QUALITY CONTROL/QUALITY ASSURANCE PROGRAM
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SUMMARY: The primary objective of the HOT program
is to collect and interpret biological, chemical and
hydrographic time-series data. In order to provide
accurate and reliable data, to the oceanographic
community, the JGOFS component of HOT has established
a quality control/quality assurance (QC/QA) program
that is designed to assess and maintain data quality.
These QC/QA procedures encompass all aspects of the
program from sample collection through data reporting.
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1. Introduction
Our QC/QA program is designed to ensure that data of the
highest quality are obtained from the HOT program. A fundamental
component of this QC/QA program is the documentation of the detailed
analytical procedures that are presented in the following chapters.
These procedures are consistently applied in our laboratory analyses.
This chapter describes the HOT program QC/QA procedures that are
independent of the specific analytical protocols presented in
subsequent chapters. These QC/QA procedures include field sampling,
analytical facilities and instrument maintenance, interlaboratory
comparisons and data reporting.
2. Precision and Accuracy
The precision and accuracy of each analytical procedure is
discussed in the appropriate chapter. Accuracy is a measure of
how close an analyzed value is to the true value. In general,
the accuracy of an analytical method is determined by the use
of calibrated, traceable reference standards. However, it is
important to bear in mind that the assessment of accuracy based
upon primary standards can be misleading if the standards are not
prepared in seawater because many of our chemical determinations
exhibit matrix (i.e., salt) effects. In addition, it must be
recognized that most of the HOT program core measurements (e.g.,
dissolved oxygen, pH, pCO2, primary production, etc.), do not
have readily available reference materials.
Precision is a measure of the variability of individual
measurements (i.e., the analytical reproducibility) and in the
HOT program two categories of replicates are measured; field and
analytical replicates. Analytical replication is the repeated
analysis of a single sample and is a measure of the greatest
precision possible for a particular analysis. Field replication
is the analysis of two or more samples taken from a single
sampling bottle and has an added component of variance due to
subsampling, storage, and natural within sample variability.
The variance of field and analytical replicates should be equal
when sampling and storage have no effect on the analysis (assuming
the analyte is homogenously distributed within the sampling bottle).
Therefore, the difference between field and analytical replicates
provides a first order evaluation of the field sampling procedure.
Higher level variance due to sample bottle replication (multiple
bottles on same cast or multiple casts) is not well-resolved in the
current HOT sampling protocols.
It is apparent from these definitions that precision and accuracy
are not necessarily coupled. An analysis may be precise yet inaccurate,
whereas the mean of a variable result may be quite accurate. Therefore,
precision and accuracy must be evaluated independently.
3. Overview of the Quality Control/Assurance Program
The basic framework of the HOT-JGOFS QC/QA program addresses field
sampling, laboratory facilities, laboratory analysis and data reporting.
Quality control in the field is primarily attained by utilizing modern
sampling equipment that is properly maintained. The quality of field
and laboratory instruments is preserved with appropriate instrument
maintenance, periodic calibration and careful documentation procedures.
Laboratory analysis QC/QA is evaluated on the basis of periodic review
of methodology, variance evaluations (control charts), reference
materials (where available) and inter- and intralaboratory comparisons.
Quality control procedures associated with data reporting include sample
documentation, tracking and evaluation of analytical results, relative
to sample documentation, and comparison of results to historical values.
4. Field Sampling and Strategy
Specific aspects of the time-series field sampling strategy have
been presented (see Chapter 2), and will not be repeated here except
to emphasize key aspects of our QC/QA program. Station KAHE (see map
in Chapter 1) serves as a representative coastal site for the collection
and interpretation of long-term environmental data and as an equipment
test station. At Station KAHE, an initial cast is performed using
only a weight to test the winch and to inspect the condition of the
hydrowire. This test cast is followed by a CTD-rosette cast to 1000 m
with a full complement of 24 12-liter water bottles. The latter serves
to test the CTD, pylon and deck box, to collect water column samples
and to provide a hands-on opportunity for novice members of the
scientific party to participate in the deployment and retrieval of
the rosette and the collection of water samples. Ideally, samples
are collected and processed exclusively by experienced personnel.
However, the HOT program encourages graduate and undergraduate
participation and endeavors to combine marine research with marine
science education. Consequently, we conscientiously schedule an
at-sea training session to ensure that the procedures followed are
identical from month to month.
During each HOT cruise, at least 20% of the samples are routinely
collected in duplicate or triplicate to evaluate field precision.
In addition, salinity samples are drawn and on-deck sample temperatures
(for those casts where oxygen samples are drawn) recorded from each
water bottle sampled. Both procedures are useful for the identification
of sample mistrips (i.e., the collection of water from a depth other
than intended).
