|ACCURACY: The closeness of agreement between an
observed value and an accepted reference value.
BATCH: A group of samples which behave similarly with
respect to the sampling or the testing procedures being employed
and which are processed as a unit. For QC purposes, if the
number of samples in a group is greater than 20, then each group
of 20 samples or less will all be handled as a separate batch.
CONTINUING CALIBRATION BLANK: A blank which is
analyzed at the beginning of each analytical batch to verify
that the instrument baseline is zero and that the instrument is
free of contamination. This is used primarily for metals and wet
CONTINUING CALIBRATION STANDARD: A mid-level standard
which is analyzed with each analytical batch to verify the
EQUIPMENT RINSATE or EQUIPMENT BLANK: A sample of
analyte-free media which has been used to rinse the sampling
equipment. It is collected after completion of decontamination
and prior to sampling. This blank is useful in documenting
adequate decontamination of sampling equipment.
ESTIMATED QUANTITATION LIMIT (EQL): The lowest
concentration that can be reliably achieved within specified
limits of precision and accuracy during routine laboratory
operating conditions. The EQL is generally 5 to 10 times the MDL.
However, it may be nominally chosen within these guidelines to
simplify data reporting. For many analytes the EQL analyte
concentration is selected as the lowest non-zero standard in the
calibration curve. Sample EQLs are highly matrix-dependent. The
EQLs in SW-846 are provided for guidance and may not always be
FIELD DUPLICATES: Independent samples which are
collected as close as possible to the same point in space and
time. They are two separate samples taken from the same source,
stored in separate containers, and analyzed independently. These
duplicates are useful in documenting the precision of the
INTERFERENCE CHECK STANDARD: A standard that contains
interfering elements at high concentrations and other
non-interfering elements at trace concentrations to prove that
the background correction intervals and inter-element correction
factors have been set properly. Used in ICP metals analysis
INTERNAL STANDARD: A spike added to each organic
analysis that is used in analyte quantitation. The internal
standard is also used to verify instrument response and
retention time stability.
LABORATORY CONTROL SPIKE: A known matrix spiked with
compound(s) representative of the target analytes. This is used
to show that sample preparation procedures do not contribute to
loss of analytes.
MATRIX: The component or substrate (e.g., surface
water, drinking water) which contains the analyte of interest.
MATRIX DUPLICATE: An intralaboratory split sample
which is used to document the precision of a method in a given
MATRIX SPIKE: An aliquot of sample spiked with a known
concentration of target analyte(s). The spiking occurs prior to
sample preparation and analysis. A matrix spike is used to
document the bias of a method in a given sample matrix.
MATRIX SPIKE DUPLICATES: Intralaboratory split samples
spiked with identical concentrations of target analyte(s). The
spiking occurs prior to sample preparation and analysis. They
are used to document the precision and bias of a method in a
given sample matrix.
METHOD BLANK: An analyte-free matrix to which all
reagents are added in the same volumes or proportions as used in
sample processing. The method blank should be carried through
the complete sample preparation and analytical procedure. The
method blank is used to document contamination resulting from
the analytical process.
METHOD DETECTION LIMIT (MDL): The minimum
concentration of a substance that can be measured and reported
with 99% confidence that the analyte concentration is greater
than zero and is determined from analysis of a sample in a given
matrix containing the analyte.
ORGANIC-FREE REAGENT WATER: For volatiles, all
references to water in the methods refer to water in which an
interferant is not observed at the method detection limit of the
compounds of interest. Organic-free reagent water can be
generated by passing tap water through a carbon filter bed
containing about 1 pound of activated carbon. A water
purification system may be used to generate organic-free
deionized water. Organic-free reagent water may also be prepared
by boiling water for 15 minutes and, subsequently, while
maintaining the temperature at 90?C, bubbling a contaminant-free
inert gas through the water for 1 hour.
For semivolatiles and nonvolatiles, all references to water
in the methods refer to water in which an interferant is not
observed at the method detection limit of the compounds of
interest. Organic-free reagent water can be generated by passing
tap water through a carbon filter bed containing about 1 pound
of activated carbon. A water purification system may be used to
generate organic-free deionized water.
PERFORMANCE EVALUATION SAMPLES: Spiked samples
containing an unknown identity and amount of target analyte(s).
They may be prepared internally or provided by an outside
PRECISION: The agreement among a set of replicate
measurements without assumption of knowledge of the true value.
Precision is estimated by means of duplicate/replicate analyses.
These samples should contain concentrations of analyte above the
MDL, and may involve the use of matrix spikes. The most commonly
used estimates of precision are the relative standard deviation
(RSD) or the coefficient of variation (CV).
REAGENT GRADE: Analytical reagent (AR) grade, ACS
reagent grade, and reagent grade are synonymous terms for
reagents which conform to the current specifications of the
Committee on Analytical Reagents of the American Chemical
REAGENT WATER: Water that has been generated by any
method which would achieve the performance specifications for
ASTM Type II water. For organic analyses, see the definition of
organic-free reagent water.
REFERENCE MATERIAL: A material containing known
quantities of target analytes in solution or in a homogeneous
matrix. It is used to document the bias of the analytical
SPLIT SAMPLES: Aliquots of sample taken from the same
container and analyzed independently. In cases where aliquots of
samples are impossible to obtain, field duplicate samples should
be taken for the matrix duplicate analysis. These are usually
taken after mixing or compositing and are used to document
intra- or inter-laboratory precision.
STANDARD ADDITION: The practice of adding a known
amount of an analyte to a sample immediately prior to analysis.
It is typically used to evaluate interferences.
STANDARD CURVE: A plot of concentrations of known
analyte standards versus the instrument response to the analyte.
Calibration standards are prepared by successively diluting a
standard solution to produce working standards that cover the
working range of the instrument. Standards should be prepared at
the frequency specified in the appropriate section. The
calibration standards should be prepared using the same type of
acid or solvent and at the same concentration as will result in
the samples following sample preparation. This is applicable to
organic and inorganic chemical analyses.
SURROGATE (or SYSTEM MONITORING COMPOUND): An organic
compound which is similar to the target analyte(s) in chemical
composition and behavior in the analytical process, but which is
not normally found in environmental samples.
TRIP BLANK: A sample of analyte-free media taken from
the laboratory to the sampling site and returned to the
laboratory unopened. A trip blank is used to document
contamination attributable to shipping and field handling
procedures. This type of blank is useful in documenting
contamination of volatile organics samples.