Multivariate data analysis for x-ray fluorescence spectrometry

A multivariate data analysis procedure that uses singular value decomposition and the Ho-Kashyap algorithm is proposed to obtain calibration constants for x-ray fluorescence spectrometry. These calibration constants can be used to obtain results from experimental data by means of a simple dot product calculation. The method was tested on experimental data from the literature. Comparison of results showed that the method performs at least as well or better than the Rasberry-Heinrich method or its modifications. The method can be used to express calibration results obtained with a theoretically based program in such a way that they can be used conveniently in routine applications.     

Practical method validation: Validation sufficient for an analysis method

Validation of an analysis method depends on the purpose of the method, the chosen technique and the procedure in question. Methods are used for different research, product development, process control and quality control purposes. The human and economical importance of results vary. Each of the techniques used, such as chromatography-(HPLC, HRGC, TLC), capillary electrophoresis-(CE), spectrophotometry-(UV/VIS, IR, fluorescence, AAS, ICP) or spectrometric techniques (NMR, MS) as well as the hyphenated methods, have their own special features and deficiencies which must be considered. The method can include a simple pretreatment or it may include many demanding steps, it can use automation and data processing in various ways, it can have an official status, it can be a thoroughly verified or less studied one. How should these differences be accounted for during the validation? What would be a sufficient certainty that the method does what is expected, that the method fits for the purpose it was intended? The client (or authority) decides the required timetable, cost and quality level. This is why within a laboratory different quality levels and associated levels of validation exist. This paper tries to outline a practical test frame for validation efforts to assist the analyst when planning validation of a method.     

Mercury analysis: a special example of species analysis

Summary Mercury species analysis requires the determination of numerous different compounds with very different behaviour regarding environment and toxicity. For these differing species several new and more sensitive analytical methods have been developed and tested. Mercury species cannot be detected directly in most cases, and are normally derivatized by different agents and determined by different detector systems. In a new HPLC method with photometric detection more than 10 different organomercurials could be analysed as their thio-ethanol complexes. By alkylation of mercury compounds they can be separated by GC and analysed with an AAS or AFS as detector. Volatile organic species of Hg can be separated on Carbotrap^®, where Hg⁰ is not adsorbed, and analysed thereafter. With atomic fluorescence the detection limit for Hg⁰ measurement is improved significantly when compared with the widely used atomic absorption method. Results obtained with this new method are shown and discussed. Future developments for species analysis are outlined; not only to analyse the covalent metal — carbon/oxygen compounds — primary species-analysis — but also compounds with ionic or complex bonding: secondary species-analysis. With these developments, prediction of species behaviour in the environment, including toxicity assessment and decontamination proposals, should be made possible.     

Using blood hemoglobin for blood analysis

This paper demonstrates that the spectrophotometric properties of blood hemoglobin (Hb) can be used for the direct determination of biochemical compounds in blood. Glucose is used as a model, but the methodology can be applied to many other compounds (only a previous enzymatic reaction producing H(2)O(2) is needed). In order to develop the method, a model relating the Hb absorbance variation during the reaction with the glucose concentration has been developed to provide theoretical support for the method and to predict its application to other compounds. In addition, clear blood samples need to be prepared without pre-treatment and lateral reactions of H(2)O(2) with other blood constituents need to be blocked; this has been achieved with 100 : 1 v/v blood dilution in bi-distilled water and azide addition. The linear response range of the method can be fitted between 2 and 540 mg dL(-1) glucose relative to the original blood sample (RSD about 4%, 70 mg dL(-1)). The analyte concentration can be obtained by an absolute calibration method or by the standard addition method; both have been applied for direct glucose determination in several blood samples and good correlations with those obtained by an automatic analyzer have been obtained.     

