NATIONAL BUREAU OF STANDARD;'' WW 9 W% Proceedings of the Conference Held at the National Bureau of Standards, Gaithersburg, Md. March 22-24, 1972 Edited by R. Mavrodineanu, J. I. Shultz, and O. Menis Analytical Chemistry Division Institute for Materials Research National Bureau of Standards Washington, D.C. 20234 U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director Issued May 1973 Library of Congress Catalog Card Number: 73-600066 National Bureau of Standards Special Publication 378 Nat. Bur. Stand. (U.S.), Spec. Publ. 378, 268 pages (May 1973) CODEN: XNBSAV Reprinted from the National Bureau of Standards Journal of Research, Section A. Physics and Chemistry Vol. 76A, Nos. 5 and 6, Sept.-Oct., and Nov.-Dec. 1972. For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13. 10:378). Price: 84.85, domestic postpaid; $4.50, GPO Bookstore Abstract This volume contains the 18 papers presented at the Conference on Accuracy in Spectrophotometry and Luminescence Measurements organized by the Analytical Chemistry Division of the National Bureau of Standards and held from March 22 to 24, 1972. These papers discuss the problems encountered in accurate spectrophotometry and luminescence measurements of materials. They also define the status of these competences from the standpoint of basic principles, critical factors involved in the measurements, and the instrumental conditions which must be fulfilled to assure accurate measurements. Particular attention is given to the selection, production, and use of Standard Reference Materials in spectrophotometry and spectrofluorometry. Problems related to health are also covered in six of the papers, two of which include original contributions to the application of luminescence techniques to specific biochemical problems. Key words: Accuracy, critical parameters; instrumentation; linearity; quantum efficiency; spec- trofluorometry; spectrophotometry; standards. HI Foreword "When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind ; it may be the beginning of knowledge but you have scarcely, in your thoughts, advanced to the stag? of science," by William Thompson, Lord Kelvin, Popular Lectures and Addresses 11891-18941. This work presents the formal Proceedings of the Conference on Accuracy in Spectrophotometry and Luminescence Measurements which was organized by the Analytical Chemistry Division of the NBS Institute for Materials Research. The Conference was held at NBS from March 22 through March 24, 1972. The papers contained in this volume have also been published in two consecutive issues of the Journal of Research of NBS, Volume 76A, Nos. 5 and 6, 1972. This Conference brought together a number of leading authorities from the United States and from overseas whose broad knowledge and experience provided valuable scientific contributions to the various topics of the Conference. The papers assembled in these Proceedings focus attention on the problems associated with accuracy in spectrophotometry and luminescence measurements of materials, and define the status of these competences from the standpoint of basic principles, in- strumental parameters, measurements, and Standard Reference Materials. A major objective of the Conference was to provide the analytical chemist with the means to establish and maintain accuracy in spectrophotometric and luminescence measurements. The works presented in these Proceedings should contribute significantly to the advancement of spec- trophotometric and luminescence measurements and constitute a solid ground for further progress. W. Wayne Meinke, Chief Analytical Chemistry Division May 1973 IV Preface This volume is divided in two parts. The first part consists of six invited lectures and four invited panel discussions on the subject of accuracy in spectrophotometry. The three invited lectures and five invited panel discussions, which constitute the second part of the volume, are devoted to the topic of accuracy in luminescence measurements. These contributions are intended to interrelate theory and instrumentation with methodology for measuring "real samples" which are encountered in the general field of analytical chemistry, and more specifically in the fields of health and environment. The roles of the basic principles and in- strumentation in the science of measurements are reflected in several papers. Three of these, by Clarke, by Mavrodineanu, and by Mielenz, represent parallel approaches to the evaluation of accuracy of spectrophotometers and serve to augment the other contributions. At the same time, independent measurements of a series of glass filters (NBS-SRM-930), serve to establish