Kalman filtering-aided time-resolved solid-surface room temperature phosphorimetry for simultaneous determination of tetracyclines in solution

Tetracycline, chlortetracycline and oxytetracycline react with Eu (III) to form complexes which exhibit analytically useful room temperature phosphorescence (RTP). The RTP features of the three complexes are similar and the RTP spectra completely overlap. However, their three phosphorescence decay rates are quite different. These differences are utilized here to analyze the time-resolved RTP data by Kalman filtering. Simultaneous quantification of all the three complexes is demonstrated and a method is proposed for the simultaneous determination of the three tetracyclines in mixtures by RTP optosensing. Analytical errors observed are within ± 5%.     

维生素B的同时测定─—神经网络与紫外光谱法

研究了反向传播神经网络（ＢＰＮＮ）及改进算法，经比较发现ＢＰＮＮ在某些方面优于滤波分辨及多元校正。将其应用于多元分析及光谱定量，可不经分离同时测定Ｂ族维生素，操作简便，结果良好。从而开发了一种多组分同时光谱测定新方法。     

微分脉冲伏安法用于血液中两种核苷类抗病毒药物的同时测定

采用微分脉冲伏安法考察了两种核苷类抗病毒药物阿昔洛韦(aciclovir)和喷昔洛韦(penciclovir)在乙二胺修饰的玻碳电极上的电化学行为及其在代谢血样中的同时测定方法,并探讨了电极修饰和电极反应的机理。在pH2.56的Britton-Robinson缓冲溶液中,阿昔洛韦和喷昔洛韦在乙二胺修饰的玻碳电极上均有一灵敏的不可逆氧化峰,峰电位分别为1.20和1.17 V。在优化的实验条件下,阿昔洛韦和喷昔洛韦分别在0.20~4.0 mg/L和0.02~0.40 mg/L浓度范围内与峰电流呈线性关系,其检出限分别为77和12μg/L。引入化学计量学方法对其混合组分的伏安谱进行解析,实现了两组分的同时测定,并对小鼠血液中代谢的两种核苷类抗病毒药物进行了同时测定。     

Mass spectrometry molecular fingerprinting of mineral and synthetic lubricant oils

The molecular composition of lubricating oils has a strong impact on how automotive engines function, but the techniques used to monitor the quality parameters of these oils only inspect their gross physical–chemical properties such as viscosity, color, and bulk spectroscopy profiles; hence, bad-quality, adulterated, or counterfeit oils are hard to detect. Herein, we investigated the ability of direct infusion electrospray ionization mass spectrometry (ESI-MS) to provide simple, rapid but characteristic fingerprint profiles for such oils of the mineral and synthetic types. After a simple aqueous extraction, ESI-MS analyses, particularly in the positive ion mode, did indeed show characteristic molecular markers with unique profiles, which were confirmed and more clearly visualized by partial least squares-discriminant analysis (PLS-DA). Nuclear magnetic resonance and Fourier transform infrared-attenuated total reflection spectroscopy were also tested for the bulk samples but showed nearly identical spectra, thus failing to reveal their distinct molecular composition and to differentiate the oil samples. To simulate adulteration, mixtures of mineral and synthetic oils were also analyzed by ESI(+)-MS, and additions as low as 1% of mineral oil to synthetic oil could be detected. The technique therefore offers a simple and fast but powerful tool to monitor the molecular composition of lubricant oils, particularly vias their more polar constituents.     

熵最小算法解析中药挥发油GC-MS谱中同分异构体的研究

采用以熵最小算法为基本原理的化学计量学方法,结合气相色谱-质谱联用分析法,对玫瑰精油及茉莉花挥发油中的2对同分异构体重叠峰进行重建分析,并分别得到各组分的重建质谱,同时采用NIST数据库相似度检索、质谱碎片信息比对及程序升温指数对分析得到的各组分进行定性分析。通过分析,分别从玫瑰精油和茉莉花挥发油的GC-MS重叠峰中分离得到1对同分异构体。分析结果显示,采用熵最小算法可以成功地对重叠峰中的各组分进行定性分析。该研究为类似同分异构体混合物中各组分的测定提供了参考。     

Reevaluating the conventional approach for analyzing spectroscopic ellipsometry psi/delta versus time data. Additional statistical rigor may often be appropriate

A standard approach for confirming the stability of thin films consists of probing them over an extended period of time by spectroscopic ellipsometry (SE) and plotting the resulting psi (Ψ) and delta (Δ) values versus time at a few selected wavelengths across the spectral range. In general, if Ψ and Δ remain constant with time, or essentially constant, the material is deemed to be stable. Here, we suggest that in addition to this ‘eyeball’ approach, a statistical analysis of the data may often be appropriate. In particular, we reevaluate a set of Ψ/Δ versus time data from a sputtered bismuth–tellurium–selenium film that appear to remain essentially constant by the traditional approach, subjecting it to a distance analysis, a principal components analysis, and a cluster analysis. The application of these statistical tools, especially to range‐selected data (300–989 nm), reveals previously unobserved changes, suggesting that either the film in question or the analytical approach itself had changed during the course of the measurements. Weighted distance formulas for Ψ and Δ were also applied so that the data did not need to be range selected for the key effects to be observed. The distance approach was similarly applied (i) to a set of SE data from a thin carbon film, which revealed consistent changes in the material that were not apparent in the standard approach, and (ii) to samples that were deliberately contaminated or improperly measured. Thus, we recommend a more rigorous, statistical approach to the analysis of SE Ψ/Δ versus time data. Copyright © 2016 John Wiley & Sons, Ltd.     

