目标特征谱线选取对猪肉中Cr元素LIBS检测精度比较

结合激光诱导击穿光谱和线性回归对猪肉中Cr元素进行定量分析,比较了Cr特征谱线单变量分析与多变量分析对猪肉中Cr元素检测精度的影响。先采用特征谱线Cr I425.43nm进行单变量分析,得到Cr浓度与LIBS强度的线性相关系数为0.9434;再利用Cr的三特征谱线Cr I425.43nm,Cr I427.48nm,Cr I428.97nm进行多变量分析,研究了Cr元素预测质量分数与实际质量分数之间的线性相关性。结果显示,单变量分析与多变量分析的线性相关性分别为0.9749和0.9769,定标集平均预测相对误差分别为4.8%和4.2%,验证集AREP分别为5.3%和3.3%。结果表明,选取目标元素Cr的单特征谱线与多特征谱线均能对样品Cr含量进行有效预测,多变量分析能在一定程度上提高Cr元素含量预测的准确性但与单变量比较差异性不大,且采用单一最灵敏线定量分析更简便可行。     

基于遗传算法和偏最小二乘法的土壤激光诱导击穿光谱定量分析研究

在空气环境下,采用激光诱导击穿光谱(LIBS)技术对土壤成分进行检测,建立了基于遗传算法(GA)和偏最小二乘法(PLS)的定量分析模型。将配制的58个土壤样品分为定标集、监控集和预测集,对11种组分Mn,Cr,Cu,Pb,Ba,Al2O3,Ca O,Fe2O3,Mg O,Na2O和K2O的含量分别进行预测。结果表明,GA作为一种谱线选择的预处理方法,可以有效减少用于PLS建模的光谱谱线的数目,从而简化模型。对于土壤中的大部分组成成分,GA-PLS模型能够显著改善传统PLS模型的预测能力。以Mn元素为例,浓度预测均方根误差(RMSEP)从0.0215%降低至0.0167%,平均百分比误差(MPE)从8.10%降低至5.20%。本研究为进一步提高土壤的LIBS定量分析准确度提供了方法参考。     

双脉冲激光诱导击穿光谱结合多元定标法定量分析大豆油中的铅

应用双脉冲激光诱导击穿光谱(DP-LIBS)对大豆油中的铅(Pb)含量进行检测。配制9个大豆油样品,采用一定规格圆柱形桐木对样品中Pb进行富集,然后通过Ava-Spec二通道高精度光谱仪采集其LIBS光谱信号。根据样品的LIBS谱线图和美国国家标准技术研究所(NIST)原子光谱数据库,确定选用CaⅡ393.284 nm,CaⅡ396.752 nm,NⅡ399.399 nm和PbⅠ405.685 nm的特征谱线强度作为自变量,得到Pb含量的多元线性回归定量分析模型,并通过方差分析和t检验验证分析模型的可行性。结果表明,采用Pb元素直接定标法得到的平均相对误差约为16%,拟合度R2为0.981 8;采用多元线性回归模型得到的平均相对误差为7.25%,拟合度R2为0.997 1,3个检验样品的相对误差均在合理范围内。采用多元校正分析模型可以充分利用光谱中的有效信息,降低基体效应的影响,从而提高LIBS分析的准确性。     

基于激光诱导击穿光谱对钛元素自吸收效应的分析

为了减小谱线自吸收效应对样品物质中元素定量分析带来的干扰,提高激光诱导击穿光谱技术(LIBS)对钢铁中微量元素的检测准确度和精度,以攀钢生铁标准样品作为研究对象,选取Fe(Ⅰ)438.4 nm、Fe(Ⅰ)347.6 nm作为内标线,以原子线Ti(Ⅰ)506.5 nm、离子线Ti(Ⅱ)334.9 nm作为分析线,对Ti元素谱线的自吸收效应进行校正,分别建立内定标曲线,并建立了相应的量化模型。先通过指数函数拟合定标曲线来表征自吸收效应,然后对自吸收效应进行校正。自吸收校正后,Ti两组定标曲线的决定系数R²分别从0.882增加到0.994、0.881增加到0.917,分别提高了12.7%和4.0%。定量分析时,2^#和5^#样品用于验证,结果显示两验证样品中Ti预测浓度的相对误差都降低到了10%以内,预测浓度的相对误差分别减少了72.01%、97.10%,测量精度得到明显提高,并且自吸收校正后的预测浓度近似于等于标准浓度。实验表明,通过指数函数拟合定标曲线的方式来量化自吸收效应,并对其进行校正的方法可以提升对Ti的分析精度,方法为...     

共轴双脉冲激光诱导击穿光谱和最小二乘支持向量机法定量分析植物油中铬

利用共轴双脉冲激光诱导击穿光谱( DP-LIBS)技术对植物油(大豆油、花生油和玉米油)中的重金属铬( Cr)含量进行定量分析。采用Ava-Spec双通道高精度光谱仪采集样品的LIBS光谱,然后通过其LIBS谱线图确定了CN分子谱线(421.49 nm)、Ca原子谱线(422.64 nm)及Cr的3条原子谱线(425.39、427.43和428.87 nm),根据上述谱线建立了Cr元素的单变量定标模型和最小二乘支持向量机(LS-SVM)校正模型,并用验证样品对它们进行检验。研究结果表明,对于单变量定标法,大豆油、花生油及玉米油验证样品的平均预测相对误差(PRE)分别为12.57%,12.11%和13.72%;对于三变量LS-SVM法,其定标样品真实值与预测值之间的拟合度 R2分别为0.9785,0.9792和0.9654,验证样品的平均 PRE 分别为8.92%,8.33%和10.98%;对于五变量LS-SVM法(增加两基体元素谱线变量),其定标样品真实值与预测值之间的拟合度R2分别为0.9895,0.9901和0.9855,验证样品的平均PRE分别为7.46%,8.96%和8.95%。由此可知,LS-SVM校正模型性能优于单变量定标法,且五变量LS-SVM校正模型性能优于三变量LS-SVM校正模型;采用LS-SVM法及引入合适的基体元素谱线( CN、Ca)能有效减小定量分析误差,提高LIBS技术对植物油中Cr含量预测的精度。     

