36
•
Place the vial into the holder and
push it completely down. Ensure that
the vial orientation respect to the
holder is the same as the blank.
• Press TIMER and the display will show the countdown prior to the
measurement. Alternatively, wait for 5 minutes and press READ
DIRECT. In both cases "SIP" will blink during measurement.
• The instrument directly displays concentration in
mg/L of nitrate-
nitrogen
(NO
3
-
-N) on the Liquid Crystal Display.
• To convert the reading to mg/L of nitrate NO
3
-
, multiply by a factor
of 4.43.
INTERFERENCES
Interference may be caused by:
Barium (Ba
2+
): above 1 mg/L (negative error)
Chloride (Cl
-
): above 1000 mg/L
Nitrite (NO
2
-
): above 50 mg/L (positive error).
Samples containing up to 100 mg/L nitrite may be
measured after the following treatment: add 400 mg
of urea to 10 mL of sample, mix until dissolution is
complete, then proceed with the usual measurement
procedure.
Nitrate
45
•
Remove the cap from the vials and add the content of one packet
of HI 93767-0 Total Nitrogen Reagent to each vial. Replace the
cap tightly and shake gently the vials for 15 seconds.
•
Wait for 2 minutes (without shaking the vials)
to allow the reaction to complete.
• Remove the cap from two Reagent Vials (
white
cap vials).
• Add exactly 2.0 mL of digested sample (from the digested red cap
sample vial) to one Reagent Vial (sample vial), and 2.0 mL of
digested blank (from the digested red cap blank vial) to the other
vial (blank vial), while keeping the vials at a 45-degree angle.
• Replace the cap tightly and invert
the vials 10 times.
Warning
: as the vials become hot
during mixing, be careful in handling
them.
Note
: the method is technique
sensitive: to obtain most reproducible
results it is strongly recommended
to follow carefully the “invert”
procedure described on page 14.
←
white cap
→
Nitrogen, Total HR