Peak Height Measurements Research Articles

Flow-injection hydride generation atomic absorption spectrometric study of the automated on-line pre-reduction of arsenate, methylarsonate and dimethylarsinate and high-performance liquid chromatographic separation of their l-cysteine complexes

An automated on-line pre-reduction of arsenate, monomethylarsonate (MMA) and dimethylarsinate (DMA) using flow injection hydride generation atomic absorption spectrometry (FI-HGAAS) is feasible. The kinetics of pre-reduction and complexation depend strongly on the concentration of l-cysteine and on the temperature in the following increasing order: inorganic As(V)<DMA<MMA. Arsenate is pre-reduced/complexed within less than 50 s at 70–100°C compared to 1 h at room temperature, while MMA and DMA require 1.5–2 min at 70–100°C and up to 1–2 h at room temperature. The characteristic masses and concentrations for 100 μl injections are 0.01 ng and 0.1 μg l −1 in integrated absorbance and 0.2 ng and 2 μg l −1 in peak height measurements, and the limits of detection are ca. 0.5 ng and 5 μg l −1, respectively. In a high-performance liquid chromatography (HPLC)–HGAAS system, the l-cysteine complexes of inorganic As(III), MMA and DMA are best separated within 7 min by HPLC on a strongly acidic cation exchange column such as Spherisorb S SCX 120×4 mm (5 μm) with a mobile phase containing 12 mmol l −1 phosphate buffer (KH 2PO 4/H 3PO 4)–2.5 mmol l −1 l-cysteine, pH 3.3–3.5. Upon dilution to l-cysteine levels below 10 mmol l −1, which are compatible with HPLC separations, the DMA–cysteine complex is unstable on storage. No baseline separations are possible with anion exchange and reverse phase C 18 HPLC columns. The limits of detection with 50 μl injections in peak area mode are ca. 0.5 ng and 10 μg l −1, respectively.

On-line UV-photooxidation with peroxodisulfate for automated flow injection and for high-performance liquid chromatography coupled to hydride generation atomic absorption spectrometry

An automated on-line UV photooxidation with peroxodisulfate of some environmentally relevant organoarsenic and organotin compounds in a system built from commercially available modules has been studied and optimised with a view to both species-independent quantification of the total arsenic or tin in samples containing different organic species by flow injection hydride generation atomic absorption spectrometry (FI–HGAAS) and speciation analysis by coupled high-performance liquid chromatography (HPLC) with HGAAS detection. For organoarsenicals, the reaction with alkaline peroxodisulfate in a 10–15-m knotted reactor for >1.5 min insures >90% transformation of inorganic As(III) and six organoarsenic species to arsenate: monomethylarsonate, dimethylarsinate, arsenobetaine, arsenocholine, trimethylarsine oxide and tetramethylarsonium. For organotins, the UV photooxidation with acidic peroxodisulfate at 95–100°C provides recoveries of >80% for the inorganic tin, dimethyltin, trimethyltin, triethyltin, tripropyltin, triphenyltin, monobutyltin, dibutyltin and tributyltin but only approximately 15% for tetrabutyltin. The best characteristic masses in integrated absorbance ( A int) and peak-height ( A p) measurements, respectively, are 30 pg and 480 pg for arsenic(V) and 22 pg and 410 pg for tin(IV), employing 100-μl injections. The RSDs are 5.5% and 8.5% at 5 ng As(V) levels and 4.3% and 6.4% at 10 ng Sn(IV) levels in A int and A p modes, respectively. The limits of detection (LOD, 3σ) for As are 7 μg l −1 and 4 μg l −1 in FI-UV–HGAAS and HPLC–UV–HGAAS, respectively. The LODs for i-Sn(IV) are 2 μg l −1 in FI-UV–HGAAS, with both A int and A p measurements. The sample throughput rates are 20 and 12 samples per hour with 10-m and 15-m knotted reactors (i.d. 0.5 mm), respectively. Urine certified reference materials containing 0.052–0.48 μg ml −1 As have been analysed for their total arsenic content.

