Java applets for viewing one- and two-dimensional NMR spectra

Two Java applets, which allow viewing and simple reprocessing operations of one- and two-dimensional NMR spectra from within a web page, are described. For the 1D viewer, phasing, integration, peak picking and referencing are supported. Bruker, Varian and JCAMP-DX processed data files can be opened. The 2D viewer allows f2 phasing and referencing, and can read native Bruker processed data. The compiled applets are available from the author on request.     

Optimisation of data handling and detection conditions for automated chromatographic assay software

Summary The principle of automated chromatographic peak detection and analysis software is summarized, and critical steps are systematically studied. As the only parameter to be entered is the acquisition frequency, evaluation of its effect on software performance is discussed. In the case of relatively noisy chromatograms, it is shown experimentally that numerous points per peak have to be taken, leading to quite fast computer acquisition procedures. The use of discrete Fourier transform filtration techniques can modify peak shapes and a comparative study evaluates the relative errors induced in the shapes and characteristics of the chromatographic profiles. Optimisation of filtering conditions is achieved and it is shown that for a filter position only 2% of the Nyquist frequency no deformation occurs in the chromatographic profile. Detection of the start and finish of chromatographic peaks is optimized according to a simple four step iterative procedure. In the case of simulations, the difference between the values used to simulate peaks and those calculated by the software are less than 1%.     

Remarks on the analysis of the photopeaks of scintillation gamma-ray spectra

Physical considerations permit the asymmetry of the photopeak in scintillation γ-spectra to be represented by a second Gaussian peak of lower intensity, accompanying the principal peak. The problem of finding the peak parameters is described as one reduced to solving an over-determined system of non-linear equations, when the numbers of counts in the channels of the analyzer are given. The nature of ill-conditioned linear steps is discussed for the case of solving the problem by Newton's method. A solution procedure based on the regulation of the iteration process is proposed, and the concept of ‘α-approximative solution’ of the given problem is introduced. The calculation procedure is illustrated on actual numerical examples by tables and diagrams, and the possibilities of checking the physical hypothesis and of additional control of the experimental conditions are described.     

Referencing strategies and techniques in stable isotope ratio analysis

Stable isotope ratios are reported in the literature in terms of a deviation from an international standard (delta-values). The referencing procedures, however, differ from instrument to instrument and are not consistent between measurement facilities. This paper reviews an attempt to unify the strategy for referencing isotopic measurements. In particular, emphasis is given to the importance of identical treatment of sample and reference material ('IT principle'), which should guide all isotope ratio determinations and evaluations. The implementation of the principle in our laboratory, the monitoring of our measurement quality, the status of the international scales and reference materials and necessary correction procedures are discussed.     

Software tool for coupling chromatographic total ion current dependencies of GC/MSD and MCC/IMS

More than 90,000 ion mobility spectrometer (IMS) are in use worldwide, mostly without coupling to chromatographic columns for pre-separation of the neutrals entering the ionization region of the IMS. Related to new application fields e.g. breath analysis or determination of volatile metabolites of cell cultures and bacteria/fungi an effective way for pre-separation is needed strongly. The acceptance of IMS within the analytical world will be enhanced by supplying automatic procedures for peak finding, referencing and database-related identification of the signals within IMS-Chromatograms. Some papers are available concerning the internal loop of relation of IMS signals between different instruments, alignment for automatic interpretation with respect of reference analytes used and interpolation within the different members of classes of analytes in case that some missed e.g. within a homologous row of chemicals. With respect to inter comparison of recent findings using MCC/IMS and GC/MS experiments effective alignment procedures are developed. In the present paper we describe a software tool making the visualization of the total ion current (TIC) from chromatograms of GC/MSD possible in direct relation to the corresponding IMS-Chromatogram of MCC/IMS. Thus, parallel measurements of e.g. samples of human breath using MCC/IMS and thermodesorption (TD)-GC/MSD become comparable directly. On the other hand, the direct identification and relation of so far unknown peaks found in IMS-Chromatograms will be supported using the TIC results of GC/MSD.     

Verification of gamma-spectroscopy programs: Accuracy and detectability

The newly revised ANSI N42.14^1.2 has provided analysis software developers with a set of well defined, consistent and unbiased procedures designed to evaluate the accuracy and limitations of peak search and peak area analysis programs. This work uses two of the procedures outlined in this standard to evaluate five peak analysis algorithms currently in use in Canberra and Nuclear Data software packages. The first procedure examines a program's behavior as the centroid separation and peak height ratio of a doublet are varied. A previous review of these data³ demonstrated significant peak area inaccuracies at peak separations at or below 1.5 FWHM. We will discuss improvements made to some of these programs and the impact on the doublet results. The second procedure examines a program's behavior as the Compton continuum beneath a fixed peak area is increased. For the same five algorithms we will discuss the dependence of peak area on Compton continuum and also explore the limits of peak detectability.     

