基于计算最大差异光谱的目标转换因子分析用于解析混合物红外光谱

基于因子分析的目标转换法[1]利用抽象光谱构成的矩阵具有使纯物种光谱向自身逐步逼近的性质[2],用于混合物红外光谱的解析,简单明确[3]．在进一步的探索中,我们发现该算法对原始光谱的构成具有较强的依赖性．本文特别构造了这样的体系,即在混合物样品中剔除了某一物种占优势的样品,应用新算法后,避免了对采样的依赖性．1方法与原理根据自模拟曲线分辨算法（SelfModelingCurveResolution,SMCR）[4~6],纯物种光谱可写成式中,Akj为抽象正交光谱,Xik为系数,Fij为纯物种光谱,n为物种数．根据吸光度不能为负这一限制条件,可以…     

目标识别因子分析解析完全未知混合体系的研究

本文以目标识别因子分析为基础, 将因子分析与聚类分析相结合, 给出了从完全未知混合体系中提取纯物种光谱的新方法。所得纯物种光谱经光谱检索作定性判别, 然后利用外标法对混合物中的各组份进行标定。该方法用于计算机模拟体系及三组份实际混合体系的红外光谱解析, 结果令人满意。     

一种检测溶液中高浓度物种的边带差分吸收光谱方法

本发明属于分析化学和工业监控领域,涉及一种检测溶液中高浓度物种的边带差分吸收光谱方法。以已知目标物种浓度的溶液为参比溶液,且参比溶液所含目标物种的浓度大于待测样品溶液中目标物种的浓度。待测样品溶液的吸收光谱是与上述参比差分的结果,吸收峰位于以试剂空白为参比的传统吸收光谱的边带区域。吸收峰波长处的样品溶液与参比的差分吸光度与样品浓度的关系符合朗伯比尔定律,由此确定待测样品溶液的浓度。本发明提供的方法检测高浓度样品时不需要稀释样品,且差分吸收光谱位于传统吸收光谱的边带区域,检测波长一般会红移,所以不加显色剂即可实现,操作简便。     

傅里叶变换用于铁和锌的同时光度测定

研究了傅里叶变换技术用于铁锌二组分的同时分光光度测定，采用傅里叶变换对吸光度数据进行预处理，再结合目标转换因子分析或偏最小二乘分析，结果较普通的目标转换因子分析或偏最小二乘法有显著改善。以傅里叶变换－偏最小二乘法就用于实际铝合金样品中铁和锌的同时测定，结果令人满意。     

目标转换因子分析与库检索相结合用于红外混合体系定性分析

将库检索与目标转换因子分析相结合利用抽象浓度的分布信息确定可能解域，其最大可能解即为体系包含的物种。可能解域的确定大大减少了计算量，应用于严重重叠的甲苯和乙苯二组份和苯，甲苯及乙苯三组份混合体系，结果令人满意。     

卡尔曼滤波光谱法用于化学平衡研究

提出了光谱法与卡尔曼滤波及因子分析相结合的新方法以研究化学平衡,将复杂的化学平衡视为特殊的多组分混合体系,其中各物种在不同介质中存在相互的平衡,卡尔曼滤波及因子分析被用作有效的化学计量学分辨工具,从光谱数据中提取信息,已用于确定所存在的物种数目和浓度以及平衡常数,本文以部分三苯甲烷试剂为例确定其酸碱平衡常数。     

基质固相分散技术在兽药残留分析中的应用

基质固相分散技术是对痕量化合物分析时应用的一种样品前处理技术,它能够直接用于从固态、半固态和粘稠基质样品中提取目标化合物,具有样品和溶剂用量少、分析时间短及提取和净化过程一步完成等优点.本文主要介绍了该技术的原理及其在兽药残留分析中的应用.     