Determination of elemental mercury by cavity ringdown spectrometry

Cold vapor cavity ringdown spectroscopy has been successfully applied to the detection of elemental mercury. Using an absorption cell 0.18 m in length, detection limits of 0.027 and 0.12 ng were obtained using peak area and peak height measurements, respectively. For the peak area measurement, this corresponds to a gas phase concentration of less than 25 ng m−3. For comparison, using a similar absorption cell, standard AAS yielded a Hg detection limit (peak height) of 9 ng, (gas phase concentration of ≡ 8.3 μg m−3).

Study for Analyzing Unevenness of Negative Corona Discharge

We have been studying the basis of the air flow effect which increases the uniformity and stability of negative corona discharge. The possibility that the stability of the negative corona is disturbed by some interruption for the flow of light to the surface of the wire electrode is investigated. Spectra distributions of the corona discharge in air atmosphere and in N2 atmosphere are measured as a first step. Major peaks are seen in the ultraviolet band. Measured peak heights in negative corona discharge are found to be four times bigger, in air, than those in positive corona discharge. Almost all major peaks in air were confirmed to have the same wavelength as was measured under N2. The measured difference in the spectrum distribution curves between positive and negative corona discharges indicates differences in the discharge mechanisms and a hint for analyzing the air flow effect in negative corona discharge.

Determination of selenite and selenate in human urine by ion chromatography and inductively coupled plasma mass spectrometry

The selenium species selenite, selenate and selenomethionine were separated in aqueous solution by ion chromatography. The separation was performed on an IonPac AG11 in series with an AS11 anion exchange column by elution with 25 mM sodium hydroxide in 2% methanol. The 78Se and 82Se isotopes were monitored in the inductively coupled plasma mass spectrometry (ICP-MS) detector. When the chromatographic system was applied to analysis of urine samples diluted 1 + 1, the selenomethionine signal appeared in the front together with other unresolved selenium species, while the selenite and selenate signals were well separated. Calibration curves obtained after spiking a urine pool with standards in the range 2–50 µg Se l−1 were linear for selenite as well as selenate. The precision at the 10 µg l−1 level was better than 1%. The limits of detection were 0.4 and 0.8 µg l−1 for selenite and selenate, respectively, corresponding to absolute amounts of 8 and 16 pg, respectively. Calculations were based on peak height measurements of the 82Se isotope. In 23 analysed urine samples, the concentration of selenite was in the range <0.4–7.1 µg l−1, while the range of the total selenium concentration was 12.4–97.6 µg l−1. No detectable amounts of selenate were found in any of the samples. There was no correlation between selenite and total selenium concentration. No loss of selenite in the samples was observed within 7 h.

Usefulness of Single Voxel Proton MR Spectroscopy in the Evaluation of Hippocampal Sclerosis

ObjectiveThe purpose of our study was to determine the ability of H-1 MR spectroscopy (MRS) to lateralize the lesion in patients with hippocampal sclerosis.Materials and MethodsTwenty healthy volunteers and 25 patients with intractable temporal lobe epilepsy whose MR imaging diagnosis was unilateral hippocampal sclerosis were included. This diagnosis was based on the presence of unilateral atrophy and/or high T2 signal intensity of the hippocampus. Single-voxel H-1 MRS was carried out on a 1.5-T unit using PRESS sequence (TE, 136 msec). Spectra were obtained from hippocampal areas bilaterally with volumes of interest (VOIs) of 6.0 cm3 and 2.25 cm3 in healthy volunteers, and of either 6.0 cm3 (n = 14) or 2.25 cm3 (n = 11) in patients. Metabolite ratios of NAA/Cho and NAA/Cr were calculated from relative peak height measurements. The capability of MRS to lateralize the lesion and to detect bilateral abnormalities was compared with MR imaging diagnosis as a standard of reference.ResultsIn healthy volunteers, NAA/Cho and NAA/Cr ratios were greater than 0.8 and 1.0, respectively. In patients, the mean values of these ratios were significantly lower on the lesion side than on the contralateral side, and lower than those of healthy volunteers (p < .05). The overall correct lateralization rate of MRS was 72% (18/25); this rate was lower with a VOI of 6.0 cm3 than of 2.25 cm3 (64% versus 82%, p < .05). Bilateral abnormalities on MRS were found in 24% (6/25) of cases.ConclusionAlthough its rate of correct lateralization is low, single-voxel H-1 MRS is a useful and promising diagnostic tool in the evaluation of hippocampal sclerosis, particularly for the detection of bilateral abnormalities. To improve the diagnostic accuracy of H-1 MRS, further investigation, including the use of a smaller VOI and measurement of the absolute amount of metabolites, are needed.

