Coleman Instruments, Inc

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New efficiency for fluorometric measurement For the r a p i d , precise analysis by fluorescence of Vitamins, Quinine, Atabrine, Fluorescein, Porphyrins, Steroids, metal complexes and other compounds susceptible to fluorometric measurement. Full A C O p e r a t i o n . The Model 12C is entirely A C lineoperated and employs no batteries. The high intensity mercury vapor lamp source and the photo-tube amplifier are automatically stabilized against line voltage variations. G r e a t e r Sensitivity a n d S t a b i l i t y E x t e n d R a n g e o f Use. The combination of increased sensitivity to low intensity fluorescence and the new non-drifting measuring circuit subs t a n t i a l l y e x t e n d s the a b i l i t y to a n a l y z e solutions o f extremely low concentration. The speed and facility of

measuring higher concentrations, such as are found in feeds and grains, is likewise enhanced. Simple Controls—Easy O p e r a t i o n . Only 3 simple controls adjust the measuring circuit and permit fluorescence measurements over a wide range of sample concentrations. Readings made directly from meter on instrument panel. W i d e Filter S e l e c t i o n . A wide selection of optical filters is available for isolating the sample from both the mercury vapor light and the phototube. Blank filter holders' available for special filter combinations when needed.

For complete details write for Bulletin B-230 Dept. A. Coleman Instruments, Inc., Maywood, III.

THE NEW MODEL 12-C

pH COLEMAN 20 A

·

Coleman Photofluorometer

ANALYTICAL CHEMISTRY

..For further information, circle number 20 A on Readers' Service Card, page 75 A

REPORT FOR ANALYSTS Emission spectrography Fluorometry Gas analysis Gravimetric analysis Magnetic susceptibility methods Mass spectrography Mass spectrometry Melting point and freezing point change method Microscopical analysis Nephelometry Neutron capture Polarimetry Polarography Potentiometric titrimetry Raman spectrography Refractometry Sonic methods Spectrophotometry Thermal conductivity method Titrimetry Turbidimetry Viscometry Volume of liquid distilled Volume of precipitate X-ray diffraction analysis Zymometry" 11 I t seemed fitting to conclude the list with a Ζ so the author's associates invented Zymometry, the "determination of enzymes."

After he has made up such a list, he is not much better off. The correlations, if any, between the methods are not evident. What is needed is a classifica­ tion method to show how each method fits into the whole scheme of analysis. This problem is not new. It has been recognized for many years. Many competent analysts have made efforts to de\ase a classification system. In an earlier article (3), the author described the virtues and faults of several of these. Requisites of an Ideal System Requirements of an ideal classifica­ tion system are: 1.

A division must be exhaustive.

2. The constituent species of the genus must exclude one another. 3. A division must proceed at every stage upon one principle, the fundamentum divisionis. 4. It must be based upon generally accepted divisions of chemistry and physics. 5. It must use a generally accepted vocabulary. 6.

It must be of definite utility.

7. It must not involve theoretical knowledge on a level above that of an undergraduate in chemistry. 8. The criteria for differentiation must be simply and clearly defined. 9.

It must be capable of expansion

and intensification without the necessity for radical revision. A practical system, even though it does not meet all these criteria, can still be a very useful guide. One problem in most classification systems arises from the careless use of ' 'physicochemical. ' '

FREE

TO ANALYTICAL CHEMISTS

From: Carl Schleicher & Schuell Co. KEENE,For:NEW HAMPSHIRE

Requisites for Practical System A classification system, to be most useful, the author feels, should be based on the operations involved—that is, the fundamental nature of the operations which are carried out upon the material to be analyzed. It can be physical, chemical, or biological in nature. The objective of using an operational (func­ tional) basis is to clarify the funda­ mental nature of the operation itself, as this is a source of confusion in the organization of the science of analytical chemistry. The next step is to differentiate between operations involved in prepara­ tion and operations involved in measure­ ments. Definition. "Method of analysis" is defined as a procedure or sequence of operations which makes possible a quantitative estimation of the chemical composition of any material. "Deter­ mination" denotes an operation which involves a measurement of amount. "Preparation" denotes any operation to which the material must be subjected before a measurement can be applied.

Classification of Quantitative Analytical Methods The classification system proposed for quantitative analytical methods is based on (1) methods of preparation of sample, and (2) methods of determina­ tion of the desired constituent. Preparational operation can generally be differentiated on the basis of being either essentially physical or essentially chemical. Such a distinction, while difficult to make on a fundamental scientific basis, is relatively simple when based on traditional considerations. The distinction between a chemical and physical process is made by considering whether or not the chemical composition of the system changes as a result of the process. To be useful, a classification of the methods available for measurements must achieve a high degree of differenti­ ation. In this connection, biological methods of measurement constitute a large sub­ division. Whether or not a method is biological depends on (1) whether the

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Circle Nos. 21 A-1, 21 A-2 on Readers' Service Card, page 75 A

VOL. 29, NO. 3, MARCH 1957 ·

21 A