Chemistry Reference
In-Depth Information
Dilution
Chromophore
UV/ V is Spectrophotometer
Sample + IS
Sample + IS + Chromophore
Separation/Preconcentration
Signal readout
S=S
Analyte
/S
IS
Figure 3.9
General scheme of UV/V is spectrophotometric procedure with the application of IS.
Table 3.2
Comparison of the characteristics of classical batch procedure versus micro-scale procedure for
extractive-spectrophotometric determination of bismuth.
Procedure
Phase
Final volume
Detection Limit
%
Extraction
Batch Procedure
Aqueous Phase: sample
+
25 ml
H
2
SO
4
+
5
%
KI
+
5
%
ascorbic
acid
+
1
%
BTAB
Organic Phase: chloroform
10 ml
0.5
μ
g ml
−
1
99.5
±
0.6
%
Micro-scale
Procedure
Aqueous Phase: sample
+
800
μ
l
H
2
SO
4
+
5
%
KI
+
5
%
ascorbic
acid
+
1
%
BTAB
+
IS
Organic Phase: chloroform
400
μ
l (chloroform only)
0.6
μ
g ml
−
1
99.8
±
0.5
%
should match closely the physicochemical characteristics of analyte(s) which would assure similar
behavior of these species during sample preparation and signal registration. The general scheme of
microscale UV/Vis spectrophotometric procedure with the application of IS method is shown schematically
in Figure 3.9 [28].
Green laboratory proposal
[29]
In the pharmaceutical industry quantification of the active compound is an
issue. For example, different batch spectrophotometric procedures are available for pharmaceuticals
containing bismuth compounds. Among them, the procedure based on the formation of tetraiodobismuthate
(III) in aqueous sulfuric acid medium, ion-pair formation with benzyltributylammonium cation (BTAB) and
extraction to chloroform has been selected and downscaled. Nile blue was selected as the IS. The spectral
bands of bismuth complex (
623 nm) did not present any overlapping, so the
analytical signal was measured from zero-order spectra (S
λ
max
=
491 nm) and IS (
λ
max
=
A
491nm
/A
623nm
). Another important selection
criterion was similar extraction yield of analyte and IS to chloroform. The effect of reagents and ion-pairing
agent concentrations on the IS and bismuth signal was systematically studied, which enable extraction yields
99.5 ± 0.6
=
respectively for the two species. In Table 3.2, the experimental parameters and
some analytical figures of merit evaluated for classical batch procedure and micro-assay by the present
method are compared.
%
and 99.8 ± 0.5
%
Comments
According to green chemistry principles, the micro procedure offers reduced consumption of
reagents and consequently lower waste generation. One special feature of the method is that there is no need
