Report for Analytical Chemists
because most of the atomic vapor occurs in the ground state, atomic absorption is sensitive for a large number of elements. This is in cont r a s t to flame photometry where the light emitted from the small amount of excited atomic vapor is measured. Recent improvements have been m a d e in the construction of hollow cathode lamps. The "high intens i t y " lamps offer greater sensitivity and linearity for elements such as nickel and cobalt in which nearby nonabsorbing lines cannot be resolved from the absorbing line. These, however, require a separate power supply to operate auxiliary electrodes. T h e "shielded" hollow cathode lamps exhibit greater intensity t h a n conventional lamps and do not require a separate power source. These are commercially available for most elements now.
desired, and a calibration curve straightener. A new P e r k i n - E l m e r model will include these latter features. Jarrell-Ash is developing an instrument with internal s t a n d a r d capabilities. H e w l e t t - P a c k a r d now markets an inexpensive instrument in which a conventional monoehromator is replaced by a series of interference filters. This allows the rapid determination of six elements just by changing the hollow cathode lamp and pushing a button to change the filter. While this will not be as sensitive as, and will be more subject to interference than, prism or grating instruments, it is quite convenient for routine determinations. A welcome feature on several new instruments is the inclusion of a number of safety features in the ignition systems, especially for nitrous oxide-acetylene flames.
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Methods of Sample Preparation
Commercial competition in atomic absorption instrumentation has mushroomed in the last year or two. There are over t w e n t y commercial models now available. Major manufacturers and distributors in this country include JarrellAsh, I n s t r u m e n t a t i o n Laboratories, Perkin-Elmer, Beckman, HewlettP a c k a r d , Varian ( T e c h t r o n ) , Aztec, Bendix (Southern A n a l y t i c a l ) , and Bausch and Lomb. There are several models available in the $3000— 4000 range which are designed for routine analyses. These are not so sophisticated or as sensitive as the larger instruments. The higher quality line of most companies is in the price range of $7000-9000. W i t h the recent increased competition in this field, several improved innovations have appeared on new models. T h e I n s t r u m e n t a t i o n L a b oratory Model 153 incorporates an internal standard system, similar to t h a t in their familiar flame photometer. T h e ratio of the absorbance of the sample to t h a t of an internal s t a n d a r d is read. This allows improved precision and sensitivity. I n addition, a true m a t h e m a t i c a l integration of the entire signal over a preset period of time gives increased precision. Other improvements, which other instruments now have or soon will have, include direct readout in a n y concentration units
I n principle, very little or even no sample preparation is required for biological fluids prior to analysis by atomic absorption spectroscopy. The amount and n a t u r e of preparation needed will depend on the type of sample, the element to be analyzed, its concentration, and precision and accuracy needed. No one general procedure can therefore be described for all or even several analyses. Some metals can be determined directly in urine or blood, but others do not have such favorable absorption characteristics or are present in such small concentrations t h a t matrix effects become intolerable. In a large number of cases, some method of sample destruction is required. This is true, of course, for all nonliquid samples such as tissues. M e t a l s can often be extracted (dissolved) from ground plant or soil samples. After destruction of organic matter, some metals can be determined directly in the solution of the ash or digest without interference from matrix residues, provided the metal is of sufficient concentration to be detected. Often, however, a preconcentration or separation step is necessary in order to eliminate interferences a n d / o r to render the desired element in a concentration high enough to be determined.
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'M'cfii ' w a n * m o r e information on ^*~ why Series " C " P r e s s u r e L o k liquid syringes are better. NAME
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TITLE CO Μ ΡΑ Ν Υ ADDRESS
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Circle No. 66 on Readers' Service Card
VOL.
4 1 , NO. 1, JANUARY 1969
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27 A
