Direct Spectral Analysis Research Articles

Analytical possibilities of elemental analysis of water solutions based on the emission spectrum of a laser spark on the surface

The possibilities of spectrochemical methods of analysis of substances using lasers for atomization were investigated in detail in [1-4]. In particular, the formation and development, in both time and space, of a laser spark on the surface of metals and solid dielectrics were studied in detail [5, 6]. The investigations showed that the emission line spectrum of the laser plasma arises after the continuous background emission pulse, which lasts for several hundreds of nanoseconds [7]. The efficiency of excitation of the atoms and ions formed and the temporal characteristics of their emission depend on the power of the laser pulse [8, 9]. In addition, the ratio of the line and continuous emission intensities depend significantly on the spatial arrangement of the emitting zone in the plasma flame. All these investigations have shown that the contrast of the emission spectrum can be significantly increased [i0, ii] by optimizing the plasma flame formation process (by changing the density of the medium into which the material vaporized by the laser radiation expands, using two irradiation pulses, and optimizing the spatial and time intervals for the measurements), and in the process the relative detection limit can reach a value of the order of 10-5% [6, 7], while the sensitivity of the direct laser spectral analysis, which is of the order of 0.01% [4], is too low.

Electrospray ionization mass spectrometry of platinum anticancer agents

Quantification and identification of platinum drugs and their metabolites in biological samples has always been difficult because these compounds are thermally unstable, non-volatile and insoluble. We have demonstrated that electrospray ionization mass spectrometry can be a valuable technique for direct mass spectral analysis of platinum anticancer agents and for obtaining structural information as a result of fragmentation. Full-scan spectra were obtained with approximately 10 pmol samples. These results show the potential of applying this technique in pharmacokinetic studies of platinum anticancer drugs.

Clonidine Reduces Blood Pressure and Heart Rate Oscillations in Hypertensive Patients

Short-term fluctuations in blood pressure (BP) and heart rate (HR) were analyzed in a group of eight men with essential hypertension. Indirect finger BP was measured by a Finapres device. Analog-to-digital conversion of the BP was used to determine systolic (SAP), diastolic (DAP), and mean arterial pressure (MAP) and HR every second. The equidistant sampling allowed a direct spectral analysis using a fast Fourier transform algorithm. The effects of an oral dose of clonidine (150 micrograms) were studied in a double-blind, crossover, placebo-controlled study. Clonidine markedly reduced the variability of BP and HR after 90 min as indicated by a reduction in the standard deviations of BP by 36.7% for SAP, 21.0% for DAP, 22.1% for MAP, and 26.0% for HR. At this time clonidine reduced the average BP by 19.7 mm Hg for SAP, 10.6 mm Hg for DAP, 16.0 mm Hg for MAP, and 1.0 beat/min for HR. Spectral profiles of BP and HR illustrated the alterations in the spontaneous oscillations underlying the standard deviation changes. Clonidine dramatically reduced the amplitude of BP and HR oscillations in the mid-frequency region 66-129 mHz, which depends on the activity of the autonomic nervous system. We suggest that an increased sensitivity of the baroreflex is responsible for the apparent better control of BP and HR with clonidine.

Clonidine Reduces Blood Pressure and Heart Rate Oscillations in the Conscious Rat

We investigated the effects of clonidine on the fluctuations that underlie the spontaneous variability of blood pressure (BP) and heart rate (HR) in conscious rats. Analog-to-digital conversion of the intrafemoral BP was used to determine systolic, diastolic, and mean BP and HR every 200 ms. The equidistant sampling allowed a direct spectral analysis using a fast Fourier transform algorithm. An i.v. dose of 10 micrograms/kg of clonidine markedly reduced the variability of BP and HR after 20 min as indicated by a reduction in the variances by approximately one-half of the control value for BP and to one-third of the control value for HR. At this time, clonidine had not significantly altered BP or HR. Spectral profiles of systolic BP and HR illustrated the alterations in the spontaneous oscillations underlying these variance changes. Clonidine dramatically reduced the amplitude of BP and HR oscillations in the frequency region of 195-605 mHZ, which depends on the activity of the autonomic nervous system. We suggest that an increased sensitivity of the baroreflex is responsible for the apparent better control of BP and HR with clonidine.

