Agriculture Reference
In-Depth Information
Glass wool
Sodium hydroxide
Purified water
Glass wool
Valve
Figure 7.1.
Purified water container protected from carbon dioxide by a drying tube containing
sodium hydroxide (
Caution
: adsorption of water by N
2
OH produces caustic solution).
all the information that the researcher needs. In all cases solvents must be pro-
tected from exposure to light, which can cause the formation of degradation
products that may cause interferences during analytical procedures. Common
organic solvents and their characteristics are listed in Table 7.1.
Solvents come in many grades that are designated in different ways. There
are 7 grades of hexane and 10 grades of hexanes offered by one supplier. These
range from 98.5% hexane through American Chemical Society (ACS) grade,
to various chromatographic and other grades. In some cases it will be essen-
tial to use the specific grade designated for a particular analysis; in other cases
further purification may be necessary. The most important example is the case
of water where a solvent designated as being anhydrous may still contain
enough water to interfere with reactions, instrumentation, or analysis that are
highly sensitive to water. Additional drying may be called for, and care must
be taken to make sure that drying agents introduce no contamination.
Solvents must be protected not only from light but also, as with water, from
absorbing vapors and from the atmosphere. Solvents must be kept tightly
sealed and where the highest purity must be maintained, stored under nitro-
gen. Another approach that can be used is to purchase solvents in individual,
small-volume, containers where the whole bottle is used in one analysis, in one
day or over a short period of time [20].
7.3.
DRYING AGENTS
In all cases where drying agents are to be used, both their composition and
purity must be ascertained to ensure that they will not introduce any inter-
fering contaminates to the material, including soil, being dried (see Sections
7.4, 7.5.2, and Table 7.2). As with water and solvents, exposure of drying agents
to the atmosphere allows for the introduction of foreign components, in this