the magnitude of the bias in this calibration. In this manner a better understanding of the needs and limitations of a material in a measurement situation has been established. Points of view on the philosophy of spectrophotometric standards are expressed by Venable. In the area of luminescence measurements, the three papers by Melhuish, by Crosby, Demas and Callis, and by Winefordner survey the basic problems and instrumental criteria. Their descriptions include a discussion of the state of the art and provide a clear prediction of the direction of future efforts. The two papers describing the absolute calibration of light sources and photodetector linearity by Rutgers, and by Sanders relate equally to both measurement problems. The three papers by Burke, Deardorff and Menis, by Reisfeld, and by Velapoldi, interface the instrumental performance with real sample measurements through the development of suitable material standards in spectrophotometry and spectrofluorimetry. On the other hand, the important areas of health and environment are ex- tensively covered in four papers by Penton, Widdowson, and Williams, by Burnett, by Rand, and by Chen. They help to pinpoint the problems and progress associated with automation and clinical measurements. Finally, the papers by Udenfriend, and by Guilbault present insight into original contributions to the application of luminescence techniques to specific health measurement methodology. This collection assembles in one volume valuable and original contributions, and constitutes a unique and important source of information which should serve equally well the workers in the field of research and applications of spectrophotometric and luminescence measurements. The NBS Committee responsible for the organization of the Conference were Oscar Menis, general chairman and panel discussion moderator; James I. Shultz, associate general chairman; Radu Mavrodineanu, program chairman; Ranee A. Velapoldi, associate program chairman; Robert W. Burke, arrangement chairman ; and Sara R. Torrence, arrangement liaison. The Conference had the encouragement of the National Institute of General Medical Sciences, who also cooperated with the National Bureau of Standards in supporting part of the work of the Analytical Chemistry Division. This work led to the design and development of instrumentation for high accuracy spectrophotometry; for the study, preparation and evaluation of liquid absorbance standards, and in the investigations related to solid compounds and inorganic ion glasses as Standard Reference Materials for spectrofluorometry. This support resulted in the issuance of a number of standards which assure that more meaningful measurements will be made in the field of biochemistry and related areas. The undertaking of the Conference and publication of this book would not have been possible without the cooperation and assistance of many persons. The important contributions of all speakers and the assistance of the session chairmen is acknowledged with deep appreciation. V The NBS Office of Technical Information and Publication, under the direction of W. R. Tilley, gave invaluable assistance to the publication of this volume; we wish to acknowledge in particular the assistance of Mrs. Betty L. Oberholtzer, Mrs. Bertha S. Darrow, and Mrs. Mary V. Betizel. Within the Analytical Chemistry Division, special thanks are given to Mrs. Mary Pantazis for her tireless efforts in typing some of the manuscripts, and her diligent work in taking care of correspon- dence and program publications. Particular appreciation is expressed to Mrs. Rosemary Maddock for providing coordination and invaluable assistance in the many phases of preparing this volume. Special thanks are also extended to R. A. Velapoldi for his assistance in reviewing the papers on luminescence and for preparing the author index. R. Mavrodineanu J. I. Shultz O. Menis May 1973 VI Contents Page Foreword IV Preface V Part I. Spectrophotometry High Accuracy Spectrophotometry at the National Physical Laboratory F. J. J. Clarke 1 An Accurate Spectrophotometer for Measuring the Transmittance of Solid and Liquid Materials R. Mavrodineanu 31 Absolute Spectroradiometric Measurements G. A. W. Rutgers 53 Accurate Measurements of and Correction for Nonlinearities in Radiometers C.L. Sanders 63 Physical Parameters in High-Accuracy Spectrophotometry K.D.Mielenz 81 Liquid Absorbance Standards R. W.Burke. E. R. Deardorff, and O. Men is 95 Accurate Measurement of Molar Absorptivities Robert W. Burnett 109 Problems Associated With the Need for Standardization in Clinical Spectrophotometric and Fluorometric