To further remove the fat in the aqueous phase, we added different volumes of n-hexane to the aqueous phase extract of the standard sample and performed multiple extractions.
- Extract with 5ml n-hexane
Se-cyst
c = 19.421 µg/L
+/- 1.495 µg/L (7.70%)
-200n
-150n
-100n
-50.0n
-1.9e-005
0
-2.00e-5 0
2.00e-5
c (g/L)
4.00e-5
Add 5ml of n-hexane to the aqueous extract, shake for 5 minutes and let stand, wait for the layers to separate. Separate the n-hexane phase, collect the aqueous extract. Take 10ml of the aqueous extract and measure the DPCSV according to the optimal conditions given in Table 3.14. Proceed similarly and increase the number of extractions, the results are shown in Figures 3.56 to 3.64.
Se-cyst
c = 20.513 µg/L
+/- 0.246 µg/L (1.20%)
-150n
-100n
-50.0n
-2.1e-005
0
-2.00e-5
0
2.00e-5
c (g/L)
4.00e-5
I (A)
I (A)
Figure 3.56: DPCSV curve and standard addition graph to determine the form of selenium in the aqueous phase after removing fat with 5ml of n-hexane (1 time)
Figure 3.57: DPCSV curve and standard addition graph to determine the form of selenium in the aqueous phase after removing fat with 5ml of n-hexane (2 times)
Se-cyst
c = 20.486 µg/L
+/- 0.428 µg/L (2.09%)
-200n
-150n
-100n
-50.0n
-2e-005
0
-2.00e-5
0
2.00e-5
c (g/L)
4.00e-5
I (A)
Figure 3.58: DPCSV curve and standard addition graph to determine the form of selenium in the aqueous phase after removing fat with 5ml of n-hexane (3 times)
The research results showed that after 3 extractions with n-hexane, the concentration
Se-cyst
c = 20.212 µg/L
+/- 1.342 µg/L (6.64%)
Se(IV)
c = 0.126 µg/L
+/- 0.006 µg/L (4.75%)
-50.0n
-150n
-40.0n
-100n
-30.0n
-20.0n
-50.0n
-10.0n
-2e-005 -1.3e-007
0 0
-2.00e-5 0 2.00e-5 4.00e-5 -2.50e-7 0 2.50e-7 5.00e-7 7.50e-7 1.00e-6
c (g/L) c (g/L)
The Se-Cyst changed insignificantly, while the peak of Se(IV) was still not detected.
I ( A )
I ( A )
Figure 3.59: DPCSV curve and standard addition graph to determine the selenium form in the aqueous phase after defatting with 5ml n-hexane (4 times)
Figure 3.59 shows that the Se(IV) peak appeared next to the Se-Cyst peak, but the content found was very small (0.126 µg/l).
Se-cyst
c = 19.904 µg/L
+/- 0.306 µg/L (1.54%)
Se(IV)
c = 0.640 µg/L
+/- 0.013 µg/L (2.11%)
-200n
-150n
-150n
-125n
-100n
-100n
-75.0n
-50.0n
-50.0n
-2e-005
-6.4e- -25.0n
007
0
-2.00e-5 0
2.00e-5
c (g/L)
4.00e-5
0
-1.00e-6-5.00e-7 0 5.00e-71.00e-61.50e-62.00e-6
c (g/L)
I ( A )
I ( A )
Figure 3.60: DPCSV curve and standard addition graph to determine the form of selenium in the aqueous phase after removing fat with 5ml of n-hexane (5 times)
Figure 3.60 shows that the Se(IV) content found increased significantly (0.640
µg/l) compared with the case after 4 extractions.
Se-cyst
c = 21.617 µg/L
+/- 0.760 µg/L (3.51%)
-150n
-125n
I ( A )
-100n
-75.0n
-50.0n
-2.2e-005 -25.0n
0
-2.00e-5 0 2.00e-5 4.00e-5
c (g/L)
Se(IV)
c = 0.850 µg/L
+/- 0.079 µg/L (9.34%)
-100n
-80.0n
I ( A )
-60.0n
-40.0n
-20.0n
-8.5e-007
0
-1.00e-6 0 1.00e-6 2.00e-6 3.00e-6
c (g/L)
Figure 3.61: DPCSV curve and standard addition graph to determine the form of selenium in the aqueous phase after removing fat with 5ml of n-hexane (6 times)
Se-cyst
c = 20,800 µg/L
+/- 1.214 µg/L (5.84%)
Se(IV)
c = 0.901 µg/L
+/- 0.037 µg/L (4.15%)
-120n
-100n
-150n
-80.0n
-100n
-60.0n
-40.0n
-50.0n
-2.1e-005
0
-2.00e-5 0
2.00e-5
c (g/L)
4.00e-5
-20.0n
-9e-007
0
-1.00e-6 0 1.00e-6 2.00e-6
c (g/L)
I ( A )
I ( A )
Figure 3.62: DPCSV curve and standard addition graph to determine the form of selenium in the aqueous phase after removing fat with 5ml of n-hexane (7 times)
Figure 3.62 shows that the Se(IV) content found is close to the actual value in the standard sample (above 90%).
