New Microbalances, Sensitivity _ to 0.1 jig I
Focus
(a)
10 7
10 s
Whenever accuracy and pre cise weighings are required, such as quantitative or elemen tal analysis, filter weighings, standards preparation, etc., see Calm's new Series-20 Automatic Electrobalances.· D Wide dynamic range — Most weighings can be done without tare
ce c ο
M 105
or s u b s t i t u t i o n " weights. D Simple to operate. Π Automatic calibration. D Port able. D BCD output standard. Write for catalog to Cahn Instruments, Inc., 16207 South Carmenita Road, Cerritos, Cali fornia 90701.
10"
10 3
CAHN
Five Catalog
Where weighing a little means a lot. CIRCLE 34 ON READER SERVICE CARD
Why are Milli-Q®owners switching toGelman's Versacap? Hundreds of lab water system u s e r s have switched to the Gelman Versacap capsule be cause it costs less, works better, lasts longer than any other final filtration unit available.
Versacap is available i m m e d i a t e l y from American Scientific Products, Fisher Scien tific, VWR, CMS and A.H. Thomas. Order a capsule today and start saving money, time and trouble.
"Great flow; no drop in water quality. " —G.S., Belchertown, MA
"Low operating pressure; works fine. —R.K., Longview, WA
"Lasted six weeks; no plugging, —Y.F., A n n Arbor, M I
no cracking. '
Gelman Sciences Inc. ^2i^
60
° South Wagner Road, Ann Arbor, Michigan 48106
CIRCLE 67 ON READER SERVICE CARD 386 A · ANALYTICAL CHEMISTRY, VOL. 55, NO. 3, MARCH 1983
0»
I
Retention Volume
Figure 1. SEC calibration (a) Typical calibration plot for a column set. (b) Chromatogram that might be obtained with the same column. Ε is the exclusion limit for the packing. Molecules that are too large to enter any of the pores will elute en masse at this point. Ρ is the total permeation limit, where all solutes small enough to enter all the pores will elute. The frac tionation range is the mostly linear region be tween these two points. In this area, sample com ponents will separate out on the basis of molecu lar size
particle packings, low eluent flow rates must be used, and this leads to long analysis times. The new microparticulate packed columns, with their much smaller dp values, promote much more rapid mass transfer across phase boundaries. "The most out standing advantage of high-perfor mance packings," said Howard G. Barth of Hercules, Inc. at the EAS
