Definitions of Basic Terms in Analytical
Chemistry
Interference: An effect which alters or obscures the
behavior of an analyte in an analytical procedure (Sources
contaminants, reagents, instrumentation used for the
measurements)
Standards: Materials containing a known concentration
of a substance. They provide a reference to determine
unknown concentrations or to calibrate analytical
instruments.
Primary Standard: A substance whose purity and
stability are particularly well-established and with which
other standards may be compared. It is a pure substance
which reacts in a quantitative and known stoichiometric
manner with the analyte or a reagent.
Primary standard is a reagent that is extremely pure,
stable, has no waters of hydration, and has a high
molecular weight.
Criteria:
1. High Purity (testable easily)
2. High Stability in condition it is stored
(nonhygroscopic, non-volatile, not deliquescent,
unreactive towards atmosphere)
3. Larger molecular/equivalent weight (to decrease
relative error in weighing)
4. Cost-effectiveness
Certified reference material (CRM): A material that is
verified to contain a known amount of analyte(s) or to
have known physical properties. Usually available from
commercial suppliers. Also referred to simply as reference
material (RM) 4 See http://nist.gov/srm/definitions.cfm
for more details.
Standardization: Determination of the concentration of
an analyte or reagent solution from its reaction with a
standard or primary standard.
Procedure: A description of the practical steps involved in
an analysis.
Method: The overall description of the instructions for a
particular analysis.
Technique: The principle upon which a group of methods
is based (AAS, XPS etc.)
Speciation analysis: The determination of the specific
forms of an analyte. Common examples are elemental
mercury versus organomercury and different oxidation
states such as Cr(III) versus Cr(VI).
Method development. Determining the experimental
conditions for sample collection, preparation, and
measurement that produce accurate and repeatable
results.
Validation of Method:
- to validate the method by analyzing standards
which have an accepted analyte content, and a matrix
similar to that of the sample.
- Performing control experiments to verify the
accuracy, sensitivity, specificity, and reproducibility of test
methods.
Signal: The detector output that is displayed or recorded.
Noise: Random fluctuations in the signal. Usually
quantified using the standard deviation of multiple
measurements of a blank.
Selectivity: The ability of a method or instrument to
measure an analyte in the presence of other constituents of
the sample or test portion. (Pure & Appl. Chem. 2001, 73(8),
1381-1386.]
Sensitivity: The change in the response from an analyte
relative to a small variation in the amount being
determined. The sensitivity is equal to the slope of the
calibration curve (the change in detector signal versus the
change in amount of analyte), being constant if the curve is
linear. In other words, it is the ability of a method to
facilitate the detection or determination of an analyte. A
higher sensitivity may allow measurement of a lower
analyte concentration, depending on the signal to-noise
ratio.
Determination: A quantitative measure of an analyte
with an accuracy of considerably better than 10% of the
amount present.
Estimation: A semi-quantitative measure of the amount
of an analyte present in a sample, with accuracy no better
about 10% of the amount present.
Detection Limit: The smallest amount or concentration of
an analyte that can be detected by a given procedure and
with a given degree of confidence. It is the minimum
measured concentration at which an analyte may be
reported as being detected in the test portion or sample.
Limit of linearity (LOL): The concentration at which the
signal deviates from linearity.
Limit of quantitation (LQ): An analytical value, X above ₁
which quantitative determinations are possible with a
given minimum precision.