基于不同物候期苹果树叶片光谱特征预测果实糖度

苹果糖度是评价苹果品质的重要指标.通过分析苹果开花期、新梢生长期、萌芽开花坐果期、新梢旺长期、花芽分化期和落叶期等6个重要的生理物候期果树叶片的光谱特征,并与最终采集到的对应位置的果实糖度信息进行二维相关运算,获得了果树叶片光谱信息中反映果实糖度的敏感谱段,构建了糖度敏感光谱,通过引入计算获得的不同物候期糖度贡献权重,最终构建了带权糖度敏感光谱,并基于该光谱进行了糖度预测.通过对不同物候期的二维相关分析获得了果实糖度敏感谱段(530 ～570 nm和700 ～ 720 nm),经过主成分分析分别获得了不同生理物候期的果叶光谱主成分,利用不同物候期的主成分进行了果实糖度回归分析,量化了某单一时期果树生长对果实糖度的贡献比例,并获得了光合作用强度变化等重要信息.利用各物候期的糖度贡献权重对原始果叶糖度敏感光谱进行变换,最终获得带权果叶糖度敏感光谱,并基于该光谱进行了果实糖度预测.分别建立了基于主成分分析的多元线性回归模型以及基于参数优化的支持向量机回归预测模型,结果显示,利用参数优化的支持向量机回归模型获得了较高的糖度预测精度.其测定系数Rc2为0.9202,RMSEC=0.3892 Brix,预测Rv2达到0.9443,均方根误差是0.5246 Brix.利用不同物候期果叶光谱预测苹果糖度的研究结果进一步揭示了果实糖度的积累过程.     

钕基体效应对电感耦合等离子体发射光谱法测定9种微量金属杂质的影响

研究了钕基体效应对电感耦合等离子体发射光谱法测定钕中9种微量金属杂质元素(Na、Mg、Al、K、Ca、Fe、Cr、Zn、Cu)的影响.通过对比筛选多条谱线确定了钕基体中各元素的优选分析谱线,溶液体系酸度影响研究发现酸度对钕基体溶液中各元素强度影响较小,研究了基体浓度对每一个杂质元素谱峰强度和含量测试影响程度及趋势.当钕...     

激光诱导击穿光谱检测青菜中镉元素的多变量筛选研究

利用激光诱导击穿光谱(LIBS)技术与常规化学分析方法获取28个浓度梯度含Cd元素的青菜样品的LIBS谱线信息以及Cd含量信息.对获取的光谱信息结合标准归一化处理(SNV)、一阶导数(FD)、二阶导数(SD)、中心化处理(Center)作为偏最小二乘法(PLS)模型的优选方法;再根据4种预处理方法的预测结果选取最佳方法,同时将该方法作为间隔偏最小二乘法(iPLS)与联合区间间隔偏最小二乘法(SiPLS)优选青菜LIBS谱线的最佳波长区间.结果表明:通过SiPLS优选的特征波长区间分别为214.72 ～ 215.82 nm,215.88～ 216.97 nm,225.08 ～ 226.35 nm,并且经过中心化预处理后建立的验证模型效果最好,结果显示交叉验证均方根误差(RMSECV)为1.487,验证均方根误差(RMSEP)为1.094,相关系数(R)为0.9942,平均相对误差(ARE)为11.60％.研究结果表明,所选优化方法适合青菜中重金属Cd元素的LIBS校正模型的建立,且具有较好的预测效果.     

微波消解-ICP-OES法测定哈氏C-276合金中Cr、Fe、Mo、W元素

建立了微波消解-电感耦合等离子体发射光谱法同时测定哈氏C-276合金中Cr、Fe、Mo、W元素含量的分析方法.采用10 m L HCl-HNO3-HF(体积比为10:1:1)混合酸溶解试样.研究了合金不同溶解方式、元素谱线的选择、背景校正等试验条件,并对仪器分析参数进行了优化,确定了最佳的试验条件,各元素分析谱线依次为Cr2 67.716 nm、Fe 238.204 nm、Mo 202.031 nm、W 209.712 nm,建立的校准曲线各元素相关系数均在0.999 5以上.实际样品分析中,加标回收率为97.8%~102.7%,重复测定结果的相对标准偏差小于1.64%(n=6),试验测定结果与镍基标准样品标准值做对照,结果表明方法准确、快速,能够满足日常生产的检测要求.     

样条变换集成罚函数偏最小二乘方法用于光谱数据重构和定量分析

针对高维小样本光谱数据所显现的函数型数据(Functional data)特性、与性质参数的非线性关系及变量间存有的严重共线性,采用了样条变换集成罚函数偏最小二乘回归新技术.它首先以三次B基样条变换实现非线性光谱数据的线性化重构,随后将重构的新光谱矩阵交由罚函数偏最小二乘法(Penalized PLS)构建其与性质参变量间的校正模型,其中罚函数中的光滑因子由交叉验证优化确定以调控模型的拟合精度.最后,通过小麦样品水分含量的近红外光谱定量分析,结果显示该技术光谱数据重构稳健,去噪明显,并有效解决高维小样本的过拟合和变量间的共线性,而预测集的均方根误差(RMSEP)为0.1808%,方法的非线性校正模型预测能力得到了明显提高.     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.