Hach DR/700 Procedures Manual page 246

LEAD,
continued
Samples containing levels exceeding these concentration values may be
diluted 1:1 and re-analyzed. Multiply the value obtained by 2 to
determine the lead present in the original sample.
Every effort has been made to prevent contamination in packaging the
reagents. Use of black rubber stoppers, black dropper bulbs and
droppers with inked graduations may contaminate the sample and
should be avoided. Use the plastic droppers provided in the reagent set.
Glassware and plastic ware should be rinsed with a dilute nitric acid
solution such as 0.1 N Nitric Acid Standard Solution or a few drops of
pPb-1 Acid Preservative Reagent to prevent sample contamination,
especially if the previous sample had a high lead level. The sample cell
walls will become colored from the pPb-5 Indicator and should be
rinsed. The Extractor plunger is intended to be used for more than one
test and should be rinsed as well.
STATISTICAL EVALUATION
A single operator repetitively tested samples of two laboratory prepared
solutions, using one DR/700, matched cells and two representative lots
of testing reagents. Testing 100 µg/L Pb concentration samples the
standard deviation was ±3.0 µg/L Pb.
Testing zero concentration samples, the limit of detection was 3.0 µg/L
Pb. The limit of detection was calculated as three times the standard
deviation when testing zero concentration samples (Adapted from
Analytical Chemistry, 1980, 52, 2242-2249).
SUMMARY OF METHOD
2+
Acid soluble lead, as Pb , in a potable water sample is first concentrated
on a Fast Column Extractor. The lead is then eluted from the Extractor
and determined colorimetrically with an indicator.
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