Automatic Microdetermination of Carbon and Hydrogen

Abstract

In a series of experiments combustion cycles for the analysis of a rather wide range of compound types were determined, using a semiautomatic combustion unit.The unit is described and the conclusions drawn from its operation are applied to fully automatic units now in routine use. The combustion cycles employed are compared with those of other automatic units previously described. INTHE microdetermination of carbon and hydrogen in organic compounds, a combustion unit which operates automatically shows important advantages over the conventional, manually operated apparatus. Stated briefly, the more outstanding advantages are:1. One analyst can operate two units simultaneously; if only one unit is in operation, he is free to attend to other duties.2. Combustion conditions can be held essentially constant, to give extremely uniform analyses.3. Since the human factor has been minimized, inexperienced or untrained personnel can perform better analyses than are possible using a manually operated outfit.Two automatic combustion units for the microdetermination of carbon and hydrogen have been described in the literature ($, 6). Although in each case it was indicated that satisfactory analyses could be obtained, no extensive experimental data were given upon which to base a fair comparison of automatic and manual methods from the standpoint of accuracy and precision. Because of the lack of such data, and because of the wide variety of samples to be analyzed in this laboratory, it seemed advisable not to construct a fully automatic apparatus at the outset, but to start with what might be called "semiautomatic" operation. In this type of unit the movable vaporization furnace is advanced by means of a motor-driven rotating screw, the rate of advance being controlled by the analyst rather than by mechanical means.A successful semiautomatic unit was developed, and combustion cycles adaptable to the rapid analysis of samples covering a wide range of compositions were determined. The fully

Automatic Operations in Quantitative Analysis

“…Many units for automatic combustion of organic substances have been described (382). Use of automatic combustion methods has been made in the Dumas determination of nitrogen (565) and also in the Pregl determination of carbon and hydrogen (95,229,566), in which the tube containing the sample (solid, liquid, or gas) can be heated electrically little by little.…”

Organic Microchemistry

“…Although many prefer to keep the temperature at 650°to 750°C. (40,55,83,96,219), there is a trend toward increasing it, even as high as 10000 C. (8,232). The need for a preheater or preburner is also doubtful.…”

Microdetermination of Carbon and Hydrogen

“…samples and semiautomatic operation, an accuracy of ±0.02% absolute can be attained; this furnishes a method of high accuracy requiring relatively small amounts of sample for such difficult problems as the determination of the constitution of high molecular weight compounds. PREGL'S micromethod (10) has undergone development in three directions: The sample size has been decreased (2, 9), the combustion has been made automatic (4,5,11,13,16), and the precision and accuracy have been increased (3, 6-8). In the absence of a practicable ultramicrobalance the first and third are mutually exclusive; higher accuracy requires larger amounts of sample.…”