Silica
Silica
Page 2 of 4
Silica_PP_High_SLM_Eng_Ody.fm
Interferences
Occasionally a sample contains silica which reacts very slowly with molybdate.
The nature of these “molybdate-unreactive” forms is not known. A pretreatment
with Sodium Bicarbonate (Cat. No. 776-01), then Sulfuric Acid (Cat. No. 1270-32)
will make these forms reactive to molybdate. The pretreatment is given in
5. Touch the timer icon.
Touch
OK.
A ten-minute reaction
period will begin.
6. When the timer
beeps, add the contents of
one Citric Acid Powder
Pillow to the sample cell.
Swirl to mix.
Any yellow color due to
phosphorus is removed in
this step.
7. Touch the timer icon.
Touch
OK.
A two-minute reaction
period will begin.
Perform step 8–step 11
within three minutes after
the timer beeps.
8. Fill a second sample
cell with 10 mL of the
original sample (the
blank).
9. Place the blank into
the cell holder.
10. Touch Zero.
The display will show:
0.0 mg/L SiO
2
11. Place the prepared
sample into the cell
holder.
12. Touch Read.
Results will appear in
mg/L SiO
2
.
Interfering Substance Interference Levels and Treatments
Color Eliminated by zeroing the instrument with the original sample.
Iron High levels of Fe
2+
and Fe
3+
interfere.
Phosphate
Does not interfere below 50 mg/L PO
4
3–
. At 60 mg/L PO
4
3–
, a negative 2% interference occurs.
At 75 mg/L PO
4
3–
, the interference is negative 11%.
Sulfides (S
2–
) All levels interfere.
Turbidity Eliminated by zeroing the instrument with the original sample.
10 mL
Zero
10 mL
Read
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