Rapid determination of gemcitabine in plasma and serum using reversed-phase HPLC

Gemcitabine (2'2'-difluorodeoxycytidine) is a pyrimidine analog used in the treatment of a variety of solid tumors. After intravenous (i.v.) administration, it is rapidly inactivated to 2'-deoxy-2',2'-difluorouridine (dFdU). A sensitive analytical method for the quantitation of gemcitabine is required for the assessment of alternative dosage and treatment schemes. A rapid and robust RP-HPLC assay for analysis of gemcitabine in human and animal plasma and serum was developed and validated using 2'-deoxyuridine (dU) and 5-fluoro-2'-deoxyuridine (5FdU) as internal standards. It is based on protein precipitation, the use of an Atlantis dC18 column of 100 mm length (inner diameter, 4.6 mm; particle size, 3 microm) and isocratic elution using a 10 mM phosphate buffer, pH 3.0, followed by isocratic elution with the same buffer containing 3% of ACN. For gemcitabine, RSD values for intraday and interday precision were < 4.4 and 5.3%, respectively, the LOQ was 20 ng/mL, and the assay was linear in the range of 0.020-20 microg/mL with an accuracy of > or =89%. The recovery for gemcitabine, dU and 5FdU was 86-98%. The assay was applied to determine gemcitabine levels in plasma samples of patients collected during and shortly after conventional infusion of 25-30 mg/kg body mass (levels: 2.0-18.9 microg/mL) and rats that received lower doses (1.5 mg/kg) via i.v., subcutaneous and oral drug administration (levels: 0.20-2.60 microg/mL). It could also be applied to estimate dFdU levels in human plasma.     

Anomalous scaling in epitaxial growth on vicinal surfaces: meandering and mounding instabilities in a linear growth equation with spatiotemporally correlated noise

We have undertaken an extensive analytical and kinetic Monte Carlo study of the (2+1) dimensional discrete growth model on a vicinal surface. A non-local, phenomenological continuum equation describing surface growth in unstable systems with anomalous scaling is presented. The roughness produced by unstable growth is first studied considering various effects in surface diffusion processes (corresponding to temperature, flux, diffusion anisotropy). We found that the thermally activated roughness is well-described by a generalized Lai–Das Sarma–Villain model with non linear growth continuum equation and uncorrelated noise. The corresponding critical exponents are computed analytically for the first time and show a continuous variation in agreement with simulation results of a solid-on-solid model. However, the roughness related to the meandering instability is found, unexpectedly, to be well described by a linear continuum equation with spatiotemporally correlated noise.     

高效液相色谱法测定水体中的氯虫酰胺残留量

采用Kromasil C18不锈钢柱(250mm×4.6mm i.d..5μm),以甲醇-水混合溶剂(65:35,V/V)为流动相,流速1.0mL/min,光电二极管阵列检测器,检测波长236nm和柱温35C,建立了不同水体中氯虫酰胺残留的高效液相色谱分析方法.氯虫酰胺水样直接用二氯甲烷进行液-液分配萃取.在0.10-10mg/L的浓度范围内,氯虫酰胺峰面积(y)与质量浓度(x)呈现良好的相关性,其线性回归方程为y=2170.4x 2641.7,r2=0.9991.井水和池塘水中添加质量浓度为0.01-1.00mg/L时,其平均回收率分别为94.70%-100.37%和89.14%-100.22%,变异系数分别为0.81%-5.11%和1.81%-5.30%,水样中的氯虫酰胺最低检测质量浓度(LOQ)为7.5×10-3mg/L,方法快速、灵敏度高、重现性好,具有较好的准确度和精密度,可用于环境中水样和土壤样中氯虫酰胺的残留检测分析.     

Markoff triples and quasifuchsian groups

We study the global behaviour of trees of Markoff triples overthe complex numbers. We relate this to the space of type-preservingrepresentations of the punctured torus group into SL(2,C). Inparticular, we explore which Markoff triples correspond to quasifuchsianrepresentations. We derive a variation of McShane's identityfor quasifuchsian groups. In the case of non-discrete representations,we attempt to relate the asymptotic behaviour of Markoff triplesto the realisability of laminations in hyperbolic 3-space. Wealso consider how some of these issues might be related formore general surfaces. 1991 Mathematics Subject Classification:57M50.