What's Happening in Chemistry? • Screening g e n e s for defects c a n b e d o n e 10 t i m e s faster n o w a n d with greater accuracy. • Astrochemists eagerly a w a i t d a t a from t h e H u b b l e S p a c e Telescope. • Early r e s e a r c h r e s u l t s indicate zinc m a y b e effective a g a i n s t t h e c o m m o n cold. • National R e s e a r c h Council r e p o r t s e e s vast potential a h e a d from c h e m i s t r y . • A b a c t e r i u m could b e t h e p r e d o m i n a n t culprit in p e p t i c u l c e r s . • Nylon s t o c k i n g s , plastic b a g s a n d bottles b e c o m e " i v o r y " a n d diet pills. • Chemically treated crop wastes b e c o m e t a s t y feed for a n i m a l s . • " P r e s c r i p t i o n s " s t u d i e d for r e d u c i n g acidity of l a k e s . These are but a few of the more than two dozen exciting and interesting subjects covered in the new edition of WHAT'S HAPPENING IN CHEMISTRY?, the American Chemical Society's annual compendium of research reports from the frontiers of the chemical sciences. This award-winning publication is researched and written by Joseph Alper, one of the nation's foremost science writers. Anyone can understand, enjoy and be enlightened by WHAT'S HAPPENING IN CHEMISTRY? You won't want to miss it! Paperbound copy $4.00 each
Order form QUANTITY COST @ $4.00 Foreign add $1.50 TOTAL •ALL ORDERS MUST BE PREPAID· Charge my Π VISA/MasterCard • American Express Π Diners Club/Carte Blanche Π Barclaycard
Π Access
Card I
Exp. Date _
Interbank I (MasterCard only)
Telephone Signature Name (Please type or printl Organization Address
City. State. Zip (ACS 56170/7390/A1131
American Chemical Society. Department of Public Communication 1155 Sixteenth St.. N.W.. Washington. DC 20036
940 A · ANALYTICAL CHEMISTRY, VOL. 58, NO. 8, JULY 1986
Figure 6. Mg (285.2 nm) in an air-acet ylene flame (a) Calibration curves and (b) relative concentra tion errors using the stepped modulation wave form shown In Figure 5. Curves 1 and 2 corre spond to the type 1 and 2 absorbances shown In Figure 5
that reflect either the emphasis of the investigation or a compromise pattern. One compromise sampling pattern is shown in Figure 5. This pattern was designed to optimize sampling at five locations over the course of one modu lation cycle (two passes across the pro file). Sampling points are concentrat ed at the middle of the profile, at both sides two-thirds of the distance to ward the extremes, and at both ex tremes. The type 1 absorbance is com puted using all 40 intensity measure ments, and the less sensitive type 2 absorbance is computed from 24 in tensity measurements in the wings of the absorption profile. This sampling pattern was designed for use with flame atomization where the signal is static. Two full passes require 36 ms, which is a slow response time for car bon furnace atomization. The result ing calibration curves and relative concentration error plots are shown in Figure 6 for Mg (285.2 nm) in an airacetylene flame. Data processing
All the data processing for SIMAAC is handled by three computer pro grams—the data acquisition, the data display, and the data reduction pro grams. The data acquisition program can acquire 18,000 intensity measure ments per second for up to 30 s. This program drives the galvanometer with the appropriate modulation waveform and collects data as described in the previous section. The raw intensity data are stored directly on a disk and
