Changes In Peak Area Research Articles

Data smoothing and distortion of X-ray diffraction peaks. I. Theory

A general model of smoothing-induced distortions of an X-ray diffraction (XRD) peak is derived from theoretical analyses by convoluting a Savitzky–Golay (S.–G.) polynomial filter with the Gaussian, Lorentzian and pseudo-Voigt curves. This is based on the assumption that an XRD peak consists of five basic parameters and two additional parameters. Flattening and broadening are the general effects of smoothing. No change in peak area after smoothing is a new feature revealed by this analysis. An unusual change (sharpening with narrowing first, then flattening with broadening as usual) of the peak in a short smoothing range is found for an asymmetric peak. This phenomenon is variable, being governed mainly by the degree of asymmetry of the peak and factors such as peak shifting, curve type, state of the peak top and smoothing range. Formulae describing the smoothing changes of all parameters of a peak are derived. Constants used to link these formulae are set and their properties are analysed with different functions, different states of the peak top, coefficients of shape perfection (`shape-perfect coefficients'), degrees of asymmetry and smoothing ranges.

Effects of a Stereotactic Headframe Assembly on Proton Magnetic Resonance Spectroscopy

The effects of a magnetic resonance-compatible stereotactic headframe assembly on single voxel proton magnetic resonance spectroscopy (MRS) were investigated. Multiple stimulated echo acquisition mode (STEAM) spectra were obtained within a commercially available brain metabolite phantom placed within the headframe assembly (Leksell, Model G). All acquisition parameters were kept constant, except voxel location. Maximal distortion occurred for voxels acquired in the immediate vicinity of a headframe fixation pin, manifested by spectral broadening, changes in peak area and height and distortion of the baseline, rendering these acquisitions nondiagnostic. The range of this interaction was short, and a voxel acquired with nearest edge located 2.0 cm or greater from the fixation pin tip produced NAA/Cr, Cho/Cr and mI/Cr ratios differing by less than 7.5% from a spectrum obtained at the phantom center. The feasibility of performing single voxel MRS with a stereotactic headframe in place is demonstrated.

Affinity capillary electrophoresis investigation of an epitope on human immunodeficiency virus recognized by a monoclonal antibody.

Affinity capillary electrophoresis (ACE) has been used to investigate the epitope on the human immunodeficiency virus (HIV) core protein p24 recognized by the monoclonal antibody (mAb) 13-102-100. The affinity of a series of peptides with N- and C-terminal truncations of the epitope sequence determined by mass spectrometry was studied. The peak area change assay was used for the study of the interactions of the mAb with those peptides, exhibiting tight binding to the mAb, and the migration time shift assay was used to probe the relative affinities of peptides showing weak binding to the mAb. The experimental results show that the monoclonal antibody 13-102-100 recognizes the peptide VHPVHAGPIAP with highest affinity. Smaller peptides incorporating only part of the epitope, however, are recognized to some extent in the ACE experiments.

Evaluation of a capillary electrophoretic method for rapid screening of single-component combinatory libraries

The potential utility of capillary electrophoresis (CE) as an analysis and biological assay method for rapid screening of single-component combinatory libraries is demonstrated by mimicking a 5×5 drug matrix. Twenty-five compounds (some drugs, vitamins, metabolites, etc.) that include biotin are selected as the test analytes and avidin is treated as the biological activity screening reagent. In order to rapidly screen the compounds, five mixtures of nine components each are created at the diagonal of the matrix by pooling each component from the same column and row. The separation power of CE and related techniques is such that the components in these randomly generated nine-compound mixtures are almost always resolved using a single logical set of separation conditions. After obtaining optimum separation conditions, affinity testing produces the locations of the possible active component(s) based on changes in peak area. Blind tests are conducted that successfully locate the active component(s) of the matrix. With each test requiring about 14 separations (7 with and 7 without avidin) and each separation within 15 min, we were able to analyze the mixture and identify the exact locations of two possible active compounds (biotin and an unexpected compound) in the 5×5 matrix. The effect of avidin concentration on the screening procedure is assessed. Another protein, myglobin, was tested to compare specific and nonspecific interactions and to assign a threshold value (percent decrease in peak area) for determining a positive affinity response. © 1998 John Wiley & Sons, Inc. J Micro Sep 10: 653–660, 1998