Evaluation and comparison of mid-infrared,Raman and near-infrared spectroscopies for characterization and determination of the compositions in fully biodegradable poly(lactic acid)/poly(propylene carbonate)/poly(butylene adipate-co-terephthalate) blends combined with chemometrics

In this work, mid-infrared (MIR), Raman and near-infrared (NIR) spectroscopies were evaluated and compared for characterization and determination of the compositions in poly(lactic acid)/poly(propylene carbonate)/poly(butylene adipate-co-terephthalate) (PLA/PPC/PBAT) blends via chemometrics. Qualitative analysis of MIR, Raman, and NIR spectra of the three compositions was performed. Partial least squares (PLS) models were developed based on each spectroscopy for quantitative determination of the concentrations. The data suggested that MIR and Raman have an advantage over NIR in terms of qualitative recognition of the three compositions. The data also showed that Raman and NIR succeeded in determining the concentrations, while the concentration determined via MIR was inaccurate. Hence, Raman is the optimal analytical tool for qualitative characterization and quantitative determination of the compositions in fully biodegradable PLA/PPC/PBAT blends. The characteristic bands in the Raman spectra clearly identify PLA, PPC, and PBAT to be 392 cm^?1 (δ CCO), 948 cm^?1 (ν C?O?C) and 1600 cm^?1 (ν C ? C in benzene ring), respectively. The optimal calibration models based on Raman for PLA, PPC, and PBAT exhibited root mean square error of prediction (RMSEP) values of 3.140%, 3.576%, and 2.538%, respectively.     

实时直接分析-四极杆飞行时间质谱法快速鉴别油茶籽油真伪

建立了实时直接分析-四极杆飞行时间质谱(DART-QTOF-MS)技术结合化学计量学分析快速鉴别油茶籽油的方法。4种食用油(油茶籽油、菜籽油、花生油和大豆油)用甲醇-异丙醇(50∶50,含5 mmol/L乙酸铵)稀释后经实时直接分析离子源解吸电离,在正离子模式下以TOF MS和信息依赖采集模式获得质谱数据,对4种食用油的质谱图进行了初步鉴定,并采用化学计量学建立主成分分析(PCA)和正交偏最小二乘法-判别分析(OPLS-DA)模型,以实现数据可视化和油茶籽油的快速鉴别。结果表明,4种食用油的质谱图存在明显差异,主要为甘油三酯(TAG)氨加合离子［TAG+NH4］+(m/z 850~1 100)、甘油二酯(DAG)氨加合离子［DAG+NH4］+(m/z 600~700)和DART源内碎片离子,共检出20种甘油三酯和6种甘油二酯。进一步采用化学计量学对4种植物油指纹图谱进行分析,发现该方法可准确鉴别和预测油茶籽油、菜籽油、花生油和大豆油,具有前处理简单、分析速度快、操作方便和准确可靠等优点,可用于油茶籽油的鉴别研究。     

Investigating the effect of flexible constraints on the accuracy of self‐modeling curve resolution methods in the presence of perturbations

Self‐modeling curve resolution methods have continuously been improved during recent years. Many efforts have been made on curve resolution methods to reduce the rotational ambiguity by means of different types of constraints. Choosing proper constraints and cost functions is critically important for the reduction of the rotational ambiguity because the constraints have a direct influence on the accuracy of the area of feasible solution (AFS). In this work, we introduce a new improved cost function, which serves to apply nonnegativity, unimodality, equality, and closure constraints. We also investigate the reduction of the AFS under hard and soft constraints. Another point of this work is to evaluate the accuracy and precision of the reduced AFS in the presence of noise and perturbations, under hard and soft implementation of nonnegativity, unimodality, equality, and closure constraints. A comparison is given between the reduced AFS with soft constraints (small deviations from constraints are accepted) and the reduced AFS under hard constraints (restrictedly forced constraints). A graphical visualization of this comparison is presented for various model problems. The results show that an AFS computation with soft constraints provides more reliable results, especially in the presence of noise. The test problems substantiate significant advantages of soft constraints over hard constraints because the obtained profiles are closer to the potentially true noisy profiles, which contain small deviations from ideal responses. Using tunable parameters ϵ,γ,ω,δ is one of the advantages of soft constrained cost function that allows the small deviations from ideal responses. Ultimately, soft constraints can help to reduce the lack‐of‐fit, and they are a proper instrument to handle the effect of noise on the AFS. Copyright © 2016 John Wiley & Sons, Ltd.     

Controlled Tautomeric Switching in Azonaphthols Tuned by Substituents on the Phenyl Ring

A series of new tautomeric azonaphthols are synthesized and the possibilities for molecular switching are investigated using molecular spectroscopy, X‐ray analysis and density functional theory quantum chemical calculations. Two opposite effects that influence switching are studied: attaching a piperidine sidearm, and adding substituents to the phenyl ring. On the one hand, the attached piperidine moiety stabilizes the enol form leading to a controlled shift of the equilibrium upon protonation. On the other hand, the relative stability of the azonaphthol tautomers strongly depends on the effects of the substituents on the phenyl ring: electron donors tend to stabilize the enol tautomer, whereas electron acceptors lead to stabilization of the keto form. However, these effects do not shift fully the equilibrium towards either of the tautomers. Nevertheless, the effect of the substituents can be an additional tool to affect the switching between “on” and “off” states. Electron‐withdrawing substituents stabilize the keto form and impede switching to the off state, whereas electron donors stabilize the enol form. The effect of the piperidine unit is dominant overall, and with strongly electron‐withdrawing substituents at the phenyl ring, the enol form exists as a zwitterion.