Using a Buffer Gas Modifier to Change Separation Selectivity in Ion Mobility Spectrometry

The mobilities of a set of common α-amino acids, four tetraalkylammonium ions, 2,4-dimethyl pyridine (2,4-lutidine), 2,6-di-tert-butyl pyridine (DTBP), and valinol were determined using electrospray ionization-ion mobility spectrometry-quadrupole mass spectrometry (ESI-IMS-QMS) while introducing 2-butanol into the buffer gas. The mobilities of the test compounds decreased by varying extents with 2-butanol concentration in the mobility spectrometer. When the concentration of 2-butanol increased from 0.0 to 6.8 mmol m(-3) (2.5×10(2) ppmv), percentage reductions in mobilities were: 13.6% (serine), 12.2% (threonine), 10.4% (methionine), 10.3% (tyrosine), 9.8% (valinol), 9.2% (phenylalanine), 7.8% (tryptophan), 5.6% (2,4-lutidine), 2.2% (DTBP), 1.0% (tetramethylammonium ion, TMA, and tetraethylammonium ion, TEA), 0.0% (tetrapropylammonium ion, TPA), and 0.3% (tetrabutylammonium ion, TBA). These variations in mobility depended on the size and steric hindrance on the charge of the ions, and were due to formation of large ion-2-butanol clusters. This selective variation in mobilities was applied to the resolution of a mixture of compounds with similar reduced mobilities such as serine and valinol, which overlapped in N(2)-only buffer gas in the IMS spectrum. The relative insensitivity of tetraalkylammonium ions and DTBP to the introduction of 2-butanol into the buffer gas was explained by steric hindrance of the four alkyl substituents in tetraalkylammonium ions and the two tert-butyl groups in DTBP, which shielded the positive charge of the ion from the attachment of 2-butanol molecules. Low buffer gas temperatures (100 °C) produced the largest reductions in mobilities by increasing ion-2-butanol interactions and formation of clusters; high temperatures (250 °C) prevented the formation of clusters, and no reduction in ion mobility was obtained with the introduction of 2-butanol into the buffer gas. Low temperatures and high concentrations of 2-butanol produced a series of ion clusters with one to three 2-butanol molecules in compounds without steric hindrance. Clusters of two and three molecules of 2-butanol were also visible. Ligand-saturation on the positive ions with 2-butanol molecules occurred at high concentrations of modifier (6.8 mmol m(-3) at 150°C); when saturated, no further reduction in mobility occurred when 2-butanol was introduced into the buffer gas.     

单纯形优化高效液相色谱法分离测定维生素E的各种异构体

本文用计算机辅助单纯形优化高效液相色谱法分离、测定了精炼植物油副产物中维生索E的各种异构体。探讨了单纯形优化法指导高效液相色谱选择分离的实验条件,并编写了实用的计算机程序。实验结果表明,本法可使比较困难的条件选择工作有章可循,从而提高工作效率。     

反应法去除近共沸浓度乙醇-水混合物中水的宏观动力学研究

 针对乙醇汽油制备过程中乙醇原料的除水问题,提出了用反应法除去近共沸浓度乙醇中水的新技术路线,着重进行了近共沸乙醇-水混合物与异丁烯水合醚化反应的宏观反应动力学研究. 实验以β分子筛为催化剂,在2.0 MPa和313～363 K的条件下考察了搅拌速度、乙醇中初始水含量、烯水比和温度等因素对水的转化率和叔丁醇选择性的影响. 结果表明,乙醇对异丁烯水合反应有先促进后抑制的作用,而水对异丁烯醚化反应影响较小; 水的转化率随烯水比的增大而增大,随乙醇中初始水含量的增大而减小,随着温度的升高呈现先增大后减小的趋势. 叔丁醇的选择性随初始水含量的增大而增大. 基于实验结果和Langmuir-Hinshelwood-Hougen-Watson理论,充分考虑反应体系的高度非理想性,以活度代替浓度建立了宏观反应动力学模型; 采用混合进化算法对模型进行求解,结果表明模型计算值与实验值可较好地吻合.     

A Two Factor Simplex Optimization of An Ion Pair Liquid Chromatographic Separation

Abstract

A simple two factor simplex is used to optimize the separation of several ionic naphthylamines by varying the pH and percent methanol in the eluting solvent.     

