Simultaneous quantification of human cardiac alpha- and beta-myosin heavy chain proteins by MALDI-TOF mass spectrometry

We have developed a novel method for quantifying protein isoforms, in both relative and absolute terms, based on MALDI-TOF mass spectrometry. The utility of the approach is demonstrated by quantifying the alpha and beta protein isoforms of myosin heavy chain (MyHC) in human atrial tissue. Alpha-MyHC (726-741) and beta-MyHC (724-739) were identified as isoform-specific tryptic peptides. A calibration curve was constructed by plotting ion current ratios against molar ratios of the two peptides prepared synthetically. MyHC was digested by trypsin and the ion current ratio determined for the two tryptic peptides. The ion current ratio was converted to the peptide ratio and hence the isoform ratio by reference to the standard curve. The accuracy of the method was confirmed by a comparison between these results and those determined by an established method of MyHC isoform ratio determination. So that the molar ratio could be converted to absolute values, a third peptide, an analogue of the two peptides being measured, was synthesized for use as an internal standard (IS). The measured ion current ratios of synthetic alpha-MyHC (726-741), beta-MyHC (724-739), and IS peptides were used to generate standard curves. A known quantity of the IS was added to the MyHC digests. The measured ion current ratios were converted to the actual quantities of the isoform-specific peptides and hence the actual quantity of each protein isoform by reference to the standard curves. This method is of general applicability, especially when isoform quantification is required.     

基于静力称重法的微小容量光学检测系统标定

实验室常用静力称重法对微量液体容量进行检测,该方法在1μL容量的精确度达到2.18%,重复性为1.85%,但该方法无法在实验室外进行。现有的光学测量微量液体容量法的在1μL的精度为6.09%,重复性为1.31%。该法可实现在线检测,但其精度不如静力称重法。对光学测量微量液体容量的方法进行研究分析,提出了一种新的标定容量参照标准的方法,该标定方法将静力称重法与光学测量法两者结合,以静力称重法容量测量结果为参照标准,代替光学法原先的标准液。新的标定方法在原理上将参照标准由点扩展到线,可将光学测量法在10μL点的精度提高到2.014%,重复性1.30%。     

Method of regularized multipeak reference intensity ratio for quantitative X-ray phase analysis of polycrystalline materials

The development of the regularized multipeak modification of the reference intensity ratio method (RRIR) is reported. The RRIR method consists in the simulation of the experimental X-ray pattern by a linear combination of the reference standard spectra of the identified phases taken from the PDF ICDD database, application of the regularized Tikhonov LSM and the data on quantitative elemental composition upon the optimization of the model spectrum, and harnessing of the scaling coefficients of reference spectra to calculate the phase concentrations. The peculiarities of application and accuracy of RRIR achieved in the analysis of texturized multiphase mixture of minerals used in Round Robin on QPA CPD IUCr are discussed.     

Inductively coupled plasma—mass spectrometry drift correction based on generalized internal references identified by principal components factor analysis

Abstract factor analysis is applied to repeated measurements of inductively coupled plasma—mass spectrometry (ICP-MS) responses for several elemental masses in a multielement standard. During good operation, over 90% of the variance in response is accounted for by two or three factors. These factors tend to correlate with different mass ranges, and these correlations allow a rational basis for selection of candidates for internal reference elements. Internal references selected from these candidates were used to evaluate three different mathematical methods for correcting ICP-MS responses of all elements. The line ratio internal reference method and the analyte internal reference correlation method, which use a single internal reference for all elemental masses, improved precisions for most elements but decreased or had no effect on precisions of other elements. The generalized internal reference method, which may use more than one elemental mass in the correction calculation, improved precisions for all elements in most experiments.     

