A temperature-controlled graphite tube furnace for the determination of trace metals in solid biological tissue

A temperature-controlled graphite furnace for atomic-absorption analysis has been built and tested. The temperature of the graphite tube was monitored with an infrared-sensitive detector. Samples were introduced directly or via a separately heated graphite cup. Micro-samples of solid biological tissue were analysed directly for Zn, Mn and Co and the sensitivities for 1% absorption were 0.05,2 and 10 pg respectively. The salt content of the tissue limits the sample sizes, owing to non-specific absorption. The ashing conditions were investigated and found to be especially critical for Zn.     

Direct filtration through porous graphite for A.A. analysis of beryllium particulates in air

A method is described for the determination of beryllium particulates in air by furnace atomic absorption. A small volume of air is filtered through the walls of a porous graphite cup. The cup containing the entrapped particulates is then inserted in a constant temperature graphite furnace. Measurements can be made over the concentration range 2–20 μg/m³ with sample vol of 50 cm³. The observed analytical precision is 15%.     

Capacitive-discharge-heated anisotropic pyrolytic graphite furnace used for atomic absorption spectrometry Part. 1 Thoeretical Modelling of the Heating Characteristics of the Furnace Surface and of the Gas Phase

A model of the temperature distribution in the tube wall and in the gas phase of an anisotropic pyrolytic graphite furnace heated by capacitive discharge technique is proposed. The heat loss from the graphite tube by conduction via the contact electrodes to the water-cooled electrode supports and by radiation to its surroundings are the main processes condidered. In calculating the gas temperature, heat transfer by conduction from the tube wall to the gas phase is the only mode taken into account. The instantaneous temperature of a graphite furnace is expressed in the form of a differential equation. A finite-difference form of the differential equation is used in a computer program to calculate the temperature at each time step. The computer simulation offers the capability of studying the factors affecting the characteristics of temperature/time profiles and the distribution of surface and gas phase temperatures of the furnace. The results of simulation studies of the effect of the capacitance and the initial voltage of the capacitor bank on the heating characteristics of the furnaces show a reasonable agreement with those obtained experimentally.     

Reduction of temperature variation in the atomic absorption graphite furnace

The temperature variation that is experienced along the length of the graphite furnace tube of the Massmann design can be reduced by the use of a contoured tube. An analytical model of the steady-state temperature distribution along the graphite tube has been developed and has been shown to agree quite well with experimental data. Steady-state and time-dependent measurements along the length of the graphite tube are reported for different conditions. With conventional tubes at thermal equilibrium, there is a temperature difference exceeding 1000°C between the center and the ends when the center of the tube is at 2500°C. With a contoured tube this temperature gradient has been reduced to 100°C.     

The graphite probe constant temperature furnace

A graphite probe, on which the sample is deposited, is thrust into a heated graphite furnace tube, providing a constant temperature furnace environment. By comparison with wall sampling, the graphite probe system provides equal or improved sensitivity and detection limit and considerably less memory effect. Experiments with metals that range from volatile to refractory show that the peak width is the same at the same atomization temperature. A tube was designed that provided a curtain of argon to limit the absorbance path to about 15 mm.     

Determination of the temperature of the graphite probe surface in graphite probe furnace atomic absorption spectrometry

An apparatus for determining the temperature of a graphite probe in graphite probe furnace atomic absorption spectrometry has been developed and tested. By measuring the change in the reflection of a laser beam from various pure metals which are deposited on the probe surface at the usual location for sample deposition, it has been found that the heating of the graphite probe surface occurs in two stages. When the probe is inserted into a pulse-heated, commercial graphite furnace after it has been heated to a steady-state temperature, the probe surface is initially rapidly heated by the radiation from the heated graphite tube wall, and thereafter the probe maintains that steady-state temperature for a short time. For a given graphite probe, the heating rate at the initial stage and the corresponding steady-state temperature at the final stage are mainly determined by the final tube wall temperature; the steady-state temperature of the probe is considerably lower than the final tube wall temperature because of thermal conduction by the probe to that part of its body which is lying outside the tube wall. The higher the final tube wall temperature, the higher is the heating rate of the probe at the initial stage, the higher is its steady-state temperature at the final stage, and the less is the difference between the final tube wall temperature and the steady-state temperature of the probe surface. The heating rate of the probe surface at 1600 K is 180 K s⁻¹, whereas at 2300 K it is 3600 K s⁻¹; the differences between the probe surface and tube wall temperatures at the former temperature is 700 K, whereas at the latter temperature it is 250 K.     