Optimization of Phytosterols Dispersion in an Oil/Water Emulsion Using Mixture Design Approach

Major problems related to enrichment of products with phytosterols are high melting temperature, chalky taste and low solubility in water phase. Dispersion of phytosterols in an emulsion was optimized using a mixture design with four components (phytosterols, emulsifier, soy oil, and water). It was found that the particle size of the dispersed phase decreased with the increase in emulsifier concentration. The appearance viscosity was increased with decreasing particle size. The stability of these emulsions could be correlated with the decrease in surface tension and particle size by using oil and emulsifier as components of oil phase.     

用MATLAB简化溶液氢离子浓度计算的教学内容

溶液氢离子浓度计算涉及大量公式及繁杂的使用条件,是公认的教学重点和学习难点。将分布分数代入质子条件式即得关于氢离子浓度的一元高次方程,可用MATLAB方便地求解。因此,只要会写质子条件式就能迅速得到氢离子浓度,从而摆脱大量公式的烦扰,便于学生将精力更有效地集中于分析化学主体知识的学习。     

Correlation between the Limiting pH of Metal Ion Solubility and Total Metal Concentration

As an alternative to species distribution diagrams (pM vs pH curves in aqueous solution) drawn for a fixed total metal concentration, this work has developed simple linear models for correlating the limiting pH of metal ion solubility-in equilibrium with the least soluble amorphous metal hydroxide solid phase-to the total metal concentration. Thus adsorptive metal removal processes in complex systems can be better designed once the limiting pH of heavy metal solubility (i.e., pH*) in such a complex environment can be envisaged by simple linear equations. pH* vs pMt (Mt = total metal concentration that can exist in aqueous solution in equilibrium with M(OH)2(s)) linear curves for uranyl-hydroxide, uranyl-carbonate-hydroxide, and mercuric-chloride-hydroxide simple and mixed-ligand systems and cupric-carbonate-hydroxide complexes in equilibrium with mixed hydroxide solid phases may enable the experimental chemist to distinguish true adsorption (e.g., onto hydrous oxide sorbents) from bulk precipitation removal of the metal and to interpret some anomalous metal fixation data-usually attributed to pure adsorption in the literature-with precipitation if the pMt at the studied pH is lower than that tolerated by pH* vs pMt curves. This easily predictable pH* corresponding to a given pMt may aid the design of desorptive mobilization experiments for certain metals as well as their adsorptive removal with the purpose of simulating metal adsorption and desorption cycles in real complex environments with changing groundwater pH. Copyright 1999 Academic Press.     

直接电位法测定中电动势与离子浓度的关系

针对理论公式和实测数据不一致的原因进行探究,发现：理论公式是以复合电极中参比电极连接正极的条件来推导的,而实验中复合电极连接正极的不是参比电极,而是指示电极。进一步探讨了待测物质是阴、阳离子的情况下,电动势与离子浓度的关系式：E电池=K±0.059 2/nlgci,得到：（1）前式中K后面的符号是“+”还是“-”,也就是说电动势随待测离子浓度的增加是上升还是下降,不仅取决于离子本身的电荷性,还取决于指示电极和参比电极跟仪器的正负极连接情况;（2）标准比较法和标准加入法的定量计算,也需要考虑K后面的正负符号,不同情况下,推导出的定量公式也不一样,建议联立能斯特方程求解样品含量。     

Aromatic Interactions in Organocatalyst Design: Augmenting Selectivity Reversal in Iminium Ion Activation

Substituting N‐methylpyrrole for N‐methyindole in secondary‐amine‐catalysed Friedel–Crafts reactions leads to a curious erosion of enantioselectivity. In extreme cases, this substrate dependence can lead to an inversion in the sense of enantioinduction. Indeed, these closely similar transformations require two structurally distinct catalysts to obtain comparable selectivities. Herein a focussed molecular editing study is disclosed to illuminate the structural features responsible for this disparity, and thus identify lead catalyst structures to further exploit this selectivity reversal. Key to effective catalyst re‐engineering was delineating the non‐covalent interactions that manifest themselves in conformation. Herein we disclose preliminary validation that intermolecular aromatic (CH–π and cation–π) interactions between the incipient iminium cation and the indole ring system is key to rationalising selectivity reversal. This is absent in the N‐methylpyrrole alkylation, thus forming the basis of two competing enantio‐induction pathways. A simple L ‐valine catalyst has been developed that significantly augments this interaction.     

