Environmental Engineering Reference
In-Depth Information
table 3.3
Recommended Containers and Preservation Methods for Inorganic and Total Mercury Measurements
Analyte
Matrix
Preservative
Container
Hold time
Total Hg
Water
0.5% HCl
Tefl on or glass
90 days
a
Total Hg
Water
0.5% HCl
Tefl on or glass
180 days
b
Elemental Hg
Water
NA
Tefl on or glass
0 days
b
Reactive Hg
Water
4
2°C
Tefl on or glass
2-3 days
b
Total Hg
Sediment
Frozen/freeze-dried
Tefl on, glass or plastic
1 year
a
Total Hg
Tissue
Frozen/freeze- dried
Tefl on, glass or plastic
1 year
a
NA
not applicable.
a. According to EPA Method 1631.
b. According to Parker and Bloom 2005.
Polytetrafl uoroethylene (PTFE) or fl uorinated ethylene pro-
pylene (FEP). Signifi cant contamination can occur with
plastics such as polyethylene and polypropylene, and
therefore these are not recommended for aqueous samples.
Plastic containers cannot be as rigorously cleaned as glass
or Tefl on and are highly permeable to vapor-phase Hg
0
,
allowing Hg to readily freely diffuse into (or out of) sam-
ples depending on the concentration gradient between the
sample and surrounding air (Gill and Fitzgerald, 1987).
Rigorous cleaning procedures must be used for all labora-
tory ware and other equipment that comes into contact
with samples. There are several cleaning procedures that
are suitable for laboratory ware and sampling equipment:
(1) aqua regia treatment followed by soaking in dilute
(~5-10%) nitric acid for a week; (2) soaking in a hot oxidiz-
ing mixture of KMnO
4
and K
2
S
2
O
8
, followed by NH
4
OCl
rinsing and soaking for a week in 5M HNO
3
; (3) soaking in
a 1:1 mixture of concentrated chromic and nitric acids for
a few days; and (4) soaking in a BrCl solution (mixture of
HCl and KBrO
3
).
Tefl on ware is usually cleaned in hot concentrated HNO
3
for 48 hours, followed by numerous rinses with a high-
purity (low Hg content) laboratory water supply (e.g., 18 M
surface waters is usually performed by hand, using arm-
length plastic gloves. Samples are taken upwind of a rubber
raft or a fi berglass boat. When it is not possible to collect
a grab sample, acid-cleaned, contamination-free sampling
devices (e.g., Tefl on or Go-Flo samplers) are commonly
used for the collection of water samples. Alternatively, the
water can be pumped through acid-cleaned Tefl on tub-
ing using a peristaltic pump. Precipitation samples can be
collected by automatic samplers, with in-line fi ltration if
desired (Landing et al., 1998).
Water samples should be collected in acid-cleaned glass
or Tefl on bottles. If the samples are to be analyzed for dis-
solved Hg, the sample must either be fi ltered using a peri-
staltic pump with precleaned in-line fi lters during sample
collection or within 48 hours of collection once samples
are returned, on ice, to the laboratory. Samples for total or
dissolved Hg should be preserved as soon as possible after
collection (generally within 48 hours) with high-purity,
low-mercury-content HCl (typically 0.5%) or HNO
3
(typi-
cally 0.2%). Water samples for the analysis of total mer-
cury only may also be preserved by direct addition of the
oxidizing agent 0.2N BrCl (typically 0.5%) as described
in Environmental Protection Agency (EPA) Method 1631
(EPA, 2002). If MMHg is also to be analyzed along with
total Hg on the same sample, only HCl preservation
should be used, as HNO
3
can destroy MMHg. Water sam-
ples for the determination of elemental Hg should not be
preserved with acid and the Hg
0
isolated from the solution
immediately upon collection to avoid loss from solution.
Samples for the analysis of reactive Hg cannot be pre-
served and must be stored cold and processed as soon as
possible after collection (Parker and Bloom, 2005). Ideally,
samples for reactive mercury are reduced and purged to
gold amalgamation traps in the fi eld immediately after
collection.
Containers and other sampling equipment that come
into contact with water samples should be made of
borosilicate glass, Tefl on, or silica glass and rigorously
deionized water or double distilled water) and dried on a
class-100 clean air bench. Items are then generally placed
in a sealed plastic bag to avoid dust contamination and
stored in an environment known to be low in atmo-
spheric mercury content. Some authors recommend stor-
age of laboratory ware in dilute HNO
3
or HCl acids until
use. For collection of samples to be analyzed for both total
Hg and MMHg analyses, the bottles must be prepared
with extreme caution to ensure that the containers do
have residual HNO
3
from the cleaning process. Soaking of
laboratory ware, particularly Tefl on, in hot (70°C) 1% HCl
removes any traces of oxidizing compounds that may sub-
sequently destroy MMHg in solution.
Water samples are often collected by grab sampling
upstream of sources of contamination. Collection of
