PHOTODIODE ARRAY DETECTORS continued


would be seen in both the sample and reference standard to which it is compared, points out Schulenberg-Schell. Yet, as discussed above, parameters such as the technology type and pathlength of the fl ow cell, data rate, whether there is a second lamp (and thus capabilities to detect in the visible range, as well as spectral resolution), and number of diodes in the PAD, can have an eff ect.


The sensitivity—which allows the detector to identify smaller peaks faster—is principally driven by the noise. While vendors will typically list this specifi cation, “the user has to be care- ful of the conditions under which the noise is specifi ed,” such as the time fi lter and the solvent


Table 2 – Providers of diode array detectors Agilent Technologies Gilson


Hamamatsu Corp. JASCO


Malvern Instruments Shimadzu Corp.


Thermo Fisher Scientifi c Inc. Waters Corp.


used, says Franz. “When a vendor refers to ASTM conditions, the noise should be comparable, but not every supplier sticks to it.”


Another spec is drift, which refers to the stabil- ity of the detector, Schulenberg-Schell notes. Many vendors such as Agilent build in elec- tronic thermal controls to help mitigate drift.


A list of purchasing considerations for diode array detectors is given in Table 1.


Dynamic range solutions One of the main challenges faced by DADs is that a choice typically needs to be made between sensitivity to low light levels and the


ability of the detector to quantitate higher levels without becoming saturated. A variety of strategies have recently been introduced to deal with dynamic range.


For example, with variable integration time, which combines software and hardware, “you can identify pixels that have a lot of signal in them, and read them more quickly and integrate those for shorter periods of time than pixels that have less signal on them,” ex- plains Gilmore.


Agilent’s 1260 Infi nity High Dynamic Range DAD strategy is to “basically cluster two DADs” together—one with a 3.7-mm-pathlength fl ow cell and the other with a 60-mm-pathlength fl ow cell—into a single unit, and computationally combine the signals, says Schulenberg-Schell.


Santa Clara, CA Middleton, WI Bridgewater, NJ Easton, MD


Westborough, MA Columbia, MD Waltham, MA Milford, MA


www.agilent.com www.gilson.com


www.hamamatsu.com/us/ www.jascoinc.com www.malvern.com www.shimadzu.com


www.thermoscientifi c.com www.waters.com


Shimadzu uses its Intelligent Dynamic Range Extension Calculator (i-DReC) to detect when a peak becomes saturated and automatically shift the profi le to a wavelength with lower absorp- tion, generating a correction factor to calculate the peaks at the original target wavelength.


Although there are many specialized detec- tors, querying various parameters that can be used to interrogate samples coming off a liquid separation—from fluorescence to electrochemical to light scattering to radio- activity—the photodiode array detector is arguably the most versatile, and most neces- sary, tool for the research laboratory.


Table 2 lists some providers of diode array de- tectors. For more information, please visit www. labcompare.com.


American Laboratory invites you to subscribe! ®


Join over 45,000 scientists and researchers and begin accessing cutting-edge information to stay up-to-date with the latest technological advances and trends.


We Focus On: • Chemistry • Clinical Diagnostics • Drug Discovery • Environmental • Food & Beverage • Forensics • Materials Science • And More!


Reference 1. ACQUITY UPLC Photodiode Array and


eλPhotodiode Array Detector Operator’s Overview and Mainenance Guide. http:// www.waters.com/webassets/cms/support/ docs/715002209ra.pdf.


Each issue combines in-depth articles, news and video to deliver the latest advances. American Laboratory®


is a critical resource to ensure


your work is always on the cutting edge. Sign up today! americanlaboratory.com/subscribe


AMERICAN LABORATORY • 42 • SEPTEMBER 2014


Josh P. Roberts has been a full-time biomedi- cal science writer for more than a decade. After earning an M.A. in the history and philosophy of science, he went through the Ph.D. program in molecular, cellular, developmental biology, and genetics at the University of Minnesota, with dis- sertation research in ocular immunology; e-mail: tcwriter@msn.com


American Laboratory Practical Resources for Laboratory Scientists September 2013 Volume 45, Number 8 DNA in Forensics


Determination of Total Mercury Content in Wood Materials, Part 2: ICP-MS—A Multielement Method


Determining the Quantity, Integrity, and Molecular Weight Range of Genomic DNA Derived From FFPE Samples


Rapid Characterization of Large Areas of Graphene Using Raman Spectroscopy


Advancements in Instrumentation for Viscosity Measurements


UHPLC: Pushing the Limits of HPLC


Is Your Gas Delivery System As Green and Safe As It Can Be?


A Novel Sensor for Uric Acid Based on an Electropolymerization Technique


Viscometers: The Science of Measuring Fluid Flow


High-Throughput Screening of Multiple Protein Complexes


www.americanlaboratory.com www.labcompare.com


®


FC_ALSept2013.indd 1


8/28/13 9:46 AM


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52