Determination of copper in milk powder by electrothermal atomic absorption and atomic emission spectrometry

Summary Electrothermal atomic absorption spectrometry (ETA-AAS) and atomic emission spectrometry (ETA-AES) have been applied to the determination of copper in powdered milk. A homogeneous dispersion procedure for the preparation of the milk powder is described which was found to be simple, rapid and less susceptible to contamination than dry ashing or wet digestion methods. Both ETA-AAS and ETA-AES techniques were found to provide satisfactory results using conventional tube wall atomisation only when the method of standard additions was employed. The application of graphite probe atomisation in ETA-AES and ETA-AAS allowed the development of direct methods for the determination of copper in milk powder using aqueous standard calibration curves. The accuracy of the probe ETA-AAS method was confirmed using new reference materials prepared by the EEC Community Bureau of Reference. Acceptable agreement was obtained for the other procedures using a commercial milk powder sample with a copper content of 6.0g g^–1.     

Human albumin as a reference material for trace elements

Summary An investigation through interlaboratory comparison using different analytical techniques has been carried out in order to assess the suitability of a plasma protein solution as a source for a trace element reference material in clinical analysis. Reasonable agreement was obtained for a number of elements from the range studied: Al, Ba, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Sr, V and Zn. The techniques used included flame and furnace atomic absorption spectrometry (FAAS and ETA-AAS), furnace atomic emission spectrometry (ETA-AES), inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), and simultaneous multi-element atomic absorption spectrometry (SIMAAC). Results indicated that this plasma protein solution may prove useful as a source for a reference material covering trace element levels outwith the range found in normal human plasma.

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Humanalbumin als Referenzmaterial für Spurenelemente

     

A square-wave wavelength modulation system for automatic background correction in carbon furnace atomic emission spectrometry

A square-wave wavelength modulation system, based on a rotating quartz chopper with four quadrants of different thicknesses, has been developed and evaluated as a method for automatic background correction in carbon furnace atomic emission spectrometry. Accurate background correction is achieved for the residual black body radiation (Rayleigh scatter) from the tube wall and Mie scatter from particles generated by a sample matrix and formed by condensation of atoms in the optical path. Intensity modulation caused by overlap at the edges of the quartz plates and by the divergence of the optical beam at the position of the modulation chopper has been investigated and is likely to be small.     

A microcomputer-controlled dual-channel monochromator for plasma atomic emission spectrometry with time-constant and transient signals

Concept and operation of a microcomputer-controlled dual-channel monochromator system are described. A 0.9-m Czerny-Turner monochromator is equipped with two stepping motors: one for wavelength adjustment by rotating the grating, the other for driving a quartz refractor plate as a means for flexible background measurement. Instrument control as well as data acquisition and processing are performed by a 16 bit Intel 8088 based microcomputer system. The whole system is operated via a console keyboard with a simple dialogue. Main topics of the software are: setting operational parameters; automatic wavelength access using a peak searching routine with a screening window down to 0.05 nm; simple line intensity measurement; line and background measurement alternatively in one channel and simultaneously in two channels with a wavelength distance up to ± 0.05 nm using the quartz refractor plate, and stepwise intensity measurement (“profiling”) with an increment down to 0.0007 nm. Intensity values are acquired with a 12 bit resolution. Results are printed on a console typewriter. The performance of the instrument is demonstrated by applications in inductively coupled plasma atomic emission spectroscopy (ICP-AES) with steady and transient signals.     

