ISSN:0886-9383    

DOI:10.1002/cem.1180050302

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractWith the goal of understanding global chemical processes, environmental chemists have some of the most complex sample analysis problems. Multivariate calibration is a tool that can be applied successfully in many situations where traditional univariate analyses cannot. The purpose of this paper is to review multivariate calibration, with an emphasis being placed on the developments in recent years. The inverse and classical models are discussed briefly, with the main emphasis on the biased calibration methods. Principal component regression (PCR) and partial least squares (PLS) are discussed, along with methods for quantitative and qualitative validation of the calibration models. Non‐linear PCR, non‐linear PLS and locally weighted regression are presented as calibration methods for non‐linear data. Finally, calibration techniques using a matrix of data per sample (second‐order calibration) are discussed

ISSN:0886-9383    

DOI:10.1002/cem.1180050303

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractReal‐time monitoring of pollutant levels from a mobile measuring platform requires fast, flexible data analysis methods. This paper reports a method for rapid analysis of passive remotely sensed infrared data with the aid of a Kalman filter. The background spectra produced by emission from the atmosphere are modelled at the start of the data collection sequence with a simple principal components model obtained by eigenanalysis of the initial ‘blank’ data taken with the spectrometer. The species of interest are included in the state space model by a separate measurement of their infrared spectra. It is demonstrated that for best filter performance in detecting the simulated pollutant species SF6in the atmosphere, a filter model with two principal components describing the emission background works best. The filter ‘maps’ of SF6closely follow the integrated spectral intensities measured after removal of suitable ba

ISSN:0886-9383    

DOI:10.1002/cem.1180050304

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractPrincipal component analysis is used to examine large multivariate databases. The graphical approach to exploratory data analysis is described and illustrated with a single example of chemical composition data obtained on environmental dust particles. While the graphical approach to exploratory data analysis has certain advantages over the numerical procedures, the empirical approach described here should be viewed as complementary to the more robust treatments that statistical methodologies afford.

ISSN:0886-9383    

DOI:10.1002/cem.1180050305

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractChemometrics is defined as the application of mathematical and statistical methods to chemical systems. Systems theory is seen to be useful for organizing and categorizing the inputs to and outputs from chemical systems. Advances in measurement science in the 1950s and 1960s, particularly in analytical chemistry, created a need for a multivariate approach to data analysis. Early chemometrics emphasized the use of structure‐finding methods for existing data sets. In many instances, data sets can be obtained from designed experiments. Such data sets are more likely to contain the desired information and the data can usually be acquired at less cost. Renewed interest in statistical process control will provide many new, more robust data sets in the futur

ISSN:0886-9383    

DOI:10.1002/cem.1180050306

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper describes the simultaneous determination of cobalt, nickel, copper, zinc and cadmium by spectrophotometry and the Kalman filter method. Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) react with 5‐bromo‐2‐(2‐pyridylazo)‐5‐diethylaminophenol (5‐Br‐PADAP) in the presence of cationic surfactant cetyl pyridinium bromide (CPB) to form five different coloured ternary complexes. The absorption curves of these complexes overlap severely in the scanning range 500–620 nm. The Kalman filter algorithm is successfully applied to resolve the overlapped absorption curves and therefore makes the simultaneous determination of these metallic ions possible without tedious pretreatment. The proposed method is applied to analyse the titled elements in synthetic samples and in environmental samples such as hair, fingernail and river water samples with sat

ISSN:0886-9383    

DOI:10.1002/cem.1180050307

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractAn additive model is used to express the observed value of a sample characteristic as the sum of the true sample characteristic and a value of the data collection error, commonly known as experimental error. The data uncertainty of the experimental results (or of a survey data set) is defined as the expected squared error. The expected squarred error may change with the sample characteristic, e.g. the error moment could be concentration‐dependent. The relationship between the error variance and the analyte concentration may not be very distinct. In such a case the data transformation to stabilize the error moments may not be appropriate. A step function is proposed as an alternative way to represent the second moment of the error. The data uncertainty is defined as the weighted average of the step values of the second raw moment of the error, using the appropriate proportions of the routine samples as weights. The data uncertainties associated with the different data collection stages were evaluated by using regional soil survey dat

ISSN:0886-9383    

DOI:10.1002/cem.1180050308

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractA simple algorithm for deconvolution and regression of shot‐noise‐limited data is illustrated in this paper. The algorithm is easily adapted to almost any model and converges to the global optimum. Multiple‐component spectrum regression, spectrum deconvolution and smoothing examples are used to illustrate the algorithm. The algorithm and a method for determining uncertainties in the parameters based on the Fisher information matrix are given and illustrated with three examples. An experimental example of spectrograph grating order compensation of a diode array solar spectroradiometer is given to illustrate the use of this technique in environmental analysis. The major advantages of the EM algorithm are found to be its stability, simplicity, conservation of data magnitude and guaranteed conver

ISSN:0886-9383    

DOI:10.1002/cem.1180050309

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe statistical analysis of compositional data is of fundamental importance to practitioners in general and to chemists in particular. The existing methodology is principally due to Aitchison, who effectively uses two transformations, a ratio followed by the logarithmic, to create a useful, coherent theory that in principle allows the plethora of normal‐based multivariate techniques to be used on the transformed data. This paper suggests that the well‐known class of Box–Cox transformations can be employed in place of the logarithmic to significantly improve the existing methodology. This is supported in part by showing that one of the most basic problems that Aitchison managed to overcome, namely the specification of an interpretable covariance structure for compositional data, can be resolved, or nearly resolved, once the ratio transformation has been applied. Hence the resolution is not directly dependent on the logarithmic transformation. It is then verified that access to the general Box–Cox family will allow a more accurate use of the normal‐based multivariate techniques, simply because better fits to normality can be achieved. Finally, maximum likelihood estimation and some associated asymptotics are employed to construct confidence intervals for ratios of the true, unknown compositional constituents. Heretofore this had not been done even in the context of the logarithmic transformation. Applications to real data are

ISSN:0886-9383    

DOI:10.1002/cem.1180050310

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractMultivariate outliers in environmental data sets are often caused by atypical measurement error in a single variable. From a quality assurance perspective it is important to identify these variables efficiently so that corrective actions may be performed. We demonstrate a procedure for using two multivariate tests to identify which variable ‘caused’ each outlier. The procedure is tested with simulated data sets have have the same correlation structure as selected water chemistry variables from a survey of lakes in the Western United States. The success rates are evaluated for three of the variables for sample sizes of 50 and 100, significance levels of 0.01 and 0.05 and various amounts of mean shift. The procedure works best for highly correlated variab

ISSN:0886-9383    

DOI:10.1002/cem.1180050311

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY