Molar mass and molar mass distribution of polystyrene particle size standards

Monodisperse polystyrene microspheres and nanospheres are often used as particle size standards for calibration of size-measuring instruments. They are potentially useful as the mass standards for particle mass spectrometry as well. We demonstrated in this work that it is possible to achieve high-precision mass determination for single polystyrene spheres using a quadrupole ion trap. We introduced the particles into the trap by laser-induced acoustic desorption and probed them with light scattering. Mass-to-charge ratios of the individual particles were determined from applied trap-driving frequencies, voltage amplitudes and the observed starlike oscillatory trajectories projected on the radial plane. Creation of one-electron differentials through charge-state changes by electron bombardment allowed determination for the absolute mass of a single trapped particle to a precision better than 0.1%. Both molar mass and molar mass distribution were deduced from a large number of measurements for NIST polystyrene particle size standards (SRMs 1690 and 1691). Our results are in excellent agreement with the size measurement for the 0.895-microm spheres (NIST SRM 1690), but a small discrepancy (4%) in number-average mass was found for the 0.269-microm spheres (NIST SRM 1691).     

Effect of metal ions on the molecular weight distribution of humic substances derived from municipal compost: ultrafiltration and size exclusion chromatography with spectrophotometric and inductively coupled plasma-MS detection

The effect of metal ions (Co, Cu, Ni, Pb, Zn) on the molecular weight distribution of humic substances (HSs) obtained from compost is studied. We believe this is the first of this type of study applied in this way to humic substances. Size exclusion chromatography is coupled with two on-line detection systems (spectrophotometric and ICPMS) to study the binding of metal ions by humic substances leached from compost. ICPMS provided highly specific, sensitive, and multielement analytical information that enabled obtaining direct experimental evidence for the participation of metal ions in molecular size distributions of humic compounds. The compost extract or its high molecular weight fraction (>5,000) was put in contact with EDTA or citrate ions, thereby competing with HSs for binding metals. The experiments were carried out by varying the pH maintained by Tris-HCl or CAPS buffer (pH 8.0 and 10.3) and keeping the ionic strength constant. The elution profile of humic substances using UV/ visible detection was compared with those from ICPMS detection of Co, Cu, Ni, Pb, and Zn in the same chromatographic runs. The results obtained suggested that both bridging between small molecules and complexation/ chelation by individual molecules are involved in metal ion binding to humic substances. The use of ICPMS to study the role of metal ions in aggregation/disassociation of humic substances proposed in this work is promising. Coupling element-specific detection with SEC or other separation systems allows better understanding of the mobility and bioaccessibility of elemental species in the environment and further elucidation of the dissolved humic structure.     

Application of the general height equivalent to a theoretical plate equation to size exclusion chromatography. Study of the mass transfer of high-molecular-mass compounds in liquid chromatography

The mass transfer of nonretained, high-molecular-weight polystyrene standards in a chromatographic column packed with 4-microm-diameter silica particles for SEC (average pore size 80 A) and eluted with tetrahydrofuran was investigated. The HETPs of nine polystyrene standards (MW 560, 760, 1780, 3680, 6400, 13,200, 19,300, 31,600, and 90,000) and of ethylbenzene were measured by the method of moments. These HETPs were accounted for by a general HETP equation previously derived for the mass transfer of low-molecular-weight compounds in RPLC (Gritti, F.; Guiochon, G. Anal. Chem. 2006, 78, 5329.). The best fit between the experimental and the theoretical HETPs allowed the estimation of the internal restricted diffusion coefficients of the polymers. The internal diffusion coefficients of the polystyrene standards were also measured, using the peak parking method. Both methods give comparable results and show that the restriction diffusion coefficient gammapKD decreases linearly with increasing logarithm of the polymer mass, from 0.56 for Log MW = 2.0 to 0 for Log MW = 4.8. Interestingly, the C term or limit slope of the high-velocity branch of the HETP curve passes through a maximum (highest mass-transfer resistance) for a polymer mass of 10 kDa. This maximum is well accounted for by the theoretical expression of the trans-particle mass-transfer contribution.     

Nonnegative least-squares truncated singular value decomposition to particle size distribution inversion from dynamic light scattering data

The weak symmetry relationship between the relative error and solution norm holds in our developed nonnegative least-squares truncated singular value decomposition method. By using this relationship to specify the optimal regularization parameters, we applied the proposed algorithm to recover particle size distribution from dynamic light scattering (DLS) data. Simulated results and experimental validity demonstrate that the proposed method, which compliments the CONTIN algorithm, might serve as a powerful and simple approach to the inverse problem in DLS.     