The collection of representative samples is paramount to a successful
time-series program and is contingent upon the use of appropriate
sampling equipment which is well-maintained and operationally sound.
A field sampling equipment maintenance program is administered by our
Marine Technician. The program consists of a documented inspection
of field equipment at regular intervals. A record of repairs,
modifications and any other pertinent information is also maintained.
In addition, diagrams outlining all sampling equipment and assembly
procedures for sediment trap and in situ primary productivity arrays,
radio direction finder tracking equipment, Argos satellite transmitter
and on-deck incubation system have been drawn and are updated as necessary.
Sample collection quality control measures are based upon the
concept of applying time-tested oceanographic sampling techniques in
a standardized and coordinated manner supervised or conducted by
experienced personnel (details of each sampling procedure are outlined
in the following chapters). Specific sampling data are recorded on
log sheets at the time of collection, identifying the type of samples
collected, cruise, station, time, cast number, sample number and any
other pertinent metadata. These "metadata," along with copies of the
CTD console log and property vs. depth plots are retained in the
appropriate HOT cruise notebook. Records are maintained to identify
sample tracking from collection through analysis and data reporting.
Any problems associated with a particular sample are noted on the
appropriate log sheet or data file and are evaluated relative to
routine quality control proceures (Fig. 2).
5. Analytical Facilities
All analyses are conducted at the University of Hawaii at Manoa
in modern, well-equipped research laboratories. Specialized analytical
equipment used in the JGOFS project include: Packard model #4640
liquid scintillation counter, UIC model #5011 coulometer, Biospherical
microprocessor-controlled ATP photometer, Perkin-Elmer model #2400
carbon/nitrogen analyzer, Technicon autoanalyzer and accessories,
automatic Winkler titration system consisting of Brinkmann Dosimat 665,
Orion EA 940 ion analyzer and IBM compatible computer, Guildline Autosal
model 8400A salinometer, Antek model #720 nitrogen oxides analyzer,
Zeiss epifluorescence, phase contrast and inverted microscopes, Coulter
Epics dural-laser flow cytometer, Ionics model #555 carbon analyzer,
Beckman DU-640 ultraviolet-visible light spectrophotometer, Spectra-
Physics model SP8800 HPLC equipped with Waters model 440 absorbance
and model 470 fluorescence detectors, Waters model 990 photodiode array
spectrometer, Turner model AU-10 fluorometer, Perkin-Elmer model #LS-5
fluorescence spectrophotometer with data station, Cahn C-31 microbalance
and LAL model #5000 optical analyzer.
In addition to the above, the JGOFS laboratories are well equipped
with standard laboratory equipment, including: fume hoods, analytical
and toploading balances, centrifuges, freezers, refrigerators,
volumetric glassware, pipettes, muffle furnaces, pH meters, computers
and other general laboratory equipment and glassware. The facilities
are maintained to provide optimum conditions for a wide scope of
analytical procedures. Quality control measures include service
contracts (balances and selected equipment), verification of performance
through the use of calibration curves, standards bracketing samples,
wavelength verification and calibration, measurement of secondary
standards, utilization of NIST Class S weights, NIST traceable
thermometers and analysis of appropriate known and unknown reference
samples. Instrument operating, service, and calibration manuals
are retained and the calibration, repair and service history of
JGOFS-utilized equipment documented and retained for use by laboratory
personnel.
6. Chemicals and Reagents
All chemicals and reagents used in our routine sample analyses are
ACS quality, or better. Incoming chemicals are marked with date
received and recorded on the chemical inventory sheet. Distilled
deionized water (DDW) is used in the preparation of solutions and
the chemical resistivity of the DDW is continuously monitored to
confirm purity. New chemicals or reagents are compared to previous
reagent performance and are discarded when: (1) the expiration date
has elapsed or (2) when the analytical performance is deemed inadequate.
7. Laboratory Analysis
The specific analytical methodologies outlined in the subsequent
chapters have resulted from extensive methods evaluation (Table 1).
These procedures are conducted by experienced personnel familar with
oceanographic laboratory protocols and instrumentation. Where applicable,
analytical runs include a series of standards bracketing samples,
replicates (>20%), analysis of reference (control) samples, as well
as procedural, reagent, refractive index, salt, dilution and time-zero
blank corrections. All analytical results are documented and original
hard copies are archived in the appropriate HOT notebooks.