迭代目标转换因子分析光度法用于地质样品中15个稀土元素同时测定的研究

本文以三溴偶氮氯膦(TB-CPA)为显色剂,采用迭代目标转换因子分析(ITTFA)法,对地质样品中15个稀土元素进行同时测定,分析结果的相对误差小于15％;标准偏差为3.8×10~(-4)～5.5×10~(-2);相对标准偏差为0.22～3.5％;各元素的检测下限为(1.0～3.0)×10~(-8)。本文采用模式识别方法,用欧氏距离和方差作为分类特征,进行未知样品分析结果的可靠性判别。初步证明因子分析光度法用于解决复杂地质样品分析是可行的。还对目标向量的构成,最佳主因子数的确定对计算结果的影响等问题作了讨论。     

校正变换矩阵法及其在多组分直接同时测定中的应用

将目标变换因子分析中自由浮动技术引入多元校准中，提出了一种新的多组分同时校准法———校正变换矩阵法。该法用于四组分氨基酸人工混合样品分析，结果令人满意，通过与传统目标变换因子分析法比较研究，表明该法用于组分光谱严重共线的波长范围时，其校准能力大大优于传统目标变换法。     

迭代目标转换因子分析法在光度分析中的应用研究——用三溴偶氮氯膦同时测定15个稀土元素

以三溴偶氮氯膦为显色剂,应用迭代目标转换因子分析光度法对15个稀土元素混合物合成样品进行同时测定,结果的平均相对误差为2.9％～5.6％。对标准数据阵的构成。主因子数的确定以及组份间浓度比对计算结果的影响等问题作了讨论。     

Enhanced target factor analysis

Target testing or target factor analysis, TFA, is a well-established soft analysis method. TFA answers the question whether an independent target test vector measured at the same wavelengths as the collection of spectra in a data matrix can be excluded as the spectrum of one of the components in the system under investigation. Essentially, TFA cannot positively prove that a particular test spectrum is the true spectrum of one of the components, it can, only reject a spectrum. However, TFA will not reject, or in other words TFA will accept, many spectra which cannot be component spectra. Enhanced Target Factor Analysis, ETFA addresses the above problem. Compared with traditional TFA, ETFA results in a significantly narrower range of positive results, i.e. the chance of a false positive test result is dramatically reduced. ETFA is based on feasibility testing as described in Refs. [16–19]. The method has been tested and validated with computer generated and real data sets.     

Fmoc solid-phase synthesis of peptide thioesters using an intramolecularn,S-acyl shift

[reaction: see text] We describe the Fmoc solid-phase synthesis of peptide thioesters based on the alkylation of the safety-catch sulfonamide linker with a protected 2-mercaptoethanol derivative. The thioester is generated on the solid phase after the peptide chain assembly as a consequence of an intramolecular N,S-acyl shift. Depending on the stability of the spacer separating the sulfonamide linker from the resin toward TFA, treatment of the peptidyl resin with TFA led to a soluble or supported deprotected thioester.     

Evaluation of gaseous hydrogen fluoride as a convenient reagent for parallel cleavage from the solid support

We have tested the limits of gaseous hydrogen fluoride as an agent for parallel detachment of organic molecules from the solid support. Peptides were chosen as relatively sensitive models for this reaction. Acid-catalyzed amide bond hydrolysis, side chain modification (tryptophan and other unnatural amino acids) by the protecting group residues as well as dehydration of serine and asparagine was followed. The technique of cleavage of side chain protection prior to the resin cleavage has given satisfactory results. Two-step deprotection and cleavage from benzhydrylamine resin by TFA and HF was compared to the deprotection and cleavage by TFA from Knorr resin.     

Chiral Modification of Platinum by Co‐Adsorbed Cinchonidine and Trifluoroacetic Acid: Origin of Enhanced Stereocontrol in the Hydrogenation of Trifluoroacetophenone

Cinchonidine (CD) adsorbed onto a platinum metal catalyst leads to rate acceleration and induces strong stereocontrol in the asymmetric hydrogenation of trifluoroacetophenone. Addition of catalytic amounts of trifluoroacetic acid (TFA) significantly enhances the enantiomeric excess from 50 to 92 %. The origin of the enantioselectivity bestowed by co‐adsorbed CD and TFA is investigated by using in situ attenuated total reflection infrared spectroscopy and modulation excitation spectroscopy. Molecular interactions between the chiral modifier (CD), acid additive (TFA) and the trifluoro‐activated substrate at the solid–liquid interface are elucidated under conditions relevant to catalytic hydrogenations, that is, on a technical Pt/Al₂O₃ catalyst in the presence of H₂ and solvent. Monitoring of the unmodified and modified surface during the hydrogenation provides an insight into the phenomenon of rate enhancement and the crucial interactions of CD with the ketone, corresponding product alcohol, and TFA. Comparison of the diastereomeric interactions occurring on the modified surface and in the liquid solution shows a striking difference for the chiral preferences of CD. The spectroscopic data, in combination with calculations of molecular structures and energies, sheds light on the reaction mechanism of the heterogeneous asymmetric hydrogenation of trifluoromethyl ketones and the involvement of TFA in the diastereomeric intermediate surface complex: the quinuclidine N atom of the adsorbed CD forms an N?H?O‐type hydrogen‐bonding interaction not only with the trifluoro‐activated ketone but also with the corresponding alcohol and the acid additive. Strong evidence is provided that it is a monodentate acid/base adduct in which the carboxylate of TFA resides at the quinuclidine N‐atom of CD, which imparts a better stereochemical control.     

