Sample Preparation for Trace Analysis
Authors: Begerow Jutta , Dunemann Lothar 
Published: December 2006

The article contains sections titled:

1.Introduction1.1.A Strategy Appropriate to Trace Analysis1.2.Avoidance of Systematic Errors1.2.1.Trace Losses and Contamination1.2.2.Uncertainty2.Sample Preparation and Digestion in Inorganic Analysis2.1.Sample Treatment after the Sampling Process2.1.1.Stabilization, Drying, and Storage2.1.2.Homogenization and Aliquoting2.1.3.Requirements with Respect to Materials and Chemicals2.2.Sample‐Preparation Techniques; General Considerations2.2.1.Special Factors Associated with Microwave‐Assisted Digestion2.2.2.Safety Considerations2.3.Wet Digestion Techniques2.3.1.Wet Digestion at Atmospheric Pressure2.3.2.Pressure Digestion2.3.2.1.Thermally Convective Pressure Digestion2.3.2.2.Microwave‐Assisted Pressure Digestion2.4.“Dry” Digestion Techniques2.4.1.Combustion in Air2.4.2.Combustion in Oxygen2.4.3.Cold‐Plasma Ashing2.4.4.Fusion2.5.Illustrative Examples2.5.1.Sample Preparation as a Function of Analytical Method2.5.2.Combined Use of Multiple Decomposition Techniques2.5.3.Comparative Merits of the Various Sample‐Preparation Techniques2.5.4.Decomposition Procedures for Determining Nonmetals2.6.Evaluation Criteria2.6.1.Completeness2.6.2.Uncertainty2.6.3.Time Factors2.6.4.The Final Result2.7.Concentration and Separation of Inorganic Trace Materials2.8.Automation and Direct Analysis2.8.1.Automation2.8.2.Direct Analysis2.9.Analysis of Element Species3.Sample Preparation in Organic Analysis3.1.Sample Treatment after the Sampling Process3.1.1.Stabilization, Drying, and Storage3.1.2.Homogenization and Aliquoting3.1.3.Requirements with Respect to Materials and Chemicals3.2.Separation of the Analyte3.2.1.Hydrolysis3.2.2.Liquid ‐ Liquid Extraction3.2.3.Soxhlet Extraction3.2.4.Microwave‐Assisted Solvent Extraction3.2.5.Supercritical Fluid Extraction (SFE)3.2.6.Solid‐Phase Extraction (SPE)3.2.7.Solid‐Phase Microextraction (SPME)3.2.8.Stir‐Bar Adsorptive Extraction (SBSE)3.2.9.Miscellaneous Techniques3.3.Headspace Techniques3.3.1.Static Headspace Technique3.3.2.Dynamic Headspace Technique (Purge and Trap)3.4.Determination of Trace Organic Materials in Air Samples3.5.Analyte Concentration3.6.Derivatization3.7.Coupled Techniques

Trace analysis is a very relevant and applications‐oriented branch of analytical chemistry. The sample preparation for trace analysis must be custom‐tailored to the problem at hand. Systematic errors can arise by contact with vessel materials, reagents, or the ambient atmosphere, as well as any change in chemical or physical state.

In inorganic analysis, sample preparation has to meet the requirements for a substantially trouble‐free determination of the analyte. Digestion of the matrix (microwave digestion, wet digestion, dry digestion techniques) and subsequent careful comparison of several decomposition techniques is therefore an essentially important step. Some separation and concentration techniques of the analytes are liquid –liquid extraction, solid‐phase extraction, special precipitation reactions, and electrolytic deposition. The introduction of laboratory robots should make it possible to incorporate a significant degree of automation into the time‐consuming, labor‐intensive area of sample preparation as well, leading to more efficient, reliable, and reproducible sample work‐up.

The goal of sample preparation in organic trace analysis is to isolate the analyte from the sample matrix (e.g., liquid‐liquid extraction, Soxhlet extraction, microwave‐assisted solvent extraction, steam distillation) and then concentrate it and convert it into a form suitable for analysis by the selected method. Separation and concentration of an analyte must often be followed by some type of derivatization. Various coupled sample preparation and determination processes are increasingly utilized in trace organic analysis.