Chromatographic analysis of lignans

Methods and procedures for analysis of lignans in trees and other plants are reviewed. The importance of cautious sample handling and pretreatment procedures to avoid contamination, loss of sample, and unwanted chemical reactions is discussed. Sequential extraction with a non-polar solvent followed by extraction with acetone or ethanol is recommended to separate the lignans from the plant matrix. An additional step of acid, alkaline, or enzymatic hydrolysis may be necessary for some plant matrixes. Flash chromatography is a convenient method for preparative separation and isolation of pure lignans from raw extracts. TLC is very suitable for qualitative screening of extracts and for monitoring of lignan isolation and purification steps. Trimethylsilyl ethers of lignans can be separated and quantified by GC even in the case of complex mixtures of lignans and other polyphenols, and the lignans can be identified by GC-MS in a routine manner. HPLC on reversed-phase columns is especially suited for analysis of lignans and their metabolites in biological matrixes. The recent development of HPLC-electrospray ionisation (ESI)-iontrap MS (MS(n)) and corresponding techniques with high sensitivity and selectivity has proven valuable in lignan analysis. Lignan enantiomers can be separated on chiral HPLC columns.     

Determination of calcium in waters, milk and wine by discontinuous-flow analysis

The flow-based analysis method, discontinuous-flow analysis (DFA), was used for the determination of total calcium in drinking water, milk and wine by titration with ethyleneglycoltetraacetic acid. The detector is a coated-wire calcium-selective electrode. The titration can be cycled continuously with a cycle time of about 1 min. This can be carried out with a single sample or with different samples using an autosampler. The method for waters and wine is simple, fast and highly reproducible. For milk, a back-titration method was used because of the complex matrix of the sample.     

Alternative moving window factor analysis for comparison analysis between complex chromatographic data

In this investigation, a novel chemometric method is developed for the analysis of five possible relationships of components or spectral features between two correlative but different hyphenated chromatographic systems. It is very helpful for comparison study of components present in different complex systems in both chemistry and systems biology. The proposed method, named alternative moving window factor analysis (AMWFA), could be utilized to determine the number of common components between different samples and then to identify their corresponding spectra half-automatically. AMWFA can alternatively be employed to mind for the selective information hiding in anyone of the two compared data X and Y, and to self-verify the resolution results by changing the extracted target matrices in analysis. From the results of comparison of simulated hyphenated chromatographic data, volatile chemical components in drug pair rhizoma ligustici chuanxiong-radix paeoniae rubra (RLC-RPR) and its single herbal medicines, and analysis of Angelica oral solution and its plasma sample after oral intake to rabbit, powerful ability of the proposed method is shown.     

Simultaneous immunoblotting analysis with activity gel electrophoresis in a single polyacrylamide gel

We describe here that a simple diffusion blotting method can couple immunoblotting analysis with another biochemical technique in a single polyacrylamide gel. The efficiency of protein transfer was evaluated by serial dilutions of nephrosin, a metalloproteinase of the astacin family, and by immunodetection. It is estimated that diffusion blotting produces 25-50% of the signal intensity compared to the classical electrophoretic transfer method. However, with diffusion blotting it is possible to generate several replicas from a single gel. In addition, a protein blot can be obtained from a sodium dodecyl sulfate (SDS)-polyacrylamide gel for zymography assay or from a native polyacrylamide gel for electrophoretic mobility shift assay (EMSA). In this regard, a particular signal in zymography or EMSA can be confirmed by simultaneous immunoblotting analysis with a corresponding antiserum. Therefore, diffusion blotting allows a direct comparison of signals between gels and replicas in zymography assay and EMSA. These advantages make diffusion blotting desirable when partial loss of transfer efficiency can be tolerated or be compensated by a more sensitive immunodetection reaction using enhanced chemiluminescence substrates.     

Steepest-descent algorithm for vibrational analysis calculations

In this paper we consider problems concerning the effectiveness of iterational calculations on vibrational analysis. Instead of the widespread least-squares method of force field refinement, another method is proposed based on the steepest-descent algorithm for calculation of the functional minimum of many variables. The new method does not require inverting of a large, poorly conditioned matrix or the introduction of experimental damping coefficients for improving the convergency of the calculations. Test calculations performed for several molecules exhibit a significant “elasticity” of the proposed algorithm allowing more precise reproduction of the molecular vibration frequencies than can be found in recently published works.     