Quantitative LC-MS of polymers: determining accurate molecular weight distributions by combined size exclusion chromatography and electrospray mass spectrometry with maximum entropy data processing

We report on the successful application of size exclusion chromatography (SEC) combined with electrospray ionization mass spectrometry (ESI-MS) and refractive index (RI) detection for the determination of accurate molecular weight distributions of synthetic polymers, corrected for chromatographic band broadening. The presented method makes use of the ability of ESI-MS to accurately depict the peak profiles and retention volumes of individual oligomers eluting from the SEC column, whereas quantitative information on the absolute concentration of oligomers is obtained from the RI-detector only. A sophisticated computational algorithm based on the maximum entropy principle is used to process the data gained by both detectors, yielding an accurate molecular weight distribution, corrected for chromatographic band broadening. Poly(methyl methacrylate) standards with molecular weights up to 10 kDa serve as model compounds. Molecular weight distributions (MWDs) obtained by the maximum entropy procedure are compared to MWDs, which were calculated by a conventional calibration of the SEC-retention time axis with peak retention data obtained from the mass spectrometer. Comparison showed that for the employed chromatographic system, distributions below 7 kDa were only weakly influenced by chromatographic band broadening. However, the maximum entropy algorithm could successfully correct the MWD of a 10 kDa standard for band broadening effects. Molecular weight averages were between 5 and 14% lower than the manufacturer stated data obtained by classical means of calibration. The presented method demonstrates a consistent approach for analyzing data obtained by coupling mass spectrometric detectors and concentration sensitive detectors to polymer liquid chromatography.     

Simultaneous determination of the aerosol complex index of refraction and size distribution from scattering measurements of polarized light

In this study we attempt to determine the aerosol complex index of refraction and size distribution from scattering measurements of polarized light. We illustrate that the scattering matrix elements M(2)(100 degrees ) and D(21) (150 degrees ) can be selected as an optimum set of matrix elements for determination of the complex index of refraction. We also illustrate that errors increase if we include insensitive scattering matrix elements in the determination of the complex index of refraction. A method is developed for the simultaneous determination of the complex index of refraction and the size distribution. In our method, we selected two sets of matrix elements, M (2) (100 degrees ) and D (21) (150 degrees ), for the determination of the complex index of refraction and others, which are much less sensitive to the complex index of refraction than M(2) (100 degrees ) and D(21) (150 degrees ), for the determination of the size distribution, based on their sensitivity analyses. A modified inversion library algorithm is adopted to solve the coupled system. Numerical experiments show that both the complex index of refraction and the size distribution can be determined with reasonable accuracy when we apply our method to scattering measurements of polarized light.     

Limitations of electrospray ionization of fulvic and humic acids as visible from size exclusion chromatography with organic carbon and mass spectrometric detection

A method was developed to link size exclusion chromatography electrospray ionization mass spectrometry (SEC-ESI-MS) analyses of fulvic and humic acids with SEC and organic carbon detection (SEC-OCD), the latter providing an absolute measure of the amount of organic matter eluting from the SEC column. This approach allows us to determine which molecular weight fraction of the complex polydisperse mixtures is detectable by ESI-MS. It could be shown that the cone voltage setting for the ESI interface has strong impact on ESI-MS detection. Using conventional settings for low molecular weight compounds, the high molecular weight (HMW) compounds are hardly amenable to ESI-MS. With increasing cone voltage, an increasing signal intensity is obtained for the HMW fraction that elutes at shorter retention times. However, mostly fragment ions are obtained under these conditions. Thus, the range of compounds amenable to ESI-MS analysis is restricted by the limited stability of the fulvic and humic acid molecules of higher molecular weight in the electrospray process rather than by the mass spectrometer used. Compounds above 1000 amu are hardly visible as intact ions. However, insight into structural characteristics of these compounds can be gained by investigating their fragment ions by SEC-ESI-MS. The use of SEC-OCD parallel to SEC-MS helps to assess and optimize the detection potential of ESI-MS for polydisperse mixtures.     

Application of molecular beam deflection time-of-flight mass spectrometry to peptide analysis

The application of molecular beam deflection time-of-flight mass spectrometry (MBD-TOFMS) to peptide identification is described. The technique permits a simultaneous measurement of molecular mass and electric dipole susceptibility. The mass and susceptibility are not strongly correlated, and the results can be presented as a two-dimensional map. The susceptibility provides a useful way to disperse isobaric and isomeric peptides, and at least for small peptides, the susceptibility is significantly different for different amino acid sequences. Results for peptides in the mass range 1000-2300 Da show that the mass and susceptibility lead to a higher identification score than mass spectra alone.     