Spectral analysis of blood pressure and heart rate in conscious rats: effects of autonomic blockers

We investigated the fluctuations which underly the spontaneous variability of blood pressure and heart rate in conscious rats. Intrafemoral blood pressure was computed to generate evenly spaced signals (systolic, diastolic, mean blood pressure, heart rate) at 200 ms intervals. This equidistant sampling allowed a direct spectral analysis using a Fast Fourier Transform algorithm. Systolic blood pressure and heart rate exhibited low-frequency oscillations (Mayer waves, 20–605 mHz) and a high- frequency oscillation related to respiration (1855 mHz). The respiratory fluctuations in heart rate were almost abolished by vagal blockade (atropine). Heart rate fluctuations in the low-frequency regime were diminished by vagal blockade or cardiac sympathetic blockade (atenolol). The respiratory frequency fluctuations in systolic blood pressure were markedly increased by α-sympathetic blockade (prazosin). In contrast, the low-frequency oscillations in systolic blood pressure were reduced by α-sympathetic blockade. These data indicate that in conscious rats: (1) the heart rate oscillation with respiration is vagally mediated; (2) the heart rate fluctuation in the low-frequency range is jointly mediated by β-sympathetic and parasympathetic activities; (3) the respiratory oscillation in systolic blood pressure depends on fluctuations in cardiac output and is normally counteracted by the sympathetic tone; (4) the low-frequency oscillations in systolic blood pressure reflect the sympathetic activity to the resistance vessels.

Structural characterization of cisplatin analogues by fast atom bombardment (FAB) and laser microprobe mass spectrometry (LAMMA)

The present study is concerned with the investigation of the potentials and limitations of fast atom bombardment (FAB) and laser microprobe mass spectrometry (LAMMA) for the structural characterization of a series of cisplatin analogues. The limiting factors for obtaining good quality FAB spectra are the solubility and the stability of the organometallic platinum complexes in the FAB matrix. In the case of a suitable matrix being found, molecular weight information is derived from the (M + H) + and/or (M — H) − ions. Drawbacks of the application of FAB are (i) the low signal intensities of the molecular ion-like species as compared to the matrix signals and (ii) the scarcity of fragmentation necessary for structure determination. Combination of FAB with tandem mass spectrometry was used to overcome these problems. LAMMA provides a valuable alternative for the direct mass spectral analysis of cisplatin analogues. For some compounds, LAMMA results in useful mass spectra, whereas FAB fails. The abundant fragmentation yields structural information which is complementary for positive and negative ions. The laser power density applied to the sample is of critical importance for the quality of the spectra.

On subordinacy and analysis of the spectrum of Schrödinger operators with two singular endpoints

SynopsisThe theory of subordinacy is extended to all one-dimensional Schrödinger operatorsfor which the corresponding differential expressionL= –d2/(dr2) +V(r) is in the limit point case at both ends of an interval (a,b), withV(r) locally integrable. This enables a detailed classification of the absolutely continuous and singular spectra to be established in terms of the relative asymptotic behaviour of solutions ofLu = xu, x εℝ, asr→aandr→b. The result provides a rigorous but straightforward method of direct spectral analysis which has very general application, and somefurther properties of the spectrum are deduced from the underlying theory.

Directional spectral analysis and filtering of geophysical maps

The detection of linear anomalies in map data is facilitated by studying the two‐dimensional power spectrum, because the directivity of the energy in the map is preserved in the Fourier transform. The lineaments associated with individual peaks in the spectrum are then separated from the map data by directional filtering and studied independently of other map features. Gravity and magnetic maps from an active rift area in southwestern Iceland are analyzed in this manner. The agreement between the filtered maps is good and they fit the observed tectonic features quite well.