Analysis of Air Toxic Compounds by Using Chromatography and Computer-Assisted FTIR Intelligent Method

In the Title Ⅲ of Clean Air Act Amendments of 1990,a list of 189 air toxic compounds were identified to be controlled from stationary source emissions,which means that US EPA must have the capability to quantitatively measure the emissions of these pollutants. FTIR is considered to have great potential in measurement emissions of substantial number of toxic organic air pollutants of interest to US EPA. However,not much of the FTIR work was conducted for stationary source emissions, and too little is known about its applicability and reliability for monitoring toxic air pollutant source emissions. US EPA needs a worldwide international cooperation to understand the advantages and disadvantages of FTIR and signed the cooperative agreement with us in 1994:Research on FTIR (Including its Utility) for Monitoring Toxic Air Pollutants in Stack Gas Emissions (Contract No.:CR822820-01).     

Computer-Assisted HPLC Method Development for Determination of Tolmetin and Possible Kinetic Modulators of Its Oxidative Metabolism in Vivo

Following administration of the acidic drug tolmetin (TOL) anaphylactic reactions occurred, which have been hypothesized to be related to the formation of reactive acyl glucuronides. Recently, glutathione adducts have been detected upon incubation of TOL with human liver microsomal preparations, which proved that oxidative activation might also be a pathway of formation of reactive—possibly toxic—glutathione metabolites of TOL. The aim of this work was to develop a new and robust HPLC method to investigate the in vivo effect of 2 coadministered drugs/nutritional supplements on the kinetics of TOL in rats (cimetidine; CIM) known to be a potent inhibitor of CYP3A4, an enzyme that catalyzes the oxidative metabolism and Quercetin; and QUE which induces UGT1A6, an enzyme involved in glucuronidation of acidic drugs. DryLab^®, a computer simulation software package, was used to assist in the development and optimization of the HPLC method used for separation of TOL and the two potential kinetic modulators together with three potential internal standards (zomepirac, carvedilol and fexofenadine). The method was validated in biological samples obtained from rats. Non-compartmental pharmacokinetic analysis of data obtained from plasma and rat liver tissue showed significantly higher concentrations of TOL in the presence of CIM; and significantly longer elimination half-life lives in presence of QUE, which implies that drugs or food components interacting with CYP3A4 cause alteration in the metabolic oxidative biotransformation of TOL in vivo leading to accumulation of TOL in the body through a decrease of its clearance. These findings might account for to the side-effects associated with TOL when co-administered with such kinetic modulators.

     

Effects of pH and Concentration on Cs Ions Sorption and Diffusion in Crushed Granite by Using Batch and Modified Capillary Method

A comprehensive evaluation of Cs ions sorption to and diffusion in crushed granite was conducted in this study. The sorption capacity of crushed granite suggested by the Langmuir model was 5.48 × 10^?6 mol‐Cs/g‐granite. The distribution coefficient (Kd) was around 7.5 mL/g and pH independent. By using an in‐diffusion method with a modified capillary column, some diffusion relevant parameters of Cs ions in crushed granite were derived. The apparent diffusion coefficient (Da) seemed unaffected by Cs concentration (1.15 × 10^?10 to 2.82 × 10^?10 m²/s, at 10^?7 and 10^?3 M, respectively). The determined effective diffusion coefficients (De) were located in the window from 8.59 × 10^?10 (10^?7 M) to 1.69 × 10^?9 (10^?3 M) m²/s. Under various pH environments, pH independent Da (9.0 × 10^?9 m²/s) and De (1.0 × 10^?9 m²/s) values were observed. Under current systems, consistently higher De than Da implied the diffusion of Cs ions was governed by surface diffusion phenomenon. Whereas the pH insensitive feature indicated the Cs sorption to crushed granite was mainly through ion‐exchange reaction. Moreover, further SEM/EDS mapping clearly showed the adsorbed Cs ions were highly concentrated on the fracture surface of biotite.     

Optimization of two-factor(pH and ion concentration)simultaneous selection in HPLC using a statistical method

A computer-assisted method is presented for simultaneous optimization of pH and ion con-centration selection for the optimal separation in reversed-phase HPLC.The method is based on apolynomial estimation from nine preliminary experiments according to two-factor rectangular design.This is followed by a two-dimension computer scanning technique.Resolution is used as the selectioncriterion.Good agreement was obtained between predicted data and experimental results.     

