524 was eliminated primarily via acyl glucuronidation followed by biliary excretion of the acyl glucuronide, M2, the major drug-related entity in bile. [ABSTRACT FROM AUTHOR]

A novel coplanar waveguide (CPW) antenna is proposed to operate from 2.9 to 13 GHz. It consists of an elliptic radiator, an elliptic ground plane and a CPW transmission line. The designed antenna has compact dimensions of 20 by 23 mm and an approximate omnidirectional pattern across the major bandwidth. This antenna can be especially applied as the element of UWB antenna arrays for UWB application. [ABSTRACT FROM AUTHOR]

Beta toxin (CPB) is a lethal toxin and plays a key role in enterotoxemia of ruminants caused by Clostridium perfringens type C strain. The existing vaccines based on crude CPB need time-consuming detoxification and difficult quality control steps. In this study, we synthesized the rCPB m4 of C. perfringens type C strain and small ubiquitin-like modifier (SUMO)-tag CPB m4 (rSUMO-CPB m4 ) by introducing four amino acid substitutions: R212E, Y266A, L268G, and W275A. Compared with rCPB m4 , rSUMO-CPB m4 was expressed with higher solubility in Escherichia coli BL21 (DE3). Neither rCPB m4 nor rSUMO-CPB m4 was lethal to mice. Although rCPB m4 and rSUMO-CPB m4 were reactogenic with polyclonal antibodies against crude CPB, rabbits vaccinated with rSUMO-CPB m4 developed significant levels of toxin-neutralizing antibody (TNA) titers that conferred protection against crude toxin challenge. These data suggest that genetically detoxified rSUMO-CPB m4 is a promising subunit vaccine candidate for C. perfringens type C beta enterotoxemia.

Objective: To understand the knowledge, attitude, and current status of vaccination of herpes zoster vaccination among urban residents aged 25 years and above in China. Methods: In August to October 2022, a convenience sampling method was used to survey residents aged 25 years and above at 36 community centers in 9 cities across China. Questionnaires were used to collect basic information, knowledge, and attitude toward herpes zoster and its vaccination, as well as vaccination status and reasons for non-vaccination among residents. Results: A total of 2 864 urban residents were included in the study. The total score of residents' cognition of herpes zoster and its vaccine was 3.01±2.08, and the total score of their attitude was 18.25±2.76. Factors such as being male ( β =-0.45, P <0.001), older than 40-59 years ( β =-0.34, P =0.023) or ≥60 years ( β =-0.68, P <0.001), married ( β =-0.69, P =0.002) were negatively associated with knowledge score. The educational level of high school or secondary school ( β =0.44, P =0.036), college ( β =0.65, P =0.006), bachelor's degree and above ( β =1.20, P <0.001), annual net household income ≥120 000 Yuan in 2021 ( β =0.42, P =0.020), having urban employee medical insurance ( β =0.62, P =0.030), having public or commercial medical insurance ( β =0.65, P =0.033), and having a history of chickenpox ( β =0.29, P =0.025) were positively associated with knowledge scores. Being male ( β =-0.38, P =0.008) and not remembering a history of chickenpox ( β =-0.49, P =0.012) were negatively associated with attitude scores. Annual net household income in 2021 was between 40 000-80 000 Yuan ( β =0.44, P =0.032) or between 80 000-120 000 Yuan ( β =0.62, P =0.002) or ≥120 000 Yuan ( β =0.93, P <0.001), and a history of herpes zoster ( β =0.59, P =0.004) were positively associated with attitude scores. Of the 2 864 residents surveyed, only 29 (1.01%) had received the herpes zoster vaccine, with a vaccination rate of 1.70% for those aged 50 years and above, with the main reason for non-vaccination being lack of knowledge about the herpes zoster vaccine, followed by the high price. 42.67% of the population said they would consider getting the herpes zoster vaccine in the future. Conclusion: Low knowledge of herpes zoster and its vaccine, positive attitudes towards the preventive effects of herpes zoster and its vaccine, and extremely low vaccination rates among the urban population in China call for multiple measures to strengthen health education and vaccination recommendations for residents, especially for the elderly, low-education and low-income populations.