The height of the maximum ionospheric electron density over the MU radar

Ionospheric F 2-layer peak height h m F 2 variations, as measured over 1986–1995 by the MU radar (34.85°N, 136.1°E) and as calculated with a theoretical model, are discussed. The diurnal variations of the measured peak height for different seasons and levels of solar activity are compared with those estimated from ionosonde M3000 F 2 and IRI predictions. Also given are the measured ion drift velocities and meridional neutral winds needed to understand the dynamic behavior of the F 2-layer. It is found that: (1) h m F 2 is generally higher during periods of the solar maximum than during periods of the solar minimum, and higher in summer than in winter; (2) for the solar maximum, h m F 2 drops markedly in the morning and in the afternoon, while, for the solar minimum, the h m F 2 minimum occurs in the morning during summer and usually in the afternoon during winter. In general, the measured h m F 2 is well reproduced by our model when we use the observed drift velocities and plasma temperatures as inputs. Our modeling study shows that the neutral wind contributes strongly to the diurnal variation of h m F 2 in winter by lowering the ionization layer by day, particularly for the solar maximum; it also helps to enlarge the day–night difference of h m F 2 in summer. The northward electromagnetic drifts that usually cancel the neutral wind effect have only a minor effect for the location of the MU radar. Other features of the observed h m F 2 variations, e.g., the solar maximum–minimum difference, the summer–winter difference, and the morning and afternoon drops, are explained by the basic processes of O + production, loss and diffusion, as influenced by the atomic oxygen concentration and neutral and plasma temperatures.

Determination of total and inorganic mercury in biological and environmental samples with on-line oxidation coupled to flow injection-cold vapor atomic absorption spectrometry

A method for determination of inorganic and total mercury by flow injection-cold vapor atomic absorption spectrometry (FI-CVAAS) with on-line oxidation was developed. Potassium peroxodisulphate and sulphuric acid were used as oxidizing agents so that decomposition of organomercury compounds could be achieved. Depending on the temperature selected, inorganic or total mercury could be determined with the same FI manifold. In order to assess the method performance, synthetic wastewater, wastewater, urine and saline water samples were spiked with inorganic mercury, methylmercury and phenylmercury. Quantitative recoveries were obtained for the three mercury species, except with the synthetic wastewater when the chemical oxygen demand value was higher than 1000 mg l−1. In most cases, the standard addition method was usually needed for calibration. LODs calculated as 3 σ/m were 0.47 μg l−1 for inorganic mercury and 0.45 μg l−1 for total mercury. R.S.D. values corresponding to peak height measurements were 1.5 and 2.2% for inorganic mercury and total mercury, respectively. The accuracy of the method was tested by analyzing 5 mol l−1 hydrochloric acid extracts of seven biological and environmental CRMs. LODs in the solid CRMs ranged from 0.032 to 0.074 μg g−1.

