About the Official Methods
of Analysis
of AOAC INTERNATIONAL
Electronic publishing arrived just in
time to save the Official
Methods of Analysis of AOAC
INTERNATIONAL from its own success. Each of the two volumes
of the 17th Edition has grown to an almost unmanageable size. Now, online
capability captures the results of 120 years of review and approval of
collaboratively studied methods. The old methods are still there, but
their use is probably confined to teaching “agricultural chemistry.”
The properties of methods do not deteriorate with age and the “classical”
analytes still need to be determined. But the change in emphasis with
the regulatory winds is obvious: Microbiology and nutrition have blossomed
as regulatory emphasis has shifted from economics to safety and health.
New drug and food additive approval, based on preclearance of manufacturing
operations and continuous quality control as well as safety and efficacy,
have reduced the need for regulatory control through market sampling and
analysis.
Most notable has been the shift from classical
stoichiometric chemistry, based on the balance and buret, to calibration
chemistry, based on an instrumental comparison of a response of an analyte
with that of a standard. This shift was initiated by the remarkable separation
powers of chromatography allowing an analyte to be separated from interfering
components before being measured by the instrument. Chromatography moved
analytical chemistry from the realm of gram quantities into microgram
quantities but not without unrecognized sampling problems. The sensitivity,
stability, and speed of modern electronics permit the performance of analytical
work automatically, from the measurement of the test portion, through
detection, amplification, and interpretation of the signal, to the printing
of the analytical report.
The analytical problem has shifted from
measurement to control. Much of the analytical operation has moved from
an operator to a black box in a computer. Changes in physical properties,
such as light intensities or ion conductances, are measured automatically
and converted into analytical reports continuously, changing the laboratory
into an automated factory. But the facility for automated performance
allows the responsibility for reliability to easily shift from the analyst
to the instrument. This is also true of the blind application of computer
programs with no review of the applicability of the program to the problem.
The computer has the ability not only to extract hidden information from
a jungle of background, but also to formulate spurious peaks that it has
been programmed to guess ought to be there.
AOAC initiated the procedure of validation
of methods through interlaboratory studies. These studies produce results
from a single sample of method performance in the hands of an assumed
random sample of laboratories. Unfortunately, time and expense rarely
permit performing additional studies. Therefore, the initial studies usually
stand as the sole published evidence of satisfactory interlaboratory performance.
AOAC members are investigating surrogates for this necessary, but lengthy
and costly procedure.
The latest methods are predominantly microbiological or chromatographic
in nature, all of them subjected to the rigors of an interlaboratory study.
Many of these methods incorporate internal controls to ensure that the
reactions are proceeding as intended. Most appealing is the introduction
of system suitability specifications into chromatographic systems that
permit flexibility without sacrificing reliability. For over a century,
the guiding principle in the application of standard methods has been
to follow instructions to the letter to obtain results equivalent to those
originally obtained. But the competition for improvements in systems advanced
the science of separation and detection so rapidly that suitability specifications
for introducing flexibility without sacrificing performance had to be
invented.
Internal controls require that the methods
meet repeatability performance specifications. An appreciable fraction
of the new microbiological methods are screening tests involving preassembled
immunoassays kits. Relatively quickly, these kits separate laboratory
samples that can be discarded as negative from those that presumably contain
pathogenic organisms, requiring the application of confirmatory tests.
These kits also invariably contain the requirement for accompanying positive
and negative controls that provide concurrent assurance of proper performance.
An important feature of the Official
Methods of Analysis is the international source of many
of the methods, with many countries and international organizations contributing
their expertise to method standardization. It is also gratifying to see
the introduction of quality control features into the methods, which provide
the analyst with guides to proper performance. On the other hand, the
ease with which results are obtained from computers also permits the introduction
of unanticipated errors, detected only by the unreasonableness of the
results. In the absence of a blueprint of what is to be expected, gross
errors may be made. The introduction of quality assurance principles into
the laboratory may assist in minimizing such occurrences.
Numerous individuals, volunteer scientists,
and professional staff have contributed enthusiastically to this century-old
program of method validation. The analytical community is grateful for
their continued valuable efforts.
—William Horwitz, Editor |