A photon counting dynamic digital lock-in amplifier for background suppression in glow discharge atomic emission spectrometry

A photon counting dynamic digital lock-in amplifier, (PC-DDLIA), has been developed for the suppression of Ar lines in glow discharge lamp atomic emission spectrometry, (GDL-AES). The experimental set-up consists of a Grimm-type GDL, a prism-type scanning monochromator, photon counting electronics, an Apple Ile computer with an interface card and a computer controllable high voltage power supply. The photon counting electronics are designed to convert the photon pulses to logic pulses. A discriminator is used to reject pulses below a threshold level. The high voltage power supply is modulated with a square waveform generated from DAC and photon pulses are counted synchronously by the timer/counter chip, versatile interface adaptor (VIA-6522) on the interface card of computer. The data are analyzed in two steps. In the “learn mode”, the GDL is modulated with a square waveform between 370 and 670 V and two spectra consisting of only Ar lines are obtained in a spectral window between 287.1 and 290.0 nm. A new modulation waveform is computed from these spectra which yields two overlapped spectra when the PC-DDLIA is scanned over the same spectral window. In the “analysis mode” of data acquisition, a target material with the analyte element(s) in it is used and the spectrometer is scanned with a dynamically varying rectangular waveform over the same spectral window. The net spectrum consists of pure atomic lines free from any Ar lines. The detection limit for the determination of Si (288.2 nm) in the presence of interfering Ar lines (288.1 and 288.4 nm) is found to be 0.083%, whereas suppression of Ar lines over the same spectral window lowers the detection limit to 0.013%.     

Construction and Evaluation of a Fluorescent Sensor for the Detection of High Explosives

A sensor for the detection of airborne nitrate explosives was developed and laboratory tested. The device consisted of a quartz optical fiber, of which a 4-cm length was stripped and treated with an aminoalkylmethoxysilane. A fluorescent surface was produced by chemically attaching a sulfonated polyaromatic fluorophore to the amino group of the silylated quartz. Excitation was effected by radiation admitted through the fiber. When explosive laden air was drawn across the fluorescent surface, the analyte molecules interacted with the fluorophore and caused the emission to be quenched. This signal was monitored as an indicator of the explosive and was shown to be effective for TNT, di- and mononitrotoluenes, Tetryl, RDX, and HMX (marginal). Sensitivities were in the ng/m³range, and the surface could be flushed and restored after a quenching episode. Few interferences were encountered among common substances brought in contact with the surface.     

Sliding spark spectroscopy

Summary A new analytical radiation source combined with fiber optics linked to a diode array detection device with modified software is described. The direct-reading spectrometer simultaneously covers the wavelength range 185–510 nm with a spectral resolution of <1.5 nm. Intense optical emission is observed when positionally stable high-current surface sparks supplied by a pulse-generator with definite discharge parameters (max. 800 Ampere/pulse) are sliding over compact non-conductive materials such as plastics, glasses, quartz filters or powder pellets. Substrate vaporization, ionization and excitation processes in the surface discharge plasma channel generate emission corresponding to neutral and ionic states. The spectra are essentially composed of lines emitted by the electrode material (e.g. copper, silver), from the substrate under investigation, radiation continuum as well as structured background from the surrounding air atmosphere. Due to the occurrence of emission lines of reactive fillers, inorganic pigments and stabilizers, a rapid multi-element screening method is demonstrated. A rapid identification system (mix-up test) of PVC or fire-retardant thermoplastics within one second has been realized from the atomic emission line intensity originating from the sputtered copper electrode material according to its increased volatility in the presence of chlorine (modified Beilstein test).Puls-Plasma-Technik GmbH, Dortmund     

A method for measuring cross sections for electron-impact excitation out of metastable levels of atoms

A method for measuring cross sections for electron-impact excitation out of the metastable levels of the He atom is described. A hollow cathode discharge is used to produce an atomic beam consisting of ground-level He atoms and the He(2¹S) and He(2³S) metastable atoms. An electron beam of energy below 20 eV crosses the atomic beam exciting the metastable atoms to higher levels, and the intensity of the radiation emitted by atoms in these higher levels is utilized to determine the cross sections. Because of the very low concentration of metastable atoms in the atomic beam, the emission signal is extremely weak. A number of special techniques have been developed to detect these very low-level signals. Absolute calibration of the cross section is accomplished by referencing the emission signal that resulted from electron excitation out of the metastable level to the emission signal that resulted from the 2³S3³P or 2¹S3¹P laser optical absorption.     

