Water Resources--Office of Water Quality
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QUALITY CONTROL FOR EQUIPMENT-CLEANING PROCEDURES
By A.J. Horowitz, M.W. Sandstrom, and F.D. Wilde
Quality-control samples are required for any sampling and analysis program.
Without quality-control information, the quality of the environmental data
collected can be neither evaluated nor qualified. If the user has no means of
knowing the associated errors, the data cannot be interpreted properly.
The purpose for obtaining quality-control (QC) samples following equipment
cleaning is to ensure that the equipment and the procedures used for cleaning
the equipment do not contaminate or otherwise affect the environmental samples
that were or will be collected. The QC sample used to assess the adequacy of
cleaning procedures before field work commences is called the equipment blank.
||Blank water. Blank water is used to develop specific types of QC
samples (National Water Quality Laboratory Memorandum 92.01). The water
is a solution that is free of analyte(s) of interest at a specified detection
level. USGS personnel are required to use blank water that has been analyzed
and certified to be of a specific grade and composition.
||Use IBW to collect blank samples for analysis of inorganic constituents.
||Use PBW to collect blank samples for analysis of pesticides. (Do
not use PBW when collecting samples for VOC analysis.)
||Use VBW to process blank samples for analysis of VOCs. VBW is also
suitable as a blank sample for pesticide analysis.
||Use PBW or VBW as the quality-control sample for total and dissolved
organic-carbon analysis (TOC and DOC). This cannot be documented as
a blank sample because neither PBW nor VBW is certified to be free
of organic carbon.
Equipment blank. An equipment blank is blank water that is processed
under controlled conditions in the office laboratory by being passed sequentially
through each component of the sample processing and collection equipment.
An equipment blank represents an entire sampling system (fig.3-7)
and is required:
||When a cleaning procedure is followed for the first time
||When new equipment will be used for the first time.
To fulfill equipment-blank requirements:
- Allow enough time in the study workplan to collect the annual equipment
blank, complete laboratory analyses, and review analytical results before
field work for the study commences.
- Process the annual equipment blank in a clean, controlled environment in
the office laboratory, after the equipment has been cleaned using office-laboratory
- Analyze the annual equipment-blank data before collecting and processing
the first water-quality sample of either the fiscal year or the study.
- If the equipment-blank data indicate that the equipment does not introduce
contaminants that will bias study results, sampling can proceed.
- If the equipment-blank data indicate unacceptable concentrations of analytes
of interest, the cause must be identified and the equipment or cleaning
procedures must be changed or modified before sampling can proceed.
|Plan ahead: Assess equipment-blank data
before environmental samples are collected.
||Field blank. The field blank is blank water that is processed at
the field site by being passed sequentially through each component of the
equipment being used to collect environmental samples. The procedure for
processing the field blank, like the equipment blank, can also result in
a set of sequentially collected blank samples (fig.
3-7) (Horowitz and others, 1994). Other types of blank samples also
are collected at the field site (NFM 4). At least one field blank per
sampling run is recommended; the numbers and distribution of QC samples
depend on study objectives, the target analytes, and site conditions.
||Process field blanks through clean equipment.
||If equipment is used at several sites during a field trip, process
a field-equipment blank after the last sample has been collected and
again after the equipment has undergone the prescribed field-cleaning
||If multiple sets of office-cleaned equipment are used during a field
trip, process a field blank at any site during the course of the trip.
In this case, the blank must be processed before sampling to avoid
contaminating the blank with residues from an environmental sample.
||Process field blanks onsite and under the same conditions as the
Before filling the QC sample bottle with the appropriate blank water:
- Check that sample bottles are clean, are the correct type, and are labeled
- Check the certificate of analysis for the lot of blank water to be sure
that it is appropriate for quality control of target analytes.
- Record the date and lot number of the IBW, PBW, and (or) VBW used and of
the preservative used. To the extent possible, use preservative from the same
lot number for an entire sampling trip for both the environmental and quality-control
- Rinse sample bottles for inorganic constituents three times with a small
quantity of the blank water.
Use the following strategy for QC data collection and analysis:
- For inorganic-constituent samples, initially send only the final equipment-blank
sample for the routine inorganic blank-sample analysis or for inorganic analytes
targeted by the study.
Check the analytical results for the equipment blank and field blanks as
soon as possible and before the next field trip.
- Archive the remaining sequentially processed blank samples (fig.3-7)
until the inorganic-constituent analysis of the equipment-blank sample has
- Do not archive blank samples for organic-compound analysis.
Additional QC data collection and (or) analysis is required if the equipment
blank has greater than acceptable analyte concentrations.
- If analytical results indicate that the equipment is clean within acceptable
limits, the equipment may be used for field work without additional testing
- Use of equipment is not recommended if analysis of the equipment blank
sample indicates greater than acceptable analyte concentrations.
- For inorganic-sample analysis. Submit the rest of the sequential
blank samples for laboratory analysis and use the analytical results from
the sequential blank samples to identify potential source(s) of contamination.
Modify equipment-cleaning procedures if contamination can be remedied by
a change in cleaning procedure. Repeat collection of equipment blanks until
the blank data verify that the equipment is suitable for use.
- For organic-sample analysis. Modify the equipment cleaning procedure
if the source of contamination is known or suspected and contamination can
be remedied by a change in cleaning procedure. If the source of contamination
is not known, reclean equipment using office-laboratory procedures and collect
and analyze blanks for each part of the sampling system that could be a
source of contamination. Repeat collection of equipment blanks until the
blank data verify that the equipment is suitable for use.
The equipment blank is
the last sample of a set of sequentially processed blanks collected
in the office laboratory and documents the suitability of the equipment
for the samples that are to be collected and analyzed. Field blanks
are collected in the field in the same manner as the equipment blank
but document the effectiveness of the field-cleaning procedures plus
any ambient contamination.
- Surface water: collect the series of five sequential
blank samples listed below for routine surface-water sampling.
- Ground water: collect the source-solution blank (Sample
1) and either a sampler blank (Sample 2) or pump blank (Sample 4)
(depending on the type of sampling device being used) along with the
filter blank (Sample 5) .
|Source solution (SS)
Put on disposable gloves. Pour the IBW, PBW, or VBW directly into
appropriate SS blank-sample bottle.1
Add chemical treatment and (or) chill, as required for the analytes
|SS + Sampler
Bottle or bag sampler: Fill sampler container with SS; attach
sampler cap and nozzle; decant sample into blank-sample bottle through
the nozzle. Preserve sample (add chemical treatment and (or) chill)
as required (NFM 5).
Bailer or thief sampler: Fill sampler with SS; install bottom-emptying
device; empty sample into blank-sample bottle through the bottom-emptying
device. Preserve sample, as required.
Submersible or nonsubmersible pumps: Go to Sample 4 (Pump
|SS + Sampler + Splitter2
If a cone or churn splitter is used, decant remainder of the SS
into sampler container, and then through splitter (through nozzle
or bottom-emptying device). Refill sampler container with SS to
fill churn with 3 to 5 liters of water. Alternatively, pour enough
SS from samplers through cone splitter to fill splitter-blank bottle.
Collect SS into blank-sample bottle through churn spigot or cone-splitter
exit port(s). Preserve sample, as required.
|SS + Sampler + Splitter + Pump
Nonsubmersible pump (peristaltic, vacuum, or valveless metering
pump): Secure intake end of clean pump tubing into churn splitter
or into a subsample split with the cone splitter. Pump some sample
to waste to rinse tubing, and fill pump-blank bottle directly from
the discharge end. Preserve sample, as required.
Submersible pump: Place pump in blank-water standpipe and
fill standpipe with enough SS to cover pump intake and allow for
drawdown. Start pump at low pumping rate, discharge 0.5 liter of
SS to waste, then fill blank-sample bottle with SS. Preserve sample,
|SS + Sampler + Splitter + Pump
Pump SS through a prerinsed filtration assembly (plate filter or
capsule filter); pump the first aliquot to waste and then pump SS
directly into the blank-sample bottle. Preserve sample, as required.
1Process the source-solution
blank in the protected environment of the office laboratory only, not
in the field (NFM 4).
2 For ground-water quality
control: A splitter blank is included if a cone splitter is used; a standpipe
blank often is collected if a submersible pump is used.
Figure 3-7. Sequence of sample collection to obtain
the equipment blank
factors and abbreviations
Return to Section 3.3 Specific Procedures for cleaning selected
types of equipment
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Maintainer: Office of Water Quality
Webversion by: Genevieve Comfort
Last Modified: Wednesday, 28-Dec-2016 18:48:40 EST