Evaluation of a capillary electrophoretic method for rapid screening of single‐component combinatory libraries

The potential utility of capillary electrophoresis (CE) as an analysis and biological assay method for rapid screening of single-component combinatory libraries is demonstrated by mimicking a 5×5 drug matrix. Twenty-five compounds (some drugs, vitamins, metabolites, etc.) that include biotin are selected as the test analytes and avidin is treated as the biological activity screening reagent. In order to rapidly screen the compounds, five mixtures of nine components each are created at the diagonal of the matrix by pooling each component from the same column and row. The separation power of CE and related techniques is such that the components in these randomly generated nine-compound mixtures are almost always resolved using a single logical set of separation conditions. After obtaining optimum separation conditions, affinity testing produces the locations of the possible active component(s) based on changes in peak area. Blind tests are conducted that successfully locate the active component(s) of the matrix. With each test requiring about 14 separations (7 with and 7 without avidin) and each separation within 15 min, we were able to analyze the mixture and identify the exact locations of two possible active compounds (biotin and an unexpected compound) in the 5×5 matrix. The effect of avidin concentration on the screening procedure is assessed. Another protein, myglobin, was tested to compare specific and nonspecific interactions and to assign a threshold value (percent decrease in peak area) for determining a positive affinity response. © 1998 John Wiley & Sons, Inc. J Micro Sep 10: 653–660, 1998

Use of Pyrolysis GC/MS for Assessing Changes in Soil Organic Matter Quality

There is a need for rapid methods of assessing changes in the quality of agricultural soils because of the need to monitor such changes under different land management practices. For example, the increasing interest in use of agricultural lands for application of coal combustion byproducts, such as fluidized bed ash, has led to concern that such use may be detrimental to the quality of soil organic matter. Pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) techniques hold promise as rapid procedures for detecting changes in the organic matter composition of soils, which contrasts with the often laborious chemical methods used commonly for analyzing soil organic matter. To evaluate Py-GC/MS for this use, we characterized changes in the organic matter composition of bed ash-amended soils by both chemical and pyrolytic analyses. The chemical analysis of the soil samples had shown substantial degradation and loss of organic matter as a result of the ash amendments, and the pyrolytic analyses reflected these losses of soil organic matter by decreases in the total peak areas within the total ion chromatogram. Information on the changes in composition of soil organic matter was reflected by changes in peak area for individual pyrolytic products, and the identity of more than 40 pyrolytic products was determined from their mass spectral data. This permitted identification of various pyrolytic signature products for the protein, carbohydrate, and humic fractions of soil organic matter. The change in peak areas of these different signature products could be correlated with changes in the content of different constituents in the soil organic matter as measured by chemical analysis. The pyrolysis product furfural was correlated with changes in carbohydrate content. Changes in production of 2-methoxyphenol, guaiacol, vinylphenol, vinylguaiacol, and isoeugenol represented changes within the humic fraction. Nitrile and propane pyrolysis products were correlated with changes in protein content. The good agreement between classical chemical analysis and pyrolytic analysis indicates that Py-GC/MS can be used to monitor changes in the organic matter composition of agricultural soils subjected to environmental stress.

Determination of the association constant for slow phosphoserine-anti-phosphoserine interaction kinetics by capillary zone electrophoresis.

Capillary zone electrophoresis (CZE) was used to study the interaction of a monoclonal anti-phosphoserine antibody with its antigen. A model system that allows the determination of the real binding constant in a solution based on the change in peak areas at different concentrations of phosphoserine has been used for studying slow monoclonal antibody-antigen interaction kinetics involving low-molecular-weight antigens. CZE was applied in preincubation experiments. The slow interaction kinetics led to band broadening and resulted in far lower efficiency of the separation of complexed antibody from unbound antibody. However, when the run-to-run reproducibility of free phosphoserine was examined, it was found that it can be recovered quantitatively under electrophoresis conditions. On the basis of measurement of peak areas at different phosphoserine concentrations, the association constant was estimated (Ka = 5.21 X 10[5] M[-1]) and shown to be in close agreement with that obtained by equilibrium dialysis (Ka = 4.65 X 10[5] M[-1]). As long as the antigen participating in the interaction can be detected and recovered quantitatively in the CZE system, the method is generally useful for the study of monoclonal antibody-antigen interaction where the kinetics is slow and where the charge/ mass ratio of the unbound antigen differs from that of the complexed molecule.