To explore the genetic causes of 3 male infertility patients with acephalospermia and the outcome of assisted reproductive technology. Clinical diagnosis, sperm morphology examination, sperm transmission electron microscopy examination were performed on 3 patients, and the whole exome sequencing technology was used for screening, Sanger sequencing verification, mutation pathogenicity analysis, and protein sequence homology comparison. Assisted reproductive technology was implemented to assist pregnancy treatment. The 3 patients were all sporadic infertile men, aged 25, 42 and 26 years, and there was no obvious abnormality in the general physical examination. Male external genitalia developed normally, bilateral testicles were normal in volume, and bilateral epididymis and spermatic vein were palpated without nodules, cysts, and tenderness. Repeated semen analysis showed that a large number of immature sperm could be seen, and they had the ability to move. The SUN5 gene of the 3 male infertile patients was a case of homozygous missense mutation c.7C>T (p.Arg3Trp), a case of compound heterozygous missense mutation c.1067G>A (p.Arg356His) and nonsense mutation c.216G>A (p.Trp72*) and a case of homozygous missense mutation c.1043A>T (p.Asn348Ile), of which c.7C>T (p.Arg3Trp) and c.1067G>A (p.Arg356His) were new variants that had not been reported. SIFT, Mutation Taster and PolyPhen-2 software function prediction results were all harmful, the nonsense mutation c.216G>A (p.Trp72*) led to the premature termination of peptide chain synthesis which might have a greater impact on protein function. The homology regions in the protein sequence homology alignment were all highly conserved.The 3 male patients and their spouses obtained 4 biological offspring through intracytoplasmic sperm injection, all of which were boys, and one of them was a twin.Three male infertile patients might be caused by SUN5 gene mutations. Such patients could obtain their biological offspring through assisted reproductive technology. It was still necessary to pay attention to the genetic risk of ASS, it was recommended that both men and women conduct genetic counseling and screening at the same time. In clinical diagnosis, whole exome sequencing technology could be used to perform auxiliary examinations to determine the treatment plan and assisted reproductive methods as soon as possible to reduce the burden on the family and society. The newly discovered mutation sites of SUN5 gene provided clues and directions for elucidating the pathogenic mechanism, and at the same time expanded the pathogenic mutation spectrum of ASS.

Objective: To analysis the expression of CD7 in NK/T-cell lymphoma as well as study the correlations between CD7 and clinical survival and prognosis. Methods: The clinical and pathological indicators of 112 NKTCL patients who were admitted to or consulted at the First Affiliated Hospital of Zhengzhou University between May 2008 and December 2019 were analyzed retrospectively. The CD7 expression in the tumor tissues was detected using immunohistochemistry staining, and the influence of CD7 expression on the survival and prognosis in the patients was analyzed. Results: The CD7 expression rate was 84.82% in 112 NKTCL patients, and its expression was not influenced by sex, age, and the primary site. An analysis of the complete clinical data of 72 patients showed that the CD7 expression was significantly correlated with the PINK score, tumor metastasis, and peripheral blood EBV-DNA level. However, the Ann Arbor stage, bone marrow involvement, B symptoms, IPI/aaIPI score, Ki-67, EBER, TIA-1, Granzyme B, LDH, and β(2)-MG were not associated with the CD7 expression. The 1-year, 3-year, and 5-year overall survival (OS) rates of the 72 patients were 81.2%, 61.8%, and 58.8%, respectively, and the progression-free survival (PFS) rates were 53.5%, 29.4%, and 24.0%, respectively. The median overall survival (median-OS, mOS) was 81 mon, and the median progression-free survival (median-PFS, mPFS) was 14 mon. The 3-year OS rates in the CD7-positive group and the CD7-negative group were 58.1% and 83.9%, respectively, ( P >0.05) . The 3-year PFS rates were 21.7% and 51.9%, respectively ( P <0.05) . The univariate analysis showed that age, primary tumor site, Ann Arbor stage, IPI/aaIPI score, PINK score, LDH, β(2)-microglobulin, EBV-DNA, Ki-67, and CD7 influenced patient prognosis. The multivariate analysis showed that Ann Arbor stage and CD7 were independent prognostic factors for PFS, while PINK score and Ki-67 were independent prognostic factors for OS. Conclusions: The expression rate of CD7 in NKTCL was high and was closely related to poor patient prognosis. The patients with high levels of EBV-DNA, metastatic disease, or high PINK score were more likely to express CD7.