Periodic forcing in composite aquifers

Observations of periodic components of measured heads have long been used to estimate aquifer diffusivities. The estimations are often made using well-known solutions of linear differential equations for the propagation of sinusoidal boundary fluctuations through homogeneous one-dimensional aquifers. Recent field data has indicated several instances where the homogeneous aquifer solutions give inconsistent estimates of aquifer diffusivity from measurements of tidal lag and attenuation. This paper presents new algebraic solutions for tidal propagation in spatially heterogeneous one-dimensional aquifers. By building on existing solutions for homogeneous aquifers, comprehensive solutions are presented for composite aquifers comprising of arbitrary (finite) numbers of contiguous homogeneous sub-aquifers and subject to sinusoidal linear boundary conditions. Both Cartesian and radial coordinate systems are considered. Properties of the solutions, including rapid phase shifting and attenuation effects, are discussed and their practical relevance noted. Consequent modal dispersive effects on tidal waveforms are also examined via tidal constituent analysis. It is demonstrated that, for multi-constituent tidal forcings, measured peak heights of head oscillations can seem to increase, and phase lags seem to decrease, with distance from the forcing boundary unless constituents are separated and considered in isolation.

Co-operative study for precision and limit of detection in HPLC analysis.

The limit of detection (LOD) was determined for three p-hydroxybenzoic acid esters at nine laboratories. The result of each laboratory was analyzed by computer software (called TOCO) which predicts the precision and LOD based on the baseline fluctuation without repeated measurements. In every laboratory, the shorter was the retention time of the analytes, the lower was the LOD. In each analyte, the peak-height measurement was more precise than the entire area measurement. The LOD obtained by the laboratories ranged from 0.16 to 30 μg/l. The validity of the TOCO, when applied in practical situations, has been proved.

Alternative method for determination of ceftazidime in plasma by high-performance liquid chromatography

A high-performance liquid chromatography procedure was developed to analyze ceftazidime concentrations in plasma. The procedure consisted of solid phase extraction followed by ion-pairing reverse-phase chromatography. An excellent linear relationship between ceftazidime peak height measurements and concentrations was demonstrated over the concentration range of 1–200 μg ml −1. The advantage of this assay is the elimination of interference at the ceftazidime elution time that has been noted in previous studies and in our experience. Thus, this study describes an alternative, simple methodology that is clinically useful for analyzing ceftazidime in the research setting.

Quantitative determination of glucose in blood plasma by homonuclear proton decoupled water attenuation transverse relaxation Carr-Purcell-Meiboom-Gill (WATR-HDCPMG) NMR spectroscopy

Glucose in 5% D2O/95% H2O solution was successfully determined quantitatively by measurements of the 1H NMR peak height (intensity) of the single peaks at δ(1H) = 5.22 and 4.64 ppm corresponding to the α-D and the β-D-glucose spectrum, respectively. The single peaks were obtained from decoupling of the high field part of the AX spectrum of the α-D- or the β-D-glucose by incorporation of time shared homonuclear decoupling in the WATR-CPMG method (WATR-HDCPMG) without re-attenuation of the water peak. The method was applied to the determination of total glucose in blood plasma from human subjects undergoing oral glucose tolerance test (OGTT) in the teaching hospital. The results compared favorably with those obtained from the standard glucose oxidase method obtained in a hospital pathology laboratory. The accuracy of the results obtained using the WATR-HDCPMG method was within 3.5% of the glucose oxidation method.

X-ray photoelectron spectroscopy characterization of the oxidation of electroplated and sputter deposited copper surfaces

X-ray photoelectron spectroscopy (XPS) was used to study the surface oxidation of sputtered and electroplated copper films following exposure to ambient air and chemical processing reagents used during the fabrication of interconnect structures. Exposure of both sputtered and electroplated copper films to ambient air and deionized (DI) water resulted in the formation of thin copper oxide layers. For ambient exposed copper films, the topmost layer contains Cu2+ oxide species, and the next Cu+ oxides. For DI water exposure, only Cu+ oxide species were observed. Oxidation was more rapid for the electroplated compared to the sputtered copper films as measured by copper oxide to copper metal concentration ratios calculated from XPS curve fitting results and photon-induced Auger peak height measurements. For the electroplated copper films, oxygen uptake was slower as a result of exposure to ambient compared to DI water treatments. Electroplated copper films exposed to common wet chemical etchants also show indications of oxidation of the copper surface region with evidence of mechanical instability between the formed oxide and underlying copper film, resulting in adhesion loss. A method for the removal of the oxide layer has also been investigated to improve adhesion to overlying passivation films.

