Common Operations and Wet Chemical Methods in Environmental Laboratories - Fundamentals of Environmental Sampling and Analysis - page 128

accuracy sometimes depends on the careful calibration using classical wet chemical
methods or the common techniques described in this chapter.
A unique feature of this chapter is the description of underlying chemical
principles of common wet chemical methods. The chemical reactions and
stoichiometry are often excluded in standard cookbooks by the U.S. EPA and
APHA. The comprehension of these fundamental principles is not only important for
the acquisition of quality data, but also important to enhance the work efficiency. In
many cases, this knowledge helps solving the problem when complications arise
while following the recipes of standard methods, or when modifications are needed
because of sample-specific interferences.
Csuros (1997) made a similar argument regarding the importance of
understanding the chemistry rather than just following the step-by-step cookbook.
As she stated, ''A true chemist, or analytical chemist, has several characteristics. He
or she has knowledge of the methods and instruments used for analysis, and
understands the principles of the analysis. Laboratory analysts should have a
chemistry background adequate to understand and correctly apply all of the
laboratory rules and to evaluate and interpret the results of their analysis. They have
to know how to plan and organize laboratory work so the time is used efficiently.
Thus, a laboratory technician should be a skilled, well-trained chemist—in sharp
contrast with the so-called 'determinators' who simply twist the dials of an

instrument or follow 'cookbook' analytical procedures''.

6.1 BASIC OPERATIONS IN ENVIRONMENTAL
LABORATORIES

6.1.1 Labware Cleaning Protocols for Trace Analysis

Proper cleaning techniques are critical to obtain quality data. This is particularly
essential for trace environmental analysis. A thorough cleaning will reduce the
chance of obtaining erroneous results and simplify troubleshooting procedures.
Even though there has been an increased use of disposable labwares, not all labwares
will be disposable and laboratory cleaning can account for a significant portion (up
to one-third) of an analyst's time in trace analysis. In a multi-users' lab, such as the
case in academic settings, it is imperative not to share other people's glassware and
plasticware. In many cases, it appears clean to the naked eye, but in fact, it contains
enough residue to completely overwhelm the amount of a trace chemical in an
environmental sample.
The cleaning technique varies depending on the analyte of interest—the
optimal cleaning method for analyzing trace organics will not be the same as the
method for trace metal analysis. A general rule of thumb is that an acid wash is
required if trace metals are the analytes of interest, and an acetone wash is minimally
required if trace organic contaminants are the target analytes. The following are
basic guidelines for routine cleaning, but they may be not relevant for every type of
analysis: