by B. W. Thomas
he flame photometer, often referred
Tto as the poor man’s emission spec-
trograph, has been developed into a highly useful analysis tool during the past 10 years and offers some promise toward continuous determination of certain elements in fluidized process streams or products (6, 7). Operation of the flame photometer is similar to that of the emission spectrograph (1, 4, 6, 8, 9). The sample under study is burned in a self-supporting flame and the emitted light, over and above the light from the flame alone, is measured quantitatively for determination of elemental constituents in the test sample. Cost of the most elaborate flame photometer is less than $5000 as compared with perhaps $20,000 for the simplest emission spectrograph. Identification of the measured elements is a function of wave length for the emitted light, while intensity of the isolated energy region or band serves as a concentration measurement of the unknown element. For dispersion of the emitted light into a spectrum or for isolation of certain wavelength regions the flame photometer may be equipped with entrance and exit slits as well as a quartz prism, a glass prism, a diffraction grating, or a set of specially selected wave-length filters. Any of several fuels may be used
Fuels for support of the flame in which test specimens are burned for analysis include natural gas, LPG propane, acetylene, and hydrogen in various arrangements for appropriate mixing with air or oxygen to obtain the desired temperature of combustion. Means for intensity measurement of the isolated energy band in a flame spectrum include barrier layer photocells, single plate photoelectric tubes, and photomultiplier tubes in different combinations with galvanometers, current amplifiers, and electronic recording circuitry. Since the extent to which an element November 1955
emits light depends on temperature and the temperature of a gaseous flame is low relative to the temperature of a n electric arc or spark, the spectra produced by a flame photometer are much simpler than spectra from the emission spectrograph. Many elements do not reach their emission temperature in a gas flame; hence, they have no flame spectra. For other elements, only the more easily excited wive-length regions or bands are present in the flame spectrum. Obviously, elements requiring emission temperaturcs in excess of the gaseous flame cannot be determined on the flame photometer. On the other hand, bothersome interference often encountered because of the multiplicity of emitted wave lengths in emission spectra is usually nonexistent in flame spectra.
lute intensity values. If the flame photometer is to be applied to a flowing stream, automatic means should be provided for rather frequent periodic switching to a reference or standard sample. Analysis by comparison of known and unknown samples aids considerably in reducing errors caused by viscosity effects, the presence of acids or salts, and fluctuations in air or gas pressure. Lithium is most widely used as an internal standard in flame photometry. Several types of flame photometers are available
According to literature publications, components built by Beckman Instruments, Inc., Fullerton, Calif. (3, 3 , 5 ) , are perhaps most often used in the field of flame photometry although successful operation has been achieved on flame photometers t h a t have been Proper handling of sample is key developed by the Perkin-Elmer Corp., to success of flame photometer Norwalk, Conn. (2, S), and the North Whether used for analysis of spot American Philips Co., M t . Vernon, ssmples or flowing streams, equilib- n-. Y. (6). Beckman made its entrance into rium introduction of test material into the flame is perhaps the most flame photometry instrumentation by difficult feat of flame photometry. providing flame attachments for the Materials in which one or more of such laboratory ultraviolet spectrophotomelements as sodium, potassium, lith- eter. Spectral dispersion tliroughium, barium, and calcium have been out the ultraviolet and visible regions measured in the 0.01 to 1.0 p.p.m. con- is provided by the standard quartz centration range include water, lube prism and line or band intensities are oil, heating oil, cement ( 2 ) ,milk, blood measured on the usual null-balance (6), urine, and metallic ores (4). metered system or by means of a Other elements for which analyses for specially arranged recorder attachhigher concentrations have been made ment. The instrument mag be opon the flame photometer include boron, erated at a fixed wave length for concesium, chromium, cobalt, copper, tinuous monitoring of one element in a manganese, nickel, and silver. Tetra- dynamic test stream or i t may be arethyllead ( 3 ) in gasoline has also ranged to scan a wide energy range for been measured on the flame photom- a static sample. A new energy-recording attachment for the DU spectroeter. Reduction of solid test samples t o an photometer provides continuous reaqueous solution for atomisstion into cording of either emission or absorpthe burning flame may require water tion spectra from a flame for the region extraction, ashing, or acid digestion of 2200 to 10,000 A. The attachment followed by suitable dilution. For includes a n automatic wave-length best results, light intensity ratios be- drive and a strip chart recorder tween test specimen and standard equipped n-ith a linear output consamples are measured instead of abso- version unit. With a. choice of five
INDUSTRIAL AND ENGINEERING CHEMISTRY
75 A
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Full range of sizesand ratings in portable, screw-plug and flanged types. Available with copper, steel or alloy sheaths to resist corrosion. Used for heating water, asphalt, greases, molten salts, pickling and plating baths, process kettles; for superheating steam and compressed air; for melting lead, solder, babbit; and for a wide range of similar applications. l e t the Chromalox Sales-Engineering staff solve your heating problems. electrically.