A mid-latitude E-layer peak height model

While the E-layer peak height is given in the IRI-95 model as a constant equal to 110 km this is not confirmed by the rocket and incoherent scattering radar data. In fact the E-layer peak height at mid latitudes is constant only a certain time around noon. The proposed model is based on averaged measurements of the E-layer peak height made by the mid-latitude radar of Kharkov Institute of Ionosphere for different zenith angles, seasons and solar activities from which a new software has been developed. Distinct from other models the new one for all seasons gives more accurate values for the E-layer peak height in the vicinity of local noon.

Liquid chromatography-Fourier transform infrared spectrometric determination of cholesterol in animal greases

Stearic acid, cholesterol and cholesteryl palmitate have been separated in less than 14 min by liquid chromatography on a column (3.9 mm i.d.×150 mm) of Nova-Pack C 18 (5 μm) using chloroform–acetonitrile (45 : 55) as mobile phase pumped at 0.5 ml min −1; Fourier transform infrared (FTIR) spectrometry was employed for both, general detection at 2868 or 2855 cm −1 and selective detection at 3285 cm −1 for stearic acid and 3526 cm −1 for cholesterol. In all cases a baseline established at 3900 cm −1, 9-point smoothing and chromatographic peak height measurements were used. The method has been validated by application to the determination of cholesterol in animal greases and fish oils. Samples, previously saponified with KOH, were extracted with petroleum ether, redissolved in chloroform and the final solution injected into the chromatographic system. The percentage recoveries were 95–99% for samples spiked with cholesterol and 100–102% for samples spiked with cholesteryl palmitate.

Upgrading the AOCS infrared trans method for analysis of neat fats and oils by fourier transform infrared spectroscopy

AbstractAn automated protocol for the direct, rapid determination of isolated trans content of neat fats and oils by Fourier transform infrared (FTIR) spectroscopy was devised, based on a simple modification of the standard AOCS trans method, eliminating the use of CS2 and methylation of low trans samples. Through the use of a commercially available, heated transmission flow cell, designed specifically for the analysis of neat fats and oils, a calibration (0–50%) was devised with trielaidin spiked into a certified, trans‐free soybean oil. The single‐beam spectra of the calibration standards were ratioed against the single‐beam spectrum of the base oil, eliminating the spectral interference caused by underlying triglyceride absorptions, facilitating direct peak height measurements as per the AOCS IR trans method. The spectrometer was preprogrammed in Visual Basic to carry out all spectral manipulations, measurements, and calculations to produce trans results directly as well as to provide the operator with a simple interface to work from. The derived calibration was incorporated into the software package, obviating the need for further calibration because the program includes an automatic recalibration/standardization routine that automatically compensates for differences in optical characteristics between instruments, instrument drift over time, and cell wear. The modified AOCS FTIR analytical package was evaluated with Smalley check samples for repeatability, reproducibility, and accuracy, producing SD of ± 0.07, 0.13, and 0.70 trans, respectively, the FTIR predictions being linearly related to the Smalley means (r=0.999; SD=± 0.46), and well within one SD of the Smalley sample means. Calibration transfer was assessed by implementing the calibration on a second instrument and reanalyzing the Smalley check samples in cells of two different pathlengths (25‐ and 50‐µm). There were no statistically significant differences between the FTIR trans predictions obtained for the Smalley samples from the two instruments and two cells, indicating that the software was able to adjust the calibrations to compensate for differences in instrument response and cell pathlength. The FTIR isolated trans analysis protocol developed by the McGill IR Group has the benefit of being based on the principles of an AOCS‐approved method, matches its accuracy, and allows the analysis to be performed on both neat fats and oils, producing trans predictions in less than 2 min per sample. It is suggested that this integrated approach to trans analysis, which requires a minimum level of sample manipulation and operator skill, be considered as a modification of the proposed Recommended Practice CD14b‐95.

