4.3 Preliminary Operations
153
rise to gross errors - much greater than those typically made in the other steps
of the CMP. Such errors arise both from the technical complexity of the operations and from the so-called "human factor". This potentially adverse implication of preliminary operations is the origin of their significance.
Systematic control of preliminary operations is not as affordable or convenient as is that of an instrument (in the second step of the CMP) through calibration. Checks during preliminary operations involve the painstaking testing of
all apparatus and instruments used (e.g. with mass or volume measurements),
and also confirming that they operate as scheduled. There are three ways of assuring quality in preliminary operations, namely:
(a) By systematic application of quality assurance systems in the analytical
laboratory concerned, in the form of internal or external assessment (described in detail in Chap. 8).
(b) By global evaluation of the CMP, using samples of known composition (e. g.
blind samples, certified reference materials) and matrices similar to those of
the real samples. If the differences between the results and the known or
certified values for the samples are not statistically significant, then the CMP
will have been properly carried out and the preliminary operations correctly
conducted.
(c) By using a combination of the previous two approaches, which is bound to
provide greater assurance of quality in the operations.
The preliminary operations carried out in the first step of a CMP are a
potential source of human and environmental hazards. Thus, the use of analytical tools such as acids, solvents, pressurized gases, digesters, distillers, etc., can
have adverse hygienic and health effects on laboratory personnel in the short to
long run. For example, the specific preliminary operations involved in some
CMPs produce variable amounts of toxic waste that requires careful handling and
disposal.
For all these reasons, preliminary operations playa crucial role in CMPs. As
such, they warrant special attention on the part of both laboratory personnel and
quality control and assessment officials. As can be seen from Fig. 4.8, these
operations have a strong impact on the three types of analytical properties
(capital, basic and accessory) and thus call for dedicated research and development work. Thus, preliminary operations exert a direct influence on accuracy
(through systematic errors), representativeness (through sampling errors),
precision (through random errors) and accessory analytical properties (expeditiousness, cost-effectiveness and personnel-related factors). Also, they have
indirect effects on selectivity (through interference removal) and sensitivity
(through preconcentration), as well as on accuracy as a whole (through their
individual effects on precision, sensitivity and selectivity).
153
rise to gross errors - much greater than those typically made in the other steps
of the CMP. Such errors arise both from the technical complexity of the operations and from the so-called "human factor". This potentially adverse implication of preliminary operations is the origin of their significance.
Systematic control of preliminary operations is not as affordable or convenient as is that of an instrument (in the second step of the CMP) through calibration. Checks during preliminary operations involve the painstaking testing of
all apparatus and instruments used (e.g. with mass or volume measurements),
and also confirming that they operate as scheduled. There are three ways of assuring quality in preliminary operations, namely:
(a) By systematic application of quality assurance systems in the analytical
laboratory concerned, in the form of internal or external assessment (described in detail in Chap. 8).
(b) By global evaluation of the CMP, using samples of known composition (e. g.
blind samples, certified reference materials) and matrices similar to those of
the real samples. If the differences between the results and the known or
certified values for the samples are not statistically significant, then the CMP
will have been properly carried out and the preliminary operations correctly
conducted.
(c) By using a combination of the previous two approaches, which is bound to
provide greater assurance of quality in the operations.
The preliminary operations carried out in the first step of a CMP are a
potential source of human and environmental hazards. Thus, the use of analytical tools such as acids, solvents, pressurized gases, digesters, distillers, etc., can
have adverse hygienic and health effects on laboratory personnel in the short to
long run. For example, the specific preliminary operations involved in some
CMPs produce variable amounts of toxic waste that requires careful handling and
disposal.
For all these reasons, preliminary operations playa crucial role in CMPs. As
such, they warrant special attention on the part of both laboratory personnel and
quality control and assessment officials. As can be seen from Fig. 4.8, these
operations have a strong impact on the three types of analytical properties
(capital, basic and accessory) and thus call for dedicated research and development work. Thus, preliminary operations exert a direct influence on accuracy
(through systematic errors), representativeness (through sampling errors),
precision (through random errors) and accessory analytical properties (expeditiousness, cost-effectiveness and personnel-related factors). Also, they have
indirect effects on selectivity (through interference removal) and sensitivity
(through preconcentration), as well as on accuracy as a whole (through their
individual effects on precision, sensitivity and selectivity).