TECH NOLOGY
Instrument Makers Court Atomic Absorption Beckman enters field with accessory for UV spectrophotometers; Perkin-Elmer, Jarrell-Ash, and Aztec bring out new models Atomic absorption photometry is fast shaping up as one of the current darlings of the analytical instrument business. Latest to pay court is Beckman Instruments, which this week is entering the field with the introduction of an accessory that converts three of its ultraviolet spectrophotometers to atomic absorption photometers. At the same time, new instruments are being readied by current suppliers Perkin-Elmer, Jarrell-Ash, Aztec Instruments, and Engis Equipment. Atomic absorption, the center of all this attention, is a relatively new field of analytical chemistry. But it has grown rapidly since 1961 when commercial instruments first became available. Perkin-Elmer president Chester W. Nimitz, Jr., for example, estimates the current annual market for the U.S. and Canada at $3 million. Considering the potential, this could just be a good-sized scratch on the surface. The uses for atomic absorption range far and wide, wherever there is a need to know the concentration of trace metals: body fluids and tissues, plants, foods and beverages, agricultural chemicals, soils, air pollutants, petroleum catalysts, chemical process streams, metallurgical specimens, industrial electrolytes, and marine chemistry and biology. At present, the clinical market appears to be the largest, with agriculture running a possible second. Now going into production, with first deliveries scheduled after July, Beckman's accessory will make atomic absorption analysis available to owners of the DU, DU-2, and DB spectrophotometers for about $2800 to $3200. Also, the accessory provides for flame emission spectrometry and makes it possible to use the spectrophotometer itself for conventional UV absorption analyses. List Growing. Atomic absorption photometry can analyze for more than 60 metals in the parts-per-million and parts-per-billion ranges, depending on the element, and the list is still 48
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ACCESSORY. Dr. Juan Ramirez-Munoz, who is responsible for evaluating the performance of Beckman's new atomic absorption accessory, changes a hollowcathode lamp prior to starting a series analyses for element concentration
growing. The technique is fast, easy, and accurate. Determinations that might drag out for several days by conventional wet-analysis methods can take only minutes. Although the observation that led to atomic absorption spectroscopy dates back to 1802, and other workers recognized its potential for analysis in 1872, its birth as an analytical technique didn't take place until 1955. That was the year that Dr. Alan Walsh and his group at Australia's Commonwealth Scientific and Industrial Research Organization developed practical instrumentation for the method. Rapid expansion of its use, however, has come only within the past few years with the introduction of commercially available instruments. Flame emission photometry and atomic absorption photometry are re-
lated methods, but it is the difference that is all-important. The first one measures the light emitted by excited atoms as they drop back to the ground state, whereas the latter measures light absorbed by the atoms in the ground state as they go into an excited state. One technique complements the other. The flame emission method works very well for atoms that are easily excited by energy from the flame, thus giving a high population of excited atoms. The bulk of the metals, however, are not excited so easily. Most of the atoms of a given element stay in the ground state at flame temperatures. In some cases (zinc, for example), practically all the atoms remain in the ground state. Atomic absorption takes full advantage of this former drawback.