On-line coupling of size exclusion chromatography with electrospray ionization-tandem mass spectrometry for the analysis of aquatic fulvic and humic acids

A method was developed for the analysis of humic and fulvic acids by size-exclusion chromatography-electrospray ionization-tandem mass spectrometry using a completely volatile eluent. Humic and fulvic acids were separated into three peaks. These fractions occupied different mass ranges and showed differences in the fine structure of their mass spectra. The low-molecular-weight (LMW) fraction of fulvic acids is most sensitively determined by ESI-MS, and it appears that previous results obtained by infusion-ESI-MS were primarily determined by this fulvic acid fraction. The average molecular weight of this fractions turned out to be lower than that reported from infusion-ESI-MS measurements. Its scan spectra and the product ion spectra of some of its molecular anions perfectly match those previously obtained from whole fulvic acid mixtures. Obviously, a class of well-defined polycarboxylated molecules exist that occurs in all fulvic acid fractions thus far investigated. With decreasing elution time and increasing molecular weight, detection by ESI-MS loses sensitivity as compared to the parallel UV recording, and the fine structure of the scan spectra becomes increasingly uniform for both fulvic and humic acids. The average molecular weight of the HMW fraction exceeds those values calculated from infusion experiments. Scan spectra and product ion spectra of the high-molecular-weight (HMW) fraction of both the humic and the fulvic acids suggest that the HMW fraction consists of several subunits that originate from the LMW fraction.     

高分子量PAN的粒径分布与均匀度关系的考察

对高性能碳纤维原丝性能有重要影响的聚合物粒径均匀度问题目前尚未有人研究过。本研究率先采用沉淀聚合合成高分子量PAN,根据其微观形貌,应用第四统计力学群子统计参数理论研究了聚合物的粒径分布与粒径均匀度的关系,表明粒径均匀度与混合溶剂无关,而与混合溶剂的配比有关,DMSO含量越少,粒径分布越均匀。     

Derivation of the aerosol size distribution from a bistatic system of a muitiwavelength laser with the singular value decomposition method

Estimation of aerosol size distributions from measurements of scattered light intensity by the use of a bistatic system with a multiwavelength laser is presented. We investigated the effects of inversion of the scattered intensity on calculated aerosol size distribution in a numerical experiment. Two model aerosol size distributions were used, one a Junge type widely known as a typical example of the size distribution of suspended particles in the atmosphere and the other a log-normal type as an example of the monodisperse distribution. A singular value decomposition was applied to the inversion to infer the size distribution from the kernel function and the scattered light intensity. In the physical experiment, the size distributions were successfully inferred from analysis of the scattered light intensity from an artificial polystyrene latex aerosol.     

Use of Yb-based catalyst for AGET ATRP of acrylonitrile to simultaneously control molecular mass distribution and tacticity

Yb-based catalyst was used for the first time for atom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) of acrylonitrile (AN) with 2-bromopropionitrile (BPN) as initiator, 2, 2′-bipyridine (bipy) as ligand, and tisn(II) bis(2-ethylhexanoate) (Sn(EH)₂) as reducing agent in the presence of air. With respect to AGET ATRP of AN catalyzed by CuBr₂, an evident increase of polymer tacticity was observed for AGET ATRP of AN. The increase of syndiotacticity became more and more pronounced than the increase of isotacticity of polyacrylonitrile (PAN) along with YbBr₃ content. The block copolymer PAN-b-PMMA with molecular weight at 60,000 and polydispersity at 1.36 was successfully prepared.     

On-line preconcentration prior to on-column derivatization monolith octadecasiloxane capillary electrochromatography for the determination of biogenic amines

To expand the applications of the on-line preconcentration technique with capillary electrochromatography (CEC) to biogenic amines that have no specific chromophore or fluorophore in their molecules, a method of on-line preconcentration prior to on-column derivatization CEC is presented. A monolithic ODS capillary column (20 cm effective length x 75 microm i.d.) for CEC was fabricated using a thermal sol-gel reaction of tetraethyl orthosilicate to capture ODS particles (5-microm particle diameter) in a capillary tube. A standard model biogenic amine solution consisting of histamine, methylhistamine, and serotonin was electrokinetically injected from the anodic site of the capillary column with 5 kV, and these amines were effectively concentrated at the inlet site of the capillary column by a field-amplified sample stacking, a gradient effect mode, or both. This preconcentration occurred whenever the several types of solvent for reconstitution of the amines, e.g., water (noneluting solvent or low-conductivity solvent), 0.9% sodium chloride (noneluting solvent or high-conductivity solvent), or 60% acetonitrile in 10 mM borate buffer (pH 10) (eluting solvent) were employed. After concentration, the amines were subsequently derivatized, separated, and detected during CEC with an optimum CEC run buffer solution containing 60% acetonitrile in 5 mM o-phthalaldehyde/2-mercaptoethanol-10 mM borate buffer (pH 10) when 5 kV was continuously applied. Using the present system, equipped with a fluorescence detector instead of a UV/visible detector, the detection sensitivity for amines reached a 0.1 microM level, which increased sensitivity by a factor of 10(3) times greater than that of normal on-column derivatization CEC.     

