57-36
QUATERNARY AMMONIUM COMPOUNDS, continued
c) Analyze 25 mL of the 5 mg/L CTAB standard solution according to
the preceding procedure. The result should be 5.0 ±0.1 mg/L.
Standard Additions Method
a) Use a TenSette Pipet to add 0.5, 1.0 and 1.5 mL of Q.A.C. Standard
Solution, 100 mg/L as CTAB, to three 50-mL samples. Mix thoroughly.
b) Analyze 25 mL each sample according to the above procedure. The
QAC concentration should increase by 1.0 mg/L CTAB for each 0.5 mL
addition of standard.
INTERFERENCES
Interference studies were conducted by preparing a CTAB standard
solution of approximately 3 mg/L as well as a solution of the potential
interference. The constituent was said to interfere when the resulting
concentration changed by 10%.
Constituent Level Above Which
Positive Interferences: Constituent Interferes (mg/L)
Calcium (as CaCO
3
)1,350
Chlorine, HOCl and OCl
-
7
Igepal nonionic surfactant 3
Iodine, I
3
-
3
Iron, Fe
3+
80
Liquimine 14-P, filming amine 1,825
Magnesium, Mg
2+
1,350
Sodium polyphosphate 1,325
Tribenzylamine 7
Triton X-100 nonionic surfactant 4
Urea 8
Negative Interferences:
Cyanuric acid 70
Niaproof anionic surfactant 11
Polyacrylic acid 16
Sodium lauryl sulfate 8
Highest Concentration
No Interferences: Tested (mg/L)
Potassium alum, AlKS
2
O
8
500
Silica, H
2
SiO
3
400
Sodium thiosulfate, Na
2
S
2
O
3
30
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