Sample analysis quality assurance relies heavily on replicate
analysis and use of certified reference standards as determinants of
precision and accuracy, respectively. Replicates are the primary
determinants of variance and, as discussed previously, can be divided
into two categories; field replicates, providing a measure of sampling
and natural variability, and analytical replicates, providing a measure
of the analytical precision. As previously stated, at least 20% of the
samples are collected and processed as field replicates. An additional
number of analytical replicates are analyzed to evaluate analytical
variance. Where appropriate, internal standards are analyzed on
selected samples. When necessary additional quality control measures
may include matrix matching, standard additions and comparison of
results with independent methodologies. When available, traceable
certified reference standards are used to assess the accuracy of each
set of determinations.
Analogous to the field preventative maintenance program is an
instrumental service and calibration program. This program identifies
and documents service intervals for balances and other specialized
equipment. Because the analytical equipment used in the JGOFS program
experiences regular use the performance is routinely evaluated. If a
problem develops, sample analysis is terminated until normal operation
is restored. In addition, the dependency of many analytical procedures
on the proper and accurate operation of the analytical balance is
recognized and evaluated by weighting secondary standards during periods
of use and periodic comparison to NIST traceable class S weights. All
calibration, repair, modifications and service histories are maintained
in written logs.
Where relatively small temporal changes are expected in the ambient
concentrations of dissolved and particulate analytes of interest to
the HOT program scientists, it is of paramount concern to quantify
the temporal performance of resulting analytical results in terms of
the accuracy of primary standards. This can be achieved by routinely
analyzing the same reference standard over a relative long period of
time. These need not be certified reference standards, however, the
analyte must be temporally stable (ideally greater than 1 year) in
the sample matrix. We have found that frozen (-20 °C) unfiltered
inorganic nutrient samples (for inorganic nutrient analysis), dried
pulverized net plankton (particulate carbon, nitrogen and phosphorus),
and a (-20 C) stored pure chlorophyll a standard (fluorometric analysis)
are adequate for assessing temporal variability.
A great asset to any analytical quality control and assurance
program is participation in inter-laboratory programs. Interlaboratory
programs allow an independent evaluation of analytical quality and
performance relative to participating laboratories. The HOT program
has had the opportunity to participate in the following intercomparison
studies:
* NSF-JGOFS intercalibration of plant pigments coordinated by R. Bidigare
and M. C. Kennicutt of Texas A&M
* ICES Marine Chemistry Working Group-sponsored intercomparison of
inorganic nutrient analyses coordinated by D. Kirkwood, United Kingdom
* monthly total CO2 intercomparison with C. D. Keeling, Scripps
Institution of Oceanography
* periodic total CO2 intercomparison with P. Quay, University of Washington
* periodic dissolved oxygen intercomparison with S. Emerson, University
of Washington
* periodic dissolved oxygen intercomparison with Omar Calvario-Martinez,
Instituto de Ciencias del mar y Limnologia, Estacion Mazatlan
* periodic salinity intercomparisons with C. Collins, Naval Postgraduate
School
* methods intercomparison with Bermuda da Atlantic Time-Series, Bermuda
Biological Station for Research
* DON intercomparison coordinated by C.S. Hopkinson, Jr. Marine
Biological Laboratory, Woods Hole, Massachusetts
* DOC intercomparisons coordinated by J. Hedges University of Washington
and J. Sharp, College of Marine Studies, University of Delaware
8. Data Evaluation and Reporting
Data evaluation and reporting are the final steps in the quality
control process and comprise an essential part of the quality assurance
program. Here the data are reviewed in the context of the entire
sample collection, storage and analytical process. Discrepancies or
anomalous results are noted at various stages of the analytical process
(Fig. 2) and the final data evaluated for correctness of analysis by
plotting the analyte profile vs. depth and density and investigating
those points outside the historic data envelope. Data outside the
historic data envelope are not automatically flagged as "bad," but
rather investigated for the source of the problem through the sample
documentation. If the problem remains unidentificable the data are
flagged "questionable" if the values are outside the 95% confidence
interval (greater than 2 standard deviations from the historical mean),
and "good" if within this error envelope. If a source for the discrepancy
is discovered the data are flagged "bad." At this point all data inside
the historic envelope are flagged "good" and together with the
"questionable" data added to the historic data set. Finally, all
the data are summarized and reported in our annual data report along
with the appropriate quality flag.
9. References
American Public Health Association. 1989. Standard Methods for
the Examination of Water and Wastewater, 17th edition. American
Public Health Association, Washington, DC.
Dux, J.P. 1990. Handbook of Quality Assurance for the Analytical
Chemistry Laboratory, New York: Van Nostrand Reinhold, 203 pages.
Dickson, A.G. 1991. Measuring Oceanic CO2: Progress on Quality
Control. U.S. JGOFS Newsletter vol. 3, number 2, pp. 4-5.
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