Xinhua Dai

Accurate analysis of urea in milk and milk powder by isotope dilution gas chromatography-mass spectrometry.

A high order method for measuring urea concentrations in milk and milk powder was developed. The method can be applied to certify the concentration of urea in some new milk and milk powder CRMs. This high accurate method for analysis of milk is valuable given the inherent challenges associated with the complexity of the sample matrix. A measurement procedure based on gas chromatography/isotope dilution mass spectrometry (GC/IDMS) was developed. Samples were pre-treated with acetonitrile to remove proteins and the method was applied to determine urea concentrations in milk and milk powder. Excellent precision was obtained, with within- and between-set coefficients of variation of 0.15-0.46 and 0.18-0.65%, respectively. The measurement uncertainty is evaluated. The method can trace to mass.

Certified reference materials (GBW09170 and 09171) of creatinine in human serum

Creatinine is the most widely used clinical marker for assessing renal function. Concentrations of creatinine in human serum need to be carefully checked in order to ensure accurate diagnosis of renal function. Therefore, development of certified reference materials (CRMs) of creatinine in serum is of increasing importance. In this study, two new CRMs (Nos. GBW09170 and 09171) for creatinine in human serum have been developed. They were prepared with mixtures of several dozens of healthy peoples and kidney disease patients serum, respectively. The certified values of 8.10, 34.1 mg/kg for these two CRMs have been assigned by liquid chromatography-isotope dilution mass spectrometry (LC-IDMS) method which was validated by using standard reference material (SRM) of SRM909b (a reference material obtained from National Institute of Standards and Technology, NIST). The expanded uncertainties of certified values for low and high concentrations were estimated to be 1.2 and 1.1%, respectively. The certified values were further confirmed by an international intercomparison for the determination of creatinine in human serum (Consultative Committee for Amount of Substance, CCQM) of K80 (CCQM-K80). These new CRMs of creatinine in human serum pool are totally native without additional creatinine spiked for enrichment. These new CRMs are capable of validating routine clinical methods for ensuring accuracy, reliability and comparability of analytical results from different clinical laboratories. They can also be used for instrument validation, development of secondary reference materials, and evaluating the accuracy of high order clinical methods for the determination of creatinine in human serum.

Optimization of selective pressurized liquid extraction and ultrasonication-assisted QuEChERS methods for the determination of polybrominated diphenyl ethers in sediments

Two fast analytical methods, selective pressurized liquid extraction (SPLE) and ultrasonication-assisted QuEChERS methods (Quick, Easy, Cheap, Effective, Rugged and Safe) followed by GC-MS/MS, were optimized for the determination of polybrominated diphenyl ethers (PBDEs) in sediments. Ultrasonication was used to improve the extraction efficiency of QuEChERS. The experimental parameters of SPLE and ultrasonication-assisted QuEChERS, such as sorbent type, composition and elution solvents, were optimized in detail. The obtained recoveries of both methods were satisfactory for PBDE analysis. The inter/intra-day RSDs were <7%. The limits of quantification (LOQ) were ≤0.1 ng g−1 dry weight (d.w.). The figures of merit were at the same level as former reported results. The proposed methods were validated for the analysis of PBDEs in standard reference materials (SRM 1944 and 2585). The results indicated that both optimized methods were feasible for the analysis and monitoring of PBDEs. Besides, the comparison between two methods revealed that elevated temperature and pressure could weaken the interaction between PBDEs and sediment matrices, resulting in improvement of extraction efficiency. Both proposed methods were successfully applied to the analysis of 3 sediment samples and the determination of BDE 47, 99, 100 and 153 suggested that both methods are practical and suitable for PBDE analysis in real sediment samples.