Evaluation and optimization of ion-current ratio measurements by selected-ion-monitoring mass spectrometry

Stable isotopically labeled compounds are regularly used as internal standards in quantitation and as tracers of in vivo metabolism. In both applications, the ratio of unlabeled to labeled analogues is determined from an ion-current ratio measured by a mass spectrometer. The precision of the ion-current ratio measurement defines the detection limit for quantitation and for tracer enrichment measurement. We have used standard models of noise to develop a method that evaluates ion-current ratio noise (i) that varies with the signal intensity and (ii) that is signal independent. This model produces a simple equation that defines the ion-current ratio precision using constants that can be evaluated empirically from the measurement of two ion-current ratios from a single standard measured multiple times. We demonstrate that our approach can predict the effect of signal intensity, ion-current ratio magnitude, and internal standard or tracer choice on the measurement precision. The standard deviations predicted by our method are shown to equal standard deviations of samples measured experimentally. This method allows a simple evaluation of a mass spectrometry system and can define the precision of new quantitation and tracer methods.     

A Note on the Graphical Analysis of Multidimensional Contingency Tables

The technique of half-normal plotting in the analysis of factorial experiments is adapted to multidimensional contingency tables. A logistic transformation is applied to the cell proportions before calculating and plotting the standard contrasts. An approximate theoretical slope is available for the half-normal plot. One use of the method is in the preliminary analysis of complex quanta1 data, in particular to help in choosing a model for more formal analysis. An illustrative example is discussed.     

Determination of serum cholesterol by a modification of the isotope dilution mass spectrometric definitive method

An isotope dilution mass spectrometric (ID/MS) method for cholesterol is described that uses capillary gas chromatography with cholesterol-13C3 as the labeled internal standard. Labeled and unlabeled cholesterol are converted to the trimethylsilyl ether. Combined capillary column gas chromatography and electron impact mass spectrometry are used to obtain the abundance ratio of the unlabeled and labeled [M+.] ions from the derivative. Quantitation is achieved by measurement of each sample between measurements of two standards whose unlabeled/labeled ratios bracket that of the sample. Seven pools were analyzed by this method: standard reference material (SRM) 1951, which consists of three frozen serum pools with low, medium, and high levels of cholesterol; SRM 1952, which consists of three freeze-dried serum pools with low, medium, and high levels of cholesterol; and SRM 909, a freeze-dried serum pool. The method is a modification of our original definitive method for cholesterol. The modified method uses much better chromatographic separations to assure specificity and a new method of implementing selected ion monitoring on a magnetic mass spectrometer to obtain high-precision measurements of ion intensity ratios on narrow gas chromatographic peaks. The modified method has a coefficient of variation (CV) of 0.22%, which is an improvement over the original method's CV of 0.36%. The measurements were found to be free of interference. The high precision and absence of bias qualify this method as a candidate definitive method.     

A Stability-Indicating HPLC Method to Determine Cyproterone Acetate in Tablet Formulations

A simple and accurate liquid chromatographic method was developed to estimate cyproterone acetate (CA) in pharmaceuticals. The drug was chromatographed on a reversed-phase C18 column. Eluents were monitored at a wavelength of 254 nm utilizing a mixture (60:40) of acetonitrile and water. Solution concentrations were measured on a weight basis to avoid the use of an internal standard. The method was statistically validated for linearity, accuracy, precision, and selectivity. Due to its simplicity and accuracy, we believe that the method can be used for routine quality control analysis. No specific sample preparation is required except for the use of a column guard and a suitable prefilter attached to the syringe.     

A stability-indicating HPLC method to determine cyproterone acetate in tablet formulations

A simple and accurate liquid chromatographic method was developed to estimate cyproterone acetate (CA) in pharmaceuticals. The drug was chromatographed on a reversed-phase C18 column. Eluents were monitored at a wavelength of 254 nm utilizing a mixture (60:40) of acetonitrile and water. Solution concentrations were measured on a weight basis to avoid the use of an internal standard. The method was statistically validated for linearity, accuracy, precision, and selectivity. Due to its simplicity and accuracy, we believe that the method can be used for routine quality control analysis. No specific sample preparation is required except for the use of a column guard and a suitable prefilter attached to the syringe.     

