4.3 Preliminary Operations
149
the use of standards for equipment and method calibration in CMPs; thus, it
describes the use of the different types of standards in CMPs based on primary
(absolute and stoichiometric) and relative methods for qualitative and quantitative purposes.
Equipment (apparatus and instrument) calibration encompasses the three
steps of a CMP. As shown in Fig. 4.5 (AI), apparatus (e.g. stoves, reactors, extractors) must be checked to operate as scheduled by calibrating parameters
related to physical quantities (e.g. temperature, pressure). When an instrument
(e.g. a chromatograph) integrates some preliminary operation, the apparatus or
devices involved must also be calibrated (Fig. 4.5,A2). The dramatic advances in
computer science in recent years have promoted the use of a variety of electronic interfaces to instruments and apparatus that must also be subjected to
calibration (Fig. 4.5, A 3). Equipment calibration proper affects the second step of
the analytical process, both in absolute (e.g. the balance in gravimetries),
stoichiometric (e.g. the burette in titrimetries) and relative methods (e.g.
photometers, tluorimeters, polarographs, mass spectrometers); also, it assures
proper performance of the instruments and apparatus used (Fig. 4.5, 11). As
stated above, any instruments used in the first step of the analytical process (e. g.
balances, pipettes) must be calibrated as well (Fig. 4.5, 12).
Method calibration (MC) pertains essentially to the second step of the CMP
(see Fig. 4.5, MCI) in relative methods based on an unequivocal relationship
between the concentration (or some other property) of the analyte and the
analytical signal it produces. In titrimetries, one must additionally consider
standardizing the titrant (see Box 3.7), which corresponds to link MC2 in Fig. 4.5.
4.3 Preliminary Operations
The generic term "preliminary operations" is used to designate a wide variety of
actions that connect uncollected, unmeasured, untreated samples to the main
measuring instrument in the second step of a CMP.
The first step of a CMP makes the strongest difference from physical measurements, where it rarely exists. Because of the special technical features of preliminary operations - particularly their difficulty -, the first step of a CMP is
especially relevant as it has major implications on the quality (accuracy and
representativeness) of the results and a strong impact on accessory properties
( expeditiousness, cost-effectiveness and personnel-related factors) .
Spectacular breakthroughs in equipment technology and computers have
dramatically raised quality in the last two steps of the CMP. By contrast, on the
edge of the XXI century, the first step continues to demand generous R&D
endeavours despite the brilliant - though still insufficient - advances in this field
in recent years.
The first step of a CMP can involve the use of materials, methods and approaches of widely varied nature (see Fig. 1.2) depending on the factors shown
in Fig. 4.3.
149
the use of standards for equipment and method calibration in CMPs; thus, it
describes the use of the different types of standards in CMPs based on primary
(absolute and stoichiometric) and relative methods for qualitative and quantitative purposes.
Equipment (apparatus and instrument) calibration encompasses the three
steps of a CMP. As shown in Fig. 4.5 (AI), apparatus (e.g. stoves, reactors, extractors) must be checked to operate as scheduled by calibrating parameters
related to physical quantities (e.g. temperature, pressure). When an instrument
(e.g. a chromatograph) integrates some preliminary operation, the apparatus or
devices involved must also be calibrated (Fig. 4.5,A2). The dramatic advances in
computer science in recent years have promoted the use of a variety of electronic interfaces to instruments and apparatus that must also be subjected to
calibration (Fig. 4.5, A 3). Equipment calibration proper affects the second step of
the analytical process, both in absolute (e.g. the balance in gravimetries),
stoichiometric (e.g. the burette in titrimetries) and relative methods (e.g.
photometers, tluorimeters, polarographs, mass spectrometers); also, it assures
proper performance of the instruments and apparatus used (Fig. 4.5, 11). As
stated above, any instruments used in the first step of the analytical process (e. g.
balances, pipettes) must be calibrated as well (Fig. 4.5, 12).
Method calibration (MC) pertains essentially to the second step of the CMP
(see Fig. 4.5, MCI) in relative methods based on an unequivocal relationship
between the concentration (or some other property) of the analyte and the
analytical signal it produces. In titrimetries, one must additionally consider
standardizing the titrant (see Box 3.7), which corresponds to link MC2 in Fig. 4.5.
4.3 Preliminary Operations
The generic term "preliminary operations" is used to designate a wide variety of
actions that connect uncollected, unmeasured, untreated samples to the main
measuring instrument in the second step of a CMP.
The first step of a CMP makes the strongest difference from physical measurements, where it rarely exists. Because of the special technical features of preliminary operations - particularly their difficulty -, the first step of a CMP is
especially relevant as it has major implications on the quality (accuracy and
representativeness) of the results and a strong impact on accessory properties
( expeditiousness, cost-effectiveness and personnel-related factors) .
Spectacular breakthroughs in equipment technology and computers have
dramatically raised quality in the last two steps of the CMP. By contrast, on the
edge of the XXI century, the first step continues to demand generous R&D
endeavours despite the brilliant - though still insufficient - advances in this field
in recent years.
The first step of a CMP can involve the use of materials, methods and approaches of widely varied nature (see Fig. 1.2) depending on the factors shown
in Fig. 4.3.