Development of a matrix-based candidate reference material of total homocysteine in human serum

AbstractWe developed and evaluated a candidate serum reference material to help improve clinical routine measurement, and to provide traceability of the measurement results. D8-Homocystine, dithiothreitol, and acetonitrile were used as an internal standard, the reducing agent, and the protein precipitating agent, respectively. A triple quadrupole mass spectrometer with an electrospray ionization source was used for monitoring the transitions (m/z 140.0u2009→u200994.0, 136.0u2009→u200990.0) in multiple-reaction-monitoring mode. We usedxa0a calibration model relying on bracketing and gravimetric measurements to give SI-traceability and higher accuracy to serum value assignments. The method was evaluated for accuracy using NIST Standard Reference Material SRM1955. The results of the three concentrations (1, 2, and 3) of total homocysteine in human serum samples were determined by an isotope-dilution liquid chromatography-tandem mass spectrometry method; tHcy 1 is 28.8u2009±u20091.1xa0μmol/L, tHcy 2 is 17.93u2009±u20090.57xa0μmol/L, and tHcy 3 is 14.38u2009±u20090.46xa0μmol/L.n Graphical abstractThe workflow diagram.

DETERMINATION OF CORTISOL IN HUMAN SERUM USING ULTRASONIC EXTRACTION COUPLED WITH ISOTOPE DILUTION LIQUID CHROMATOGRAPHY–MASS SPECTROMETRY

A simple method for the determination of total cortisol in serum was developed. The method used ultrasonic extraction coupled with liquid chromatography–tandem mass spectrometry (LC-MS/MS), which provides high sensitivity, short pretreatment, simple experimental procedures, and low costs. In this method, cortisol in human serum was separated by ultrasound with acetonitrile as an extraction solvent and was analyzed by LC-MS/MS. Excellent precision was achieved with inter-day coefficients of variation (CVs) of 0.3–0.7% and intra-day CVs of 0.3–0.6%. The mean recovery of the assay was 100.5% with a range 99.6–101.0%. The accuracy of this method was confirmed using an international interlaboratory comparison sample (CCQM-K63a).

Ultrasensitive analysis of heat shock protein 90α with antibodies orderly arrayed on a novel type of immunoprobe based on magnetic COFs

The early diagnosis of liver cancer by target biomarkers is of great significance for improving the survival rate of cancer patients. However, it is still a challenging task to sensitively detect circulating protein biomarkers due to decreased binding activity of antibodies originating from uncontrolled orientation of immobilization on the surface of a solid matrix. In this work, a novel immunoaffinity probe, Fe3O4@TpBD-DSS-Ab-MEG, based on magnetic COFs with ordered arrangement of anchored antibodies has been developed and applied for the first time to detection of a cancer biomarker, heat shock protein 90alpha (Hsp90α). The fabricated composites possess favorable features from magnetic cores and COF shells, including strong magnetic responses (7.96u202femuu202fg-1), ordered active groups, a large amount of immobilized antibodies (111.7u202fμg/mg), good solvent and thermal stability. Fe3O4@TpBD-DSS-Ab-MEG demonstrated low detection limit (50u202fpg/mL), high selectivity (Hsp90α:BSAu202f=u202f1:1000), desirable repeatability and good stability for Hsp90α immunocapture. Compared with other immunoprobes, our materials showed higher selectivity and sensitivity, which were mainly attributed to regular arrays of surface antibodies. Furthermore, samples containing Hsp90α at the concentration of 1u202fµg/mL in human plasma were used to test our immunoprobe, and 2 peptides of Hsp90α were successfully observed. The proposed non-invasive immunoassay strategy offers enhanced ability to control the orientation of immobilized antibodies and great promise for accurate analysis of the liver cancer biomarker Hsp90α in a complicated biological matrix. In addition, the facile preparation of magnetic COFs support and the satisfactory analytical performance made the newly developed immunoprobe a potential tool for sensitive detection of other cancer biomarkers in clinical diagnosis.