Development and evaluation of a candidate reference measurement procedure for the determination of progesterone in human serum using isotope-dilution liquid chromatography/tandem mass spectrometry

Progesterone is a steroid hormone that is involved in regulating female reproductive processes. Its concentration in blood is measured to determine ovarian function. A candidate reference measurement procedure for progesterone in human serum involving isotope dilution coupled with liquid chromatography/tandem mass spectrometry (LC/MS/MS) has been developed and critically evaluated. The progesterone along with its internal standard (progesterone-13C2) was extracted from the serum matrix using liquid-liquid extraction prior to reversed-phase LC/MS/MS. The accuracy of the measurement was evaluated by a comparison of results of this method on a lyophilized human serum reference material for progesterone [Certified Reference Material (CRM) 347] with the certified values determined by gas chromatography/mass spectrometry (GC/MS) reference methods and by a recovery study for the added progesterone. The results of this method for progesterone agreed with the certified value within the uncertainty of the measurements for the CRM 347. The recovery of the added progesterone ranged from 100.1 to 100.9%. This method was applied to the determination of progesterone in frozen serum samples from three individual female donors with the progesterone concentrations ranging from 0.151 to 24.42 ng/g. Excellent reproducibility was obtained with within-set coefficients of variation (CVs) ranging from 0.1 to 1.4%, and between-set CVs ranging from 0.3 to 0.5%. Excellent linearity was also obtained with correlation coefficients of all linear regression lines (measured intensity ratios vs mass ratios) ranging from 0.9998 to 1.0000. The detection limit at a signal-to-noise ratio of approximately 3 was 1.8 pg of progesterone. This well-characterized LC/MS/MS method for serum progesterone, which demonstrates good accuracy and precision, low susceptibility to interferences, and comparability with GC/MS reference methods, qualifies as a reference measurement procedure that can be used to provide an accuracy base to which routine methods for progesterone can be compared and that will serve as a standard of higher order for measurement traceability.     

Development and evaluation of a reference measurement procedure for the determination of estradiol-17beta in human serum using isotope-dilution liquid chromatography-tandem mass spectrometry

Estradiol is the most potent natural estrogen and is derived from the ovaries. Its concentration in blood is measured to determine ovarian function. A reference measurement procedure for estradiol in serum involving isotope-dilution coupled with liquid chromatography-tandem mass spectrometry (LC/MS/MS) has been developed and critically evaluated. A deuterated estradiol (estradiol-d3) was used as an internal standard. The estradiol and its internal standard were extracted from serum matrix using solid-phase extractions and derivatized with dansyl chloride prior to reversed-phase LC/MS/MS. The accuracy of the measurement was evaluated by a comparison of results of this reference method on lyophilized human serum reference materials for estradiol [Certified Reference Materials (CRMs) 576, 577, and 578] with the certified values determined by gas chromatography/mass spectrometry (GC/MS) reference methods and by a recovery study for the added estradiol. The results of this method for estradiol agreed with the certified values within the uncertainty of the measurements for the three CRMs. The recovery of the added estradiol ranged from 100.7 to 101.8%. This method was applied to the determination of estradiol in frozen serum samples from three individual female donors. Excellent reproducibility was obtained with within-set coefficient of variations (CVs) ranging from 0.6 to 2.2% and between-set CVs ranging from 0.2 to 0.4%. Excellent linearity was also obtained, with correlation coefficients of all linear regression lines (measured intensity ratios vs mass ratios) ranging from 0.998 to 1.000. The detection limit at a signal-to-noise ratio of approximately 3 was 0.6 pg of estradiol (or 1 ng/L, as expressed as a concentration). This well-characterized LC/MS/MS method for serum estradiol, which demonstrates good accuracy and precision, low susceptibility to interferences, and comparability with GC/MS reference methods, qualifies as a reference measurement procedure that can be used to provide an accuracy base to which routine methods for estradiol can be compared and that will serve as a standard of higher order for measurement traceability.     

