INSTRUMENTATION Flame photometer accessory, developed to take advantage of resolving power and photometric precision of the Beckman spectrophotometer, is now in production
by Ralph H. Müller Κ FLAME photometer accessory for use with the Beckman spec-^*- tropliotometer is announced by the National Technical Laboratories. It has been known for many years that flame spectra can afford more than qualitative analytical information and that their utility is not confined to the alkalies or- alkaline earths. The use of "hot" flames extends the methods to more than thirty elements. The early investigators also considered the possibilities of objec tive photometric schemes. The pioneering researches of Lundegârdh, Heyes, Schuhknecht, and others are discussed in Bôttger's "Physikalische Methoden der analytischen Chemie" [Volume III, page 345, Leipzig, Akademische Verlagsgesellschaft, 1939].
Figure Λ Advantage has been taken of the resolving power and photo metric precision of the Beckman spectrophotometer by develop ing a flame photometer accessory. Samples are atomized and in troduced at a uniform rate into a very hot oxy-gas flame through a specially designed burner. The spectrophotometer isolates the desired spectral lines and measures their intensities relative to a blank or standard. The flame photometer is now in production at the National Technical Laboratories of South Pasadena, Calif. The instrument is shown in Figure 1. The base and rear panel contain the combustion controls and the sprayers appear on the right. The burner is water-cooled and is vented through a watercooled chimney. The Model DV quartz spectrophotometer serves to isolate the lines and measure their intensities. The sprayers are constructed of Pyrex, stainless steel, and neoprene. Three identical sprayers are provided with each instrument and all may be connected simultaneously, so that by operation of a
control knob the solution, standard, or blank from any of the three can be fed into the flame. A continuously uniform spray can be obtained with 10 to 20 ml. of sample. The sprayers are readily removed for cleaning and introduction of samples. Operation
of
Instrument
Thermally stabilized and humidified air from high-pressure bubblers is used to atomize the sample in the sprayer. Com pressed air at 30 to 50 pounds per square inch is supplied to an air regulator valve on the control panel where it is reduced and regulated to 15 pounds per square inch as indicated by the gage. This air is washed with water in the bubble towers where its temperature and humidity are adjusted. A "flush'' lever operates a two-way valve with which the water in the bubblers may be drained and replaced. Burner gas can be regulated by a control valve and adjusted with the aid of a gas pressure manometer to approximately 3 inches of water pressure. Oxygen from a tank is supplied through a conventional regulator to maintain 5 to 10 pounds per square inch. The burner consumes about 30 cubic feet of oxygen per hour. The sample spray is consumed in a special burner fed with illuminating gas and oxygen. The fuel is burned at many small ports located around larger holes which feed the spray to the flame. This arrangement provides a broad uniform flame which does not require precise optical alignment with the monochromator of the spectrophotometer. The hot portion of the flame is focused on the monoelrromator of the spectrophotometer. A stainless steel mirror behind the flame increases the available light by approximately 40%. Only minor changes are required to adapt the spectrophotom eter to liame photometry. One resistor in the phototube com partment must be changed and the lamp housing is removed and replaced by the burner assembly. Applicability
and Range of
Method
The results may be read directly from the dial of the photom eter in terms of line intensities expressed in arbitrary units or the instrument may be calibrated to read in parts per million. Typical results which have been obtained with the Beckman flame photometer are condensed in the following summary to give a rough indication of the applicability and range of the method. The particular element determined, the approximate minimum detectable amount in parts per million, and the spec tral lines in Angstrom units used for measurement are given in that order. B, 50. 5481; Ca, 0.5, 6182, 6203; Cs, 2, 8521; Co, 25, 35305 3502; Cu, 10, 3247; Fe, 50, 3735, 3737; Li, 0.1, 6708; Mg, 25, 2852; Mn, 1, 4031, 4033, 4035; Ni, 40, 3525; Κ, 0.5, 7655; Na, 0.1, 5890, 5896. 21 A
22 A
VOLUME
19, N O . 8
INSTRUMENTATION
Klett....
Precision No information is available concerning the precision which can be attained in these measurements. By using related tech niques, Thanheiser and Heyes were able to determine manganese in steels with an average error of 1.15% [Arch. Eisenh-iittenwesen, 11, 31(1937)) and to show that the photoelectric current was directly proportional to the manganese concentration up to 400 mg. per liter. I t may be assumed that the present techniques and instruments are not inferior to those employed in this earlier work.
Photometers fClettSiwun&iiati PUotoelecbUc
QlcM. Cell QtUo^Ufieie* No. 900-3
The Klett Fluorimeter
No. 2070
Designed for the rapid and accurate d e t e r m i n a t i o n of thiamin, riboflavin, and other substances which fluoresce in solution. The sensitivity and sta bility are such that it has been found particu larly useful in determining very small amounts of these substances.
KLETT SCIENTIFIC PRODUCTS ELECTROPHORESIS APPARATUS · BIO-COLORIMETERS GLASS ABSORPTION CELLS · COLORIMETER NEPHELOMETERS · GLASS STANDARDS · KLETT REAGENTS
Klett
Manufacturing
179 EAST 87TH STREET
Co.
NEW YORK, Ν. Υ.
Relative
Merits
of Optical
Methods
We believe it would be useful and timely to have a survey of the present status of optical methods of analysis which might in dicate the relative merits and advantages of the various types. An intercomparison of spectrographic, spectrophotometric, and photometric techniques would be useful, especially if it indicated the range, speed, specificity, precision, and relative costs. The specificity and qualitative certainty of the spectrographic method are beyond dispute but quite often its high sensitivity is overemphasized because, in a number of instances, "eolorimetric" methods possess a comparable degree of sensitivity and an equal or better precision. The superiority of spectrophotometers over filter photometers is often stressed on the basis of greater versatility and flexibility. Although these claims are valid, the relative costs are often overlooked or minimized. Quite fre quently, the advantage of spectral resolution by prism or grating is extolled in apparent neglect of the fact that many "colorimetric" procedures involve substances with very broad absorption bands. True comparisons are difficult for another reason. Modern spectrographs and spectrophotometers represent a considerable amount of research, skilled design, and good engineering. The state of affairs with many photometers is quite disappointing by comparison. I n principle, seme of them are little better than photographic exposure meters with a few pieces of colored glass and some test tubes as accessories. In few cases have any of the vast resources of electronics appeared in the construction of these devices. It is often forgotten that a half century of research and de velopment was involved in the design of visual optical instru ments. Few of these advances were relinquished in the design of modern spectrographs and spectrophotometers; indeed, many notable improvements have been added. We mention only two— coated lenses and front-surface aluminized mirrors. Improvements in photometers would seem to be warranted in view of the great number of "eolorimetric" procedures which have been devised by analysts. In some fields, notably clinical analyses, a large proportion of the methods are of this nature. We venture to suggest that small, but important, items are the annoyance and inconvenience attached to the customary sample cell or cuvette used in all these instruments. Most ο Γ them present excellent opportunities for finger marks, dribbles, spill ing, and the crowning disaster of dropping the whole thing! Will some one give us pipet types or otherwise easily handled cells or is it ever too fantastic to expect cheap injection-molded plastic cells of the "throw-away" variety? Another question may be raised, again in connection with pho tometers. Little attention seems to have been given to making them direct reading or automatic in operation. There are two notable examples of automatic direct-reading spectrographs in which the final results appear on tape or on dials. There are re cording spectrophotometers for the visible infrared and ultra violet. The comparable instrument for photometry would be considerably simpler and should find use in cases where a large number of identical "eolorimetric" analyses are required.
