Analytical Graphite Furnace Atomic Absorption Spectrometry, 1999 A Laboratory Guide Biomethods Series

"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 according­ ly is certainly the first prerequisite for successful trace and ultratrace determina­ tions. The second prerequisite is to select the method appropriate to the analyti­ cal 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 analy­ ses in laboratories around the world today.

1 AAS: a simple and rugged system for trace and ultratrace elemental analysis.- 1.1 The physical background.- 1.2 Light sources, their properties and how to obtain maximum intensity and lifetime.- 1.3 Monochromators, polychromators and other optical components: from lines to plane.- 1.4 Detectors in AAS: the revolution has just begun.- 1.5 Improving selectivity: about light modulation, photon integration, continuum sources and magnetic fields.- 1.6 A little bit about flames and a lot more about graphite furnaces for generation of atom clouds.- 1.6.1 Safety aspects and laboratory prerequirements for graphite furnace systems.- 2 Important terms and units for analytical atomic spectrometry.- 2.1 Sensitivity and characteristic mass: the way to check your spectrometer.- 2.2 Precision or detection limit: what’s the name of the game?.- 2.3 Working range of graphite furnace AAS: linear and nonlinear curves and ways to linearize nonlinear functions.- 2.4 Calibration in AAS or: never underestimate the importance of the standard.- 2.5 Effects and interferences: the harmless and the dangerous effects of matrix.- 2.6 Means and methods to provide quality assurance in AAS.- 3 Even theory can be fun: the exciting growth of knowledge in electrothermal AAS.- 3.1 History of graphite furnaces.- 3.2 Empirical observations: the stability of the characteristic mass m0.- 3.3 The dynamic temperature behaviour of a Massmann-type furnace and a Transversely Heated Graphite Atomizer.- 3.4 Chemical reactions in a gas phase at elevated temperatures enclosed by graphite.- 3.5 The influence of tube wall and platform on the atomization pulse.- 3.6 Statistical model.- 3.7 Graphite is an impressive material — but somehow and sometimes it is still black magic.- 4 Developing a method in GFAAS.- 4.1 Basic checks or “o.k., the whole thing is doing what it’s supposed to”.- 4.1.1 Automatic checks on modern instruments.- 4.1.2 Spectrometer.- 4.1.3 Graphite furnace.- 4.1.4 Blank and reference solutions including modifier.- 4.1.5 Characteristic mass.- 4.1.6 Simultaneous multielement GFAAS.- 4.2 Screening may be sufficient and may save a lot of time and annoyance.- 4.3 Systematic development of a GFAAS method: accuracy, precision, speed, long term stability.- 4.3.1 Basic considerations.- 4.3.2 Drying.- 4.3.3 Pyrolysis.- 4.3.4 Atomization.- 4.3.5 Analytical quality and long term stability.- 4.3.6 Speed.- 4.4 Chemical modifiers: the spectroscopist’s box of tricks.- 4.4.1 Modifiers which influence the thermal stability or the chemical activity of the the matrix (matrix modifiers).- 4.4.2 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.- 4.4.3 Using modifiers properly.- 4.4.4 Modifiers which are active in combination with the graphite surface in the solid phase.- 5 The first step is sample pretreatment.- 5.1 Using the right method for sample pretreatment is half the analysis.- 5.2 Autosamplers, the universal sample management systems.- 5.3 A liquid is not necessarily a prerequirement: about solids and slurries.- 5.4 Ways to separate matrix and preconcentrate analyte.- 5.5 Analyte in gaseous molecular form: horror or benefit?.- 6 Use and abuse of microprocessors.- 6.1 A peak will tell you more than 1000 numbers.- 6.1.1 What do we see on the screen?.- Blank firings.- Absorbance by analyte only.- Background only.- 6.2 Everything you need may be in your PC’s memory.- 6.3 Check functions and quality control.- 6.3.1 Calibration: range, precision, recovery.- 6.3.2 Quality control samples: accuracy and long term stability of results.- 6.3.3 Accuracy of the entire analytical procedure.- 6.4 What’s to be done with all the data?.- 7 Patience Clever’s exciting voyage through the world of matrices and challenging analyses.- 7.1 Ultra pure water and chemicals.- 7.1.1 Keeping contamination under control.- 7.1.2 Optimization of the photometric noise.- 7.1.3 Graphite furnace time/temperature programs.- 7.1.4 Recoveries.- 7.1.5 Detection limits.- 7.2 Surface water, mineralized water, sea water and waste water.- 7.3 Sediments, soils and sludges.- 7.4 Plants and other biological tissue.- 7.5 Clinical samples.- 7.6 Oil and fat.- 7.7 Clean samples which are difficult to dissolve: the analysis of slurries.