Sterling revisited: The seismic source for a cavity‐decoupled explosion

In the STERLING event, a 0.38 kt nuclear device was exploded inside a roughly spherical cavity, of approximately 17 m radius. The cavity, located in the Tatum salt dome (near Hattiesburg, Mississippi), had been created by a 5.3 kt tamped explosion more than 2 years earlier (SALMON event). Analysis of data obtained in SALMON and STERLING indicated a corner frequency for STERLING near 10 Hz, a factor of 4 less than predicted by the simplest decoupling theory. We have performed a comprehensive re‐examination of the experimental records and find that the original report was incorrect, a consequence of not properly accounting for noise in the seismic analysis. The new study, based on direct spectral analysis of the free‐field data, indicates that the STERLING experiment was in near perfect agreement with theory. This is a potentially significant result for seismic monitoring of a low‐yield threshold test ban.

Additions and Corrections - Organolanthanide and Organoyttrium Hydride Chemistry. 6. Direct Synthesis and 1H NMR Spectral Analysis of the Trimetallic Yttrium and Yttrium-Zirconium Tetrahydride Complexes, {[(C5-H5)2YH]3H}{Li(THF)4} and{[(CH3C5H4)2YH]2[(CH3C5H4)2Zr-H]H}

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAdditions and Corrections - Organolanthanide and Organoyttrium Hydride Chemistry. 6. Direct Synthesis and 1H NMR Spectral Analysis of the Trimetallic Yttrium and Yttrium-Zirconium Tetrahydride Complexes, {[(C5-H5)2YH]3H}{Li(THF)4} and{[(CH3C5H4)2YH]2[(CH3C5H4)2Zr-H]H}William Evans, James Meadows, and Timothy HansuCite this: J. Am. Chem. Soc. 1984, 106, 23, 7296Publication Date (Print):November 1, 1984Publication History Published online9 April 2004Published inissue 1 November 1984https://doi.org/10.1021/ja00335a602RIGHTS & PERMISSIONSArticle Views29Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (160 KB) Get e-Alerts Get e-Alerts

Organolanthanide and organoyttrium hydride chemistry. 6. Direct synthesis and proton NMR spectral analysis of the trimetallic yttrium and yttrium-zirconium tetrahydride complexes, {[(C5H5)2YH]3H}{Li(THF)4} and {[(CH3C5H4)2YH]2[(CH3C5H4)2ZrH]H}

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOrganolanthanide and organoyttrium hydride chemistry. 6. Direct synthesis and proton NMR spectral analysis of the trimetallic yttrium and yttrium-zirconium tetrahydride complexes, {[(C5H5)2YH]3H}{Li(THF)4} and {[(CH3C5H4)2YH]2[(CH3C5H4)2ZrH]H}William J. Evans, James H. Meadows, and Timothy P. HanusaCite this: J. Am. Chem. Soc. 1984, 106, 16, 4454–4460Publication Date (Print):August 1, 1984Publication History Published online1 May 2002Published inissue 1 August 1984https://doi.org/10.1021/ja00328a027RIGHTS & PERMISSIONSArticle Views222Altmetric-Citations57LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (914 KB) Get e-Alerts Get e-Alerts

Variation of frequency spectrum of the erythrocyte flickering caused by aging, osmolarity, temperature and pathological changes

Frequency spectra of the surface undulations (flickering) of erythrocyte plasma membranes are measured by direct spectral analysis of the intensity fluctuations of the light passing the cells in a phase contrast microscope. Spectra are taken as a function (1) of the temperature (2) of the viscosity and osmolarity of the outer medium (3) of the aging of cells and (4) of pathological transformations. The spectra are approximately superpositions of two Lorentzian lines. At large frequencies, f, the spectra follow f −2. This behaviour can be interpreted in terms of cell thickness fluctuations caused by thermally excited membrane undulations provided the range of wavelengths is small. The undulations are determined by the membrane curvature elasticity while the lateral tension is negligibly small for cells of discoid shape. The technique presented allows accurate measurements of relative curvature (bending) elastic constants. The spectra of freshly drawn cells are remarkably reproducible. Aging of the cells in the medium leads to an increase in the curvature elastic constant. A decrease in osmolarity causes a reduction in the intensity and line width of the spectra and the flickering vanishes if the cell approaches a spherical shape. The effect of temperature between 10 and 40°C is astonishingly small with the exception of a sudden increase in the amplitude with increasing temperature at 35°C. The flicker spectra of a large fraction of the cells from patients suffering from cronical alcoholism exhibit a reduced line width or an increase in the curvature elastic constant.