Enhancement of sensitivity in atomic-absorption spectrometry by addition of a graphite lid to a cup furnace

By using a cup furnace covered with a graphite lid, it is possible to enhance the atomic-absorption signal for Cd, Zn, Sb, Pb, In, Cu and Fe in solution and for Pb in tin metal (directly atomized). When the analyte is atomized in the cup furnace, part of it condenses on the lid, from which it can be re-evaporated and atomized to give a second absorption signal and hence greater sensitivity. When the lid is small, so that the temperature lag is short, the initial atomic-absorption intensity is also enhanced. The enhancement is due to an increased residence time of the atomized analyte in the cup.     

流动注射氢化物石墨炉原子吸收法的应用研究 Ⅰ.——实验装置与分析性能

氢化物石墨炉联用技术的原理是先在较低温度下将氢化物蒸气通入石墨炉并分解沉积于石墨管的内表面,然后再在高温下原子化。该法能明显提高灵敏度,消除液相和气相干扰。本文采用自制的半自动氢化物石墨炉进样系统及流动注射氢化物发生器,直接在普通石墨炉上进行氢化物石墨炉分析,研究了部分元素的测定条件,建立的方法操作方便,灵敏度高,耗样少,线性范围宽,是一种值得推广的新方法。     

The gas temperature in and the gas expulsion from a graphite furnace used for atomic absorption spectrometry

A simplified model for heat transfer based on thermal conduction is used to calculate the radial gas temperature distribution inside a semi-enclosed, commercial graphite tube furnace used for atomic absorption spectrometry. In the absence of a forced convective flow of a purge gas, the gas temperature inside the graphite furnace during its heating is lower than the wall temperature. After the wall temperature has attained a steady-state value, the gas temperature approaches the wall temperature and the radial temperature gradient in the gas decreases. The difference between the wall temperature and the gas temperature depends on the temperature program used, the thermal properties of the purge gas, and the atomizer geometry. The residence time of relatively volatile analyte elements is largely controlled by expulsion when wall atomization at high heating rates and high atomization temperatures are used. Analytical sensitivities are often enhanced by vaporizing the analyte into a gas having an approximately constant temperature.     

Investigation of graphite-probe atomisation for carbon-furnace atomic emission spectrometry

A new method of sample introduction for carbon furnace atomic emission spectrometry is described. The sample is deposited on a graphite probe which is inserted into the furnace along its length, after the tube has attained its maximum temperature. The heating rate experienced by the sample in an HGA-72 furnace is considerably increased by use of probe atomisation. Improved detection limits for a number of elements are reported, and the interference of magnesium chloride on the emission signals for lead and cadmium is substantially reduced.     

Calculation of the dynamic temperature characteristics of a heated graphite tube used in electrothermal atomic absorption measurements

A method and computer program were developed for calculating the temperature of any part of a graphite furnace tube at any instant of time after onset of the heating cycle. Results for tubes of the Massman design show large differences in spatial temperature distributions during and at the end of the heating cycle when equilibrium is reached. When constant current is applied to contoured tubes, greater heating rates at the tube centres are obtained than with standard tubes.     

