CHMB16 Chapter 1

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27 Sep 2011

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Chapter 0: The Analytical Process
The Analytical Chemist’s Job
Sampling: procuring a representative sample to measure.
Homogeneous: composition of the sample is the same everywhere (milk
Heterogeneous: composition differs from place to place (milk chocolate with
Decanted: poured off and discarded.
Analytes: substances being measured; stuff you are interested in (caffeine in
Quantitative Transfer: a complete transfer from one container to another.
Slurry: a suspension of solid in a liquid.
Aqueous: a solution of anything in water.
Supernatant Liquid: liquid above the packed solid.
Sample Preparation: transforming a sample into a state that is suitable for
analysis (fat to be removed from the chocolate, analytes to be extracted into
water and residual solid to be separated from the water).
Qualitative Analysis: identifying what is in an unknown.
Quantitative Analysis: identifying how much is present.
Calibration/Standard Curve: graph of detector response as function of analyte
Standard Solutions: these need to be prepared and injected into the column
and the resulting peak heights were measured to construct the
calibration/standard curve.
Standard Deviation: measure of the reproducibility of the results (high SD, not
General Steps in a Chemical Analysis
Forming the Question: translate general questions into specific questions to
be answered through chemical measurements.
Selecting Analytical Procedures: search chemical literatures to find
appropriate procedures or devise new procedures to make the required
Sampling: the process of selecting representative material to analyze.
Sample Preparation: the process of converting a representative sample into a
form suitable for chemical analysis, usually dissolving the sample.
Analysis: measure the concentration of analyte in several identical
oReplicate Measurements: repeated measurements to assess the
variability/uncertainty in the analysis and to guard against a gross
error in the analysis of a single aliquot.
oThe uncertainty of a measurement is as important as the
measurement itself.
oIf necessary, use different analytical methods on similar samples to
make sure that all methods give same result and that the analytical
method is not biasing the result.
Reporting and Interpretation: deliver a clearly written, complete report of your
results, highlighting any limitations that you attach to them; report for the
intended audience (specialist, professor or for a general audience).
Drawing Conclusions: the more clearly a report is written, the less likely it is to
be misinterpreted by those who use it.
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