Selective and rapid determination of raltegravir in human plasma by liquid chromatography–tandem mass spectrometry in the negative ionization mode

A selective and rapid high-performance liquid chromatography–tandem mass spectrometry method was developed and validated for the quantification of raltegravir using raltegravir-d3 as an internal standard（IS）. The analyte and IS were extracted with methylene chloride and n-hexane solvent mixture from 100 mL human plasma. The chromatographic separation was achieved on a Chromolith RP-18 e endcapped C18（100 mm 4.6 mm） column in a run time of 2.0 min. Quantitation was performed in the negative ionization mode using the transitions of m/z 443.1-316.1 for raltegravir and m/z 446.1-319.0 for IS. The linearity of the method was established in the concentration range of 2.0–6000 ng/m L.The mean extraction recovery for raltegravir and IS was 92.6% and 91.8%, respectively, and the IS-normalized matrix factors for raltegravir ranged from 0.992 to 0.999. The application of this method was demonstrated by a bioequivalence study on 18 healthy subjects.

ERROR COUNTER-BASED NEGATIVE ACKNOWLEDGEMENT MODE IN CCSDS FILE DELIVERY PROTOCOL

Deep space communication has its own features such as long propagation delays,heavy noise,asymmetric link rates,and intermittent connectivity in space,therefore TCP/IP protocol cannot perform as well as it does in terrestrial communications.Accordingly,the Consultative Committee for Space Data Systems(CCSDS) developed CCSDS File Delivery Protocol(CFDP),which sets standards of efficient file delivery service capable of transferring files to and from mass memory located in the space segment.In CFDP,four optional acknowledge modes are supported to make the communication more reliable.In this paper,we gave a general introduction of typical communication process in CFDP and analysis of its four Negative Acknowledgement(NAK) modes on the respect of file delivery delay and times of retransmission.We found out that despite the shortest file delivery delay,immediate NAK mode suffers from the problem that frequent retransmission may probably lead to network congestion.Thus,we proposed a new mode,the error counter-based NAK mode.By simulation of the case focused on the link between a deep space probe on Mars and a ter-restrial station on Earth,we concluded that error counter-based NAK mode has successfully reduced the retransmission times at negligible cost of certain amount of file delivery delay.

Anomalous low-temperature heat capacity in antiperovskite compounds

The low-temperature heat capacities are studied for antiperovskite compounds AX M_3（A = Al, Ga, Cu, Ag, Sn, X = C,N, M = Mn, Fe, Co）. A large peak in（C- γ T）/T^3 versus T is observed for each of a total of 18 compounds investigated,indicating an existence of low-energy phonon mode unexpected by Debye T^3 law. Such a peak is insensitive to the external magnetic field up to 80 k Oe（1 Oe = 79.5775 A·m-1）. For compounds with smaller lattice constant, the peak shifts towards higher temperatures with a reduction of peak height. This abnormal peak in（C- γ T）/T^3 versus T of antiperovskite compound may result from the strongly dispersive acoustic branch due to the heavier A atoms and the optical-like mode from the dynamic rotation of X M_6 octahedron. Such a low-energy phonon mode may not contribute negatively to the normal thermal expansion in AX M_3 compounds, while it is usually concomitant with negative thermal expansion in open-structure material（e.g., ZrW_2O_8, Sc F_3）.

Determination of hyperoside in rat plasma after intravenous administration by UPLC-MS

Hyperoside is one of the major components of Hypericum perforatum L. and also present in many plant species such as Abelmoschus manihot （L.） Medik., Ribes nigrum L. and Rosa agrestis Savi （Rosaceae）. Because hyperoside exhibits many biological activities, the pharmacokinetics profile of hyperoside needs to be studied for further elucidating its mechanism of action. A simple method for the determination of hyperoside in rat plasma was developed by using ultra-high performance liquid chromatography coupled with mass spectrometry （UPLC-MS）. Only 50 ~tL plasma samples were required for sample preparation. The quantitative detection of hyperoside was accomplished by selected ion monitoring （SIM） in negative ion mode. Hyperoside was analyzed in less than 10 rain. Good linearity was obtained （r2〉0.999） and the intra- and inter-day precision of the method were lower than 15%. Lower limit of quantification （LLOQ） was 4 ng/mL for hyperoside in rat plasma. Our method showed advantage in the lower LLOQ compared with the reported method; furthermore, smaller amount of plasma was needed. The method was successfully applied for the pharmacokinetics study of hyperoside in rat after intravenous administration of hyperoside.

Molecular characterization of root exudates using Fourier transform ion cyclotron resonance mass spectrometry

The release of root exudates(REs) provides an important source of soil organic carbon. This work revealed the molecular composition of REs of different plant species including alfalfa( Medicago sativa L.), bean( Phaseolus vulgaris L.), barley( Hordeum vulgare L.), maize( Zea mays), wheat( Triticum aestivum L.), ryegrass( Lolium perenne L.) and pumpkin( Cucurbita maxima) using electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry(ESI FT-ICR MS). The combination of positive ion mode( + ESI) and negative ion mode(-ESI) increased the number of the molecules detected by ESI FT-ICR MS, and a total of 8758 molecules were identified across all the samples. In detail, lipids and proteins and unsaturated hydrocarbons were more easily detected in + ESI mode, while aromatic compounds with high O/C were readily ionized in-ESI mode, and only 38% of the total assigned formulas were shared by -ESI and + ESI modes. Multivariate statistical analysis of the formulas indicated that the close related plants species secreted REs with similar molecular components. Moreover, the unsaturation degree and nitrogen content were the two key parameters able to distinguish the similarities and differences of molecular components of REs between plant species. The results provided a feasible analysis method for characterization of the molecular components of REs and for the first time characterized the molecular components of REs of a variety of plant species using ESI FT-ICR MS.