Environmental Engineering FOURTH EDITION

Measurement of Water Quality 103

Large test tube

Lactose broth

Gas from

fermentation

Small test tube

Figure 5-11. Test tubes used for most probable number (MPN) coliform test.

cold-vapor atomic absorption (AA), inductively coupled plasma (ICP) and inductively
coupled plasdmass spectrometry (ICPMS), and colorimetric techniques. Samples
can be filtered and analyzed for dissolved metals or digested using strong acids to
measure total metals.
In flame AA a solution of lanthanum chloride is added to the sample, and the
treated sample is sprayed into a flame using an atomizer. Each metallic element in the
sample imparts a characteristic color to the flame, whose intensity is then measured
spectrophotometrically. Graphite furnace AA methods use an electrically heated device
to atomize metal elements, and can measure much lower concentrations of metals than
flame AA, but often have ‘‘matrix’’ interference problems caused by salts and other
compounds in the sample. Cold vapor AA is used primarily to measure arsenic and
mercury. Inductively coupled plasma and ICPMS are less sensitive to matrix problems
and cover a wide range of concentrations.

OTHER ORGANIC COMPOUNDS

One of the most diverse (and difficult) areas of pollution assessment is the measure-
ment of toxic, carcinogenic, or other potentially harmful organic compounds in water.
These organics encompass the disinfection by-products introduced earlier, as well as
pesticides, detergents, industrial chemicals, petroleum hydrocarbons, and degradation
products that these chemicals become as they are altered chemically or biologically in
the environment (e.g., DDT biodegrades to hazardous DDD and DDE).
Some of the methods described earlier in this chapter can be used to assess the
overall content of organics in water (e.g., total organic carbon analysis). Gas chro-
matography (GC) and high-per$omnce liquid chromatography (HPLC) are effective
methods for measuring minute quantities of specific organics. Gas chromatography
uses a mobile phase (carrier gas) and a stationary phase (column packed with an inert