Fundamentals of Sample Preparation for Environmental Analysis - Fundamentals of Environmental Sampling and Analysis - page 161

issue for many trace organic compounds in complex matrices such as sludge
and waste.
To change sample phase: The type of sample phase needs to be changed to fit
into a specific type of instrument. Few instruments can accept solid samples.
Although both aqueous and solvent phase samples can be directly injected
into a HPLC, GC normally accepts samples in either solvent phase or gaseous
phase. Likewise, there are special sample requirements for IR and NMR.
To liberate analyte from sample matrix: The analyte species need to be
liberated from sample matrices so that the instrument detector will respond.
The digestion of soil sample for metal analysis partially serves this purpose.
Digestion will enable metals bound to soil minerals and organics to be
dissolved in an acidic solution.
To modify chemical structure: Chemical derivatization is one such example
used to increase or decrease volatility and thermal stability for HPLC or GC
analysis.

7.1.2 Types of Sample Preparation

In general, the types of needed sample preparation described in this chapter depend
on the sample matrix, chemical properties, and the specific instrument being used
subsequently. From Figure 7.2, it is clear that distinct preparation techniques exist
between solid and liquid samples. For each matrix type, sample preparation differs
fundamentally between organic and metal analysis. Sample preparation procedures

Liquid sample
(dissolved metals):
1. Ion exchange
2. Chelation

Solid sample:
1. Acid digestion
2. Microwave
3. Alkaline digestion
4. Hydride generation

1. Static headspace
extraction
2. Purge-and-trap

Metals

Organic
(VOCs)

Organic
(SVOCs, NVOCs)

Solid sample:
1. Soxhlet
2. Soxtec
3. Ultrasonic extraction
4. Pressured fluid extraction
5. Supercritical fluid extraction

Liquid sample:
1. Liquid-liquid extraction
2. Solid phase extraction
3. Solid phase microextraction

Figure 7.2 Types of sample preparation methods (VOCs ¼ volatile organic compounds, SVOCs ¼
semivolatile organic compounds, NVOCs ¼ nonvolatile organic compounds)