REPORT FOR A N A L Y T I C A L CHEMISTS
New Reagent for
RAPID, SENSITIVE determination of
SULFATE...
Baker Analyzed'
BARIUM CHLORANILATE
Figure 2, B. Single channel, bridge balance
Instruments' Polarotrace) in which the polarogram is automatically traced on the face of a cathode-ray tube, so that a complete polarographic analysis is provided visually (or it can be photo graphed or recorded electronically) in 7 seconds, and is retraced every 7 seconds. The most significant feature of this latter development, from the point of view of the present discussion, is that not only has this elaboration of the instrumentation improved the speed and convenience of obtaining a polarogram, but by its nature it makes possible a new type of polarography in which the entire polarogram is run during the life of a single mercury drop, instead of being averaged over many drops. As a consequence, the sensitivity of detection of electrolyzable species has proved to be 1000 times or more greater than is possible with the earlier instrumentation, and the ability to resolve mixtures of substances with closely similar half-wave potentials is greatly improved. If there is any common feature that distinguishes modern analytical de vices from their forbears, it lies in their engineering. These devices have been created by the conscious application of the principles of a relatively newly recognized discipline—the science of instrumentation—to the chemical need that was to be satisfied. The science of instrumentation is a hybrid field,
drawing its content from optics, elec tronics, mechanics, circuit theory, com puter theory, psychology, and all those aspects of physics and chemistry that treat the interactions of radiant energy and electric or magnetic fields with matter. I t is becoming daily more evident that if the analytical chemist is to use his modern tools with maxi mum efficiency, he must acquire a considerable facility in the concepts and terminology of this new science. The Nature of an Instrument Every analytical instrument can be considered to be composed of four fundamental parts: a transducer, an amplifier, a computer, and an output. In many cases, one component (a com ponent is a single physical object, such as a resistor, vacuum tube, thermo couple, or ammeter) may perform more than one of these basic functions simul taneously, but the presence of these functions can nearly always be recog nized. The transducer, or detector, is the sensing element, and thus functions as the eyes, ears, and nose of the instru ment. In an analytical device, the transducer converts, or translates, the chemical or physical property of in terest into a signal—generally a cur rent, voltage, or resistance change— that is either proportional to the con centration or characteristic of the
GOOD NEWS for analysts deter mining micro amounts of sulfate (or of sulfur after conversion to s u l f a t e ) ! A determination accu rate to 1% in the range 2 to 400 ppm. with a working time less than Ά hour! MERELY ADD 'Baker Analyzed' Barium Chloranilate to a buffered, ethanolic solution of sulfate. Filter or centrifuge off barium sulfate. Then determine the concentration of the deep purple acid-chloranilate ion by colorimetric measure ment of the broad band at 538 millimicrons. T h e method is superior to mephelometric and classical gravimetric methods, and is applicable to such diverse materials as water a n d petroleum products. ORDER B a r i u m C h l o r a n i l a t e 'Baker Analyzed' R e a g e n t from your favorite laboratory supply house. SEE Analytical Chemistry, 29, 281-3 (1957) for details of the method or W R I T E for a free data sheet.
J. T. Baker Chemical Co. Phillipsburg, New Jersey
Circle No. 21 A an Readers' Service Card, page 89 A V O L . 3 0 , N O . 6, JUNE 1 9 5 8
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