The Zimmermann reaction and a correction for irrelevant absorption

Two similar modifications of a previously described aqueous Zimmermann reaction for 17-ketosteroids were studied to see whether the Allen correction for irrelevant background absorption could be accurate when pure steroids were compared against a single steroid as a calibrator. Dehydroisoandrosterone was selected as the standard because most procedures use it for that purpose. In one procedure in which varied spectral shapes, wide-ranging peak maximum values, and molar absorptivities were evident, accuracy of recovery was poor. In a second procedure, in which the primary variation was in band width rather than in either fine structures or molar absorptivities, the results were more accurate though still inaccurate as compared to peak measurement calculations. It would seem that this correction could only be valid for those procedures in which calibrator and analyte yield spectra which show better uniformity than the two procedures described here.     

Significance of data treatment and experimental setup on the determination of copper complexing parameters by anodic stripping voltammetry

Different procedures of voltammetric peak intensities determination, as well as various experimental setups were systematically tested on simulated and real experimental data in order to identify critical points in the determination of copper complexation parameters (ligand concentration and conditional stability constant) by anodic stripping voltammetry (ASV). Varieties of titration data sets (Cu_measuredvs. Cu_total) were fitted by models encompassing discrete sites distribution of one-class and two-class of binding ligands (by PROSECE software). Examination of different procedures for peak intensities determination applied on voltammograms with known preset values revealed that tangent fit (TF) routine should be avoided, as for both simulated and experimental titration data it produced an additional class of strong ligand (actually not present). Peak intensities determination by fitting of the whole voltammogram was found to be the most appropriate, as it provided most reliable complexation parameters.Tests performed on real seawater samples under different experimental conditions revealed that in addition to importance of proper peak intensities determination, an accumulation time (control of the sensitivity) and an equilibration time needed for complete complexation of added copper during titration (control of complexation kinetics) are the keypoints to obtain reliable results free of artefacts.The consequence of overestimation and underestimation of complexing parameters is supported and illustrated by the example of free copper concentrations (the most bioavailable/toxic specie) calculated for all studied cases. Errors up to 80% of underestimation of free copper concentration and almost two orders of magnitude overestimation of conditional stability constant were registered for the simulated case with two ligands.     

The role of covariance in the analysis of gamma-ray spectra

When a gamma-ray spectrum contains a number of photopeaks originating from the same nuclide, the calculation of nuclide activity depends not only on the values of, and uncertainties in, the photopeak areas, photopeak efficiencies, gamma-ray emission probabilities and peak area correction factors, but also on the correlations that exist between these quantities. When photopeaks corresponding to a group of nuclides overlap or are unresolved, simultaneous estimation of the activities of all the nuclides present in the group is necessary if the information contained in the spectrum is to be used efficiently — a procedure which can prove important when the only prominent photopeak associated with a nuclide of interest overlaps with the photopeak of another nuclide. Two procedures for activity estimation are described: both procedures take correlations into account; one procedure deals with the special case of activity estimation for a single nuclide, where unresolved photopeaks are absent or neglected; the other procedure deals with simultaneous activity estimation using all the photopeaks associated with an interrelated group of nuclides.     

Charge referencing issues in XPS of insulators as evidenced in the case of Al‐Si‐N thin films

Accurate charge referencing in XPS of insulating specimens is a delicate issue. This difficulty is illustrated in the case of Al‐Si‐N composite thin films deposited by reactive magnetron sputtering with variable composition from pure aluminum nitride to pure silicon nitride. The samples were mounted with Au‐coated metallic clamps. Argon sputter cleaning was required to remove a surface native oxide before analysis. For charge referencing implanted argon atoms from the sputter gas and a small amount of gold re‐deposited from the metallic clamps onto the specimen surface during sputter cleaning were evaluated. For the argon atoms, a surprisingly large chemical shift (～1 eV) and a significant peak broadening (0.6 eV) of the Ar 2p_3/2 photoelectron line were found with varying the Si content of the films. This could be related to chemical and structural changes of the Al‐Si‐N films. Hence implanted argon could not be used for charge referencing of Al‐Si‐N samples. In contrast to the implanted argon, the Au 4f_7/2 line width of the gold re‐deposited onto the sample surface did not depend on the Si content of Al‐Si‐N films. A constant energy shift (～1.2 eV) of the Au 4f_7/2 line as compared with bulk gold was, however, found, which was related to the size of gold particles formed on the insulating films. Therefore gold could be reliably used to study chemical shifts of sample‐relevant species in Al‐Si‐N films, but the absolute binding energies of Al 2p, Si 2p and N 1s photoelectrons could not be determined. Copyright © 2011 John Wiley & Sons, Ltd.     

Determination of photopeak energy in instrumental neutron activation analysis

The precision and accuracy of the peak energy allocation in γ-ray spectrometry govern the subsequent computer processing of the data. By applying the main procedures for peak energy determination to a well-defined case, it is possible to define the minimal statistical uncertainties to be expected. The systematic bias of the energies obtained is caused mainly by changes in the total count rate. A correction can be applied based on the pulser peak. From the precision and the accuracy of the peak energy determination, the scanning width for automatic peak indexing follows.     