电热原子吸收法测定人发中硒时不同改进剂的研究

对于生物体中硒的测定,国内外已有大量报道,所用方法也相当广泛。本文利用石墨炉原子吸收对人发中硒的测定进行了研究;对使用较多的两种硒的基体改进剂:铜与镍的作用与效果进行了研究,发现铜较镍在某些方面更为优越。当选用100 μg/mL的铜作改进剂时,硒的特征浓度为0.13 ng/1％abs,测定精度为3.4％～5.4％;线性范围达400 ng。     

石墨炉原子吸收法测定钢铁及合金中微量钒

探讨了石墨炉子吸收法测定钢铁及合金中微量钒的各种实验条件及影响因素。实验表明，采用热解涂层管与光控升温相结合并在温度稳定的情况下原子化，可改善信号峰形，提高灵敏度，消除记忆效应。方法用于钢铁及合金中钒的分析，结果令人满意。     

塞曼石墨炉原子吸收光谱法测定大鼠血,尿,肾,肝中的微量金

采用石英管加入少量硝酸高温消化的方法,用塞曼石墨炉原子分光光度计对服用含金救心丸的大鼠血,尿,肝,肾进行微量金的测定。测定方法简便快速,结果满意。     

ETV-ICP-AES联用技术的蒸发器研究

ETV-ICP-AES是样品电热气化/电感耦合等离子体激发的联用技术^[1～7],具有进样效率高并可进行微升级样品分析的特点.ETV-ICP-AES多采用石墨炉或石墨棒蒸发器.因此,蒸发器的结构、形状、升温速率以及温度分布等对分析信号有很大的影响^[3,4].本文研究了蒸发器的接口、形状、结构的影响;自行设计了插入式平台,减小死体积,还研究了在载气单向连续流动的情况下,石墨炉内部温度的大致分布,讨论了平台蒸发和管壁蒸发.     

Measurement of longitudinal atom density distributions in a graphite tube furnace using coherent forward scattering

A method for measuring longitudinal atom density distributions in a graphite tube furnace using coherent forward scattering is proposed. A transverse magnetic field is locally applied to the atomic vapor in a graphite tube. Relative atom density distributions for the elements Cd, Cu, Mn, Ni and Pb are measured.     

Aspects of the pyrometric measurement of graphite furnace temperature

Experimental results are presented to show that the radiation leaving the centre hole of tubular graphite furnace atomisers can deviate significantly from ideal blackbody behaviour. Pyrometric measurements at various wavelengths of the apparent, or brightness, temperatures of two commercial graphite tube atomisers (Varian GTA-95 and CRA-90) showed that the measured brightness temperature decreased appreciably with increasing wavelength, in accordance with the predicted behaviour for a cavity radiator with an emissivity less than unity. Measurement of the sample hole emissivity from the apparent melting temperatures of certain metal and metal carbide samples indicated mean effective hole emissivities of pyrocoated GTA-95 tubes in the range 0.76–0.92, depending on temperature and wavelength. Implications of the results for pyrometric temperature measurement in graphite furnaces are also discussed.     

Determination of Sb, Ni and V in slurry from airborne particulate material collected on filter by graphite furnace atomic absorption spectrometry

A microdigestion procedure performed directly in the autosampler cup is proposed. Small quartz filter pieces loaded with the particulate material are transferred to the cup. The sample is digested by a mixture of nitric, sulfuric and hydrofluoric acid (1:1:1) under sonication. After the addition of a boric acid solution the elements are determined by graphite furnace atomic absorption spectrometry using the autosampler to deliver the slurry into the furnace. A mixture of palladium and magnesium nitrates was used as a modifier for Sb. Spiking studies showed recoveries close to 100% using aqueous analytical curves for Ni and Sb. For V, an analytical curve in the blank slurry, obtained by submitting an unloaded filter to the same procedure, was used. The method was applied to two standard reference materials, Coal Fly Ash (NIST 1633a) and Urban Particulate (NIST 1648) and the concentrations showed good agreement with the certified or recommended values using aqueous analytical solutions.