Fernando Valcarce Codes
Físico , Técnico Facultativo del
INSTITUTO NACIONAL DE TOXICOLOGIA. MADRID. ESPAÑA
A single, low temperature range applicable to most organic materials (1), thermal analysis apparatus has been designed and implemented at this centre. It basically consists on a low power consumption, high speed response, electrical resistive heating oven and associated, two sensor based, proportional-differential electronic temperature controller as well as digital programmer and signal handling circuitry.
Main facilities offered by the system include an stainless steel conduction platform with positions for direct placement of sample and reference materials, digital readout of sample, reference and ramp control temperatures, keyboard operated control and input of selected initial and final temperature values of the programed ramp whose speed may be chosen among three diferent values ; 1 , 5 and 10 K/min within the whole available 323-673 K temperature range.
Analog output for graphical recording of temperature differences between sample and reference, start/stop remote control of recorder from ramp program and automatic switching to either isothermal or standby state when the ramp is finished are additional features of the analyser.
Temperature calibration, linearity and reproductibility tests have been carried on with appropiate standards (2), results being reasonably good for the required purpose.
Equally, measurements of temperature lag between sample or reference and control temperatures have been made, resulting on confirmation of the improved speed of response achieved with two sensor temperature controllers reletive to one sensor ones, as already described by other workers (3). The apparatus is being satisfactorily used at this centre as a complementary mean for the identification of unknown pharmaceuticals, drugs and other organic materials.
References
(1) J.L. Ford and P. Timmins in "Pharmaceutical thermal analysis" ed. E. Horwood (John Wiley and sons, 1989)
(2) G.W. Jang and K. Rajeshwar, Anal.Chem. 58 (1986) 416.
(3) S. Gal, J Murati and J. Sztatisz, J. Thermal anal. 21 (1981) 163.
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