Analytical and spectral features of atomic magneto-optical rotation spectroscopy (the atomic Faraday effect) of Sb,Bi, Ag and Cu with a hollow cathode lamp operated in a pulse mode

In order to increase source intensity, hollow cathode lamps were operated in a pulse mode and combined with instrumentation for Faraday or atomic magneto-optical rotation spectroscopy. The analytical and spectral features of this method were studied for the trace determination of elements Sb, Bi, Ag and Cu. Novel line crossings between the σ^±-components in the analytical line Bi I 306.772 nm were found from the dependence of the transmitted intensity on the magnetic field strength. This is related to the theoretically calculated Zeeman splitting pattern. The enhancement in the source radiance by the pulse mode gave an increase in the detection power by a factor of ten.     

The hollow cathode plume: A plasma emission source for solids

A hollow cathode discharge serves to form an energetic plasma plume which exhibits intense emission characteristics. The sample cathode is sputtered in the discharge to produce an atomic population which then flows into the plume through an exit orifice for subsequent excitation. Atomic absorption and emission profiles in the plume are shown. Emission spectra of major and minor elements show strong atomic and ionic lines of sputtered species, particularly from the inner core of the plume. A sample in the form of a small disc can serve as the base of the hollow cathode for more convenient sample preparation. The source is believed to have potential also in elemental analysis by mass spectrometry.     

High frequency excitation of vapours produced by hollow cathode sputtering

Using a hollow cathode discharge for producing a suitable atomic vapour, the spectral lines of elements were excited by a high frequency discharge of 2450 MHz. These lamps were used as primary light sources for atomic absorption spectroscopy and were compared with conventional hollow cathode lamps. Higher intensity of radiation as well as higher sensitivity was obtained with the high frequency discharge. The interaction of the microwave field with the hollow cathode discharge limits the ultimate intensity. The stability of radiation from these sources is good. Measurements of line halfwidths indicate gas temperatures of approximately 500°K for both the high frequency and conventional hollow cathode discharges.     

Investigation of a novel hollow cathode configuration for Grimm-type glow discharge emission

A hollow cathode configuration was designed for a Grimm-type glow discharge atomic emission spectrometer (GD-AES). The operating conditions including the hollow cathode dimension, applied pulsed voltage and argon pressure, were optimized. The 10-μs pulses at 1.8 kV in a 3-torr discharge worked best. A pulsed hollow cathode Grimm discharge (HCG) offers several advantages: efficient excitation and ionization; high sensitivity; temporal spectral resolution; and rapid sample interchange. The capability of this source for the determination of elemental composition in metals, alloys and in solution residues is investigated. Samples used in this study included copper and steel standards.     

The design and characteristics of direct current glow discharge atomic emission source operated with plain and hollow cathodes

A compact direct current glow discharge atomic emission source has been designed and constructed for analytical applications. This atomic emission source works very efficiently at a low-input electrical power. The design has some features that make it distinct from that of the conventional Grimm glow discharge source. The peculiar cathode design offered greater flexibility on size and shape of the sample. As a result the source can be easily adopted to operate in Plain or Hollow Cathode configuration. I-V and spectroscopic characteristics of the source were compared while operating it with plain and hollow copper cathodes. It was observed that with hollow cathode, the source can be operated at a less input power and generates greater Cu I and Cu II line intensities. Also, the intensity of Cu II line rise faster than Cu I line with argon pressure for both cathodes. But the influence of pressure on Cu II lines was more significant when the source is operated with hollow cathode.     

The use of discharge lamps as directly modulated atom reservoirs for selective line modulation in atomic emission spectrometry

A simple method is described for selectively modulating the atomic or ionic resonance lines emitted by an excitation source. A modified discharge lamp with a cylindrical hollow cathode is used to generate a modulated atom cloud. The emission from the excitation source is then imaged through the modulated atom cloud within the cylindrical cathode lamp, to yield a selectively modulated signal. The ability of the system to reduce spectral interferences in inductively-coupled plasma emission spectrometry is assessed and discussed.     

