ANALYTICAL FURNACE HAVING PREHEATING AND CONSTANT TEMPERATURE SECTIONS

Abstract: A furnace having a first preheating section (10) protecting outwardly from a constant and higher temperature secondary section (11) and means for moving a sample through the preheating section into the second section. Preferably both sections are graphite and the movement is by rapid movement of a rod (14). The furnace is intended for atomic spectroscopic analysis.

Description: ANALYTICAL FURNACE HAVING PREHEATING AND CONSTANT TEMPERATURE SECTIONS The present invention relates to furnaces and more particularly to a furnace system suitable for constant temperature measurement and/or analysis. Such furnaces are used for atomization of a sample in connection with analytical atomic spectroscopy, atomic absorption, atomic emission and atomic fluorescence. Currently, a sample is deposited within a graphite furnace and subjected to both thermal pretreatment and atomization in situ by applying a preset temperature programme. Several different experimental approaches to constant temperature atomization are known and have been reviewed by the inventor Prog. Analyt. Atom. Spectrosc, _4, pages 247 - 310 (1981) . The present invention consists in a furnace comprising a primary furnace and a secondary furnace, said primary furnace being of generally tubular configuration projecting outwardly from said secondary furnace, in use said primary furnace providing an increasing temperature gradient towards said secondary furnace, said secondary furnace to be operated at a predetermined substantially constant temperature greater than the maximum temperature in the primary furnace, and wherein a sample to be analysed at the constant temperature of the secondary furnace is inserted therein via movement through the primary furnace. In another form the present invention provides a method of applying a substantially constant elevated temperature to a sample comprising subjecting said sample to an increasing temperature gradient so as to apply a thermal pretreatment to said sample and then subjecting said sample to said elevated predetermined substantially constant temperature immediately following said pretreatment. An embodiment of a furnace in accordance with this invention is formed from graphite and a sample to be analysed is introduced into the secondary furnace via the primary furnace by being dried on the face of a graphite rod in situ or externally of the furnace. When dried externally the rod is inserted in the tubular primary furnace and driven toward the secondary furnace. In this way temperature programming of thermal pretreatment is achieved by moving the sample bearing rod through the different temperature zones in the primary furnace. By preheating the sample in this way a fast constant temperature atomization is achieved in the secondary furnace which results in improved analytical sensitivities. The sample to be analysed may be applied and dried in situ, either inside the secondary furnace or in the primary furnace. In situ application and drying can be carried out by introducing the sample to the tip of the rod via a suitably formed orifice, whereafter the rod may be withdrawn to, or already be located at, an appropriate position in the primary furnace for drying and thermal pretreatment before being driven toward the secondary furnace where the sample is atomized. The present invention will now be described by way of example with reference to the accompanying drawings, in which:- Fig. 1 is a part sectional view of a furnace in accordance with the present invention; Fig. 2 is a part sectional view of another embodiment of a furnace in accordance with the invention. The furnace system depicted in Fig. 1 comprises a primary furnace 10 and a secondary furnace 11 located between terminals 12. The secondary furnace 11 being connected to one terminal 12 via support rod 13 and the primary furnace 10 acting as its own support from the other terminal. - The primary and secondary furnaces as well as the sample introduction rod 14 may be formed from any suitable material, such as various forms of carbon including graphite, pyrolytic graphite, glassy carbon or the like and suitable materials will be apparent to the addressee. The sample introduction rod 14 includes a sample supporting tip 15 at its end which is inserted in primary furnace 10 and moved in a predetermined manner toward opening 16 in secondary furnace 11. Rod 14 may be manually driven through the primary furnace 10 or by such as solenoid or electro-mechanical means or pneumatic means under the action of an inert gas stream could be employed. Primary furnace 10 has an increasing temperature gradient towards secondary furnace 11 and when sample supporting tip 15 is inserted in furnace 11 it is atomized at the constant temperature maintained in the secondary furnace thereby generating a transient atomic population suitable for analysis by, say, atomic spectroscopy. The furnace of Fig. 2 is identical with that of Fig. 1 except for the provision of an orifice 17 and equivalent parts are numbered in correspondence with those of Fig. 1. In the embodiment of Fig. 2 a sample can be applied to tip 15 when inserted into primary furnace 10 by injecting the sample onto the face of tip 15 through orifice 17. By this means the sample is applied in situ so as to reduce the prospect of contamination problems which may occur where the sample is applied to tip 15 externally of furnace 10. In another method of operating the furnace the sample may be applied to the tip while it is within the furnace 11 prior to it being heated to its atomizing temperature. Thermal treatment of the sample prior to atomization can be provided by a programmed controlling movement of the rod in the primary furnace. A typical embodiment of a furnace of the form shown • by Fig. 1 or 2 comprises an inner graphite rod 14 of 3 mm diameter and a primary furnace 10 of 4.6 mm outer diameter. The scale of secondary graphite furnace 11 can be appreciated from the relative proportions as shown by the drawings. Desirably, the tip 15 is formed from pyrolytic graphite which is oriented on the end of rod 14 so as to present maximum thermal reistance in a direction axially of rod 14. This is achieved by orienting the pyrolytic graphite of tip 15 so that its parallel layers are transverse to the axis of rod 14. A sample to be analysed may be applied to the tip at ambient temperature or at an elevated temperature, say 120°C. If applied at an elevated temperature the sample solution may dry on contact. A typical graphite furnace in accordance with the embodiments can be rapidly heated to operating temperature by application of an appropriate voltage across the primary and secondary furnaces so that while the secondary furnace is heated rapidly to essentially constant temperature, a significant temperature gradient along the length of the primary furnace is achieved. By use of apparatus in accordance with this invention there can be an improvement in analytical sensitivity and a significant reduction in interference effects in connection with atomic spectroscopy analyses and the like.