Recycling size exclusion chromatography for the analysis and separation of nanocrystalline gold

Recycling size exclusion chromatography (RSEC) provides a high-resolution technique for the analysis and separation of materials based on size. We show here the application of this method to gold nanocrystals stabilized by thiols. Alternate recycling is more effective at separating nanomaterials as compared to closed-loop recycling because of its improved efficiency and high resolution. With the use of this technique, we find the resolution ratio of nanocrystal separation increases with the square root of the cycle number, in good agreement with theory. The increased resolution of the size exclusion chromatograms permits the use of RSEC in the baseline separation of nanocrystals which differ by only 6 A in size. In addition to separations, RSEC is valuable as an analytical tool. For example, after recycling processes an initially broad and chromatographic feature from a gold nanocrystal solution resolves into three distinct peaks. Transmission electron microscopy of collected fractions reveals that these peaks correspond to distinct populations of gold nanoparticles with narrowly defined sizes.     

由 Mie 散射光强反演颗粒粒度分布的一种改进正则化法

基于Mie散射的激光粒度仪广泛地应用在颗粒粒度测量中,其中由光强分布演算出粒度分布的计算方法一直是关注的热点。此反演问题属于第一类Fredholm算子方程,具有不适定性,难以得出准确的稳定解,需要用高效的数值算法。本文提出一种应用于该类仪器颗粒粒度分布反演问题的改进正则化法,采用广义交叉验证法(GCV)来选择正则参数,并引入松弛技术,将迭代值加工成一种松弛值以改善精度,得出了稳定的正则拟解(近似解)。经标准颗粒的验证和计算机模拟证实,此算法是可行和有效的。     

臭氧预氧化对城市二级处理水中残留有机物分子量分布的影响及超滤膜阻力变化分析

利用对城市二级处理水进行了臭氧预氧化,测定了水中残留有机物的分子量分布,并采用PVDF超滤膜对不同分子量分布的二级处理水进行了过滤.结果发现,水中有机物的分子量分布对膜的阻力构成影响很大,堵孔阻力和滤饼阻力对膜污染阻力起控制作用,有机物分子量分布与膜阻力之间有如下关系:1)2/151特别是d/>5/3的有机物则是形成膜表面滤饼的主体.     

Application of liquid chromatography/quadrupole-linear Ion trap mass spectrometry and time-of-flight mass spectrometry to the determination of pharmaceuticals and related contaminants in wastewater

This paper describes an enhanced liquid chromatography-mass spectrometry (LC-MS) strategy for the analysis of a selected group of 56 organic pollutants in wastewater. This group comprises 38 pharmaceuticals and 10 of their most frequent metabolites, 6 pesticides, and 2 disinfectants. The LC-MS methodology applied is based in the use of a hybrid triple-quadrupole linear ion trap mass spectrometer (QTRAP) in combination with time-of-flight mass spectrometry (TOF-MS). The join application of both techniques provided very good results in terms of accurate quantification and unequivocal confirmation. Quantification was performed by LC-QTRAP-MS operating under selected reaction monitoring (SRM) mode in both positive and negative electrospray ionization. Unequivocal identification was provided by the acquisition of three SRM transitions per compound in most of the cases and by LC-TOF-MS analysis, which allows obtaining accurate mass measurements of the identified compounds with errors lower than 2 ppm. Additionally, the use of TOF-MS permits retrospective analysis, since the full spectrum is recorded at all times with a high sensitivity. Thus, review of recorded chromatograms looking for new compounds or transformation products suspected to be present in the samples is feasible allowing one to increase the scope of the method along the monitoring program. The analytical performance of the quantitative LC-QTRAP-MS method was evaluated in effluent wastewater samples. Linearity of response over 3 orders of magnitude was demonstrated for most compounds (R(2) > 0.99). Method limits of detection were between 0.04 and 50 ng L(-1). Finally, the methodology was successfully applied to a monitoring study intended to characterize wastewater effluents of six sewage treatment plants in Spain. The presence of most of compounds was detected at concentrations ranging from 9 ng L(-1) (atrazine) to 15 microg L(-1) (paraxanthine).