Geoscience Reference
In-Depth Information
replicates). It is recommended that replicates be collected in a minimum of triplicates (if
only duplicates are collected and the data vary the replicates are of little aid). Different
types of replicates can be used dependent on the quality assurance needs and the type of
study (U.S. Geological Survey,
2006
). For example, concurrent replication refers to a num-
ber of samples of water collected at the same time or as close to one another as possible and
is the most common type of replication utilized. These replicates provide quality control
data and can be used to examine the variability introduced from sample collection, han-
dling, and processing and also the variability in laboratory handling and analysis of sam-
ples. Sequential replication refers to a number of samples that are collected consecutively
and thus it varies from concurrent replication as it allows for examination of any variation
in the water sampled between sequential replicates. Thus sequential replication examines
the temporal variability of the water under study as well as variability introduced from
sample collection, handling, and processing and also the variability in laboratory handling
and analysis of samples. Finally, split replication refers to samples derived from splitting
one bulk sample that is designated for a specific analysis (e.g., fluorescence) into a number
of subsamples. These subsamples are then submitted to different laboratories for identical
analyses (e.g., Sharp et al.,
1995
,
2004
; Jaffe et al.,
2008
; Murphy et al.,
2010
).
4.2.3 Equipment Cleaning
The aim of equipment cleaning is to remove any existing organic matter and any other
substances that may interfere with DOM fluorescence or absorbance analyses. After clean-
ing, sampling equipment should be stored dry and covered (e.g., wrapped in aluminum
foil, storage in freezer bags) to limit microbial growth and to avoid contamination. Typical
equipment cleaning protocols involve an initial cleaning with a detergent (e.g., soapy
water), followed by extensive rinsing with laboratory-grade water, then a cleaning step
with a solvent (typically methanol or acetone), again followed by extensive rinsing with
laboratory grade water. The main issue here is that soap, acetone, and methanol all inter-
fere with the optical properties of chromophoric DOM (CDOM) (
Figure 4.1
) and thus it is
imperative that if they are used in the cleaning process, that all trace of them is removed.
Sampling equipment may also be effectively cleaned by soaking in a 10% hydrochloric
acid (HCl) solution and then extensively rinsed with laboratory grade water. Where pos-
sible glass is recommended for sampling equipment (e.g., bottles), as it can be guaran-
teed to have no organic matter contamination if it is combusted at 450°C for greater than
four hours in a muffle furnace. Before combustion it is recommended to cover parts of
the glassware that may come into contact with the sample (e.g., the opening on bottles)
with aluminum foil so that they can be stored covered with foil (e.g., screw bottle caps
on over the foil, thus not exposing the inside to air until the sample is taken). Glassware
that cannot be combusted (e.g., volumetrics, pipettes) and plastics (including bottle caps)
can be cleaned as described earlier and then after the final rinsing with laboratory grade
water dried in a drying oven (60°C). Teflon tape can be very useful for sealing sampling
equipment after cleaning to avoid any contaminants getting inside cleaned materials. While