IV. A model system for mass spectrometric sequencing of orthophthalaldehyde peptide derivatives

Presented is a pilot project describing a new strategy for mass spectrometric peptide sequencing. Using orthophthalaldehyde (OPA), two peptides were derivatized and their fluorescent adducts isolated using reversed phase high performance liquid chromatography. The OPA-peptides were permethylated and the derivatized molecules subjected to direct probe mass spectral analysis. The spectra obtained from the OPA-peptides was analogous to those observed for standard N -acyl permethyl derivatives enabling the complete sequence of the peptides to be determined.

Exopeptidase digestion in combination with field desorption mass spectrometry for amino acid sequence determination

Numerous studies have been devoted in the last years to the development of mass spectrometric methods for the sequence determination of peptides [ 1,2]. Most advanced among this work has been so far the rigorous chemical derivatization of oligopeptides to achieve sufficient volatility for the application of conventional (electron impact, EI) mass spectrometry [2-41. For example, the analysis by gas chromatography-mass spectrometry (GC-MS) of mixtures of oligopeptide fragments derivatized after chemical or enzymatic hydrolysis of polypeptides has been successfully used for sequence determinations [2,5]. Major limitations of this approach are that only small peptide derivatives are amenable to GC-MS, and the relatively large amount of original peptide needed. More recently, mass spectra of underivatized peptides have been obtained by field desorption (FD) mass spectrometry [6], a technique that does not require any volatility of the sample to be ionized. It was shown that FD mass spectra of oligopeptides usually exhibit molecular ions (e.g., protonated, MH’ ions) of high intensity, with relatively little fragmentation [7,8]. While studies of thermally or collisioninduced fragmentation in FD spectra of peptides [9-l l] so far indicate only limited utility for obtaining structural information, the possibility of analysing peptide mixtures by means of the predominant molecular ions has been suggested [ 121. FD mass spectrometry in combination with Edman degradation-subtractive analysis has been reported [ 131. the available enzymes (e.g., contamination with endopeptidase or different types of exopeptidase activity), and the problem of determining repetitive amino acid residues have limited their application so far. Attempts to overcome these difficulties have been made such as the addition of endopeptidase inhibitors [ 14,151 and solid-phase sequencing with exopeptidases [ 161. However, the characteristic feature of the inhomogeneous kinetics of exopeptidase digestion which, in principle, should match well the capability of FD mass spectrometry to analyse peptide mixtures prompted our interest to test the combination of both methods for peptide sequencing. Here, fast and unequivocal sequence determinations were obtained for 2 oligopeptides by direct FD mass spectral analysis of aliquots taken from partial aminoand carboxypeptidase digests The finding that FD mass spectra of exopeptidase digests provided reliable sequence data without any separation step required, and with amounts of material at the sub-nanomole level indicate that this combination may prove to be a valuable approach among the instrumentarium for the sequence determination of peptides.

Study of the change of organic matrix during the preparation of petroleum for direct spectral analysis of trace elements

Study of the change of organic matrix during the preparation of petroleum for direct spectral analysis of trace elements

The formal equivalence between autocorrelation and power spectral analyses of photon-limited data

It is shown that direct autocorrelation and power spectral analyses yield equivalent signal-to-noise ratios from photon limited data. Apparent discrepancies in previous analyses are shown to be due to terms, at the origin of the autocorrelation, which are not generally considered.