Characterization of acoustic signals produced by ultraviolet laser ablation inductively coupled plasma atomic emission spectrometry

A simple device was designed to measure the acoustic signal accompanying laser ablation. The potential use of this signal for laser ablation-inductively coupled plasma atomic emission was examined. A frequency quadrupled pulsed Nd:YAG laser radiation was used for the ablation of glass, steel and ceramic samples. The relation between the acoustic signal, the laser energy, the analyte signal and the amount of ablated material was studied and evidence of the use of the acoustic signal for the exact focusing of the laser beam onto the sample surface was given. A more intense acoustic signal was observed for the exact focusing with a formation of larger ablation craters in glass and ceramics.     

A new atomization cell for trace metal determinations by tungsten coil atomic spectrometry

A new metallic atomization cell is used for trace metal determinations by tungsten coil atomic absorption spectrometry and tungsten coil atomic emission spectrometry. Different protecting gas mixtures are evaluated to improve atomic emission signals. Ar, N₂, CO₂ and He are used as solvents, and H₂ and C₂H₂ as solutes. A H₂/Ar mixture provided the best results. Parameters such as protecting gas flow rate and atomization current are also optimized. The optimal conditions are used to determine the figures of merit for both methods and the results are compared with values found in the literature. The new cell provides a better control of the radiation reaching the detector and a small, more isothermal environment around the atomizer. A more concentrated atomic cloud and a smaller background signal result in lower limits of detection using both methods. Cu (324.7 nm), Cd (228.8 nm) and Sn (286.3 nm) determined by tungsten coil atomic absorption spectrometry presented limits of detection as low as 0.6, 0.1, and 2.2 μg L⁻¹, respectively. For Cr (425.4 nm), Eu (459.4 nm) and Sr (460.7 nm) determined by tungsten coil atomic emission spectrometry, limits of detection of 4.5, 2.5, and 0.1 μg L⁻¹ were calculated. The method is used to determine Cu, Cd, Cr and Sr in a water standard reference material. Results for Cu, Cd and Cr presented no significant difference from reported values in a 95% confidence level. For Sr, a 113% recovery was obtained.     

Characterization of acoustic signals produced by ultraviolet laser ablation inductively coupled plasma atomic emission spectrometry

A simple device was designed to measure the acoustic signal accompanying laser ablation. The potential use of this signal for laser ablation-inductively coupled plasma atomic emission was examined. A frequency quadrupled pulsed Nd:YAG laser radiation was used for the ablation of glass, steel and ceramic samples. The relation between the acoustic signal, the laser energy, the analyte signal and the amount of ablated material was studied and evidence of the use of the acoustic signal for the exact focusing of the laser beam onto the sample surface was given. A more intense acoustic signal was observed for the exact focusing with a formation of larger ablation craters in glass and ceramics. Received: 25 June 1998 / Revised: 25 September 1998 / Accepted: 30 September 1998     

气相色谱-微波等离子体炬双检测器及其气相色谱的响应特性

提出并建立了气相色谱-微波等离子体炬(MPT)原子发射光谱和离子化双检测器系统. 以Ar气作为等离子体工作气体, O2气作为等离子体屏蔽气体, 同时获得了被测组分的原子发射和离子化信息, 并对不同种类有机化合物的相对响应系数及检出限进行了测定.     

