Hach DR/700 Procedures Manual page 648

SURFACTANTS, ANIONIC,
continued
SAMPLING AND STORAGE
Collect samples in clean plastic or glass bottles. Analyze sample as
soon as possible after collection. If prompt analysis is not possible,
o o
store samples up to 24 hours by cooling to 4 C (39 F) or below. Warm
to room temperature before analysis.
ACCURACY CHECK
Standard Additions Method
a) Snap the neck off a Detergent Voluette Ampule Standard Solution,
60 mg/L as LAS.
b) Use the TenSette Pipet to add 0.1 mL, 0.2 mL and 0.3 mL of standard,
respectively, to three 300-mL samples. Mix well.
c) Analyze and compare the results with the sample. The anionic
surfactants reading should increases 0.02 mg/L for each 0.1 mL of
standard added.
d) If these increases do not occur, see Standard Additions (Section I) for
more information.
STATISTICAL EVALUATION
A single operator repetitively tested samples of two prepared solutions,
using one DR/700, matched sample cells and two representative lots of
testing reagents. Testing 0.180 mg/L as LAS concentration samples, the
standard deviation was ±0.0036 mg/L as LAS.
Testing zero concentration samples, the limit of detection was
0.0008 mg/L as LAS. The limit of detection was calculated as three
times the standard deviation when testing zero concentration samples
(adapted from Analytical Chemistry, 1980, 52, 2242-2249).
INTERFERENCES
Perchlorate and periodate ions will interfere. High concentrations of
chloride, such as those levels found in seawater and brines, will cause
low results.
SUMMARY OF METHOD
Surfactants, ABS (alkyl benzene sulfonate) or LAS (linear alklyl
sulfonate) are determined by ion association with crystal violet dye and
extraction of the ion pair complex into benzene.
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