Hach DR/700 Procedures Manual page 596

MOLYBDENUM, MOLYBDATE, LR
The presence of the phosphonate HEDP at concentrations up to 30 mg/L
will increase the apparent molybdenum concentration reading by
approximately 10% (positive interference). For these samples, multiply
the value obtained in step 13 by 0.9 to obtain the actual molybdenum
concentration. As the concentration of HEDP increases above 30 mg/L,
a decrease in the molybdenum concentration reading occurs (negative
interference).
Highly buffered samples or extreme sample pH may exceed the
buffering capacity of the reagent and require sample pretreatment; see
pH Interference in Section I.
After a number of samples have been analyzed, the sample cells may
exhibit a build-up of a slight blue color. A rinse using Hydrochloric
Acid Solution, 1:1, will eliminate the build-up if it occurs.
SUMMARY OF METHOD
The ternary complex method for molybdenum determination is a
method in which molybdate molybdenum reacts with an indicator and
sensitizing agent to give a stable blue complex which appears green due
to excess yellow reagent.
REQUIRED REAGENTS
Description
Molybdenum 1 Reagent for Low
Range Molybdate Powder Pillows,
for 20 mL sample size . . . . 1 pillow . . . . 50/pkg . . . . . . . . 23524-46
Molybdenum 2 Reagent
for Low Range Molybdate
Solution . . . . . . . . . . . . . . . 0.5 mL. . . . . 59 mL MDB . . . 23525-12
REQUIRED APPARATUS
Clippers, for opening
powder pillows . . . . . . . . . . 1 . . . . . . . . . each . . . . . . . . . . . 968-00
DR/700 Filter Module
Number 61.01. . . . . . . . . . . 1 . . . . . . . . . each . . . . . . . . . . 46261-00
Quantity
Per Test Unit
61-40
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