Encyclopedia of Environmental Science and Engineering, Volume I and II

INSTRUMENTATION: WATER AND WASTEWATER ANALYSIS 561

(The names turbidimeter and nephelometer appear to be used

interchangeably to describe a device measuring turbidity from

the intensity of scattered light.) The unit of measurement is

the NTU, nephelometric turbidity unit.

Colored constituents in the sample can cause error by

absorbing light. A correction can be made in a number of ways:

namely, by using a wavelength of light not absorbed by the

solution, by making an absorption reading of the clarified solu-

tion, or using an instrument that combines both readings.^37

(10) Other spectroscopic instruments

Mass spectrometry is treated in the gas chromatography/

mass spectrometry Part Two Section, 4,c, ( 2 ),( a ). NMR

(nuclear magnetic resonance) spectroscopy is not discussed

in this article. The technique is, indeed, a most fruitful

means of identifying chemical entities and their structures.

However, the use in water analysis is not a primary activity.

In the identification for known natural and anthropogenic

materials its use would be invaluable. No doubt the next edi-

tion of this article or an expansion of this article will contain

a section on NMR spectroscopy.

(c) Applications of spectroscopic instruments

Standard Methods^2 includes a number of spectroscopic

methods using various instruments for the analysis of metals

(see Table 5). Colorimetric methods using uv/vis absorption

spectroscopy are available in Standard Methods for the fol-

lowing non-metals: bromide, fluoride, iodide, residual chlo-

rine, cyanide, ammonia, nitrate, nitrite, phosphate, sulfide

and sulfite. The determination of turbidity in water by neph-

elometry and the analysis of sulfate ion by a turbidimetric

method appears in Standard Methods^.^2 See Part Two Section C

for more applications.

2. Electroanalytical instrumentation
   Electroanalytical chemistry encompasses a wide variety of
   analytical measurements and includes three different types of
   correlations. The first type concerns the relationship between
   potential, current, conductance (or resistance), charge (or capac-
   itance) and the analyte. For the second is the determination,
   during the titration, of the analyte and, ultimately, the endpoint
   by electrochemical means. The conversion of the analyte by an
   electric current to a convenient gravimetric or volumetric form
   is the third type. In this section a number of methodologies and
   their corresponding instruments will be discussed. They include
   potentiometry, voltammetry, amperometry, coulometry, con-
   ductance measurements, and titrations using potentiometry and
   amperometry for endpoint detection.

WEIR

SAMPLE

OUT

LAMP

LENS

VENT

WATER

SURFACE

PHOTOCELL

SAMPLE IN

BUBBLE TRAP

FIGURE 18 Low range turbidimeter. (Used with permis-

sion of Hach Co., Loveland, CO.)

PHOTOCELL

REFLECTED LIGHT

TURBIDIMETER

BODY

REFRACTED

LIGHT

SCATTEREDLIGHT

OVER-FLOWING

SAMPLE

LENS

LAMP

LIGHT

BEAM

INST.

DRAIN

SAMPLE IN DRAIN

FLOW DIAGRAM

FIGURE 17 Surface scatter turbidimeter. (Used with

permission of Hach Co., Loveland, CO.)

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