Effect of exposure to four organic solvents on hepatic cytochrome P450 isozymes in rat

Changes of cytochrome P450 isozymes in livers of rats after exposure to four solvents at 4000 ppm for 6 h, were studied by enzyme assays and immunochemical detection using antibodies to cytochrome P450 isozymes. Toluene, benzene and trichloroethylene (TRI) exposure resulted in a significant increase in the activities of nitrosodimethylamine demethylase (152%, 134% and 118%) and 7-pentoxyresorufin O-depentylase (14-, 5- and 2.5-fold), respectively. 1,1,1-Trichloroethane (TCE) showed little effect on the activities of the enzymes. Anti-CYP2E1 and anti-CYP2Bl/2 inhibitable activity of toluene side-chain oxidase was significantly enhanced in toluene-, benzene- and TRI-treated rats. Anti-CYP2C11 inhibitable activity was greatly reduced as compared with control. The change in CYP2E1 and CYP2C11 was confirmed by the increase and decrease in the activities inhibited by 4-methylpyrazole and cimetidine, respectively. Western blot analysis revealed that the increase in peak area of bands recognized by anti-CYP2E1 was consistent with toluene inhibition results. CYP2B1/2 was not detectable in control rats, but it was strongly induced by toluene, followed by benzene and TRI. Some increases in the peak areas of bands recognized by anti-CYP2A1 and CYP-4A1 were also observed in the three solvents exposed rat microsomes. Little immunoreactivity was found with anti-CYP1A1 in all microsomes, and no obvious change in peak area of bands recognized by anti-CYP3A and anti-CYP2C13 was observed. TCE exposure showed little effect on these bands. The formation of phenol and hydroquinone from benzene was enhanced to different degree by toluene, benzene and TRI. The hydroxylation of testosterone at 6β and 7α was increased by benzene, and benzene and TRI, respectively. However, the metabolism at 16α and 2α was profoundly suppressed by the solvents except TCE. These results showed that the four solvents have different effects on specific cytochrome P450 isozymes and on the metabolism of both endogenous and exogenous substances.

A computer method of γ-ray spectra stabilization

A numerical method for correction of shift and gain instability in γ-spectroscopy has been developed. It is proposed to apply the correction to partial spectra obtained for a short counting time. The resulting spectrum is then obtained by summing up the partial spectra. The procedure does not change the peak parameters, such as peak area and the full-width-at-half-maximum (FWHM). The changes in the position of two reference peaks are used for correction. To test the method, two spectra were shifted by 0.5 channel: a standard spectrum obtained from the IAEA in Vienna and a spectrum of neutron activated geological sample. The changes in peak area and FWHM after such shifting are much smaller than their relative standard deviations. The spectra were also modified by changing the gain. The obtained results were similar to those obtained by shifting.

Ion beam effects on the composition and structure of glass surfaces

Changes in the surface composition and structure of a number of alkali silicate glasses, bombarded by 1–5 keV argon ions, have been characterized by x-ray photoelectron spectroscopy. Quantitative analyses of peak area changes indicate that the glass surfaces are dealkalized by the ion beam, and decomposition of the respective O 1s spectra reveal that the surfaces simultaneously repolymerize.

Relationship between densitometric peak area and concentration of lipid in the quantitative analysis of a lipid mixture separated by thin-layer chromatography

A mixture of the neutral lipids squalene, cetyl stearate, triolein, oleic acid and cholesterol was separated by thin-layer chromatography and the components were measured quantitatively by photodensitometry. Several empirical expressions relating densitometric peak area ( A) and lipid concentration ( C) were subjected to statistical analysis, and the relationship A = k· C B is linear in the logarithmic form log A = B·log C + log k within 95% confidence limits on the observed results. Exponent B, representing the proportionality factor in the expression relating the relative differential changes in peak area and concentration, it constant for lipids studied on the same chromatoplate, whereas the constant k is lipid dependent. All standard measurements per plate are therefore utilized for estimating a common B value, which gives greater accuracy than in the individual cases. The plate capacity for measurements of unknown lipid concentrations may consequently be increased, as a common B value, based on a reduced number of standard measurements, may be estimated with the same accuracy as an individual B value, based upon the non-reduced number of standard measurements. Equations are given for the calculation of B and k and for the determination of unknown concentrations with appropriate confidence intervals.