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Edwin L. Wiegand Company 7511 Thomas Boulevard, Pittsburgh 8, Pennsylvania
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EDWIN L. WIEGAND COMPANY 7511 Thomas Boulevard, Pittsburgh 8, Pa. I would like to have. a copy of Catalog 50 a copy of “101 Ways” 0a Sales-Engineer contact me.
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Street City
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Circle No. 76 A on Readers’ Ssrvice Card, page 1 I I A
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scanning speeds, records of the total wave-length region can be made in from 5 to 150 minutes. Additives in new or used lubricating oils have been identified and measured a t Wynn Oil Co., Azusa, Calif., using the spectral energy recording attachment (ultraviolet to near infrared) that has recently been developed for the Beckman flame photometer ( 1 ) . The flame photometer was especially helpful in providing rapid results needed in evaluating the use of “friction proofing” in heavy-duty tractor oils. Also announced recently by Beckman is a direct-reading instrument for sodium and p o t a s s i u m a n a l y s e s . Equipped with an easily replaceable stainless steel atomizer, i t i s calibrated for direct milliequivalent-milligrams of element per liter of solution-scale readings. A nebulizing chamber in the atomizer decreases particle or droplet size to the flame which reduces moisture condensation and accumulation of deposits in the burner. A dual control system for the two elements automatically inserts the correct filter for isolation of the light to be measured. Other important features of the new direct reader for sodium and potassium include a rugged industrial amplifier and chemically resistant case. Over 50 determinations per hour can be made on this apparatus, which costs approximately $650 and operates on propane or natural gas, compressed air, and standard electrical current. I n the Perkin-Elmer flame photometer, sample is introduced to the natural gas, propane, or acetylene flame through a recently improved atomizer-burner assembly. Chopped light from the flame is dispersed in a double prism optical system and split into two beams for intensity comparison of internal standard with test element. Barrier layer photocells sensitive to the appropriate color operate through balanced amplifier and meter circuitry to provide visual display of instrument response to selected test samples or ratio comparison elements. Time required per routine analysis is no more than a minute for d=2% accuracies. The North American Philips flame photometer is designed primarily for rapid analysis of sodium and potassium for which lithium is used as an internal standard. Although only one atomizing system is employed, dual
controls for sensitivity and instrument zero make i t possible to analyze a single sample preparation for widely different concentrations of sodium and potassium. Light from the methane-air flame is reduced to spectral band energy beams by means of selected filters and measured on a high sensitivity barrier layer photocell and null galvanometer arrangement without the use of an electronic amplifier. Accuracy claimed for sodium or potassium in the Norelco instrument is better than i l % of the amount present in plasma. Other flame photometers employing filter optical systems and simple photocell measuring circuits have been developed by Baird Associates, Cambridge, Mass., by E. Machlett and Son, New York, K.Y., and by Evans Electro-selenium Ltd., Harlow, Essex, England. l i t e r a t u r e cited (1) Beckman Instruments, Inc., Fullerton, Calif., Reckman Bull. 16 (1955). (2) . , Diamond. J. J.. and Bean. E. L.. Anal Chem., 23, 1053 (1951). (3) Gilbert, P. T., Jr., Ibid. (4) Harley, J. H., and Wiborly, S. E., “Instrumental Analysis,” p. 190, Wiley, New York, 1964. (5) King, W. H., and Priestley, W. M., A n a l . Chem., 23, 1054 (1951). (6) North American Philips Co., Inc., M t . Vernon, N. Y., Norelco Reporter, p. 31, March-April 1955. (7) Opler, A., and Miller, J. H., J . Opt SOC.Amer., 42, 784 (1962). (8) Perkin-Elmer Corp., Norwalk, Conn., Model 146 Flame Photometer Bull., 1955. (9) Willard, H. H., Merritt, L. L., and Dean, J. A., “Instrumental Methods of Analysis,” p. 44, Van Nostrand h-ew York, 1948. Correspondence concerning this column will be forwarded if addressed to the author, % Editor, INDUSTRIAL A N D ENGINEERING CHEMISTRY, 1155--16th S t . , N.W., Washington, 6, D. C.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 47, No. 11