Approximate weight function technique using single-layer potential for a cracked circular disc

An efficient weight function technique using the indirect boundary integral method was presented for cracked circular discs. The crack opening displacement field was presented by a single layer whose kernel was a modified form of the fundamental solution in elastostatics. The application of a single-layer potential to the weight function method leads to a unique closed-form SIF (stress intensity factor) solution. The solution can be applied to a cracked circular discs with or without an internal hole or opening. For these crack geometries over a wide range of crack ratios, the SIF solution can be applied without any modification.

The calculation procedure of SIFs for the various cracked circular discs using only one analytical solution is very simple and straightforward. The information necessary in the analysis includes only two or three reference load cases. In most cases the SIF solution using two reference SIFs gives reasonably accurate results while the SIF solution with three reference load cases may be used to improve the solution accuracy of the crack configurations, with an internal opening or hole, compared with the solutions of the available literature.     

Low loss measurement of oil concentration in a refrigerant-oil mixture in a liquid line

A method of measuring the mass concentration of lubricating oil in a refrigerant-oil mixture in a liquid line within a refrigeration system is described. It is suitable for use where the oil and refrigerant are fully miscible in the liquid phase, e.g. for mineral oil and R12. The technique involves taking a small liquid sample, measuring its volume, venting the refrigerant back into the system and weighing the residual oil. Many measurements can be made, with negligible loss of refrigerant from the system. An application of the method to a split circuit bypass type compressor load stand is also described.     

经纬仪坐标测量系统检测方法的研究

简要分析了国内外大尺寸坐标测量系统使用和检测研究现状,叙述了经纬仪测量系统的组成。测量方法和误差来源,根据我国使用现状和现有水平,提出了经纬仪测量系统性能参数、检测标准实物,适用于室内检测和现场检测,给出了室内大尺寸标准研制和现场标准实物研制的途径。     

Complete equation for the measurement of organic molecules using stable isotope labeled internal standards, exact matching, and mass spectrometry

Highly accurate measurements of the amount of substance of organic molecules in a test material can be obtained using exactly matched calibration solutions and internal standards that are labeled with stable isotope atoms by measuring the amount ratio of analyte to internal standard using mass spectrometry. Estimating the uncertainty of quantitative measurements of organic molecules is a means of evaluating accuracy and of establishing traceability to the International System of Units (SI) and requires a measurement function that fully describes the measuring system. This paper presents the derivation of the equation (measurement function) that describes this complete measurement after the internal standard has equilibrated with the test material matrix. It is similar to the equation for inorganic measurements using isotope dilution techniques, but potential biases during chemical processing arising from whole organic molecule analysis compared to inorganic atomic analysis required greater investigation of the yield factors that occur during organic molecule measurements. In the new equation, a series of ratios of proportionality factors are used to relate the amount of substance in a test material to chromatographic peak area ratios corresponding to mass spectrometer ion current ratios. All the proportionality factors are grouped together to define a measuring system factor F(X), the value of which is determined by the fundamental chemical processes affecting the yields of analyte, internal standard, and reference standard of the analyte in the measurement process. Any factors in the measurement process that affect the mole ratio of analyte to internal standard in the calibration solution differently from the test solution will result in a nonunity value for F(X) and a proportional bias to the measurement, and in this way F(X) represents the concept of recovery of the amount ratio of analyte to internal standard. Thus highly accurate measurements require F(X) or its constituent factors to be evaluated. In addition, the uncertainty in the evaluation of F(X) or of its constituent factors must be included in a complete uncertainty estimation of the analytical procedure. The many different permutations of proportionality factor ratios that may result in a unity value of F(X) are discussed resulting in a case for evaluating F(X) rather than the more common practice of evaluating individual factors for each major stage of the measurement procedure. Since the new measurement function describes the complete chemical process that constitutes the measurement, traceability to the SI is assured when all factors in the function are measured traceably and have their associated uncertainty estimated correctly. Ignoring F(X) would invalidate traceability to the SI and would prevent a complete estimation of measurement uncertainty.     