A facile strategy to prevent trifluoroacetylation of N-terminal proline peptides

Unwanted trifluoroacetylation occurred at the N-terminus of prolinyl peptides during detachment from the solid phase. This was observed when the N-α-Fmoc protecting group had been removed prior to the final TFA treatment. Subtly changing the SPPS protocol and incorporating Boc- in place of the Fmoc-protected proline as the N-terminal building block efficiently suppressed this side reaction.     

Traceless azido linker for the solid-phase synthesis of NH-1,2,3-triazoles via Cu-catalyzed azide-alkyne cycloaddition reactions

A broadly useful acid-labile traceless azido linker for the solid-phase synthesis of NH-1,2,3-triazoles is presented. A variety of alkynes were efficiently immobilized on a range of polymeric supports by Cu(I)-mediated azide-alkyne cycloadditions. Supported triazoles showed excellent compatibility with subsequent peptide chemistry. Release of pure material (typically >95%) from the solid support was readily achieved by treatment with aqueous TFA.     

Gas chromatography of metal chelates with carrier gas containing ligand vapour

The vapour of the ligand was used as carrier-gas additive in the gas chromatography of metal chelates. The effect of trifluoro-acetylacetone on non-symmetrical peaks was examined for Be(TFA)(2), Al(TPA)(3) Cr(TFA)(3), Pe(TFA)(3), U(TFA)(4) and Th(TFA)(4). All the chromatograms appeared quite normally especially those of Th(TFA)(4); Fe(TFA)(3) and Th(TFA)(4) were improved markedly by using the carrier gas containing ligand vapour.     

An improved palladium(II)-catalyzed method for the synthesis of aryl ketones from aryl carboxylic acids and organonitriles

A palladium(II)-catalyzed decarboxylative protocol for the synthesis of aryl ketones has been developed. The addition of TFA was shown to improve the reaction yield and employing THF as solvent enabled the use of solid nitriles and in only a small excess. Using this method, five different benzoic acids reacted with a wide range of nitriles to produce 29 diverse (hetero)aryl ketone derivatives in up to 94% yield.     

Facile synthesis and cleavage of imidazolidines in a novel protection strategy for the preparation of peptides containing a reduced amide bioisostere

Unsymmetrical imidazolidines were obtained in 75-91% yield by treating monoalkoxycarbonyl vicinal diamines at room temperature with aqueous 37% formaldehyde in the presence of Montmorillonite KSF as a solid catalyst. The imidazolidines were shown to be useful intermediates in a novel protection strategy for the synthesis of peptide analogues containing a reduced glycine amide bioisostere. The imidazolidine intermediate was cleaved conveniently and efficiently by 50% TFA in methylene chloride.     

Inverse temperature-dependent pathway of cellulose decrystallization in trifluoroacetic acid

An unusual inverse temperature-dependent pathway was observed during cellulose decrystallization in trifluoroacetic acid (TFA). Decreasing the TFA treatment temperature accelerated the cellulose decrystallization process. It took only 100 min to completely decrystallize cellulose at 0 degrees C in TFA, a result not achieved in 48 h at 25 degrees C in the same medium. There was neither cellulose esterification nor a change of cellulose macrofibril morphology by TFA treatment at 0 degrees C. Our IR data suggest that TFA molecules are present as cyclic dimers when they penetrate into crystalline cellulose regions, transforming crystalline cellulose to amorphous cellulose. On the other hand, the rate of TFA penetration into the cellulose matrix was greatly retarded at higher temperatures where monomeric TFA prevails. At elevated temperatures, esterification of TFA monomers on the external surface of crystalline cellulose, agglomeration of cellulose macrofibrils, as well as water released from the esterification reaction, inhibit the diffusion rate of TFA into the cellulose crystalline region and decrease the TFA swelling capability.