Current through August 26, 2024
(1) GENERAL
PROVISIONS.
(a) The laboratory shall
calibrate or verify the calibration of all analytical instruments before the
instruments are used to provide any quantitative results.
(b) Once a calibration model is selected, a
calibration function is established, and an initial calibration is finalized, a
laboratory may not change the model or calibration function after samples have
been analyzed without performing another initial calibration.
(c) The laboratory shall perform an initial
calibration if any of the following apply:
1.
After instruments undergo non-routine maintenance.
2. Conditions change the expected behavior of
the instrument.
3. When a CCV
standard fails and any of the following occur:
a. Corrective action taken does not result in
a passing CCV standard.
b. A second
consecutive (immediate) CCV standard is performed under the same conditions and
it also fails and the corrective action taken does not result in two
consecutive passing CCV standards.
(d) The laboratory shall retain all the raw
data necessary to reconstruct or reproduce calibration functions associated
with initial calibrations.
(e) For
colorimetric technologies, the laboratory may not use a method blank to zero
the instrument.
Note: For colorimetric technologies other than
those based on inverse chemistries, the instrument is to be zeroed with the
matrix of interest which is generally reagent water.
(f) The laboratory may not utilize
pre-programmed initial calibrations, provided by the instrument manufacturer,
for compliance testing.
(g) The
laboratory shall include or reference the details of initial instrument
calibration procedures including algorithms, any required equations, and
acceptance criteria in the method standard operating procedure.
(h) When required by method, the laboratory
shall process each calibration standard in the same manner as
samples.
(i) Point-to-point
calibrations are not allowed unless otherwise specified in this chapter.
(2) MINIMUM NUMBER OF
STANDARDS. To establish calibration, the laboratory shall select the number of
nonzero standard concentrations that is appropriate for the calibration model
selected and the expected range of concentrations. If a method requires
analyzing more than three standards to establish a linear calibration, and the
laboratory chooses to narrow the calibration range of the determination to no
more than two orders of magnitude, the laboratory may use 3 standards to
generate the initial calibration. The minimum number of nonzero standard
concentrations selected to establish calibration shall be three except for all
the following:
(a) Dissolved oxygen meters,
for which the minimum shall be one. Dissolved oxygen meters shall be calibrated
against water-saturated air or air-saturated water at a known temperature and
pressure. Alternatively, calibration may be performed using an iodometric
method.
(b) Conductivity meters,
for which the minimum shall be one. Conductivity meters shall be calibrated by
verifying the cell constant or adjusting the meter based on the analysis of a
potassium chloride standard solution.
(c) Inductively coupled plasma emission
spectrophotometers and inductively coupled plasma mass spectrometers, for which
the minimum number shall be one.
(d) pH meters, for which the minimum number
shall be two.
(e) Quadratic
calibration models, for which the minimum shall be five.
(f) Cubic calibration models, for which the
minimum shall be seven.
(3) CONCENTRATION LEVELS OF STANDARDS. The
concentration of the standards chosen to establish a calibration function shall
be within the same orders of magnitude as the expected concentration of
samples.
(4) CALIBRATION MODELS.
The laboratory shall select a calibration model that is appropriate for the
expected behavior of the analytical instrument to be calibrated. To generate a
calibration model, the laboratory shall select a reduction technique or
algorithm that is appropriate for the calibration model and the number of
nonzero standards used, subject to all the following:
(a) The selected algorithm or reduction
technique shall be describable mathematically and shall provide equations,
coefficients, or parameters necessary to characterize the calibration function
uniquely, unless an analytical instrument is tuned to conform to a universally
accepted scientific law or scale.
Note: The response of dissolved oxygen meters
is generally adjusted to conform to the concentration of oxygen allowable in a
given liquid at a specified temperature and pressure. The response of an ion
selective electrode is generally tuned to conform to the Nernst equation. The
response of a pH meter is tuned to conform to the universally accepted pH
scale. When these instruments are adjusted or tuned according to these
principles, characterizing the calibration reduction algorithm mathematically
is not necessary.