Claims: CLAIMS :- 1. A furnace comprising a primary furnace and a secondary furnace, said primary furnace being of generally tubular configuration projecting outwardly from in use said secondary furnace, said primary furnace providing an increasing temperature gradient towards said secondary furnace, said secondary furnace to be operated at a predetermined substantially constant temperature greater than the maximum temperature in the primary furnace, and wherein a sample to be analysed at the constant temperature of the secondary furnace is inserted therein via movement through the primary furnace. 2. A furnace as claimed in claim 1 comprising a rod for supporting a sample, said rod being adapted to be driven through the primary furnace to the secondary furnace whereby the one end of the rod contacts the secondary furnace. 3. A furnace as claimed in claim 1 or- 2 wherein the primary and secondary furnaces are formed from forms of carbon. 4. A furnace as claimed in claim 2 wherein said rod is formed from forms of carbon. 5. A furnace as claimed in claim 3 wherein the primary and secondary furnaces are formed from carbon. 6. A furnace as claimed in claim 4 or 5 wherein the carbon is in the form of graphite. 7. A furnace as claimed in claim 2 or 4 wherein the one end of the rod comprises a tip which fits an opening in the wall of the secondary furnace. 8. A furnace as claimed in claim 7 wherein the tip is formed from pyrolytic graphite. 9. A furnace as claimed in claim 8 wherein the pyrolytic graphite tip is formed with the thermal resistance of the tip being substantially greater in an axial direction of the rod than in a transverse direction of the rod. 10. A method of applying a substantially constant elevated temperature to a sample comprising subjecting said sample to an increasing temperature gradient so as to apply a thermal pretreatment to said sample and then subjecting said sample to said elevated predetermined substantially constant temperature immediately following said pretreatment.

Inventors: MATOUSEK JAROSLAV PETR, MATOUSEK, JAROSLAV, PETR
Applicants: UNISEARCH LTD, UNISEARCH LIMITED
Application year: 1985
Main classification: G01N21
IPC codes: F27B17, G01N21