Sub-microgram-scale analysis by coulometry at controlled potential

The considerations which determine the success of controlled-potential coulometric analyses on the submicrogram level are discussed, and it is shown that the ultimate sensitivity of the method is governed by the accuracy with which the requisite background corrections, especially that for the charging quantity of electricity, can be determined. A method for the coulometric determination of zinc based on these considerations is shown to contain a limiting uncertainty of ± 0.2 mμF_y, so that as little as 0.07 μg of zinc can be determined within about ± 10%, while quantities of zinc exceeding about 10 μg can be determined with an accuracy and precision of ± 0.1% or better. Possible techniques for the further extension of controlled-potential coulometric analysis into the millimicrogram range are briefly discussed.     

The analysis of dinitrotoluene isomer mixtures by nuclear magnetic resonance

NMR data are given for all the dinitrotoluene isomers. It is shown that the components in mixtures of these isomers produced for example, by the direct nitration of toluene, can be recognised readily by NMR. Quantitative analyses can be performed using the heights of the methyl proton peaks of the various isomers. The accuracy of the method and the effects of any residual toluene or mononitrotoluenes are discussed.     

Natural polyelectron population analysis

A method to perform a polyelectron population analysis of correlated molecular orbital wave functions on the basis of natural atomic orbitals (NAO s), as given by Weinhold, is presented. The method allows calculations of the probabilities of finding various types of electronic events occuring in some target AO positions, including the contributions of ionic and covalent resonance structures. This method is general and neither the theory nor the developed algorithm limit the number of electrons and holes that can be considered. Thus, the analyzed MO wave function can be a usual CI or a MCSCF one, and apart from Weinhold's NAO s. any other type of orthogonal AO s can be used as analyzers, provided that these AO s are linear combinations of the SCF-AO s. Numerical applications are given for ethylene, formaldehyde, butadiene, and acroleine, by adopting various AO basis-set levels (STO ?4G , 4–31G , and 6–31G ) and by analyzing correlated wave functions (CISD ). Improvements in the polyelectron populations when increasing the quality of AO basis sets and the corresponding valence NAO s are revealed by several examples. Furthermore, it is shown that the electroegativity of oxygen in acroleine only has an effect on contributions of ionic and covalent resonance structures, but not on delocalization of the double bonds. 1993 John Wiley & Sons, Inc.     

High-performance liquid chromatographic analysis of imidazolium and pyridinium oximes in plasma and urine

Imidazolium oximes are useful in the treatment of organophosphorus agent poisoning. However, the extant methods for analyzing oximes in plasma and urine samples are not adequate. A unique high-performance liquid chromatographic assay method was developed for quantitating either imidazolium or pyridinium oximes. Plasma or urine samples can be injected directly onto the column after a centrifugation filtration step. This method demonstrates a different approach in the method development for quaternary ammonium compounds using non-end-capped reversed-phase columns and a mobile phase containing competing cations. In addition, a preliminary pharmacokinetic study of the imidazolium oxime in rabbits was carried out using this method.     

High-throughput capillary electrophoresis analysis of biopharmaceuticals utilizing sequential injections

The complexity of biotherapeutic products implies an ever-increasing list of product quality attributes that need to be monitored and characterized. In addition, the growing interest in implementing process analytical technology in biopharmaceutical production has further increased the testing burden, together with the need for rapid testing that can facilitate real-time or near-real-time decision-making. Capillary electrophoresis (CE) has made a place in biopharmaceutical analysis but is regarded as a low-throughput method, with the instrument dead time constituting more than 80% of the total time of analysis. In this study, the dead time of CE was utilized to analyse 3 mAb samples in a single-CE run. This approach resulted in an up to 77% reduction in the total analysis time and increased the productivity by up to 300%, compared to traditional single CE-ultraviolet runs, without compromising resolution or relative peak areas. Additionally, good method reproducibility was observed. The compatibility of the method has been demonstrated with protein A eluate and cation exchange chromatography fractions. We, thus, propose that sequential injections can be applied for fast and robust CE analysis of biopharmaceuticals.     