In atomic absorption photometry, a solution of the metal is vaporized and fed into a flame with the fuel, where the metal is converted to the atomic state. A lamp whose cathode contains the metal being analyzed sends a beam of light through the flame to the spectrophotometer, which measures how much of the light is absorbed and, therefore, the concentration of the particular metal. Because the lamp's cathode is made of the metal being analyzed, the wave lengths in the light beam are characteristic of that metal. Other metals in the test solution, then, rarely interfere in the analysis. Different analyses require different lamps. The lamp housing in the new Beckman accessory for example, has connections for three lamps—two in standby and one in use, with easy switching from one -to another. All is not rosy in atomic absorption, however. There are limitations. Some metals tend to form refractory compounds, rather than atoms, in the flame. If few atoms are present, the method fails. If many of the atoms of a metal are excited by the energy of the flame (as in flame photometry), the accuracy falls off. For these and other reasons the limits of detection vary from element to element. Zinc, which fails completely in emission photometry, is easily detected in the parts-per-million range with the absorption method. Vanadium cannot yet be measured because it forms oxides, rather than atoms. To meet the needs of this new technology, instrument makers try to make their units as versatile as possible. Beckman, for example, furnishes its accessory with either of two burners, which are interchangeable. The laminar-flow burner requires less sample and is more sensitive with a limited amount. It is applicable to 60 to 70% of the metals commonly analyzed. The turbulent-flow burner—actually three burners in a line—uses hydrogen, or, for a hotter flame, acetylene. A special feature makes it possible for the light beam to pass through the flame three times for greater sensitivity than with a single pass. P-E Expanding. Perkin-Elmer is expanding its line with the Model 290, a low-cost ($2900) instrument. At the same time, the company is beefing up the performance that can be achieved with its high-powered Model 303 by offering a digital con-
centration readout accessory for use with the unit. The Model 290 is intended for routine operation where a large number of samples are analyzed for the same one or two elements. Four samples per minute can be analyzed in such cases, P-E says. Readout gives concentration directly. The unit is designed to take P-E hollow-cathode lamps, including new multiple-element lamps for calcium-magnesium and for cobalt-chromium-copper-ironmanganese-nickel. In a five-day precision study, P-E says, the 290 showed an average deviation of only 1 to 2% of calcium and magnesium present in eight preserved urine specimens. In consecutive determinations, the company says, calcium and magnesium concentrations show standard deviations well below 1% of the amount present. The digital concentration readout accessory is designed to improve the sensitivity, precision, speed, and convenience of the Model 303. It automatically computes and displays the concentration of an element in a sample being analyzed. Priced at $2100, the accessory will be ready for delivery in April, as will the Model 290. The accessory can be set to take four, eight, or 16 independent readings of the same sample and present their average. Smoothing-time-constants up to 20 sec. can also be selected. Readout is four illuminated digits which present concentration directly in whatever units the accessory is calibrated for. Meanwhile, Jarrell-Ash is readying its new Model 82600, which will cost between $8000 and $9000. It will have a 0.75-meter focal length and will handle up to 12 channels. Each hollow-cathode lamp will normally be capable of analyzing for three elements, with lamps ordered to fit the range of elements of most interest. Aztec, which markets the Australian Techtron instrument, will introduce Techtron's second-generation AA4. The unit, which will sell for less than $3000, is designed for rapid analyses in clinical and control laboratory applications. Rounding out the new instruments is a unit from England's Hilger & Watts designed around the company's Uvispec H-700. The new instrument is an a.c. unit with in-line cathode tubes. Marketed in the U.S. by Engis Equipment, it will cost $4000 to $5000 and be available this summer.
Process May Reduce Pollution From Burning Coal Refuse Piles A process designed to reduce the air pollution from burning coal refuse piles is getting a tryout this month. A pilot plant to test the process has been built at Barnesboro, Pa. The process uses a heavy liquid to separate marketable high-ash coal from nonburnable waste rock. Nearly 500 mountains of coal refuse, waste material from coal cleaning operations, are burning uncontrollably in 15 states in the U.S., according to a Bureau of Mines survey. These refuse banks, some of which weigh as much as 20 million tons, ignite spontaneously and are nearly impossible to quench. Each year they pour thousands of tons of pollutants into the atmosphere. The new approach for eliminating air pollution from this source was begun at Pennsylvania State University in 1962 by H. Beecher Charmbury, Pennsylvania's secretary of mines. The work was taken over by James K. Kindig of the department of mineral preparation at Penn State (University Park, Pa.). The pilot plant is a semimobile, four-story, L-shaped structure. Coal refuse from bituminous regions will serve as the first feed. Anthracite coal refuse is slated for a later try. In the process, the unburned coal refuse is dumped into receiving hoppers and conveyed to a screening and crushing operation. Noncoal refuse, such as mine-shaft timbers, is removed by screening. The coal is crushed to pieces less than 1 in. in diameter, and powder-sized coal particles discarded. The crushed coal refuse is carried to a cyclone extractor by a heavy slurry of flour-fine magnetite. Float. The coal particles float in the heavy liquid while slate and stone sink. The high-speed action of the cyclone forces the slate, some of the magnetite, and the rock out the bottom of the cyclone extractor while coal is recovered at the top. Slate and rock are screened and washed to recover the magnetite. Separated coal is also washed to recover the magnetite and then spun dry. Both wash streams combine, and the magnetite recycles. About 50 tons of coal refuse can be processed in an hour, Mr. Kindig says. Four tons of raw material will yield about 1 ton of usable coal. The pilot plant will be used to develop the JAN.
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