Hollow cathode lamps
Figure 3. Optical arrangement for synthesis of multicomponent radiation beam from single-element hollow cathode lamps
OUTDOOR Spectrophotometers for Water Analysis Figure 4. Tandem hollow cathode lamps for production of multicomponent radia tion beam
mounting (Figure 4). This system, however, is limited to three lamps by light losses. If each lamp were a fourelement multielement lamp, a maxi mum of twelve elements could be done simultaneously with a tandem arrangement. Strasheim and Human (16) de scribed the use of a time-resolved spark as a primary light source for multielement atomic absorption. A rotating graphite disk electrode was used to introduce solutions containing copper, zinc, calcium, and magne sium into the spark gap. Results indi cate, however, that the hollow cath ode provides higher sensitivity and better precision. Further work will be required to determine whether this system is capable of functioning with more than four elements. A final approach to the problem of light sources for simultaneous mul tielement atomic absorption is the use of the continuum source. Various workers (17-20) demonstrated that a continuum source can be used for atomic absorption in conjunction with a monochromator having suffi cient resolving power. In general, however, the detection limits are poorer with a continuum source as compared to a hollow cathode. Most workers have used a 150-W xenon arc lamp for these experiments. An addi tional problem with this source is the
low spectral radiance produced in the far ultraviolet, i.e., less than 250 nm. Nevertheless, a continuum source of fers one possibility for simultaneous multielement atomic absorption. Atomic Fluorescence. In atomic fluorescence the narrowness of the emission line of the source is less im portant (except from the point of view of scatter) since the detector does not view the source directly. What is important, however, is that the source be unreversed and have a high radiance over the absorption line width. Although sources possessing a high radiance are more difficult to pro duce, the optical arrangement of the atomic fluorescence experiment is more suited to multielement analysis. Specifically, banks of lamps may be arranged around the flame without the necessity for complicated optical arrangements or multielement lamps. The most common light source for atomic fluorescence in the past has been the electrodeless discharge tube. Although some work was done to pro duce multielement electrodeless dis charge tubes (21-25), the number of elements is limited. Using a bank of single-element electrodeless discharge tubes would be prohibitively expen sive unless one microwave power sup ply could be used to run them all. The most promising prospect for
You can't find spectrophotometers any easier to use—especially for water and wastewater analy sis. The new DR/2 Model 2504 is available in a handy carrying case; Model 2582 is a handsome laboratory instrument. Both offer the advantages of dialing any of various light wavelengths instead of selecting from a set of individual color filters for each colorimetric test. DR/2 instruments utilize a circular variable interference filter with a wave length range of 400 to 700 nanometers (nm). Special wavelength dial positions are also marked for suspended solids testing (infrared light) and for measurement of color in water. Electronics are all solid-state with transis torized voltage regulation. The carrying case model can be operated on either eight standard flashlight batteries or 115/220 V, 50/60 Hz; the laboratory model operates on either 115 or 220 Volt power. Each control is at your fingertips on the in strument panel. The spectrophotometer chassis also lifts out of its case to facilitate battery change or inspection. IT'S 2 SPECTROPHOTOMETERS IN 1 The instruments also perform well for general laboratory use. For analysts who choose to mix their own reagents and calibrate the spectro photometer on their particular sample, Hach provides special blank meter scales. The instru ment may also be fitted with an optional cell adapter which accepts commonly used 1.0 cm. sample cells. New Handbook For Water Analysis A Hach procedures handbook of simplified water and wastewater analysis is provided with each instrument. Titrations and colorimetric determinations are detailed—more than 70 tests in all. Most procedures are based on Standard Methods but have been carefully simplified so anyone can perform without previous training.
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H A C H ) First in Water Analysis
HACH CHEMICAL COMPANY P.O. Box 907, A m e s , Iowa 50010 U.S.A. (515) 232-2533, T W X : 910-520-1158 CIRCLE 98 ON READER SERVICE CARD
A N A L Y T I C A L CHEMISTRY, VOL. 45, NO. 8, JULY 1973 · 715 A
