Controls and Reliable Conclusions - Analytical Chemistry (ACS

Mar 1, 2002 - Controls and Reliable Conclusions. Royce W. Murray. Anal. Chem. , 2002, 74 (5), pp 109 A–109 A. DOI: 10.1021/ac021957i. Publication Da...
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http://pubs.acs.org/ac ISSN 0003-2700

March 1, 2002 / Vol. 74, No. 5

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The Science of Detecting Terror. They had worked unhurried for years. Now the phone rings incessantly. Cheryl Harris speaks with experts in techniques from MS to microfluidics who have years of biological and chemical warfare research and a new sense of urgency.

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False Cyanide Detection. All of the evidence in several deaths in Japan pointed to cyanide poisoning—but that conclusion wasn’t always right. The forensics of four real-life events helps Yasuo Seto of the National Research Institute of Police Science (Japan) explain why cyanide detection is so difficult.

COVER STORY

© 2002 PECK STUDIOS

features

Picking out poison. 134 A

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Isotopic Analysis of Dinosaur Bones. Scientists inch closer to answering an age-old question: What killed off the most successful vertebrates to ever inhabit the Earth? William Showers, Reese Barrick, and Bernard Genna at North Carolina State University present the innovative analytical techniques that could provide one clue: Were dinosaurs warm-blooded or cold-blooded?

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ACS Founders Were Analytical Chemists, Too. After 125 years, it is easy to forget who started it all. Roland Hirsch of the U.S. Department of Energy takes a look at just how many analytical chemists held prominent roles in the fledgling ACS.

news

Dry protein microarrays.

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AnalyticalCurrents PEGging the surface. a A question of (electronic) taste. a Thinking locally in FTICR MS. a Luminescence is a gold (cluster) rush! a Optical sensor needs its space. a Smaller is better for drug screening. a Assay resonates with intact cells. a Antibodies choose the “right” catalysts. a Tracing the pattern of aminochromes.

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Research Profiles Dry proteins may quench thirst for microarrays. Wetter is not always better. a Protein plays matchmaker for QD–antibody conjugation.

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Free, reliable sofware. 159 A

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© TOM BEAN/CORBIS

Potentially powerful pairs for medical diagnostics and biowarfare detection. a Faster analysis of PBDEs and PCBs. Polybrominated diphenyl ethers are also showing up in human and environmental samples. People 2002 ACS Awards.

Metabolic mysteries. 142 A

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Editorial Controls and Reliable Conclusions. Control experiments can be a challenge.

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In AC Research

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ProductReview Software for MS Protein Identification. Judith Handley finds that the software is reliable and can often be tried for free.

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Books and Softw are Cookbook on CE. Roger Giese of Northeastern University reviews Capillary Electrophoresis of Nucleic Acids, Vols. I and II.

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M eetings ACS National Meeting in Orlando.

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New Products

1C

AC Research Contents

927–1209

AC Research

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AuthorIndex

COURTESY OF THE U.S. DEPARTMENT OF ENERGY

departments

Technology fights terrorism.

ACS PHOTO ARCHIVES

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First came … analytical chemists. 152 A Cover Image ©2002 Peck Studios M A R C H 1 , 2 0 0 2 / A N A LY T I C A L C H E M I S T R Y

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e d i to ri a l

Controls and Reliable Conclusions O

ne of the most important of all chemical measurements is the one in which there is ideally “no response”. It’s called a control experiment. The experimenter hypothesizes a useful reaction between A (the analyte, say) and B (the reagent) and upon combining them observes a big response C. Hurrah! The next step is to combine B with D. No response. Success, the response is selective! But what about the possible interference of substances E, F, G, and so forth, and how is a small response C expressed as an uncertainty in using the A–B reaction to measure things about A and B? I am of course talking about a part of the scientific method in which the hypothesis and interpretations are challenged by experiments that assess their validity or fallacy. Such experiments are called controls or blanks. Control experiments are well accepted as requirements of quantitative analytical measurements, and there is a generally sound foundation for their statistical aspects. The world of blank and control experiments can be more complicated, however, and the notions of seeking a proper statement of uncertainty (statistical reliability) are both less well understood and less universally practiced. These are situations in which experimental results are used to make qualitative judgments about the selectivity of a reaction’s response; deductions about reaction pathways; and interpretations based on images or responses changing with time, mass, potential, or excitation energy. An example is when the shape or time dependency of an electrochemical voltammogram is interpreted as arising from the reaction of a certain substance—what control experiments can be done, and how does one express the uncertainty of the conclusion? Another example is a very difficult or time-consuming measurement, which tends to minimize the number of controls that can be undertaken before drawing a conclusion. Many papers are rejected by research journals because of unconvincing, incomplete, or poorly designed blanks and controls. Employing control experiments and expressing scientific uncertainty can be more problematic in emerging new forms

of analysis, such as binding array analysis. In this technique, the experimenter produces an atomic force microscopy (AFM) image of a square-patterned surface on which patches of molecules are bound within various squares due to arrangements of different binding chemicals. The patches of molecules are not all of the same size and clarity. Deductions are drawn that the differences in molecule patch size (or height) from square to square represent the selectivities of the binding chemicals placed there. The image and deductions become part of a report for a research journal, such as Analytical Chemistry, or for a research manager, federal agency, or venture capitalist. Let’s ask about the controls and associated statistics. Do the images really belong to the desired molecules? Have controls or blanks been carried out to ensure that a decomposition product or impurity is not being imaged? And what are the statistics on the number of molecules bound in the patches; that is, can one assign an uncertainty value for this number to each square? What is the statistical reliability that the patterns of binding chemicals have been confined to individual squares? And finally how can the selectivity of the binding asserted by the AFM measurement be assigned a numerical value with associated uncertainty? In my experience, providing satisfactory evidence of controls and expressions of uncertainty (i.e., reliability) in array analysis has been spotty at best and needs improvements. Control and blank experiments are sometimes regarded as classical, mundane, and boring procedures. But they are necessary, and sometimes their design is part of the research frontier.

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EDITOR Royce W. Murray University of North Carolina

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Iowa State University/Ames Laboratory

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University of Maryland

Scripps Research Institute

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Technische Universität München (Germany)

Iowa State University/Ames Laboratory

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