Analytical Potentials and Features of Atomic Emission Analysis Using Electron-Impact Excitation of Atoms in Helium under Atmospheric Pressure

A device is described for the atomic emission analysis of vaporous samples using electron-impact excitation in helium under atmospheric pressure. The device consists of a cathode atomizer with a test sample applied onto it and the anode located at 1–3 mm from the cathode. The electrons emitted by the cathode upon heating are accelerated by applying a constant voltage to the electrodes. The mechanism for the formation of a non-self-sustained gas discharge between the cathode and anode is considered and the properties of the discharge are compared to those of the known discharges used in atomic emission spectrometry. The influence of atomization temperature and helium pressure on the analytical and background signals was studied. It is shown that, under certain conditions, the analytical signal increases with helium pressure. The relative detection limits attained for a number of elements are from tenths to dozens of nanogram per liter; this is two or three orders of magnitude lower than those in inductively coupled plasma atomic emission spectrometry and of the same order of magnitude as detection limits in inductively coupled plasma mass spectrometry.     

Sampling statistics and considerations for single-shot analysis using laser-induced breakdown spectroscopy

A statistical analysis of single-shot spectral data is reported for laser-induced breakdown spectroscopy (LIBS). Fluctuations in both atomic emission and plasma continuum emission are investigated in concert for a homogenous gaseous flow, and fluctuations in plasma temperature are reported based on iron atomic emission in an aerosol-seeded flow. Threshold irradiance for plasma initiation and plasma absorption were investigated for pure gaseous and aerosol streams, with detailed statistical measurements performed as a function of pulse energy in the breakdown regime. The ratio of the analyte atomic emission intensity to the continuum emission intensity (peak/base) provided a robust signal for single-shot LIBS analysis. Moreover, at optimal temporal delay, the precision of the LIBS signal was maximized for pulse energies within the saturation regime with respect to plasma absorption of incident energy. Finally, single-shot temperature measurements were analyzed, leading to the conclusion that spatial variations in the plasma volume formation and subsequent plasma emission collection, play important roles in the overall shot-to-shot precision of the LIBS technique for gaseous and aerosol analysis.     

Quality control with CRMs for trace element determination in candidate reference materials

Summary Three soil samples and five candidate materials of biological origin (bovine muscle, bovine kidney, bovine blood, rye flour and wheat flour) and one already certified RM (Bovine Liver, 12-02-01) were analyzed for their contents of Cd, Cu, Cr, Pb and Zn. Pressure digestion with nitric acid in PTFE (at 180°C) and quartz (at 290°C) vessels was used for sample decomposition. The measurements were made by graphite furnance atomic absorption spectrometry (ET-AAS), inductively coupled plasma atomic emission spectrometry (ICP-AES) and square wave voltammetry. The accuracy of analysis has been checked by simultaneous analyses of six similar CRMs. An excellent agreement between the found and certified values is illustrated by highly significant correlations.     

Preliminary investigation of a medium power argon radiofrequency capacitively coupled plasma as atomization cell in atomic fluorescence spectrometry of cadmium

The single ring electrode radiofrequency capacitively coupled plasma torch (SRTr.f.CCP) operated at 275W, 27.12 MHz and Ar flow rate below 0.7 lmin(-1) was investigated for the first time as atomization cell in atomic fluorescence spectrometry (AFS) using electrodeless discharge lamps (EDL) as primary radiation source and charged coupled devices as detector. The signal to background ratio (SBR) and limit of detection for Cd determination by EDL-SRTr.f.CCP-AFS were compared to those obtained in atomic emission spectrometry using the same plasma torch. The detection limit in fluorescence was 4.3 ngml(-1) Cd compared to 65 ngml(-1) and 40 ngml(-1) reported in r.f.CCP-atomic emission (AES) equipped with single or double ring electrode. The lower detection limit in EDL-SRTr.f.CCP-AFS is due to a much better SBR in fluorescence. The limit of detection was also compared to those in atomic fluorescence with inductively coupled plasma (0.4 ngml(-1)), microwave plasma torch (0.25 ngml(-1)) and air-acetylene flame (8 ngml(-1)). The influence of light-scattering through the plasma and the secondary reflection of the primary radiation on the wall of the quartz tube on the analytical performance are discussed. The non-spectral matrix effects of Ca, Mg and easily ionized elements are much lower in EDL-SRTr.f.CCP-AFS compared to SRTr.f.CCP-AES. The new technique was applied in the determination of Cd in contaminated soils, industrial hazardous waste (0.4-370 mgkg(-1)) and water (113 microgl(-1)) with repeatability of 4-8% and reproducibility in the range of 5-12%, similar to those in ICP-AES. The results were checked by the analysis of a soil and water CRM with a recovery degree of 97+/-9% and 98+/-4%, for a confidence limit of 95%. The present EDL-SRTr.f.CCP-AFS is a promising technique for Cd determination in environmental samples.     

