Chemistry Reference
In-Depth Information
(a)
(b)
0.36
0.8
5
2
0.6
0.24
1
A
A
0.4
1
0.12
3
4
0.2
2
0
0
220
270
320
370
220
270
Wavelength (nm)
320
Wavelength (nm)
Figure 12.3
Effect of the presence of other B-group vitamins on the absorption spectrum of thiamine. (a) In
solution: (1) thiamine, (2) B
2
, (3) B
6
, (4) B
12
, and (5) mixture of thiamine, B
2
, B
6
, and B
12
. (b) On resin:
(1) thiamine and (2) mixture of thiamine, B
2
, B
6
, and B
12
. [Thiamine]
=
1.48 × 10
-5
M; [B
2
]
=
1.33 × 10
-6
M;
[B
6
]
5.90 × 10
−6
M; pH 4.8. The spectra on resin were obtained with 30 mg of resin and
10 mL sample volume. Reprinted from [9]. © 1998 American Chemical Society.
=
2.92 × 10
-5
M; [B
12
]
=
Figure 12.3 successfully illustrates selectivity performance for vitamin B
1
microdetermination by this
procedure: Figure 12.3(a) shows the UV spectra of the B-group vitamins in solution and their mixture; and
Figure 12.3(b) shows the solid phase UV spectra of both thiamine and vitamins B mixture. The excellent
selectivity shown by the UV procedure is self-evident as well as its potential for determining selectively
thiamine in the presence of other vitamins B.
Native fluorescence SPMS procedures show similar features regarding sensitivity and selectivity
compared with the respective conventional methods based on solution measurements. Besides, the inherent
increased selectivity shown by fluorescence compared to spectrophotometry should be noticed. Examples of
fluorescence SPMS are the determination of acetylsalicylic acid and pyridoxine [14]
It should be pointed out that 1 mm quartz cells are used to perform the measurements and the usual
fluorescence signal measured is the diffuse transmitted fluorescence emitted from the solid microbeads with
the retained species, the angle formed between the cell plane and the excitation beam being 45° [15].
12.4
Flow mode procedures
Batch SPMS exhibits very attractive analytical performance. Amongst the main features, one should
highlight the sensitivity increase up to four orders of magnitude higher (than the respective classical
homogeneous solution procedure) and remarkable selectivity. On one hand, in order to exploit sensitivity,
