32
Cyanide–1
10. Put on the heat-resistant gloves. Push the sample tube and D
end of each tube all the way into the preheated block so that
the collector tube stop ring touches the block. Placing 21 tubes
should take less than one minute.
11. Set the timer for 30 minutes.
12. 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.
13. Invert each collector tube and place it into the collector tube
rack, with the
D end up. It should take less than two minutes to
pull and separate all 21 tubes.
14. Allow tubes to cool for at least 10 minutes.
15. 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 a finger.
16. 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.
17. 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 0.25 M NaOH.
18. 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.
19. Determine the solution in the tube with Lachat's QuikChem
Method 10–204–00–1–X or equivalent. There is enough
distillate for two 25 second sample periods. Seal both ends of
the tube with Parafilm if the sample will not be determined
immediately.
8.2 Releasing Agent
CAUTION
Chemical and burn hazard. Upon the addition of sulfuric acid
to water, the solution will become very hot. Never add water to
concentrated acid. When preparing this reagent, follow these
steps very carefully.
ATTENTION
Risque chimique et risque de brûlure. Lorsque de l'acide
sulfurique (H
2
SO
4
) est ajouté à de l'eau, la température de la
solution augmente rapidement. N'ajoutez jamais de l'eau dans
de l'acide concentré. Lors de la préparation de ce réactif,
suivez ces étapes avec beaucoup de précautions.
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