Simultaneous Optimization of Variables in Fia Systems by Means of the Simplex Method

Abstract

A response function (RF) in order to simultaneously optimize different variables by the SIMPLEX method in FIA systems, with the possibility of applying weights, is proposed. The optimization program developed to use this RF is assayed in the optimization of two different flow injection procedures. The obtained results are discussed.     

Optimization of Wall Material of Freeze-Dried High-Bioactive Microcapsules with Yellow Onion Rejects Using Simplex Centroid Mixture Design Approach Based on Whey Protein Isolate,Pectin, and Sodium Caseinate as Incorporated Variables

For the food sector, onion rejects are an appealing source of value-added byproducts. Bioactive compounds were recovered from yellow onion rejects using a pulse electric field process at 6000 v and 60 pulses. The onion extract was encapsulated with whey protein isolate (WPI), pectin (P), and sodium caseinate (SC) with a mass ratio of 1:5 (extract/wall material, w/w). A Simplex lattice with augmented axial points in the mixture design was applied for the optimization of wall material for the encapsulation of onion reject extract by freeze-drying (FD). The optimal wall materials were 47.6 g/100 g (SC), 10.0 g/100 g (P), and 42.4 g/100 g (WPI), with encapsulation yield (EY) of 85.1%, total phenolic content (TPC) of 48.7 mg gallic acid equivalent/g DW, total flavonoid content (TFC) of 92.0 mg quercetin equivalent/g DW, and DPPH capacity of 76.1%, respectively. The morphological properties of the optimal encapsulate demonstrated spherical particles with a rough surface. At optimal conditions, the minimum inhibitory concentration (MIC) of the extract (mean diameter of inhibition zone: 18.8 mm) was shown as antifungal activity against Aspergillus niger.     

Concentration Polarization and Specific Selectivity of Membranes in Pulse Mode

Nonstationary concentration polarization of membranes was analyzed theoretically. Desalination and transport of single- and double-charged ions through MK-40 cation-exchange membrane was studied in the stationary and pulse modes with the fixed voltage. Main generalities in the changes of the pH and conductivity of desalinated solution as well as concentrations of single- and double-charged ions as the functions of solution flow velocity, voltage, frequency and off-duty ratio of pulses were established.     

单纯形最优化法测定三元配合物组成比的研究

本文运用单纯形最优化法，测定了Ｖ（Ｖ）－ＰＡＲ－Ｈ２Ｏ２以及Ｗ（Ⅵ）ＰＶ－ＣＴＭＡＢ三元配合物的组成比。提出了对应于三元配合物的λｍａｘ处二元配合物也有部分吸收时的二种处理办法及体系最初酸度调节的新看法，并经上述三元配合物体系，验证了方法的可行性，进一步完善了单纯形最优化法测配合物组成比这一手段。     

Simplex Optimization for the Simultaneous HPLC Assay of the Activities of Purine-Nucleoside Phosphorylase and Hypoxanthine-Guanine Phosphoribosyl Transferase

Abstract

The modified sequential simplex procedure is shown to be effective for maximizing a complex enzyme assay. The optlmum levels for two factors, pH and substrate concentration, for a coupled enzyme assay of hypoxanthine-quanlne phosphor Ibosy I-transferase (HGPRTase) and purine nucleoside phosphorylase (PNPase) were found by searching a factor space made up of these variables. The performance Index or response to be optimized was a function of the product of the two single activities. The maximum activity for this function was found at a pH of 7.9 and a concentration of Inosine in the reaction mix of 0.84 mM.     

HPLC Determination of Iodide in Scrum Using Paired Ion Chromatography with Electrochemical Detection

Abstract

HPLC utilizing paired ion chromatography with electrochemical detection is used for the determination of iodide in serum. Serum samples are prepared by precipitation of protein, centrifugation and removal of Interfering substances with a bonded phase column. The resulting sample is then analyzed. The method has successfully been applied to human serum and gives data that agrees well with values obtained by other methods. The method is accurate precise, and time conservative when compared to more classical methods.     

分析化学计算中单纯形法一种新的收敛准则研究

本文根据误差理论提出了单纯形法收敛准则的一种改进,导出了收敛精度计算式,并用实验进行了验证。