(b)
Non-linear functions may not be used to compensate for instrument saturation,
insensitivity, or malfunction.
(c)
The laboratory may use weighted algorithms, unless the weighted algorithms are
chosen to compensate for deviations from the expected behavior of a detector of
an analytical instrument resulting from saturation, insensitivity, or
malfunction.
(d) Except for methods
that allow average response factors and average calibration factors, the
laboratory may not use reiterative reduction techniques or algorithms that
force calibration functions through zero.
Note: Reiterative reduction techniques or
algorithms that force the calibration function through zero obtain
mathematically, by repeated application, a null response for a zero standard
that has a nonzero response or adjust calibration parameters to obtain a
theoretical null response without analysis of a calibration blank. This
paragraph does not prohibit the use of average calibration or response factors
or automatic zeroing as part of an initial calibration, when methods,
regulations, or covered programs allow those techniques.
(5) EXCLUDING
CALIBRATION POINTS. If one or more calibration standards are excluded from the
calibration, all the following criteria shall be met:
(a) The rationale for the exclusion is
documented.
(b) Any required
regulatory limits can still be met.
(c) Except for ICP, ICP/MS, and HRGC/MS, if
the highest calibration standard is removed, the linear range shall be limited
to the remaining high standard concentration.
(6) EVALUATING ALGORITHM VALIDITY. The
laboratory shall establish acceptability criteria for initial calibrations. The
type of criteria chosen, and the acceptance range shall be appropriate for the
type of analytes to be quantitated, the calibration model selected, and
reduction technique or algorithm chosen. Acceptability criteria shall be
established using any of the following:
(a)
When the x-intercept is used to evaluate the calibration, then the value of the
x-intercept of the calibration function for each analyte may not exceed its
LOD.
(b) Unless otherwise specified
by the method, when RSE is used to evaluate the calibration, the relative
standard deviation may not exceed 15% for inorganic analytes or 20% for organic
analytes.
(c) Unless otherwise
specified by the method, when residuals of each calibration standard are used
to evaluate the calibration, the standard recovery for all but the lowest
calibration point shall fall within 90% to 110% for inorganic analytes or
within 70% to 130% for organic analytes. Recovery for the lowest calibration
point shall be within 80% to 120% for inorganic analytes or 50% to 150% for
organic analytes.
(d) When average
response factors are used to reduce calibration data, the relative standard
deviation of the response factors may not exceed 20% unless the method allows a
larger percentage.
(e) When linear
regression or least squares analysis is used to reduce calibration data, the
correlation coefficient (r) of the resultant calibration shall be at least
0.995 for inorganic analytes or 0.99 for organic analytes.
(f) When quadratic
(2nd order) or cubic (3rd
order) analysis is used to reduce calibration data, the coefficient of
determination (r2) of the resultant calibration
shall be at least 0.995 for inorganic analytes or 0.99 for organic
analytes.
(7) VERIFYING
ACCURACY. Except for calibrations generated using dissolved oxygen meters, pH
meters, or conductivity meters, the laboratory shall verify all initial
instrument calibrations after the calibrations are generated, but before the
calibrations are used to quantitate any samples, with a second source standard,
referred to as an ICV standard. ICV standards shall be treated in the same
manner as the standards analyzed for the initial calibration. Unless otherwise
required by method, regulation, or covered program, the acceptance criteria for
the ICV standard shall be all the following:
(a) Obtaining concentrations within 10% of
the theoretical concentrations of all reportable inorganic analytes.
(b) Obtaining concentrations within 20% of
the theoretical concentrations of all reportable organic
analytes.
(8) EVALUATING
SENSITIVITY. When methods require an ICB be analyzed after the initial
calibration, the ICB shall be treated in the same manner as the initial
calibration standards. The concentration of an analyte in an ICB may not exceed
its LOD.