采用比较法研制二级气体标准物质

以氮中二氧化碳二级气体标准物质的研制为例,探讨采用比较法研制二级气体标准物质及其不确定度的分析计算,其中标准物质的制备采用称量法配制,并对所研制的样品进行了均匀性、稳定性试验,结果表明,所研制的氮中二氧化碳气体的标准物质在一年的考察期内,其均匀性、稳定性、量值不确定度均达到国家二级标准物质要求,符合申报条件。     

Comparison of two-, three-, and four-exposure quadrature phase-shifting holography

In standard (four-exposure) quadrature phase-shifting holography (QPSH), two holograms and two intensity maps are acquired for zero-order-free and twin-image-free reconstruction. The measurement of the intensity map of the object light can be omitted in three-exposure QPSH. Furthermore, the measurements of the two intensity maps can be omitted in two-exposure QPSH, and the acquisition time of the overall holographic recording process is reduced. In this paper we examine the quality of the reconstructed images in two-, three-, and four-exposure QPSH, in simulations as well as in optical experiments. Various intensity ratios of the object light and the reference light are taken into account. Simulations show that two- and three-exposure QPSH can provide reconstructed images with quality comparable to that of four-exposure QPSH at a low intensity ratio. In practice the intensity ratio is limited by visibility, and thus four-exposure QPSH exhibits the best quality of the reconstructed image. The uniformity and the phase error of the reference light are also discussed. We found in most cases there is no significant difference between the reconstructed images in two- and three-exposure QPSH, and the quality of the reconstructed images is acceptable for visual applications such as the acquisition of three-dimensional scene for display or particle tracking.     

利用Rietveld方法的多相粉末定量分析

利用Ｘ射线步长扫描衍射数据和全图谱（Ｗｈｏｌｅ－ｐａｔｔｅｒｎ）拟合技术（Ｒｉｅｔｖｅｌｄ方法），通过相含量和Ｒｉｅｔｖｅｌｄ修正中标度因子之间存在的简单关系，对包含不同重量的水晶和刚玉粉末的混合物样品进行了相含量的定量分析。求得的结果与原始配比一致，说明这一技术可以有效地用于多相粉末，尤其是衍射图谱严重重叠样品的定量分析研究。     

A wide range weight function for a single edge cracked geometry with clamped ends

A single edge cracked geometry with clamped ends is well suited for fracture toughness and fatigue crack growth testing of composites and thin materials. Stress intensity factors may be determined by the weight function method. A weight function for the single edge cracked geometry with clamped ends is developed and verified in this paper. It is based on analytical forms for the reference stress intensity factor and crack mouth opening displacement. The analytical forms are shown to be valid, by comparison with finite element results, over a wide range of crack depths and plate aspect ratios. Use of the analytical form enables the weight function to be calculated for any plate aspect ratio without the need for preliminary finite element analysis. Stress intensity factors and crack mouth opening displacements, predicted using this weight function, correlated well with finite element results for non-uniform crack surface stress distributions. This revised version was published online in August 2006 with corrections to the Cover Date.     

淀粉/秸秆纤维缓冲包装材料的制备及其性能

利用模压成型法制备出可替代聚苯乙烯泡沫塑料(EPS)的淀粉/秸秆纤维缓冲包装材料。通过正交实验探讨了不同配比的原材料对新材料密度及力学性能的影响,获得主要的影响因素及各组分的最优配比。结果表明:随PVA添加量增加,缓冲材料密度先减小后增大,而材料抗压强度逐渐增大;发泡剂含量越高,材料密度越小而抗压强度越低;秸秆纤维与淀粉比例为1:2时材料抗压性能较好。采用静态压缩实验比较淀粉/秸秆纤维缓冲材料与EPS力学性能的差异,并利用体式显微镜分析了淀粉/秸秆纤维缓冲材料微观结构与EPS的差异,提出两种材料差异产生的原因及改善方法。