Common Operations and Wet Chemical Methods in Environmental Laboratories - Fundamentals of Environmental Sampling and Analysis - page 131

before if proper maintenance is followed. This, however, may not be true for certain
trace instrumental analysis. As Mabic et al. (2005) pointed out, between 70 and 80%
of HPLC performance problems are attributable directly to the quality of water used
in preparing HPLC eluents, standards, and samples.

2. Common Acid and Alkaline Solutions

Table 6.2 lists the properties of commercial acids and bases commonly used in
environmental laboratories. To prepare a dilute solution, cautiously add the required
amount of concentrated acid/alkaline as received, and mix to a designated volume of
the proper type of distilled water. Dilute to 1 L and mix thoroughly.

Table 6.2 Preparation of Acid and Alkaline Solutions

Acid/Base HCl H 2 SO 4 HNO 3 H 3 PO 4 NH 4 OH

Specific gravity (room 1.18 1.84 1.42 1.70 0.90

temperature)
% active ingredient in 36 96 71 85 28

conc. reagent by mass
Molarity (normality) of 11.6 (11.6) 18.0 (36.0) 16.0 (16.0) 14.7 (44.1) 14.8 (14.8)

conc reagent
Volume (mL) needed to 83.3 27.8 64.1 22.7 66.7

prepare 1 L of 1 N
solution

3. Reagent Purity

When making a solution, one must first decide what degree of chemical purity is
needed on the basis of its analytical purpose and on the cost of the chemical.
Generally reagents with the highest grade available are purchased for environmental
trace analysis, particularly for the preparation of standard solutions. Low-grade
chemicals can only be used for special purposes, such as acetone for washing
glassware. Three common chemical grades, in order of decreasing purity, are
ACS, reagent, and technical. The ACS grade meets the requirements of the
American Chemical Society Committee on Analytical Reagents. The reagent
grade is suitable for most analytical work and is more than adequate for general
lab use. For these analytical (research) grade chemicals, the specified impurities
are often at 10-1,000 ppm levels. The technical grade is suitable for general
industrial uses and its appropriateness for lab use must be checked when substituting
for higher grades.
Since there are no universal specifications on chemical grades, various other
grades can be seen on the container labels depending on the types of chemicals, the
end uses of the chemical, and the manufacture. This may become a confounding
factor if one wants to compare the purity of chemicals from various sources.