A miniature planar magnetron glow discharge source for analysis of submicroliter volume aqueous samples using atomic emission spectroscopy

A miniature planar magnetron glow discharge source with a chamber volume of 60 ml has been designed and evaluated for the analysis of less than 1 μl of aqueous samples by atomic emission spectroscopy. Limits of detection for magnesium, silver, boron, europium and copper in the presence of a magnetic field are observed to be 3 to 40 times lower than for the source without a magnetic field when the measurements are made under the compromised discharge conditions for each type of source. Emission intensity in the presence of the magnetic field is found to increase as a square function of the discharge current. The improved detection limits for the magnetically enhanced glow discharge source are attributed to the increased current density of the discharge in the presence of the magnetic field which formed a plasma ring localized above the cathode surface. An RSD in the range 15–25% is observed for these measurements.     

Development of a laser ablation-hollow cathode glow discharge emission source and the application to the analysis of steel samples.

A novel atomic emission spectrometry comprising laser ablation as a sampling source and hollow cathode plasma for the excitation of ablated sample atoms is proposed. In this arrangement, a conventional Grimm-type discharge lamp is employed, but the polarity of the power supply is reversed so that the cylindrical hollow tube acts as a cathode and the glow discharge plasma is produced within this tube. A laser is irradiated to introduce sample atoms into the discharge plasma. Ablated atoms are excited by collisions with electrons and gas species, and emit characteristic radiation upon de-excitation. The experiments were conducted only in an atmosphere of helium gas so as to avoid a rapid erosion of the cathode hollow tube. Phase-sensitive detection with a lock-in amplifier was utilized to reject the continuous background emission of the plasma gas and emissions of sputtered atoms from the tube material. The unique feature of this technique is that the sampling and excitation processes can be controlled independently. The proposed technique was employed for the determination of Cr, Mn, and Ni in low-alloyed steel samples. The obtained concentrations are in good agreement with the reported values. The relative standard deviation (RSD), a measure of the analytical precision, was estimated to be 2-9% for Cr, 3-4% for Mn, and 4-11% for Ni determination.     

Construction and performance of an a.c. modulated magnet for Zeeman atomic absorption spectroscopy

A Zeeman atomic absorption spectroscopy system has been constructed utilizing a 50 Hz sine wave modulated magnetic field that can be directed either parallel or perpendicular to the optical axis. The amplitude of the magnetic field strength is adjustable up to 10 kG at a maximum power consumption of 0.7 kW.The readout system allows normal atomic absorption as well as d.c. and a.c. Zeeman atomic absorption measurements. Plots of experimental sensitivity vs magnetic field strength and analytical curves are in agreement with theoretical predictions.Experiments in the presence of filter simulated and real background absorbance show that the described Zeeman instrument is capable of correcting background absorption up to two absorbance units.     

Study on Arc Movement in Hollow Electrode Plasma Generators with Impressed Double Magnetic Fields

In order to prolong cathode lifetime of hollow electrode plasma generators, a method of impressed double magnetic fields with an alternating frequency is presented in this paper. The alternating frequency of the double magnetic fields is an important factor that influences the erosion rate on the area between the two coils' central planes. By analyzing the arc movement in the hollow cathode with a simplified theoretical model, the spiral curve shape of the radial arc and the relationship between the optimal alternating frequency and the intensity of magnetic fields are obtained. A photoelectric method is employed to measure the arc root rotation speed in the hollow cathode, and then the optimal alternating frequency is calculated as 319 Hz for the experimental conditions. The life testing with this alternating frequency showed that the cathode lifetime could be prolonged significantly.     