Scanometric analysis of DNA microarrays using DNA intercalator-conjugated gold nanoparticles

We introduce a scanometric detection method for the analysis of DNA microarrays using DNA intercalator-conjugated gold nanoparticles that can be analyzed with the naked eye or with an optical scanner after the enhancement of the AuNPs. Moreover, we successfully detected a hemagglutinin-subtyping DNA array using this method.     

Background-current subtraction in voltammetric detection for flow-injection analysis

A new approach for background-current subtraction for flow-injection systems using potential-scanning voltammetric detection is described. The method is based on recording voltamperograms while the sample and carrier solutions flow through the cell, and taking the difference as the net response for the sample. Background currents due to hydrogen evolution, oxygen reduction, solvent oxidation or surface processes are thus compensated, and detection limits at submicromolar levels can be obtained. The compensation for oxygen reduction current means that samples do not need to be deaerated. The method has been evaluated for reproducibility, concentration dependence, detection limit, etc. A flow-cell with a stationary disk electrode, a 200-mul sample volume, and rapid differential pulse scanning are used. At a flow-rate of 0.3 ml min about 15 samples can be assayed per hour. Chlorpromazine, phenol, acetaminophen, norepinephrine, lead, cadmium, bismuth and zinc were used as test species.     

Selectivity enhancement by flow injection analysis

Flow injection analysis offers numerous possibilities for significantly increasing the selectivity of existing methods by utilizing knowledge of the chemistry of those methods. It also enables new selective methods to be created by utilizing kinetic methods and fast separation techniques such as gas diffusion, dialysis, extraction and ion-exchange columns. Selectivity enhancements and increased sensitivity can be achieved by incorporating the kinetic techniques of kinetic discrimination and/or kinetic enhancement into the timing of the system or the reagent concentrations and conditions for a given method. Methods have been developed for quantifying ozone, chlorine dioxide, chlorate ion, and chlorite and chlorate ions sequentially. A dual-phase gas diffusion system for hydride generation provides significant decreases in the interferences observed for transition metals.     

A statistical analysis of the precision of reweighting-based simulations

Various advanced simulation techniques, which are used to sample the statistical ensemble of systems with complex Hamiltonians, such as those displayed in condensed matters and biomolecular systems, rely heavily on successfully reweighting the sampled configurations. The sampled points of a system from an elevated thermal environment or on a modified Hamiltonian are reused with different statistical weights to evaluate its properties at the initial desired temperature or of the original Hamiltonian. Often, the decrease of accuracy induced by this procedure is ignored and the final results can be far from what is expected. We have addressed the reasons behind such a phenomenon and have provided a quantitative method to estimate the number of sampled points required in the crucial step of reweighting of these advanced simulation methods. We also provided examples from temperature histogram reweighting and accelerated molecular dynamics reweighting to illustrate this idea, which can be generalized to the dynamic reweighting as well. The study shows that this analysis may provide a priori guidance for the strategy of setting up the parameters of advanced simulations before a lengthy one is carried out. The method can therefore provide insights for optimizing the parameters for high accuracy simulations with finite amount of computational resources.     

Computerized image processing for evaluation of sampling error in ion microprobe analysis

A method is described for the microscale evaluation of sample heterogeneity as applied to in-situ ion microprobe analysis. Computer feature analysis of digitized ion images is utilized to generate sampling constants, which can be related to the degree of heterogeneity present for a particular constituent in the sample. The expected precision for a series of analyses, or the number of analyses required for a desired precision can also be determined. This approach, which is experimentally verified for NBS SRM-664 low-alloy steel, can be used both to minimize sampling error and to assess the applicability of specific reference materials to microprobe analysis.     

A new flow injection titration analysis

Summary A new type of flow injection titration method where a well-stirred mixing chamber is placed in the middle of the injection loop of a 6-way valve has been developed. With this method expensive or unstable reagents can be used for the titration. Moreover, it is potentially available for slow titration reactions. Its fundamental characteristics have been investigated using acid-base titration reaction with phenolphthaleine as the indicator. The sampling rate was 60–120 samples per hour and its reproducibility was also high (3%).

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