60
Ammonia–2: Nesslerization Method
11. When 30 minutes is up, put on the heat-resistant gloves.
Remove the first tube from the block and immediately pull off its
sample tube using a downward, twisting motion as opposed to
a sideways motion. Remove the sample tube within 4 seconds
of removing it from the block or suck-back of the sample will
occur. Dispose of the sample tube and the hot solution left in it
by dropping it into the sink or waste bucket.
12. Invert each collector tube and place it into the collector tube
rack, now with the
D end up. It should take less than two
minutes to pull and separate all 21 tubes.
13. Parafilm the
M end and allow tubes to cool for at least 10
minutes.
14. For each collector tube, hold the tube horizontally and rinse its
walls with the distillate in order to homogenize it. Slowly roll the
distillate around in the tube to gather all droplets clinging to the
tube walls into the bulk of the distillate. Then, slowly return the
collector tube to an upright position so that the
D end is up.
Stubborn drops will often fall into the
M end when the tube is
flicked with the finger.
15. With the
D end still up, break the collector tube in half by pulling
the
D end hard towards the user to break it, then twisting and
tearing off the
D end. Discard the D end.
16. In the remaining
M end of the collector tube, dilute to the 6.0 mL
mark with deionized water. This results in the original sample
volume, but now in 0.043 M boric acid solution.
17. Shake the tube with a gentle whipping motion to mix in diluent
water. Do not invert the sample. With the
M end down, place
the tube into the collector tube rack.
18. Determine the solution in the tube following Standard Methods.
Seal both ends with Parafilm if the sample will not be
determined immediately.
16.2 Borate Buffer
Make this buffer solution up in a 1 L container and then place
directly in the automatic re-pipettor supplied with the starter kit. This
will make 1 L of 0.011 M Na
2
B
4
O
7
, enough to treat 1300 samples.
1. Place a 1 L container onto a top-loading balance with a 1000 g
capacity or greater. Tare the balance.
2. Dissolve 2.17 g sodium borate (Na
2
B
4
O
7
) in 964 g deionized
water into the tared 1 L container. Add 36 g 0.1 N sodium
hydroxide (NaOH). Mix well.
3. Transfer this solution to the re-pipettor, screw the cap on tight
and prime the pipet. The solution is ready to use in method
Ammonia–2.
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