HOW TO

VARIABLE

Dr. Geoffrey B. Crooks,ISCO chief design engineer:When you're buying a variablewavelength LC detector, you'llhave to sort through a lot ofspecifications and promises tofind the right one. Here is someinformation I think will help youmake your decision.

Performance. Baseline noise is a better indication ofthe detector's sensitivity than the minimum absorbancerange available. You can expect a good detector to have adry cell, peak-to-peak noise of no more than 3 x 10-5 Awith a 0.5 second rise time, at all wavelengths from 200to 300 nm. Noise should be less if measured at a longerresponse time or only in the 240nm region. Remember, noisespecified + looks twice as good aspeak-to-peak. Most detectors usea low-cost passive (resistor-capacitor) filter which reducesnoise but also reduces responsespeed and distorts peak shape.Better detectors have active fil-ters, but they're not all the same- one highly-reputed instrumenthas an active filter with bad __overshoot which is covered up byautomatic baseline correction.

Make sure that the bandwidthis narrow enough to give good ISCO's fourth generatioquantitation, and that the flow cell V4 has 190-750 nm raniquantitation, ~~~~~0.002 AUFS sensitivity;volume is small. Good detectors cells for LC, HPLC, andhave bandwidths in the 4-6 nm lamp life; and a three-y4range and cell volumes on the at $3995 without optionorder of 8 ml per cm of optical peak separator.pathlength.

Versatility. The more flow cells available, the lesslimited you'll be. If you can't later buy a 1 ll or smallercell for your detector, you won't be doing any mLC.Versatility is also enhanced by a wide wavelength rangeand the ability to read %T.

Operating ease. Consider the warm-up time re-quired. Look to see how easy flow cell changing is: aneasy-to-see cell isn't necessarily easy to remove. Aplug-in cell cassette is best. Ask if you have to physicallyremove one lamp and put in another to change from UVto VIS, or whether you can just flip a switch. Is N2 purgerequired for coldroom or short wavelength operation?

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That can be a real nuisance. And does the detector haveany special features that will be useful to you? Forexample, our V4 can be supplied with a built-in 10 cmrecorder and can control a fraction collector to putdifferent peaks into different test tubes. Other detectorshave different features, such as automatic wavelength

scanning.Value. Always consider fea-

tures and performance in relationto purchase and operating costs.See if the visible lamp and othernecessary items are included inthe base price. You should find outexpected deuterium lamp life:1000 hours is typical; over 5000hours is exceptional, but it can bedone. Is the lamp life wasted byusing it at visible wavelengths orfor long warm-ups? You can easilyspend as much on lamp relace-ment over a three to five year

variable detector. The period as you did on the detectora; 6 nm bandwidth; itIf2 x 10-5 noise; 10 flow ItseLLC; 8000 hr median D2 You and I know that salesir warranty. It's priced literature often doesn't tell theJ built-in recorder and whole story, and that some manu-

facturers use specifications ob-tained under questionable condi-

tions. You should try the instrument first, or at least buyit on approval so you can send it back if it's not what youreally want. And finally, how long is the warranty andwhat does it give you if something goes wrong?

We designed the ISCO V4 with allthese points in mind. It has top specifica- -utions and many special features thatmake it a pleasure to use, yet it's almostthe lowest priced variable detector youcan buy. To learn about it, write or call ustoll-free [800] 228-4250 for your catalog. IsISCO, P.O. Box 5347, Lincoln, NE 68505.

Circle No. 271 on Readers' Service Card

9 MARCH 1984

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Waters Pr

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al compounds,uticals and virti Compound Shaved and Collected

ie allow faster sepaiity loss than any

Isolate peptides and proteins with 99% purity

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TIME (min) 30 - _o4

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Analytical results

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30 (min) 0 19 (min)

mediate molecular weight proteins to 99% purity.

Solution: Isolate a crude synthetic peptide and proteinextract to 99% purity without loss of biological activity by:performing a thirty-minute reverse phase gradient, collect-ing an enriched fraction of product, and rechromatograph-ing a heavier load of the partially purified product underdifferent gradient conditions.

Sample: 500 mg Peptide Hydrolysate 0

Cartridge: PrepPAK®Cie, 57 mm x 30 cm (300A pore,30 ,im particle)

Solvent: A) 0.1% TFA in H20B) ACN: 0.1% TFA in H20, 40:600-100%o B in 30 min, linear

Flow Rate: 150 mI/minDetection: UV, 313 nm

iut,on: Bemloyingthe exc e shave/recycle fea-of the PrepLC 5OQA System, the effective col1umn

ith was increased to 26 feet (the sample was recycled,uccessive times without repetitive manual injectioncollection) and a 77% yield of pure isomers wasized. This compares favorably to a 26.6% yield achievedcolumn chromatography.'

