The coloured reaction studied showed high stability after 60 minutes of the mixtures preparation as demonstrated by the standard curves prepared at different reaction times (Figure 1).
 |
|
Figure 1. Stability of the coloured reaction
|
The sequence of reagents introduction in the reaction mixture was determinant to the assay. The molibdenum-stannous-tiocianate sequence produces calibration curves with good correlations (R2 > 0.99). When using the molibdenium-tiocianate-stannous sequence, however, the same was not observed (Figure 2), probably because the tiocianate also forms a complex with the molibdenum that inhibits the formation of the Mo-Sn complex.
 |
|
Figure 2. Influence of the introduction of the reagents in the reaction mixture
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The concentrations of the molibdenum solution was also investigated, in order to determine a ideal concentration for the Sn+2 range studied (no limitant) (Figure 3).
 |
|
Figure 3. The influence of the concentration of molibdenum solution
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The kit constituints had no influence in the assay reaction (Figure 4). The introduction of an equal volum of the kit preparation in each reaction mixture in the preparation of the standard curve only increased the absorbances values proportionally to the increase of Sn+2 mass.
 |
|
Figure 4. Influence of the kit constituints in the reaction
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The spectrophotometric method studied was applied to the stannous determination in 6 batches of citrate-stannous reagents. Batches from number 1 to 4 were lyophilized and batches 5 and 6 were prepared and stored at –40o C (Table 1).
Table 1.
Spectrophotometric determination of SnCl2.2H2O in citrate-stannous reagent
|
Batche
|
Theoretical SnCl2.2H2O in assayed samples (ppm)
|
Determined SnCl2.H2O in assayed samples (ppm)
(N = 10)
|
|
1
|
3.8
|
3.44 ± 1.,10
|
|
2
|
3.8
|
3.44 ± 1.01
|
|
3
|
3.8
|
3.85 ± 0.68
|
|
4
|
7.6
|
7.16 ± 0.70
|
|
5
|
3.8
|
4.32 ± 0.72
|
|
6
|
15.2
|
12.76 ± 3.54
|
The efficiency of the spectrophotometric method in the stannous determination of citrate-stannous reagent was confirmed by atomic absorption spectrophotometry (Figure 5 and Table 2).
 |
|
Figure 5 - Standard curve representative of the atomic absorption spectrophotometric assay
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Table 2.
Atomic absorption spectrophotometric determination of SnCl2.2H2O in citrate-stannous reagent
|
Batche
|
Theoretical SnCl2.2H2O in assayed samples (ppm)
|
Determined SnCl2.H2O in assayed samples (ppm)
(N = 2)
|
|
1
|
4.99
|
4.58 ± 1.79
|
|
2
|
4.99
|
4.88 ± 0.06
|
|
3
|
4.99
|
4.29 ± 0.61
|
|
4
|
9.99
|
9.04 ± 0.01
|
|
5
|
4.99
|
3.89 ± 0.86
|
|
6
|
19.98
|
22.01 ± 0.51
|
