Prediction of precision from signal and noise measurement in liquid chromatography: Mathematical relationship between integration domain and precision

Summary The precision of integration over noisy instrumental output for quantitative analysis is studied. A probability theory is developed to predict the relative standard deviation (RSD) of integration results over an integration domain from one-point integration (peak height measurement) to entire area integration in HPLC. Common integration modes of horizontal zero line and oblique zero line are taken into account, but no peak overlap is assumed. The question of the analytical superiority of peak height measurement or integration for quantitation is answered. In the HPLC apparatus used, the minimum RSD of measurements is found in the integration domain of ca. ±0.5 σ for analytes [peaks are approximated by the Gaussian signal of width, σ (standard deviation)]. The RSD of integration measurements is also shown to depend on the stochastic properties of background noise (uncorrelated noise and correlated 1/f type noise). The theoretical conclusion is verified by Monte Carlo simulation and HPLC experiments for some aromatic compounds. Second Part of series cited as Ref. [1].     

Application of the reference-element technique for fast sequential flame atomic-absorption spectrometry

Fast sequential flame atomic-absorption spectrometry (FS-FAAS) is able to measure a sequence of analyte wavelengths in one monochromator scan and so achieves or exceeds the analysis speed of sequential ICP–OES. The requirements and implementation of an FS-FAAS instrument are presented in detail. FS-FAAS is a sequential multi element technique which retains the advantages of conventional FAAS, for example ease of use. While the FS-FAAS technique is an ideal tool for routine determination of elements in the mg L^–1 concentration range, it is still subject to common sources of error such as transport problems and long-term drift. The reference-element technique can be used to correct for these types of common interference; other advantages include correction of some errors which are induced during sample preparation, and improved analytical accuracy and precision. The reference-element technique when utilizing the FS- FAAS technique is described in detail and benefits of the technique will be demonstrated by comparing performance for selected applications, for example a mineral sample and a scrap wood digest.     

高压下氮气在正庚烷-正辛烷混合溶剂中的溶解度研究

Solubilities of nitrogen in binary mixtures of n-octane and n-heptane have been measured at temperatures from 20 to 70 ℃ and pressures up to 130 atm using a precision gas-liquid solubility apparatus. Experimental results can be expressed by the following equation Inx_(N_2)=A+BP_(N_2)+CP_(N_2)~2+DInP From the results obtained, the partial molar volume of dissolved nitrogen and the Henry's Law constants have also been calculated.     

Estimation of the Cholesky decomposition in a conditional independent normal model with missing data

We investigate the problem of estimating the Cholesky decomposition in a conditional independent normal model with missing data. Explicit expressions for the maximum likelihood estimators and unbiased estimators are derived. By introducing a special group, we obtain the best equivariant estimators.     

高压下氮气在正庚烷-正辛烷混合溶剂中的溶解度研究

高压下气体在混合溶剂中溶解度的测定与研究,无论在理论研究或是实际应用方面均具有重要的意义。但由于进行这类研究,特别是在升温升压下,费时,昂贵和有一定难度,目前这方面的数据十分缺乏。作为本实验室研究系列之一部份,本文将报导文献中尚未见发表的氮气在正庚烷-正辛烷混合溶剂中的溶解度研究结果。实验部份1.试剂氮气纯度99.999%,由北京氧气厂提供;正庚烷,正辛烷由北京化工厂产分析纯试剂,本实验室又进一步精馏纯化。纯化后的试剂用气相色谱分析其纯度高于99.4%.混合溶剂的组成用重量法配制。     

多通道光路在气体分析中的应用

本文在不分光红外分析法的基础上,应用一种多通道的光路,研究在一个气室中分析多种气体成分的方法。即研究在一个气室中周期地透射多种特定的带通很狭的红外波时,其光电响应值与相对应气体成分浓度的关系。结果表明,多通道光路系统的检测精度和稳定性方面均达到了较好水平。     

基于GPS的智能农机载高光谱采集系统的初步研究

为了解决精确农业中高密度的和全面的农田信息采集的需要,本系统利用visual basic和map objects对GPS, GIS和RS进行有机集成, 一方面系统通过集成GPS, 能为采集到的光谱数据提供高精度的空间位置属性,实现光谱数据采集、定位和存储一体化; 另一方面通过集成GIS,实现了具有空间属性的光谱数据可视化管理和分析处理, 实时地显示动点轨迹和各图层对应点属性,计算作物微分光谱和植被指数NDVI等功能, 为专家系统和决策支持系统提供充足的信息。     

A microfluidic device for accurate detection of hs-cTnI

This device is aimed at ensuring that the sample is uniformly and equivalently reacted with the antibody on the NC membrane in each test when the microfluidic liquid system is introduced to the chip. In this study, the developed microfluidic chip can avoid the presence of the sample and conjugate pads in the chip, while the precision of the chromatography system can be greatly improved using the same particles, NC membrane and antibody alongside the traditional strip. The results, taking the detection of cTnI as an example, revealed that the coefficient of variation (CV) is controlled within 4%, while the maximum record of the contrast chromatographic reagent strip can reach 15%. Additionally, the detection sensitivity can maintain the same order of magnitudes with that of the traditional chromatographic strip. With the results, the determination correlation of the developed microfluidic chip has been greatly improved. In addition, the CV of the chip in this study is greatly improved in comparison with that of the traditional strip. The biggest improvement lies in the mixing between the sample and the microspheres, indicating that this is a new approach to improve the CV of the traditional strip.     

nMoldyn 3: Using task farming for a parallel spectroscopy‐oriented analysis of molecular dynamics simulations

We present a new version of the program package nMoldyn, which has been originally developed for a neutron‐scattering oriented analysis of molecular dynamics simulations of macromolecular systems (Kneller et al., Comput. Phys. Commun. 1995, 91, 191) and was later rewritten to include in‐depth time series analyses and a graphical user interface (Rog et al., J. Comput. Chem. 2003, 24, 657). The main improvement in this new version and the focus of this article are the parallelization of all the analysis algorithms for use on multicore desktop computers as well as distributed‐memory computing clusters. The parallelization is based on a task farming approach which maintains a simple program structure permitting easy modification and extension of the code to integrate new analysis methods. © 2012 Wiley Periodicals, Inc.     

Comparison of quantification strategies for one-point standard addition calibration: The homoscedastic case

Two quantification strategies for one-point standard addition calibration have been compared mathematically. One strategy involved the extrapolation of measurement points to their intercept with the x-axis to determine the analyte content in the unknown sample, and the other strategy is based upon direct calculation of the analyte content in the unknown sample using the instrumental responses obtained during measurement. The cases of both conventional standard addition calibration (C-SAC) and sequential standard addition calibration (S-SAC) have been considered. The homoscedastic situation has been considered, where the absolute precision of the instrumental response is constant. It has been determined that the precision ratio of the two strategies is dependent on surprisingly simple parameters: such as the sample to standard mass ratio (for C-SAC) and the analyte content ratio (for S-SAC).