DIAL A
INSTRUMENTATION
GRADIENT
FOR
CHROMATOGRAPHIC ELUTION OR FILLING ZONAL ROTORS.
The ISCO Model 190 DIALAGRAD Programmed Gradient Pump will form almost any two component concentration, pH, or other gradient by simply setting a series of dials. A completely mixed, essentially non-pulsating flow at a uniform rate is produced with no cams to cut or multiple solutions to mix at estimated con centrations. The shape of the curve is determined by setting eleven 0 to 100% dials which rep resent the i n i t i a l , f i n a l , and nine evenly spaced intermediate ratios. This gives 10 program in tervals, each of which are auto matically subdivided into five linear interpolations to produce a smooth gradient. Calibrated flow rates from 0.5 to 500 milliliters per hour and program durations from 10 minutes to 12 days are set with positive stop switches. The DIALAGRAD will produce linear or curved gradients with equal ac curacy and the program will be perfectly reproducible run after run. The instrument takes but a few seconds to program and re quires no attention during a program run. For more information, ask for brochure DP31G.
ISCO
INSTRUMENTATION SPECIALTIES CO., INC. 5 6 2 4 SEWARD AVE. LINCOLN. NEBR. 6 8 5 0 7
See ACS Laboratory Guide for All Products/Sales Office Circle No. 50 on Readers' Service Card
78 A
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ANALYTICAL CHEMISTRY
Figure 3. Cathode-ray tube permits the display of three registers simultaneously Some features exhibit unusual con sideration for the operator. In addi tion to the usual operating manual and for the benefit of the occasional user, a plastic instruction sheet, which briefly describes the function of all keys and includes appropriate examples, is per manently attached to the calculator in a slide-out tray. Programs may be stored on and re-entered from creditcard size magnetic cards. These are erasable and reusable. Each card will carry two 196-step programs and cards may be put in successively to link pro grams. Any recorded program can be protected permanently against acci dental erasure simply by cutting off the corner of the card. A cut corner inhibits the machine from recording new information on the card. A special card carries a protected diagnostic pro gram for quick reassurance of proper calculator performance. When will we build things like this into our analytical instruments? Service will be by ex change replacement of sub-modules to minimize downtime. A loose-leaf program library note book is also included. I t contains more than 100 sample programs. It pro vides directly usable solutions to many common scientific and engineering problems and presents examples of pro gram techniques useful to solve many more. Pads of program sheets, sup plied with the calculator, simplify the preparation and debugging of programs. The program library, among other things, includes roots of a fifth degree polynomial, solution to three simultane ous equations, Bessel functions, Fourier analyses, solution of incomplete elliptic integrals of the first and second kinds,
Fresnel integrals, real and complex polynomial evaluation. Of the hundreds of tasks which can be performed we select but two which are of constant use to analytical chem ists, as the common one of treating data to fit a straight line: y — mx + b. The method of least squares is usu ally used, squaring the deviations, then minimizing this sum of squares. The method of least squares also yields the coefficient r in the regression analysis. For perfect correlation r = ± 1 . If r yields a value near zero, there is almost no linear correlation between the vari ables. When set up for this task after the entry of an arbitrary number of data points, the 9100A gives a display on the monitor in milliseconds. The correlation coefficient appears in the Ζ register, the intercept in the Y register and slope in the X register. The problem of getting the area un der a curve for which there is no mathematical equation can be solved accurately by numerical integration. With the speed of the 9100A, integra tion becomes a routine solution with answers available as fast as the data can be entered. The program can be based on Simpson's one-third rule, or can use the Euler-Maclaurin series. This calculator should be very valu able to the analyst. One might hope that more people will become interested in giving their data more thorough treatment. While the price of $4900 is modest, we cannot afford it or justify its purchase; were that not the case we might even stop grumbling about data copied directly from recorder charts and published as such, leaving it to others to unravel its implications.