Photoacoustic soot sensor for in-situ black carbon monitoring

The PhotoAcoustic Soot Sensor (PASS) for in situ black carbon mass monitoring is presented. The sensor combines a high-power laser diode (λ = 802 nm;P = 450 mW) and a novel spectrophone setup to achieve a portable sensor system for black carbon measurements. The acoustic resonator with aQ-factor of ≈ 300 is operated in its 2nd azimuthal mode at 6670 Hz. To estimate the effects of the window position, laser beam collimation, and different loss mechanisms on spectrophone sensitivity a model treating these effects with respect to the signal strength of the azimuthal modes is described. It gives a cell constant of 5.8 V/(W m−1) in good agreement with 5.9 V/(W m−1) obtained from measurements with particulate carbon. Additionally, this model permits a method for an absolute calibration of the spectrophone. To improve the signal-to-noise ratio, the photoacoustic signal is estimated by a weighted least-squares fit to an averaged line profile of the excited normal mode instead of a direct measurement of peak height. Finally, the application of this data processing algorithm yields a detection limit of 1.5 × 10−6 m−1 or 0.5 μg black carbon per m3

Analysis and Temporal Variations of Trace Metals in Precipitation at an Atlantic Station

Abstract Weekly and half-monthly bulk samples have been collected over one year at an Atlantic station and routinely analysed for 0.08 M HNO3-leachable trace metals Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn by direct electrothermal atomic absorption spectrometry. In the presence of sea salt, interference effects may lead to important erroneous metal concentrations if peak height measurements and direct calibration with aqueous standards are used. Interference effects are minimized (to about 5%) by using integrated absorbance measurements for sea salt solutions having CNa< 100 mg/l and using standards prepared in the presence of sea salt (20 mg/l in Na). The variability of trace-metal determinations obtained for six bulk collectors for each sampling event shows that our entire analytical protocol, sampling and analysis, permits to follow their temporal variations at a coastal station for weekly or half-monthly sampling periods. A high correlation is obtained for anthropogenic metals Cd, Cu, Ni, Pb and Zn. For Cr, ...

Study of chemical modifiers for direct determination of silver in sea water by ETA-AAS with deuterium background correction

Methods for the direct determination of silver in sea water samples by ETA-AAS using different chemical modifiers were studied. The effect of salinity was studied using synthetic sea water of high (72.8‰) and low (34.2‰) salinity, and the results were compared with aqueous standard solutions. The charring temperatures achieved were 800 and 900 °C for magnesium nitrate and ammonium dihydrogen phosphate respectively, being 1100 °C for palladium nitrate and their mixtures. The best sensitivity obtained in the peak-height measurement mode was achieved by using reduced palladium (limit of detection (LOD) between 0.5 and 1.1 μg l −1 for an injection volume of 20 μ1) with analytical recoveries close to 100% for synthetic and real sea water samples. The use of ammonium dihydrogen phosphate (LOD of 1.3 μg l −1 for an injection volume of 20 μ1) produced good recoveries for low salinity; at high salinity an increase of around 25% was obtained, the method being unsuitable for sea water analysis. Finally, an interference study of the major components of sea water was carried out and applied to the analysis of surface sea water from the Galicia coast.

Signal processing of transient atomic absorption signals

This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hard copy text is accompanied by a disk with a demonstration version of the simulation program, libraries of electronic and optical component blocks, simulation models, manual, and other files. Absorbance signals for electrothermal atomization atomic absorption spectroscopy (ETA-AAS) were generated digitally and the effect of various types and sources of noise upon the precision of the absorbance measurement was evaluated by numerical calculation. Peak area measurement, peak height measurement, and matched filtering were used for processing these signals. The performance of these three techniques in the presence of various types of noises and the sensitivity of each to small variation in the atomization conditions was calculated. It is demonstrated that significant improvement in signal-to-noise ratios can be realized by application of appropriate signal processing methods. The results also indicate that one of the principal causes for loss of precision could be the variation in the heating characteristics of the furnace.