Background correction in atomic emission spectrometry using repetitive harmonic wavelength scanning and applying Fourier analysis—I. Theory

Repetitive wavelength scanning can be used as a means of detecting and correcting for unwanted background in atomic emission spectrometry (AES). This paper deals with the theory underlying such harmonic wavelength scanning in time and stresses the relative importance of the relevant parameters. A set of integrated Turbo Pascal programs for an IBM PC was developed to provide a numerical simulation for the deconvolution of a detected spectral profile during repetitive harmonic wavelength scanning. By applying this numerical analysis the theory for separating the net spectral emission signal and the background radiation by filtering specific frequency components is investigated. It is concluded that, barring the dc component, repetitive scanning over a symmetric spectral profile leads to the generation of even-numbered Fourier harmonics at the modulation frequency, while an asymmetric spectral profile generates odd-numbered Fourier harmonics.     

A study of atomic absorption and atomic fluorescence atomization systems as detectors in the gas chromatographic determination of lead

The suitability of various atomic absorption and atomic fluorescence atomizing systems connected to a gas chromatograph is compared for the determination of alkyl lead compounds. An electrothermally heated graphite tube gives the highest sensitivity but quartz tubes heated either in an air-acetylene flame or by electrical resistance wire provide adequate sensitivity for most applications. A “solvent peak” absorption thought earlier to be due to organic molecular absorption of radiation at the lead wavelength was shown to be due to deposition and remobilization of lead.     

Direct flame solid sampling for atomic absorption spectrometry: determination of copper in bovine liver

In this work a new device for the direct introduction of solid samples into flame atomizers is proposed. The determination of copper in bovine liver reference material by flame atomic absorption spectrometry (FAAS) using a conventional air–acetylene flame was chosen as an example. Between 0.05 and 0.50 mg of the test sample was weighed directly into a small polyethylene vial connected to a glass chamber. A flow of air carries the test sample as a dry aerosol to a T-shaped quartz cell positioned above the burner in the optical path. The atomic vapor generated produces a transient signal of less than 3-s duration; integrated absorbance is used for signal evaluation. Optimized conditions for air flow rate, flame stoichiometry, etc., were evaluated. There was no statistical difference between the results from the proposed system, compared with those obtained by prior sample digestion and determination by conventional FAAS. No excessive grinding of the samples was required and samples with particle size less than 80 μm were used throughout. Background signals were always low and a characteristic mass of 1.5 ng was found for Cu. The proposed system allows the determination of 60 test samples in 1 h and it can be easily adapted to conventional atomic absorption spectrometers.     

A new patterning method using photocatalytic lithography and selective atomic layer deposition

We report a new patterning method using photocatalytic lithography of alkylsiloxane self-assembled monolayers and selective atomic layer deposition of thin films. The photocatalytic lithography is based on the fact that the decomposition rate of the alkylsiloxane monolayers in contact with TiO2 is much faster than that with SiO2 under UV irradiation in air. The photocatalytic lithography, using a quartz plate coated with patterned TiO2 thin films, was done to prepare patterned monolayers of the alkylsiloxane on Si substrates. A ZrO2 thin film was selectively deposited onto the monolayer-patterned Si substrate by atomic layer deposition.