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CHE 3704 ANALYTICAL CHEMISTRY TUTORIAL LETTER 203
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- University Of South Africa (Unisa)
This document contains the answers to assignment 3 for CHE
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CHE3704/203/3/2021Tutorial Letter 203/3/2021
Analytical Chemistry III (Theory)
CHE3704
Semesters 1 & 2
Department of Chemistry
IMPORTANT INFORMATION
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website, CHE3704-2021-S1/S2, as well as your group website
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, ASSIGNMENT 03 SOLUTIONS
Question 1 Solutions
(a) Definitions of some chromatographic terms:
(i) Elution is defined as the process in which analytes are separated from one another on a column
owing to differences in the time that they are retained in the column. (It is also defined as a
process in which analyte species are washed through a chromatographic column by additions of
fresh mobile phase.)
(ii) Stationary phase is defined as a solid or an immobilized liquid on which analyte species are
partitioned during passage of a mobile phase.
(iii)Retention time is defined as the time between sample injection on a chromatographic column
and the arrival of an analyte peak at the detector.
(iv) Selectivity factor is defined as a term in chromatography that shows the relationship between
distribution constants for less and more strongly retained species. It is denoted by α and
mathematically expressed as α = = KB/KA, where KB is the distribution constant for a less
strongly retained species and KA is the distribution constant for a more strongly retained
species.
(v) Plate height is defined as a quantity (denoted by H) used to describe the efficiency of a
chromatographic column, and it is mathematically expressed as H = σ2/L, where σ2 is the
variance obtained from the Gaussian shaped chromatographic peak and L is the length of the
column packing in cm (centimetres).
(vi) Resolution is defined as the term in chromatography that measures the capacity of a column to
separate two analyte bands.
(vii) Retention factor is defined as a term in chromatography used to describe the migration of a
species through a chromatographic column, and its numerical value k is given by k = (tR – tM)/tM,
where tR is the retention time for a peak and tM is the dead time.
(viii) Dead time is defined as the time required for an unretained species to traverse the
chromatographic column. It is also called void time and denoted by tM.
(ix) Mobile phase is defined as a phase in chromatography that moves over or through an
immobilized phase (stationary phase) that is fixed in place in a column or on the surface of a flat
plate, and it is either liquid or gas.
(x) Distribution constant is defined as the equilibrium constant for the distribution of an analyte
between two immiscible solvents, and it is approximately equal to the ratio of the equilibrium
molar concentrations in the two solvents. Hence, it is simply defined as an equilibrium constant
for the distribution of a species between two phases.
2
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