Matrix sensitivity of solid sampling AAS. Determination of zinc in geological samples

Direct solid sampling techniques in AAS have several advantages over wet digestion methods such as small sample size requirements and simple calibration procedures. But some disadvantages also exist such as the sample in homogeneity and the matrix sensitivity of calibration. The calibration is commonly carried out by varying the sample mass and evaluating the peak intensity versus absolute analyte amount. It is shown here that this procedure must be considered doubtful when matrix effects are expected. In the case of zinc determination in geological samples it has been shown that calibration functions obtained by different reference materials differ significantly from each other. As an alternative a three-dimensional calibration technique can be applied that evaluates the peak intensity versus both analyte content and sample weight. The resulting calibration planes are expected to be hyperbolically curved. This three-dimensional calibration has been applied to the determination of Zn in geological samples and compared with classical solid sampling AAS calibration procedures.     

Colachrom,a command language for chromatographic data processing

A command language for the interactive computer processing of chromatograms is described. Report data files, resulting from a peak evaluation program, are processed with single-line commands. Reference peaks for quantitative evaluation or for retention index calculations can be specified, compound names or response factors be assigned, etc. Customer-specific reports can be generated. Several commands operate on the unreduced digitized chromatograms, e.g., repeat peak evaluation with modified peak search parameters or with a user-corrected baseline. Commands can be combined into procedures for semi-automatic processing of series of chromatograms. Various forms of interactive graphical presentations supplement the command language.     

Automation and Computerization of NAA

A PC controlled automatic INAA system is briefly introduced. The unique features of the system in software, hardware, and quality control procedures are described. Major performances are given to show the analytical quality and productivity of the system.     

Application of Heart-Cutting 2D-LC for the Determination of Peak Purity for a Chiral Pharmaceutical Compound by HPLC

As an alterative to photodiode array or mass spectral analysis, a heart-cutting two-dimensional liquid chromatography technique (2D-LC) can be utilized to assess peak purity. In this work, the strengths of the heart-cutting 2D-LC technique are presented by highlighting a case study where a co-eluting impurity present at 0.8 % was non-detectable using traditional methods. However, when fractions taken across the main peak were re-assayed using an orthogonal method, this peak was readily observed. With modern switching valves and up-to-date chromatography software, implementing this technique into a validation protocol for assessing peak purity is simple and can be accomplished through only minor modifications to existing HPLC equipment.     

Peak comparison in MCC/IMS-data—searching for potential biomarkers in human breath data

The essential necessity of the comparison of peaks of different IMS-Chromatograms requires the development of software procedures to search in rather large databases of different measurements for the selected characteristic peaks. The procedure of selecting an area in the IMS-Chromatogram directly, of searching in particular data-sets related to different measurements and of visualizing the findings with respect to a comparison of the peak characteristics will be presented in detail. Eucalyptol as an analyte frequently found in human breath samples was investigated as an example and data obtained from MCC/IMS were used for the application of the peak comparison procedure.     

Evaluation and improvement of the resolution of voltammetric measurements

Two approaches for estimating and improving resolution in chromatography analyses can be applied successfully to voltammetric measurements. It is shown that the resolution of voltammetric procedures yielding symmetric (or nearly symmetric) current peaks can be described by R = 2DeltaE (p)1.699 (b(1,2,1) + b(1,2,1)) where DeltaE(p) is the difference between the peak potentials of the two analytes, and b(1,2,1) and b(1,2,2) are the peak half-widths. The window diagram approach is used to improve the resolution between neighbouring voltammetric peaks by optimization of the supporting electrolyte composition. The applicability of these approaches to differential-pulse anodic-stripping measurements at the mercury film electrode is demonstrated.     

The use of digital simulation to improve the cyclic voltammetric determination of rate constants for homogeneous chemical reactions following charge transfers

Cyclic voltammetry (CV) is a very useful electrochemical tool used to study reaction systems that include chemical steps that are coupled to electron transfers. This type of system generally involves the chemical reaction of an electrochemically generated free radical. Published methods exist that are used to determine the kinetics of electrochemically initiated chemical reactions from the measurements of the peak current ratio (i_pa/i_pc) of a cyclic voltammogram. The published method requires working curves to relate a kinetic parameter to the peak current ratio.In the presented work, a digital simulation package was used to obtain improved working curves for specific working conditions. The curves were compared with the published results for the first- and second-order chemical reactions following the charge transfer step mechanisms.According to the presented results, the previously published working curve is reliable for a mechanism with a first-order chemical reaction; however, a change in the switching potential requires a recalculation of the curve. In the case of mechanisms with a second-order step (dimerisation and disproportionation), several different views exist on how the second-order chemical term should be expressed so that different values of the constant are obtained. Parameters such as electrode type, electrode area, electroactive species concentration, switching potential, scan rate and method for peak current ratio calculation modify the working curves and must always be specified.We propose a standardised method to obtain the most reliable kinetic constant values.The results of this work will permit researchers who handle simulation software to construct their own working curves. Additionally, those who do not have the simulation software could use the working curves described here.The revelations of the presented experiments may be useful to a broad chemistry audience because this study presents a simple and low-cost procedure for the study of free radicals that otherwise should be studied with more sophisticated and expensive techniques, such as ESR or pulse radiolysis.