Objective: To study the epidemiology and antimicrobial resistance of Gram-negative bacterial bloodstream infections in children, and to guide the choice of antimicrobials and the control of nosocomial infection. Method: Clinical data, bacteriology and antimicrobial susceptibility test results were collected retrospectively in hospitalized children who were diagnosed with gram-negative bacterial bloodstream infections in Yuying Children's Hospital of Wenzhou Medical University from January, 2010 to December, 2015. Result: A total of 399 cases (253 male and 146 female) were identified. The age ranged from 16 hours to 16 years (median age 10.1 months). The majority of cases were collected from division of neonatology ( n =261, 65.4%), followed by 31 cases (7.8%) from pediatric intensive care unit and 29 cases (7.3%) from Gastroenterology Department; 275 cases (68.9%) had underlying diseases, mainly including preterm birth( n =172), neonatal respiratory distress syndrome( n =67) and newborn asphyxia( n =53). Eighty cases had received invasive procedures and 20 had surgical operation; 149 cases (37.3%) were community-acquired and 250 cases (62.7%) were hospital acquired. Fifty cases had complications, among those, 40 cases had septic shock, 32 cases had multiple organ dysfunction syndrome and 7 cases had disseminated intravascular coagulation; 288 cases were cured, 48 improved, 17 gave up treatment and discharged, and 46 died; totally 408 strains were isolated from 399 children, including Enterobacteriaceae (346, 84.8%), non-fermentative Gram-negative bacteria (49, 12.0%) and other gram-negative bacteria (13, 3.2%). The resistance rates of Escherichia coli ( n =175) and Klebsiella pneumoniae ( n =106) to carbapenems, β-lactams enzyme and its inhibitors, amikacin and cefoxitin were all lower than 10%. Totally 245 multi-drug resistant strains (60.1%) were isolated, including 225 strains of Enterobacteriaceae and 18 strains of non-fermentative Gram-negative bacteria ( P <0.01) . Nine strains of Carbapenem-resistant Enterobacteriaceae were isolated, which were all sensitive to amikacin and the sensitive rates to fluoroquinolone reached 88.9%. Five strains which were detected sensitive to tigecycline were all sensitive. The proportion of Klebsiella sp in Gram-negative bacteria between 2013-2015 and 2010-2012 were 32.9% and 21.2%, respectively. The resistance rates of Escherichia coli and Klebsiella pneumoniae to β-lactams and its enzyme inhibitors and carbapenems had no significant change. Conclusion: Gram-negative bacterial bloodstream infections occur more frequently in newborns. Most children had combined underlying diseases. Escherichia coli and Klebsiella pneumoniae are the most common pathogens. β-Lactams and its enzyme inhibitors and carbapenems are the empirical choice of antimicrobial therapy for severe Enterobacteriaceae bloodstream bacterial infections.

A simply hemoglobin (Hb) molecularly imprinted polymer (MIP) was prepared using Hb as the imprinted molecule, acrylamide as the functional monomer and cross-linked chitosan beads as the supporting matrix. The MIP was achieved by entrapment of the selective soft polyacrylamide gel in the pores of the cross-linked chitosan beads by letting acrylamide monomer and the protein diffuse into the pores of chitosan beads before starting the polymerization. The chitosan beads were freed from the surrounding polyacrylamide gel by washing. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. Langmuir analysis showed that an equal class of adsorption was formed in the MIP and the adsorption equilibrium constant and the maximum adsorption capacity were evaluated. The MIP has much higher adsorption capacity for Hb than the non-imprinted polymer with the same chemical composition, and the MIP also has a higher selectivity for the imprinted molecule. The MIP can be reused in an easy way and the reproduction coefficient was approximately 100% at low concentration.

Glycosylasparaginase catalyzes the hydrolysis of the N-glycosylic bond in N(4)-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-L-asparagine in the catabolism of N-linked oligosaccharides. A deficiency, or absence, of enzyme activity gives rise to aspartylglycosaminuria, the most common disorder of glycoprotein metabolism. The enzyme catalyzes the hydrolysis of a variety of asparagine and aspartyl compounds containing a free alpha-carboxyl group and a free alpha-amino group; computational studies suggest that the alpha-amino group actively participates in the catalytic mechanism. In order to study the importance of the alpha-carboxyl group and the alpha-amino group on the natural substrate to the reaction catalyzed by the enzyme, 14 analogues of the natural substrate were studied where the structure of the aspartyl group of the substrate was changed. The incremental binding energy (DeltaDeltaGb) for those analogues that were substrates was calculated. The results show that the alpha-amino group may be substituted with a group of comparable size, for the alpha-amino group contributes little, if any, to the transition state binding energy of the natural substrate. The alpha-amino group position acts as an "anchor" in the binding site for the substrate. On the other hand, the alpha-carboxyl group is necessary for enzyme activity; removal of the alpha-carboxyl group or changing it to an alpha-carboxamide group results in no hydrolysis reaction. Also, N-acetyl-D-glucosamine is not sufficient for binding to the active site for efficient hydrolysis by the enzyme. These results provide supporting evidence for a proposed intramolecular autoproteolytic activation reaction for the enzyme. However, the results raise a question as to an important role for the alpha-amino group in the catalytic mechanism as indicated in computational studies., (Copyright 2001 Academic Press.)