Layer-by-layer spectral analysis in a discharge with hollow cathode

The in-depth resolution reached with a Grimm discharge can apparently be improved by using a discharge in a hollow cathode. It is known that the minimal width of the analyzed layer depends on the sensitivity of the determination of the element studied, With a cooled hollow cathode the sensitivity of the determination is higher than with the Grimm discharge, because of the more effective excitation of the sample analyzed [8, 9]. This procedure for improving the in-depth resolution was the subject of the present investigation, A direct spectral analysis was carried out in a negative glow discharge in a hollow cathode. The sample of the film on an electroconducting support was placed at the bottom of a cooled hollow cathode made of a highly-pure aluminum, which is more difficult to sputter than the films we studied. The energy of argon (or neon) ions bombarding the layer is about 3,102 eV [i0], and the depth of penetration of the ions does not exceed a few angstroms [4]. The density of the ionization current was 10-24 mA/cm 2. The main possible use of the cooled hollow cathode for the layer-by-layer analysis was studied for the analysis of antimony and bismuth chloride films. Alternating layers of antimony and bismuth chlorides were deposited on a graphite support. The thickness of each chlo ~ ride layerwas determined gravimetrically, and was ~i0 "'~ cm. A vacuum of i0 -~ torr was cre~ ated in the light source, and then argon was passed in to a pressure of 0,5-1 torr, and discharge was ignited. Figure 1 shows thechange in the analytical signal of antimony (first maximum), bismuth (second maximum) and carbon (right-hand branch of the curve). We used the lines of Sb I 259, 8 nm, Bi I 306, 7 nm, C I 324, 7 nm as the analytical lines, and the background served as the reference line. It is seen that the uniformity of etching the layers and the in-depth resolution are sufficient for a separate layer-by-layer analysis of films =10 -6 cm thick. The discharge with the hollow cathode was used for layer-by-layer analysis of the composition of the oxide film on the surface of chromium steel. This problem is interesting for the study of the properties of materials and alloys which are fairly stable at high temperatures, and in different types of media. Corrosion leads to a change in the composition of the surface film, and therefore the composition and thickness of the film are the indicators of the corrosion resistance of the material, Steels with different chromium content (from 8 to 18%) were analyzed. The layer-bylayer analysis was carried out also with films obtained when these steels were oxidized at a temperature of 900~ in an atmosphere for 1-2 h. As standards in the analysis of a surface of steel which was not subjected to oxidation, we used a set of standard samples No. 54 for the spectral analysis of steels, as well as sam

Analysis of cocaine and cocaine metabolites by high pressure liquid chromatography.

A high pressure liquid chromatography procedure was developed for analysis of cocaine and two metabolites (norcocaine and benzoylecgonine) in biological fluid. Following extraction with chloroform/Isopropanol (3/2), chromatography is performed with a mu-Bondapak C-18 reverse phase column eluted with water/acetonitrile/methanol (8/1/1) containing 1% acetic acid and 0.3 M EDTA. Ultraviolet detection of individual compounds was made at 235 nm and quantitation was based on peak height ratio to internal standard. Detection limit based on 0.5 mL of sample is less than 1 microgram/mL. Confirmation of the individual compounds was made by direct probe mass spectral analysis of the eluted peaks and comparison to known standards.

Direct spectral analysis of semiconducting layers

Direct spectral analysis of semiconducting layers

SPECTRAL PROPERTIES OF CHLOROPHYLL a MONOLAYERS: MONOLAYERS OF CHLOROPHYLL a AND PHEOPHYTIN AT A GAS‐WATER INTERFACE*

Abstract— Surface and spectral properties of chlorophyll a monolayers were studied at a nitrogen‐water interface. Direct spectral analysis of Chl monolayers indicated that compression results in a heterogenous mixture of Chl species. Fourth derivative and difference spectra showed the presence of minor bands at 692, 726 and 748 nm. The state of compression determines the quantity and type of spectral species formed. A Chl monolayer on an acid subphase results in the formation of a long wavelength absorbing species (705 nm) similar to that of pheophytin. The half‐band width, optical density/monolayer, and extinction coefficients of Chl monolayers are given. It is concluded that in the monolayer the formation of various aggregated species of Chl can be induced.