Fundamentals of Sample Preparation for Environmental Analysis - Fundamentals of Environmental Sampling and Analysis - page 160

greener, such as nanoparticle, microchips, stir-bar sorption extraction, and robotics.
The reader should consult further references (e.g., Mitra, 2003) for specific details.

7.1 OVERVIEW ON SAMPLE PREPARATION

7.1.1 Purpose of Sample Preparation

There are examples that sample preparations may not be needed at all. For instance,
clean drinking water can be directly used for metal analysis without acid digestion.
Several noninvasive techniques (e.g., X-ray fluorescence) need just a minimal
sample preparation. Unfortunately, most samples need a more or less tedious
preparation, which could become the rate-limiting step in trace analysis. Figure 7.1
is used to illustrate the percentage time spent in a typical chromatographic analysis.
It was estimated that an average 61% of the total time spent in a typical

chromatographic analysis is devoted to sample preparation.
The purpose(s) of environmental sample preparations can be one or a
combination of the following. Note that not all of these techniques are described
in this chapter.

To homogenize sample or remove moisture: If the collected sample is
heterogeneous or contains too much moisture, it needs air-drying, freeze-
drying (if the chemical is unstable), homogenization, grounding (size
reduction), and sieving. Doing so will remove water for convenient storage
and handling and assure that a minor portion of subsample taken for analysis
will be more likely representative.
To increase/decrease analyte concentration: Increasing analyte concentra-
tion is often needed for almost all trace analysis of environmental chemicals.
The applicable concentration apparatus such as Kuderna-Danish evaporative
concentrator and rotary evaporator have been described in Chapter 6.
Occasionally, dilution is used for the analysis of highly contaminated
samples so the concentration falls within the calibration range.
To remove interfering chemicals: Although interference is less an issue for
instrumental analysis than wet chemical analysis, it could become the main

Sample processing (61%)
Data management (27%)

Sample analysis (6%)

Sample collection (6%)

Figure 7.1 Survey results for the distribution of time that analytical chemists spend on sample
analysis (Majors, 1991, Reprinted with permission)