A method with parallel extraction columns and parallel analytical columns (PEC-PAC) for on-line high-flow liquid chromatography/tandem mass spectrometry (LC/MS/MS) was developed and validated for simultaneous quantification of a drug candidate and its six metabolites in dog plasma. Two on-line extraction columns were used in parallel for sample extraction and two analytical columns were used in parallel for separation and analysis. The plasma samples, after addition of an internal standard solution, were directly injected onto the PEC-PAC system for purification and analysis. This method allowed the use of one of the extraction columns for analyte purification while the other was being equilibrated. Similarly, one of the analytical columns was employed to separate the analytes while the other was undergoing equilibration. Therefore, the time needed for re-conditioning both extraction and analytical columns was not added to the total analysis time, which resulted in a shorter run time and higher throughput. Moreover, the on-line column extraction LC/MS/MS method made it possible to extract and analyze all seven analytes simultaneously with good precision and accuracy despite their chemical class diversity that included primary, secondary and tertiary amines, an alcohol, an aldehyde and a carboxylic acid. The method was validated with the standard curve ranging from 5.00 to 5000 ng/mL. The intra- and inter-day precision was no more than 8% CV and the assay accuracy was between 95 and 107%., (Copyright 2001 John Wiley & Sons, Ltd.)

Glycosylasparaginase catalyzes the hydrolysis of the N-glycosylic bond between asparagine and N-acetylglucosamine in the catabolism of N-linked glycoproteins. Previously only three competitive inhibitors, one noncompetitive inhibitor, and one irreversible inhibitor of glycosylasparaginase activity had been reported. Using human glycosylasparaginase from human amniotic fluid, L-aspartic acid and four of its analogues, where the alpha-amino group was substituted with a chloro, bromo, methyl or hydrogen, were competitive inhibitors having Ki values between 0.6-7.7 mM. These results provide supporting evidence for a proposed intramolecular autoproteolytic activation reaction. A proposed phosphono transition state mimic and a sulfo transition state mimic were competitive inhibitors with Ki values 0.9 mM and 1.4 mM, respectively. These results support a mechanism for the enzyme-catalyzed reaction involving formation of a tetrahedral high-energy intermediate. Three analogues of the natural substrate were noncompetitive inhibitors with Ki values between 0.56-0.75 mM, indicating the presence of a second binding site that may recognize (substituted)acetamido groups.

Conditioned place preference (CPP) is a commonly used model to detect rewarding effect of drugs. To observe the effect of peripheral electric stimulation (PES) on morphine-induced CPP, we trained the rats with morphine in a CPP paradigm. Twelve hours before the testing phase, rats were given PES via stainless-steel needles with frequencies of 2, 100, or 2/100 Hz, respectively. PES of 2 and 2/100 Hz significantly decreased CPP in morphine-trained animals in a naloxone reversible manner, while PES of 100 Hz, foot shock, needle insertion, or plain restraining, showed no effect. Thus, PES with a low-frequency component (2 Hz) could specifically inhibit the expression of morphine-induced CPP, presumably via activation of opioid receptors.

As a continuation of our efforts to improve our high-flow on-line bioanalytical approach for high-throughput quantitation of drugs and metabolites in biological matrices by high-performance liquid chromatography (LC) and tandem mass spectrometry (MS/MS), we have developed a ternary-column on-line LC/MS/MS system with dual extraction columns used in parallel for purification and an analytical column for analysis. The advantage of the dual extraction column system is that sample analysis can take place in one of the extraction columns while the other column is being equilibrated. Thus, the equilibration time does not add to the run time, hence shortening the injection cycle time and increasing the sample throughput. Moreover, the use of two extraction columns in parallel increases the number of samples that can be injected before the system fails due to an overused extraction column. Such a system has successfully been used to develop and validate a positive ion electrospray LC/MS/MS bioanalytical method for the quantitative determination of a guanidine-containing drug candidate in rat plasma. The system used for this work utilized two Oasis HLB extraction columns (1 x 50 mm, 30 microm), one C18 analytical column (3.9 x 50 mm, 5 microm), a ten-port switching value and a tandem mass spectrometer. The on-line analysis was accomplished by the direct injection of 10 microL of the sample, obtained by mixing a rat plasma sample 1:1 with an aqueous internal standard solution. Selected reaction monitoring (SRM) was utilized for the detection of the analyte and internal standard. The standard curve range was 1.00-200 ng/mL. The intra- and inter-day precision and accuracy were within 6.6%. The on-line purification step lasted for only 0.3 min and total run time was only 1.6 min., (Copyright 2000 John Wiley & Sons, Ltd.)

