Hach DR/700 Procedures Manual page 243

LEAD,
continued
APPARATUS/SAMPLE PREPARATION
Because lead is very common to our environment, care must be taken to
prevent sample contamination. Follow these steps for greatest test
accuracy:
a) Lead-free water is necessary to minimize sample contamination when
rinsing apparatus or diluting sample. The water may be either distilled
or demineralized. If the water is obtained from a grocery store, verify
the lead concentration is zero from the label. If the lead concentration is
uncertain, determine the lead concentration with the LeadTrak test.
b) Plastic or glass sample containers and lids may be checked for
contamination by rinsing with 1 mL of pPb-1 Acid Preservative. Add
100 mL of lead-free water. After 24 hours, analyze this solution using
the LeadTrak test to confirm the absence of lead.
c) Rinse labware (plastic and glass) used in this test with a small amount
of dilute lead-free nitric acid or pPb-1 Acid Preservative followed by
rinsing with lead-free water.
d) pPb-5 Indicator may be rinsed from the glass sample cells with a few
drops of pPb-1 Acid Preservative or a small amount of dilute lead-free
nitric acid.
SAMPLING
Samples may be collected either from household pipes (point-of-use) or
from water sources. Each source has its own sampling procedure under
the proposed EPA methods. Samples may be stored up to six months.
Sampling for lead contamination in household pipes for point-of-use
drinking water
a) The sample should be collected after sitting in pipes with no flow for
8 to 18 hours.
b) Add 10 mL of pPb-1 Acid Preservative to a one-liter bottle.
c) Turn on tap and collect exactly the first liter of water in the bottle
containing acid preservative.
d) Cap and invert several times to mix.
48-7