Excitation processes in an r.f.-boosted,pulsed hollow cathode lamp

Time and space resolved emission spectroscopy was used to examine the excitation processes in an r.f.-boosted, pulsed hollow cathode lamp. Sealed commercial hollow cathode lamps with copper cathodes and neon or argon buffer gases were driven with temporally spaced unidirectional current pulses and radio frequency bursts. The neon filled lamp was studied most extensively; the argon lamp was used for comparison.Three excitation periods were considered: the current pulse, the r.f. burst, and the afterglow. Each of these periods was marked by a unique set of emission characteristics that suggested different combinations of excitation processes. Excitation during the current pulse appears to be a combination electron impact and charge exchange. Charge exchange excites the 3d⁹5s levels of Cull while electron impact excites the other ion levels and the neutral levels. Charge exchange continues to excite the ion spectrum during the afterglow. Afterglow emission from the neutral spectrum apparently results from two types of recombination processes. The exact recombination mechanisms could not be unambiguously assigned. Emission results from the r.f. burst suggest that electron impact is the dominant excitation process. Excitation of the neutral and ion spectra are from their respective ground states. There appears to be little ionization by electron impact.To evaluate the lamp's suitability as a line source for analytical atomic spectroscopy the profile of the 324.8 nm neutral resonance line was examined during the current pulse and the r.f. burst. The profile during the current pulse is strongly dependent on radial position in the cathode bore. Near the edges of the cathode the line is severely self-reversed. The profile during the r.f. burst is uniform across the cathode bore and is affected only slightly by self-absorption.     

Versuche mit einem tiefgekühlten zwillingshohlkathoden interferometer-spektrometer—I

This work deals with the development of a set of twin hollow cathode tubes cooled by liquid air. The paper describes the construction of the hollow cathode device, the vacuum system and the current supply unit. The hollow cathode device is coupled to an interferometerspectrometer. The authors propose to use this arrangement for studying excitation processes in hollow cathode discharges and to apply it for emission spectrometric analysis.     

The contributions of magnetically induced dichroism and the resonant Voigt effect to the detection of silver by atomic spectroscopy

A simple theoretical analysis, based on the classical theory of the transmission of polarized light through a polarizing medium, has been developed to examine the factors determining the intensity of resonance radiation transmitted by a magnetized atomic vapour interposed between a pair of crossed polarizers. In common with other studies, this analysis predicts a quadratic dependence of the transmitted intensity on atom concentration but in addition, indicates that even at low atom concentrations differential absorption (dichroism) may make a significant addition to the transmitted intensity arising from differential refraction (birefringence). Further, by introducing a small angular off-set between the crossed polarizers, the concentration dependence of the transmitted intensity at low concentration may be increased and linearized. Experiments using a flame-generated atomic vapour of silver with a silver hollow cathode lamp or deuterium lamp as light source confirmed these predictions. When a strong magnetic field (9.75 kG) was used, a detection limit of 0.3 ppm (= μg/ml) for silver, with a near linear response up to 20 ppm was obtained.     

Construction of demountable hollow-cathode lamps for stimulating emission of organic compounds

A demountable hollow cathode has been constructed which provides emission spectra of organic compounds. The construction and operation of the hollow cathode is described. The emission spectra of organic and inorganic phosphates are illustrated and discussed.     

Baseline shifts in inverse Zeeman-effect graphite furnace atomic absorption spectrometry ascribed to the Zeeman effect of the CN molecule

The background-corrected Zeeman absorbance baseline shows shifts for lines of several hollow cathode lamps up to tenths of an absorbance unit with firings of an empty graphite furnace atomiser and clear differences in the sizes of the shifts according to whether the furnace is purged with nitrogen or argon. Baseline shifts are seen for hollow cathode lines close to listed rotation lines of the (0,0) and higher bands of the CN violet system. Such shifts, it is suggested, are caused by overlap of the hollow cathode lines with Zeeman-shifted CN lines and in support of this suggestion the known behaviour of CN lines in magnetic fields (spin doublet contraction) is cited. Evidence is presented for the existence of interfering CN lines near the main atomic absorption line of Cr (357.9 nm), as a spectral interference occurs in both the inverse Zeeman configuration (with lamps containing iron) and with continuum source correction.     

A study on the effect of the source line profile in atomic magneto-optical rotation spectroscopy (AMORS), using a Zeeman-shifted hollow cathode lamp

Summary Using a magnetized hollow cathode lamp as a Zeeman-shifted light source, the effects of the source line profile on the intensity of rotatory radiation and the calibration curve were studied for AMORS (atomic magneto-optical rotation spectroscopy). With the alteration of the source line profile, an increase in the intensity of rotatory radiation by about max. 40% was found. The rollover of the calibration curve could be avoided by selecting the strengths of the magnetic fields applied to the atomizer and the hollow cathode lamp.