Development and evaluation of microwave-assisted and ultrasound-assisted methods based on a quick, easy, cheap, effective, rugged, and safe sample preparation approach for the determination of bisphenol analogues in serum and sediments

Microwave- and ultrasound-assisted methods based on a quick, easy, cheap, effective, rugged, and safe sample preparation approach followed by high-performance liquid chromatography with tandem mass spectrometry were developed for the simultaneous determination of eight bisphenol analogues in serum and sediment. The developed methods provided satisfactory extraction efficiency for the energy provided by microwaves and ultrasound. Compositions of commercial sorbents (primary secondary amine, MgSO4 , octadecyl-modified silica, and graphitized carbon black) were evaluated. The ultrasound-assisted method was suited for serum using primary secondary amine, MgSO4 , and octadecyl-modified silica as sorbents and a mixture of hexane and ethyl acetate as extraction solvent. The microwave-assisted method worked better for sediment with tetrahydrofuran and methanol as solvents and primary secondary amine, MgSO4 , octadecyl-modified silica, and graphitized carbon black as sorbents. Other experimental parameters, such as extraction temperature and time, were also optimized. The inter- and intraday relative standard deviations ranged from 2.7 to 5.5%. The limits of detection were between 0.1 and 1.0xa0ng/mL for serum and between 0.1 and 0.5xa0ng/g dry weight for sediment. The proposed methods were successfully applied to seven sediment and 20 human serum samples. The results showed that the developed methods were practical for the analysis and biomonitoring of bisphenols in sera and sediment.

Development of Certified Reference Materials of Drug Abuse (Heroin, Etc)for Elimination of Measurement Error in Forensic Drugs

The need for certified reference materials (CRM) of illicit drug was emphasized by drug detection in the forensic science as a tool to improve comparability, ensuring accuracy and traceability of analytical results. The production, characterization and certification of reference materials (RMs) is a key activity in improving and maintaining a worldwide coherent system of measurements. For the first time, we developed 9 illicit drug CRMs, including methamphetamine, heroin, ketamine and others. This work describes the production of the series of illicit drug CRMs, according to ISO Guides 34 and 35, which comprises the material processing, homogeneity and stability assessment, CRMs’ characterization including moisture content, trace metal content. The certified values were assigned by two methods. Homogeneity of the CRMs was determined by an in-house validated liquid chromatographic methodology. Potential degradation during storage was also investigated and a shelf-life based on this value was established. The certified values for all the studied reference materials are traceable to the international system of units (SI). The application of purity CRMs with accurate value could eliminated the measurement error in the forensic labs, which could give the accurate and reliable results for the forensic evidence. NIM will continue to carry out in-depth cooperation with IFS with raising the level of science to provide a greater level of rigor and confidence in forensic evidence used in the Chinese criminal justice system. Ketamine and methamphetamine have been applied as CRM in the APMP comparison, and gave the good results (Lab(7)). These CRMs studied have been widely used as standards in routine inspection work for the labs affiliated Institute of Forensic Science. The application of purity CRMs with accurate value could eliminated the measurement error in the forensic labs, which could give the accurate and reliable results for the forensic evidence.

Structural characterization and thermally induced isomerization investigation of cis- and trans-vitamin K1 using ion mobility mass spectrometry

Since some organic isomers have different activity, choosing of an appropriate quantitative strategy for their reference material (RM) development is critical. Value assignment is the core process during RM production and, recently, mass spectrometry (MS) based quantitative methods have been the primary approaches commonly adopted. However, due to the different chemical stability, the results obtained from MS and other non-ionized analysis methods might be inconsistent. From this argument, in this work, cis- and trans-vitamin K1 were selected as they have a different spatial structure and bio-activity. Initially, liquid chromatography with the detection of fluorescence and MS were respectively employed for the quantitative comparison, and a 9.73% isomer quantity difference was observed. Next, ion mobility coupled MS (IM-MS) was adopted for the structural investigation of isomer ions. After optimization, the isomer mixture was separated in a drift tube within several milliseconds. Collision cross-section values calculated using an IM-MS matched well with the theoretical values (2.43% of minimum deviation), suggesting that the IM-MS method was reliable. Afterwards, by raising the desolvation temperature in the ion source, the relative content of the trans-isomer had increased. Tandem mass spectra of the isomers resolved by chromatographic and IM were not identical. All the results indicated that in-source isomerization occurred for the vitamin K1 isomers. The different thermodynamic stabilities of the isomers might bring uncertainty to the quantification results when using MS methods, thus, understanding such in-source isomerization is conducive to choosing an appropriate analytical approach and then the isomer RM can be developed with higher accuracy.