A bioanalytical method has been developed and validated for quantitation of a beta-lactam drug candidate and its open-ring biotransformation product utilizing high-flow high-performance liquid chromatography (HPLC) for on-line purification of plasma samples and electrospray tandem mass spectrometry for detection and quantitation. The HPLC system used two columns: an Oasis column (1 x 50 mm, 30 microm) as the on-line extraction column and a conventional C18 column (2 x 50 mm, 5 microm) as the analytical column. Each plasma standard or quality control (QC) sample (50 microL) was mixed with 50 microL of a working solution of the internal standard in aqueous 0.5 M ammonium acetate (pH 4.0). Portions (10 microL) of these samples were then injected into an Oasis column with a mobile phase consisting of 100% aqueous 1 mM formic acid at a high flow rate (4.0 mL/min), with the effluent from the Oasis column directed to waste and not to the mass spectrometer. After the purification step, the Oasis column effluent was directed to the analytical column and the mass spectrometer and the analytes were eluted with methanol/aqueous 1 mM formic acid (70:30) at a flow rate of 1.0 mL/min. The total analysis time was 1.6 min per sample. The standard curve range was 0.980 to 250 ng/mL. The accuracy, inter-day precision and intra-day precision were within 10% for both compounds., (Copyright 1999 John Wiley & Sons, Ltd.)

Four sensitive, specific and accurate methods, based on high-performance liquid chromatography (HPLC) with positive ion electrospray tandem mass spectrometry (MS/MS) coupled with liquid-Liquid extraction (LLE), have been developed and validated for the low-picogram determination of two drug candidates and a metabolite (compounds I-III) in human, monkey and rat plasma. In the LLE procedure, hexane or a mixture of hexane and methyl t-butyl ether was used to isolate these compounds from plasma of the different species after basification of each biological sample with sodium carbonate. The reconstituted extracts were then injected into a positive ion electrospray LC/MS/MS system for the quantitative analysis. The lower limit of quantitation of the methods ranged from 20 to 200 pg/mL. The use of hexane for the LLE proved to be simple, rapid and reproducible, and provided very clean extracts with little interference. The inter- and intra-day precision for the four methods was within 9%, and the accuracy was in the range 94-107%. The effect of pH on the isomerization of I (E-isomer) to its Z-isomer (II) showed that the rate of isomerization increased with decrease in pH and that there was no isomerization at pH >/=6., (Copyright 1999 John Wiley & Sons, Ltd.)

Two bioanalytical methods have been developed and validated utilizing high flow high performance liquid chromatography (HPLC) for on-line purification of plasma and serum samples and electrospray tandem mass spectrometry for detection and quantitation. Each plasma or serum sample, after mixing with an aqueous solution of the internal standard, was injected into a small diameter (1 x 50 mm) column packed with large particles of OASIS (30 microns), with a 100% aqueous mobile phase at a high flow rate (3-4 mL/min). The combination of the high linear speed (6-8 cm/s) of the aqueous mobile phase and the large particle size resulted in the rapid passage of the proteins and other large biomolecules through the column while the small-molecule analytes were retained on the column. During this purification period, the HPLC effluent was directed to waste. After the purification step, the HPLC mobile phase was rapidly changed from 100% aqueous to < or = 100% organic, the flow was reduced to 0.5-0.8 mL/min, and the column effluent was directed towards the mass spectrometer. The small molecule analytes were eluted during this period. In the method developed and validated for the quantitative determination of compound I in rat plasma (method A), the same OASIS column (1 x 50 mm, 30 microns) served as the purification and analytical (elution) column. In the method developed for the simultaneous determination of pravastatin and its positional isomer biotransformation product (SQ-31906) in human serum (method B), the purification column was connected to a conventional C18 analytical column (3.9 x 50 mm, 5 microns) to achieve the required chromatographic separation between the two isomers. For method A, where 50 microL of rat plasma mixed 1:1 with water containing the internal standard was injected, the standard curve range was 1 to 1,000 ng/mL. For method B, where 200 microL of a human serum sample mixed 4:1 with water containing the internal standard was injected, the standard curve range was 0.5 to 100 ng/mL. The total analysis time for each method was < or = 5 min per sample. The accuracy, inter-day precision and intra-day precision were within 10% for both methods.