Mercury speciation in hair by headspace injection-gas chromatography-atomic fluorescence spectrometry (methylmercury) and combustion-atomic absorption spectrometry (total Hg)

The speciation of Hg in human hair was carried out with combustion-atomic absorption spectrometry for total Hg (THg) and headspace-gas chromatography-atomic fluorescence spectrometry (HS-GC-AFS) for methylmercury (MMHg).The determination of total Hg in hair was carried out with the AMA analyzer (Advanced Mercury Analyser 254). Accuracy and reproducibility were assessed on a Certified Reference hair sample (IAEA-086 CRM), yielding, respectively, a recovery of 97.5% and a RSD of 3.2%. Analyses of 10 blank measurements resulted in a detection limit of 1.5 ng g⁻¹ of THg for a 20 mg sample of human hair.MMHg concentrations in hair were assessed with HS-GC-AFS in a single analysis step. Either acid or alkaline extraction can be applied because they yielded very similar results on a IAEA-086 CRM: we observed a recovery of 103% and a RSD of 7% with acid extraction and a recovery of 110% and a RSD of 9% with alkaline extraction. Optimization of the headspace vial, injection and GC parameters is described. The detection limit of the MMHg determination in human hair, which amounts to 0.04 ng g⁻¹ for a 20 mg sample, is far below the concentrations observed in natural samples.The number of samples that can be analyzed per hour, respectively, amounts to 8 for THg and 4 for MMHg. Finally, Hg speciation in natural human hair samples was carried out by combining both AMA and HS-GC-AFS analysis methods. THg levels were at the μg g⁻¹, level, with an average MMHg fraction of about 70%.     

牙周病患者头发微量元素的测定

为探讨牙周病与微量元素的关系,对28例牙周病患者头发Fe、Zn、Cu、Ca进行了测定,并与正常对照组做比较。结果表明,牙周病患者头发Fe、Zn、Cu、Ca较对照组明显降低。提示牙周病患者头发微量元素的含量与牙周病有密切关系。     

GC-MS法测定氧化型染发剂中的苯二胺

建立了气相色谱-质谱同时测定氧化型染发剂中邻苯二胺、间苯二胺和对苯二胺的方法。以乙酸乙酯提取氧化型染发剂中苯二胺,用气相色谱-质谱方法进行定性和定量分析。该方法对氧化型染发剂中的3种苯二胺的检出限为20 mg/kg,线性范围为0.2~10 mg/L,线性相关系数为0.999 2~0.999 9。方法的回收率为75%~110%,满足氧化型染发剂中3种苯二胺检测的需要。     

微波消解-端视电感耦合等离子体原子发射光谱法测定虎毛中的微量元素

研究了华南虎虎毛中微量元素的分析方法,通过MARS-5微波消解系统快速消解虎毛样品,利用端视电感耦合等离子体发射光谱仪测试其中Al、Ba、Ca、Cu、Fe等十三种微量元素的含量,各元素回收率在85%到110%之间,相对标准偏差小于5%.本工作为虎类研究提供了方便准确的测试方法,为评价动物生长发育和健康状况提供了简单快捷的途径.     

化学浸提-分光光度法测定沙棘叶中不同形态铝

利用KCl、NH4Ac、HCl、NaOH四种浸提液将沙棘叶中的铝浸提溶出,得到沙棘叶中铝的不同化学形态,采用分光光度法定量测定,测定结果:沙棘叶中的Al3+为10.7%,Al(OH)2+和Al(OH)+2为2.1%,胶态Al(OH)03为34.3%,有机铝为53.0%.浸提液中铝的回收率为86.9%～101.0%.     

西宁市326例儿童发锌含量分析

为了解西宁市326例儿童体内微量元素锌含量,对326例儿童发锌进行了检测分析,其中男童204例,女童122例;幼儿109例,大于3岁儿童217例。结果表明,西宁地区儿童体内锌含量普遍低于正常参考值范围。提示该地区儿童缺锌普遍且严重,需要建立预防性常规检测和规范补锌机制。     

Effect of sample pre-treatment on the determination of steroid esters in hair of bovine calves

