Analytical Graphite Furnace Atomic Absorption Spectrometry

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2 Analytical Graphite Furnace Atomic Absorption Spectrometry A Laboratory Guide Gerhard Schlemmer Bernard Radziuk Birkhäuser Verlag Basel Boston Berlin

3 Authors Or. Gerhard Schlemmer Or. Bernard Radziuk Bodenseewerk Perkin-Elmer GmbH Postfach Überlingen Germany Library of Congress Cataloging-in-Publication Data Schlemmer, Gerhard: Analytical graphite furnace atomic absorption spectrometry: a laboratory guide / Gerhard Schlemmer, Bernard Radziuk. p. cm Includes bibliographical references and index. ISBN Atomic spectroscopy. I. Radziuk, Bernard. 11. Title. QD96.A8S ' dc Deutsche Bibliothek Cataloging-in-Publication Data Schlemmer, Gerhard: Analytical graphite furnace atomic absorption spectrometry: a laboratory guide / Gerhard Schlemmer; Bernard Radziuk. - Basel; Boston; Berlin : Birkhäuser, 1999 ISBN The publisher and editor can give no guarantee for the information on drug dosage and administration contained in this publication. The respective user must check its accuracy by consulting other sources of reference in each individual ca se. The use of registered names, trademarks etc. in this publication, even if not identified as such, does not imply that they are exempt from the relevant protective laws and regulations or free for general use. This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, re-use of illustrations, recitation, broadcasting, reproduction on microfilms or in other ways, and storage in data banks. For any kind of use permission of the copyright owner must be obtained Birkhäuser Verlag, PO Box 133, CH Basel, Switzerland Softcover reprint of the hardcover 1st edition 1999 Printed on acid-free paper produced from chlorine-free pulp. TCF 00 Cover design: Gröflin Graphic Design, Basel ISBN ISBN (ebook) DOI /

4 Table of contents Prefaee... IX 11 AAS: a simple and rugged system for traee and ultratraee elemental analysis The physical background Light sources, their properties and how to obtain maximum intensity and lifetime Monochromators, polychromators and other optical components: from lines to plane Detectors in AAS: the revolution has just begun Improving selectivity: about light modulation, photon integration, continuum sources and magnetic fields A little bit about flames and a lot more about graphite furnaces for generation of atom clouds Safety aspects and laboratory prerequirements for graphite furnace systems Important terms and units for analytical atomic speetrometry Sensitivity and characteristic mass: the way to check your spectrometer Precision or detection limit: what's the name of the game? Working range of graphite furnace AAS: linear and nonlinear curves and ways to linearize nonlinear functions Calibration in AAS or: never underestimate the importance of the standard v

5 Analytical Graphite Furnace Atomic Absorption Spectrometry 2.5 Effects and interferences: the harmless and the dangerous effects of matrix Means and methods to provide quality assurance in AAS Even theory can be fun: the exciting growth of knowledge in electrothermal AAS History of graphite furnaces Empirieal observations: the stability of the characteristie mass mo The dynamie temperature behaviour of a Massmann-type furnace and a Transversely Heated Graphite Atomizer Chemieal reactions in a gas phase at elevated temperatures enclosed by graphite The influence of tube wall and platform on the atomization pulse Statistieal model Graphite is an impressive material - but somehow and sometimes it is still black magie ;I Developing a method in GFAAS Basie checks or "o.k., the whole thing is doing wh at it's supposed to" Automatie checks on modern instruments Spectrometer Graphite furnace Blank and reference solutions including modifier Characteristic mass Simultaneous multielement GFAAS Screening may be sufficient and may save a lot of time and annoyance Systematie development of a GFAAS method: accuracy, precision, speed, long term stability Basie considerations VI

6 Table of contents Drying Pyrolysis Atomization Analytical quality and long term stability Speed Chemical modifiers: the spectroscopist's box of tricks Modifiers which influence the thermal stability or the chemical activity of the the matrix (matrix modifiers) Modifiers which thermally stabilize the analyte element(s), or "Eureka! There is a universal modifier!" from the vantage point of 12 years after its introduction Using modifiers properly Modifiers which are active in combination with the graphite surface in the solid phase The first step is sam pie pretreatment Using the right method for sampie pretreatment is half the analysis Autosampiers, the universal sampie management systems A liquid is not necessarily a prerequirement: about solids and slurries Ways to separate matrix and preconcentrate analyte Analyte in gaseous molecular form: horror or benefit? Use and abuse of microprocessors A peak will tell you more than 1000 numbers What do we see on the screen?.... Blank firings.... Absorbance by analyte only Background only Everything you need may be in your PC's memory VII

7 Analytical Graphite Furnace Atomic Absorption Spectrometry 6.3 Check functions and quality control Calibration: range, precision, recovery Qual ity control sampies: accuracy and long term stability of results Accuracy of the entire analytieal procedure What's to be done with all the data? Patience Clever's exciting voyage through the world of matrices and challenging analyses U ltra pure water and chemieals Keeping contamination under control Optimization of the photometrie noise Graphite furnace time/temperature programs Recoveries Detection limits Surface water, mineralized water, sea water and waste water Sediments, soils and sludges Plants and other biologieal tissue Cl inieal sampies Oil and fat Clean sampies which are difficult to dissolve: the analysis of slurries Subject index VIII

8 Preface "One should rather go horne and mesh a net than jump into the pond and dive far fishes" (Chinese proverb) Recognizing the precise analytical question and planning the analysis accordingly is certainly the first prerequisite for successful trace and ultratrace determinations. The second prerequisite is to select the method appropriate to the analytical specification. The method itself consists of a set of available tools. The third prerequisite is that analysts and operators know the methods weh enough to enjoy challenging themselves as weh as the methods and are rewarded by the joy of high-quality data, fast and economical results and the conviction of having the analytical job under control. This skill is known among analysts or operators working with an exciting new and sometimes complicated analytical technique but is gradually lost on ce a technique becomes "mature" and a routine tool. Unfortunately, laboratory managers often do not allow sufficient training time for their analysts and technicians for "routine" techniques and thus miss an opportunity for motivating their co-workers and obtaining the full benefit of the equipment. Graphite furnace atomic absorption spectrometry (AAS) is one of the mature analytical techniques wh ich is seen as a routine method in most laboratories. More than 10,000 furnaces are operated in elemental trace and ultratrace analyses in laboratories around the world today. Although most of these probably do provide acceptable analytical data, only a few are challenged in the sense mentioned above. Having been involved in instrumental research and development, in the curricula of training courses, in the support of graphite furnace AAS, and in the development of analytical methods based on this technique for more than 15 years, we are convinced that - apart from being a routine tool - modern graphite furnace AAS is a fascinating analytical technique with much future potential. We IX

9 hope that the "Laboratory Guide" will help to impart the joy of using, playing with and challenging modern graphite furnace AAS to our readers. Überlingen, 21 February 1999 Gerhard Schlemmer Bernard Radziuk x