Sample:Cartridgqe:eMobile Phase:Flow Rate:Detector:

0.75 g Labdatriene IsomersPrePPAKKR 500 Silica, 57 mm x 60 cmn-Hexane250 ml/minRI

'Journal of Liquid Chromatography 4(3) 525-532, (1981)

Let us show you how the Waters PrepLC 500A will purifyeven your most difficult mixtures with higher yield

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Circle No. 280 on Readers' Service Card

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For a complete product summary, write or call:

SCIENTIFIC SOFTWAREPRODUCTS, INC.

5726 Professional Circle Suite 105Indianapolis, IN 46241

(317) 244-6163Apple R II is a registered trademark of Apple Computer, Inc.

Circle No. 326 on Readers' Service Card Circle No. 260 on Readers' Service Card

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For further information,contact William L. Schrader,Newman Laboratory,Cornell University, Ithaca,New York 14853(607)256-3455.

Speakers include:

* Kenneth G. Wilson* Enrico Clementi * JamesD. Gunton * Lawrence R.Klein * James A. Swanson* David A. Pensak * GaborT. Herman a Gary Demosa Roger W. Cohen mRoland W. Schmitt* PaulE. Rubbert

"0- SCIENCE, VO <Z3

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with newwLKB Horizontal

L~~~~~~~~~~~~

T ~~Achoice of3 preparative methodsI

Preparative electrofocusing in Immobiline gels is thenewest, most efficientway ofseparating proteins inquantities up to 1 gram. LKB Immobilines combinegreatly improved resolution with sample recovery ratesofup to 98%. And the absence ofsoluble carrierampholytes means that high resolution preparativeelectrofocusing oflow molecular weight substances isnow fully practicable.

-preparative electrofocusing ofhemoglobin,pH 6.0-8.5

Preparative electrofocusing in granular gels is a moretraditional method using Ampholine carrierampholytes, and is also catered for by theLKBHorizontal Electrophoresis System. The enlarged

cooling plate ofthe new Multiphor II doubles the

sample capacity, while the movable electrodes giveincreased flexibility.

-preparative isotachophoresis ofhuman serumproteins

Preparative isotachophoresis is the third choice offered

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4 -preparative electrofocusing ofhemoglobin usingImmobiline,pH 6.5 to 8.5

This is one in a series ofadvertisements describing theunrivalled versatility oftheLKB HorizontalElectrophoresis System. For further information aboutpreparative methods, and the many other applications

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the system also includes a5KV powersupply, thermostatic circulator, laserdensitometer and data evaluationsoftware.In addition to the instrumentation,LKB provides a range of18 major kitsplus a complete programme ofhighquality chemicals, supplies andaccessories, backedby the fullworldwide support ofthe market leaderin electrophoresis and electrofocusing.LKB-the electrophoresis experts.

LKB Instruments, Inc.9319 Gaither Road, Gaithersburg, Maryland 20877.

Te. 301-963-3200,Circle No. 161 on Readers' Service Card

Since its introduction, the DMS 100 Spectrophotom-eter has enjoyed unprecedented popularity, becauseit simply offers more analytical possibilities for yourinstrument investment dollar. Scientists like the way theDMS 100 displays a spectrum on the video screen inreal time; the way it stores spectral information in itscapacious memory for later retrieval; and its intelligentcell changer.

The DMS 100 with the cell changer lets you* signal-average for each cell* monitor cell temperature* print out absorbance, slope, standard deviation,and temperature

But if you need* accurate measurement of differences less than

0.01 0 Abs* plots of temperature versus absorbance* measurement of highly absorbing, scatteringsamples

you need the ultrahigh-performance Varian-Cary2200 UV-Vis Spectrophotometer.

Computer compatibility? Of course!Both the DMS 100 and the 2200interface with the Varian DS 15 DataStation to form a completelyautomatic UV-Vis system.

Circle Reader Service Number 274 for moreinformation; circle No. 275 to discuss your UV-Visneeds with a Varian representative.For immediate assistance contact: FlorhamPark NJ (201) 822-3700 * Park Ridge IL(312) 825-7772 * Sugar Land TX (713) 491-7330* Georgetown, Ontario (416) 457-4130.Or write 611 Hansen Way, Palo Alto, CA 94303In Europe: Steinhauserstrasse, CH-6300 Zug,Switzerland

IntelligentAutomation... varianfmom Varian

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TECHNOLOGY CENTERSThe US Army Chemical Research and

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Circle No. 228 on Readers' Service Card

Varian's new

_

Send todayfor your free copy

This big, new book includes LC instruments, |data systems, our new line of LC components, instruc-tional books, training videocassettes, columns and pack- | a d mechanW er~~~~~~biotechnology and fluid mlechanIcs. W haweings, and Varian's complete line Ot parts and accessories. than any other source. CaU us today

Catalog No. 22 will serve every LC user, regardless --pa--l

of the kind of liquid chromatograph you own.

How to order: Write Varian Instrument Group,

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from Varian Oel Dlone Scientific Europe, P0. Box 594, Hiiversum, HoHand, 035-19587, Telex: 43084rN o

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Circle No. 227 on Readers' Service Card

&%U MEO AU 4 C C_r 1

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