REPORT FOR ANALYTICAL CHEMISTS
PROCESS GAS MIXTURES For calibrating a process gas chroma tography unit, or performing separa tion studies on a gas stream in your plant. These mixtures can be made to match your system in almost all cases. Matheson is the world's leading supplier of high purity gas mixtures. Custom and stock mixtures of 95 gases available from mixing laboratories in 5 plants. Write for catalog.
MATHESON East R u t h e r f o r d , Ν . J. Potest Park
Ga
Joliel. I "
l a Poitt
Te.as
Newatk
Cahl
Matheson of Canada, Whitby, Ont. ' o f m o r e — f r o m Matheson Circle No. 163 on Readers' Service Card
Specify SPECTROQUALITY ®
CARBON DISULFIDE U.V. Cut-off 380 ηΐμ Evap. Residue Moisture Fluorescence
.0003% max. .05% max. .5 ppb as quinine base max. Used extensively as a solvent for bitumens, fats, gums, rubber, oils, waxes, resins, phosphorus, sulfur and many other sub stances; transmission characteristics in the NIR and IR make it one of the best solvents known for these regions of the spectrum; water solubility 0.29% (S 20° C; miscible with ethanol, ether, methanol, carbon tetra chloride, chloroform, benzene and oils; dipole moment 0.0D. Comparative tests prove MC&B Spectroquality Solvents are the highest quality most complete line of solvents for spectro photometry and fluorometry. Write for wall chart showing UV, IR, and NIR transmittance of 40 Spectroquality solvents.
Division of The Matheson Co., inc. Norwood (Cincinnati)
O., East Rutherford, Ν. Υ.
Circle No. 164 on Readers' Service Card
32 A
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ANALYTICAL CHEMISTRY
a longer term basis rather than budgeting for the individual re search project. I t is reasonable for a director to question the delay in obtaining certain analyses when he has become accustomed to having a service performed in a rapid and economical manner. The routine determination of the elements present in organic sub stances has been a sore point in an otherwise satisfactory operation. Admittedly, the determinations are difficult; skilled personnel is a t a premium, and equipment and methodology have not kept u p with our present level of technology in other scientific disciplines. This becomes a tremendous administra tive problem and is often the cause of a superficial appearance of in efficiency on the p a r t of the ana lytical department. Our analytical techniques have been aided by a number of new de vices t h a t are capable of satisfac torily carrying out great numbers of determinations and are able to pro vide analytical service at almost any level of speed and accuracy with a minimum expenditure of personnel. We are all familiar with the impact of partition chromatog raphy, more specifically the gasliquid chromatograph which is cer tainly the marvel of our age, and the host of special instruments such as the infrared spectrophotometer, the N M R , E P R , and molecular spectrographs which are taking not only structure elucidation but quantitative evaluation as well out of the analytical laboratory and onto the research chemists bench or are being incorporated directly into the manufacturing process stream. A perusal of the voluminous liter ature indicates an almost exponen tial increase in the number of papers devoted to microchemistry since World W a r I I . A more de tailed examination will reveal t h a t most of these papers are directed toward simplification of procedures, speedier operation, and modifica tions of equipment. There have not been very m a n y papers con cerned with a deeper understanding of the "first principles" involved. Claims to overcome some of the shortcomings of the classical Pregl procedures have recently appeared
in the literature and some a p p a r a t a have become commercially avail able, or will be shortly, for these purposes. As the determination of carbon and hydrogen by far appears to be the most common determination made in the organic analytical lab oratory, we might examine in some detail the present status of the art and some of the newer approaches to a solution of this problem. The determination of carbon and hydro gen is not a simple operation, but rather a series of complex opera tions subject to m a n y errors both h u m a n and instrumental. T h e late F a t h e r Power in a statistical study {12) has reviewed the various points of error in the classical Pregl procedure for the determination of carbon and hydrogen. First, let us a t t e m p t to define the problem by considering the desira ble parameters, and secondly, we will a t t e m p t to separate the deter mination into its several component operations and then discuss each one individually. A procedure for the determina tion of carbon and hydrogen should first, and above all, be accurate and reliable when applied to samples of widely differing compositions and properties. A laboratory t h a t can not consistently produce carbon and hydrogen values of high relia bility has very little if any value. Secondly, persons of reasonable but not highly specialized skill should be able to complete the determina tion in a time of less t h a n twenty minutes. Finally, the equipment and accessories should be readily available a t a reasonable cost. The determination itself can be considered in three general phases: the preparation, weighing, and han dling of the sample; the burning or oxidation of the sample; and the separation and quantitative esti mation of the combustion products. A reasonably skilled operator, using good balance equipment un der proper environmental condi tions, should have very little trou ble with the first phase. Modern microanalytical balances are gen erally very rugged and reliable in struments, and if used under the conditions of the manufacturer's recommendation and in the range