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Untersuchung der Wirkung des Linienprofils der Lichtquelle in der magneto-optischen Atomrotations-Spektroskopie (AMORS) mit Hilfe einer Hohlkathodenlampe mit Zeeman-Verschiebung

Zusammenfassung Mit Hilfe einer magnetisierten Hohlkathodenlampe als Lichtquelle mit Zeeman-Verschiebung wurden die Wirkungen des Linienprofils der Lichtquelle auf die Intensität der Rotationsstrahlung und auf die Eichkurve untersucht. Mit Änderung des Linienprofils ergab sich eine Intensitätssteigerung der Rotationsstrahlung bis zu 40%. Abweichungen der Eichkurve konnten durch geeignete Wahl der magnetischen Feldstärken am Atomizer und der Hohlkathodenlampe vermieden werden.

     

Effect of coagulant temperature and composition on surface morphology and mass transfer properties of cellulose acetate hollow fiber membranes

Cellulose acetate (CA) hollow fibers were spun via the dry‐jet wet spinning technique under various external coagulant compositions and temperatures. The surface morphology of the resulting hollow fiber was examined using field emission scanning electron microscopy (FESEM) and tapping mode atomic force microscopy (TMAFM). The pure water permeability (PWP) and the retention of dextran of the hollow fiber were also measured. The results showed that both the temperature and composition can affect greatly the surface morphology and hence the permeation performance of hollow fiber membranes when the temperature was over 55°C and the dimethyl formamide (DMF) content was higher than 15%. The on‐line draw ratio increased with the coagulant temperature and DMF content (in the range of 0 to 10%) in the external coagulant. The ultimate tensile strength also increased when the fibers were coagulated in 5–10% DMF and at 70°C. The PWP increased with the DMF content in the coagulant and the coagulant temperature. The retention of dextran decreased with the increase of the DMF content in the coagulant and the coagulant temperature. Copyright © 2005 John Wiley & Sons, Ltd.     

A novel method for atomic absorption spectroscopy based on the analyte-Zeeman effect

A new type of atomic absorption spectrometry using the Zeeman effect of sample materials is proposed. A magnetic field was applied to the sample vapor in the direction perpendicular to the propagation of light emitted from an atomic spectral source. Absorption of radiation polarized perpendicular and parallel to the magnetic field was observed alternatively. The absorption difference was proportional to the true atomic absorption, and was not interfered with by any other molecular absorption and light scattering, i.e., background absorption. The background absorption could be monitored at exactly the same wavelength as an atomic absorption line. Suitable magnetic field strength was found for each line of the various elements.     

Polarized Zeeman effect atomic absorption spectrophotometry using a flame atomizer

A static magnetic field at 10 kG$\text{\$}\text{?}$was applied to a 10cm laminar flame produced by a premix type burner, and absorptions were observed for the polarized components of the radiation from a hollow cathode lamp. The dynamic range of the measurement was 10⁴–10⁵ for typical elements.The results showed that (1) the optimal conditions for double beam measurement and accurate correction of background absorption are achieved at the same time, (2) even if the flame conditions and the light intensity are changed, the baseline is not shifted, (3) the flame fluctuation noise and the lamp flicker noise are reduced, and (4) background absorption is corrected exactly at the same wavelength as the atomic absorption line.We thus concluded that the feasibility of flame atomic absorption spectrophotometry is much improved with this technique.     

匀强电场中基态惰性原子的边界轮廓

应用原子特征边界轮廓模型, 计算了在5.292×10^-5 - 5.292×10^-3 a.u. 匀强电场下, 基态惰性原子的边界轮廓. 计算结果表明, 在电场中原子的边界轮廓呈现近椭球形, 轮廓的变化随电场强度的增强而增大; 在电场强度不变的情况下, 原子边界轮廓的变化随原子序数的增加而增大. 并且计算中得到的单位强度原子平均径向变化率与原子极化率实验结果呈现很好的线性相关性.