The effect of three sample pre-treatment steps, washing, cutting and grinding on the determination of steroid esters in hair is studied. The study is performed by using hair samples obtained after pour-on application of steroid esters to bovine calves. After sample pre-treatment the hair is treated with a mild reducing agent [tris(2-carboxyethyl)phosphine hydrochloride] to extract the steroid esters. After a solid-phase extraction clean-up step the extracts are analysed by using liquid chromatography combined with triple–quadrupole mass spectrometric detection. For the washing step the use of non-organic washing solvents like (warm) water and a solution of 0.1% sodium dodecyl phosphate and organic solutions containing different percentages of methanol are tested. By using the non-organic solvents and the organic solvents with a percentage of methanol <20% the recovery results are as good as the results obtained without washing the hair. Cutting the hair samples increases the analyte recoveries of incurred steroid esters by 20% compared to the non-cut hair. The analyte recoveries of cut hair samples are about 60–80% that of ground hair samples. The obtained surface expansion of hair samples by grinding proves to be necessary in order to achieve the highest possible analyte yields. Finally the use of pressurised liquid extraction (PLE) for the extraction of steroid esters from plain (no washing, cutting or grinding) hair is investigated. The first results show lower (up to 40%) extraction recoveries in comparison with the classical solvent extraction procedures. If the limit of detection requirement is met, PLE may be an alternative for extracting large numbers of hair samples due to the short sample treatment procedure involved.     

The complexity of minimizing the number of shape matrices subject to minimal beam-on time in multileaf collimator field decomposition with bounded fluence

The use of multileaf collimators (MLCs) is a modern way to realize intensity modulated fields in radiotherapy. An important step in the treatment planning is the shape matrix decomposition: the desired fluence distribution, given by an integer matrix, has to be decomposed into a small number shape matrices, i.e. (0,1)-matrices corresponding to the field shapes that can be delivered by the MLC used. The two main objectives are to minimize the total irradiation time, and the number of shape matrices. Assuming that the entries of the fluence matrix are bounded by a constant, we prove that a shape matrix decomposition with minimal number of shape matrices under the condition that the total irradiation time is minimal, can be determined in time polynomial in the matrix dimensions. The results of our algorithm are compared with Engel’s [K. Engel, A new algorithm for optimal multileaf collimator field segmentation, Discrete Appl. Math. 152 (1-3) (2005) 35-51.] heuristic for the reduction of the number of shape matrices.     

基于偏振反射模型和随机森林回归的叶片氮含量反演

叶片氮含量极大程度上影响植被生物化学过程,有重要的研究意义。利用机载高光谱数据反演叶片氮含量在农业遥感领域有广泛应用,但其反演精度不能完全满足精细农业的需要,有一定提升空间。叶片氮含量遥感反演精度受机理误差和算法误差的影响,机理误差主要来源于叶片表面反射。传感器探测到的反射辐射既包含叶片内部多次散射,又包含叶片表面镜面反射部分,只有前者是携带叶片内部生化组分（如氮含量）信息的,由于后者是入射光在叶表蜡质层发生的直接反射,因此该部分并不携带叶片内部信息。根据菲涅尔定律,叶表镜面反射是部分偏振的,而内部散射是非偏振的,因而通过偏振反射建模可部分去除叶表镜面反射影响,以消除机理误差。算法误差主要来源于不同氮含量反演算法对于高光谱数据挖掘能力的差别。比较了偏最小二乘法、主成分回归、支持向量机、K-近邻算法和随机森林回归在高光谱叶片氮含量反演中的表现,在调整算法参数之后,选择使用随机森林回归算法以减少高光谱反演算法误差。以常绿针叶林、落叶阔叶林和针阔混交林为研究对象,利用多角度偏振卫星POLDER/PARASOL的多光谱数据库构建二向偏振反射模型,用以模拟和分析研究区森林的偏振反射率;从HySpex传感器系统获取的机载高光谱数据中去除偏振反射率带来的光谱机理误差,以实现叶片氮含量的精确反演。以均方根误差为主要指标评估精度变化可获得以下结论：在高光谱叶片氮含量反演中,消除偏振反射率带来的机理误差后,各算法反演精度均有提升,平均提升了4.244%。其中,随机森林回归可以最大程度减小反演算法误差（可决系数达到0.803,均方根误差达到0.252）,且对光谱偏振信息最为敏感,去除偏振后精度提高了13.103%。相比于广泛使用的偏最小二乘算法,去除光谱机理误差并减小反演算法误差后,叶片氮含量反演精度整体提高了32.440%。该研究实现了基于机载高光谱数据的叶片氮含量精确反演,证明了在叶片氮含量反演中去除偏振反射率的必要性,体现了在高光谱氮含量反演中随机森林算法的应用潜力。     

催化光度法测定人发中微量碘的研究与应用

建立了催化光度法用于人发中微量碘的测定,研究了发碘的测试条件,重点研究了发样溶解条件对测试结果的影响,采用300 g/L的K2CO3溶液浸泡,105℃烘干后于550℃熔融分解。结果表明,该法的检出限为0.038μg/g,相对标准偏差为6.5%。用于儿童发碘分析,结果令人满意。