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Analytical chemistry-61
Analytical Chemistry (CHEM 203)
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- Globally assessing analytical processes (see Slides 3 and 3) by application to a certified reference material (CRM) and statistical comparison of the results for the CRM and the samples.
4.8. These are selected examples of the two types of calibration in the ana- lytical process.
4.1 Preliminary Operations of the Analytical Process
(23 Slides)
4.1.5 General Features (4 Slides)
Slide 4.
4.1. Preliminary operations (I)
Chapter 4: Generalities of the analytical process
y p ( )
anal tical
4.1.5. GENERAL FEATURES (A) First step of the analytical process Sub-step separating the uncollected, unmeasured, untreated sample from measurement of its signal (second step) Purposes (1) Facilitating the analytical process (2) Improving analytical properties Features (negative)
(B) COMPLEXITY (C) HEAVY HUMAN
“Bottleneck” (C) HEAVY HUMAN INVOLVEMENT of CMP (D) SLOWNESS (E) SOURCE OF ERRORS Systematic (F) DIFFICULT TO CONTROL (G) SOURCE OF HAZARDS TO OPERATOR AND THE ENVIRONMENT
Accidental
(A) VARIABILITY
4.9. Slides 4–4 are concerned with the preliminary operations of the analytical process. The first four (4–4) explain its general features, the next eleven (4–4) sample collection and the last eight (4–4) sample treat- ment (with special emphasis on separation systems). This slide defines “preliminary operations”, which comprise sample collection and preparation (see Slide 4). Also, its describes their general purposes (namely, facilitating the analytical process and improving analytical properties) and their seven most salient features, which are as follows:
4 Explanation of the Slides 167
(A) Variability in the operations, which is a major hindrance. In fact, virtually each sample–analyte pair requires its own specific operation (see Slide 4), which precludes designing all-purpose equipment for this purpose. (B) Preliminary operations are operationally complex as they typically involve transferring liquids, filtering, using analytical separation systems, measuring volumes, weighing, etc. (C) As a result, they are labour-intensive and difficult to automate. (D) Some operations (e., passing an eluent through a solid-phase extraction col- umn, dissolving soil) are especially sluggish and take up 60–80% of the overall time spent in conducting an analytical process. This has made “direct methods of analysis” a priority goal to by-pass preliminary operations in the analytical process. (E) One of the most negative features of preliminary operations is that they are the source of systematic and accidental errors. The former can arise from volume measurements with a poorly calibrated pipette, using inappropriate sampling equipment or not adhering to the recommended timing, for example. On the other hand, the latter are typically the result of human mistakes (e., distrac- tion, poor readings, failing to distinguish colours). Properly performing pre- liminary operations is therefore very important because any errors made will propagate through the analytical process and have an adverse impact on the quality of the results. (F) Preliminary operations are difficult to control because monitoring every single sub-step is nearly impossible. Calibrating apparatuses (e., extractors, stoves, centrifuges, thermometers) rarely suffices for this purpose. In fact, the best way to check that an analytical process is operating as expected is by assessing it— preliminary operations included—with a certified reference material (CRM). If the certified value and the result of the process are consistent, then the process can be validated and its preliminary operations assumed to be under control. (G) Preliminary operations are the source of hazards for operators and the envi- ronment since they often use pressurized gas cylinders, toxic reagents and solvents, and high pressures and/or temperatures. Also, toxic waste from the operations can obviously affect analysts and the environment. So-called “green methods” are intended to minimize personal and environmental risks.
4.9. Based on the foregoing, the preliminary operations of the analytical process possess negative connotations although they are indispensable with a view to assuring integral quality in the analytical results.
168 4 Generalities of the Analytical Process
Analytical chemistry-61
Course: Analytical Chemistry (CHEM 203)
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