Se-cyst
c = 16.283 µg/L
+/- 0.002 µg/L (0.01%)
Se(IV)
c = 1.097 µg/L
+/- 0.011 µg/L (0.98%)
-200n
-120n
-100n
-150n
-80.0n
-100n
-60.0n
-40.0n
-50.0n
-1.6e-005
0
-2.00e-5
0 2.00e-5
c (g/L)
4.00e-5
-1.1e-006 -20.0n
0
-1.00e-6 0 1.00e-6 2.00e-6
c (g/L)
I ( A )
I ( A )
Figure 3.63: DPCSV curve and standard addition graph to determine the form of selenium in the aqueous phase after removing fat with 5ml of n-hexane (8 times)
Se-cyst
c = 15.270 µg/L
+/- 0.330 µg/L (2.16%)
-200n
Se(IV)
c = 1.012 µg/L
+/- 0.083 µg/L (8.20%)
-125n
-150n
-100n
-100n
-75.0n
-50.0n
-50.0n
-25.0n
-1.5e-005 -1e-006
0 0
-2.00e-5-1.00e-5 0 1.00e-52.00e-53.00e-54.00e-5 -1.00e-6 0 1.00e-6 2.00e-6
c (g/L) c (g/L)
I ( A )
I ( A )
Figure 3.64: DPCSV curve and standard addition graph to determine the form of selenium in the aqueous phase after removing fat with 5ml of n-hexane (9 times)
- Extract with 10ml n-hexane:
Add 10ml of n-hexane to the aqueous extract, shake for 5 minutes and let stand, wait for the layers to separate. Separate the n-hexane phase, collect the aqueous extract. Take 10ml of the aqueous extract and record the DPCSV according to the optimal conditions given in Table 3.14. Proceed similarly but increase the number of extractions, the results are shown in the figures from
Se-cyst
c = 20.238 µg/L
+/- 1.165 µg/L (5.76%)
-200n
-150n
-100n
-50.0n
-2e-005
0
-2.00e-5
0
2.00e-5
c (g/L)
4.00e-5
3.65 to 3.70.
I ( A )
Figure 3.65: DPCSV curve and standard addition graph to determine the form of selenium in the aqueous phase after removing fat with 10ml of n-hexane (1 time)
Se (IV)
c = 0.335 µg/L
+/- 0.017 µg/L (5.12 %)
-80.0n
-60.0n
)
A -40.0n
( I
-20.0n
-3.3e-007
0
-5.00e--27 .50e-7 0 2.50e-75.00e-77.50e-71.00e-6
c (g/L)
Se-cyst
c = 20.319 µg/L
+/- 0.108 µg/L (0.53%)
Se (IV)
c = 0.335 µg/L
+/- 0.017 µg/L (5.12 %)
-80.0n
-150n
-60.0n
-100n
-40.0n
-50.0n
-20.0n
-2e-005
-3.3e-007
0
-2.00e-5 0
2.00e-5
c (g/L)
4.00e-5
0
-5.00e--72.50e-7 0 2.50e-75.00e-77.50e-71.00e-6
c (g/L)
I ( A )
I ( A )
Figure 3.66: DPCSV curve and standard addition graph to determine the form of selenium in the aqueous phase after removing fat with 10ml of n-hexane (2 times)
In figure 3.66, the peak of Se(IV) appeared, but the content found was small (0.335µg/l).
Se-cyst
c = 20.941 µg/L
+/- 0.436 µg/L (2.08%)
-200n
Se(IV)
c = 1.155 µg/L
+/- 0.095 µg/L (8.22%)
-120n
-150n
-100n
-80.0n
-100n
-60.0n
-40.0n
-50.0n
-2.1e-005
-1.2e-006
-20.0n
0
0
-2.00e-5 0
2.00e-5
c (g/L)
4.00e-5
-1.00e-6
0
c (g/L)
1.00e-6 2.00e-6
I ( A )
I (A )
Figure 3.67: DPCSV curve and standard addition graph to determine the form of selenium in the aqueous phase after removing fat with 10ml of n-hexane (3 times)
Figure 3.67 shows that the content of Se-Cyst and Se(IV) found is over 100%.
Se-cyst
c = 19.606 µg/L
+/- 0.740 µg/L (3.77%)
-200n
-150n
I ( A )
-100n
-50.0n
-2e-005
0
-2.00e-5 0 2.00e-5 4.00e-5
c (g/L)
Se (IV)
Se (IV)
c = 1.103 µg/L
+/- 0.053 µg /L (4.81 %)
-150n
-125n
-100n
A -75.0n
)
( I
-50.0n
-1.1e-006 -25.0n
0
-1.00e-6 0 1.00e-6 2.00e-6
c (g/L)
c = 1.103 µg/L
+/- 0.053 µg /L (4.81 %)
-150n
-125n
-100n
I (A )
-75.0n
-50.0n
-1.1e-006 -25.0n
0
-1.00e-6 0 1.00e-6 2.00e-6
c (g/L)
Figure 3.68: DPCSV curve and standard addition graph to determine the form of selenium in the aqueous phase after removing fat with 10ml of n-hexane (4 times)
Se-cyst
c = 17.316 µg/L
+/- 0.625 µg/L (3.61%)
-200n
-150n
A -100n
)
( I
-50.0n
-1.7e-005
0
-2.00e-5 0 2.00e-5 4.00e-5
c (g/L)
Se-cyst
c = 17.316 µg/L
+/- 0.625 µg/L (3.61%)
-200n
Se(IV)
c = 1.014 µg/L
+/- 0.083 µg/L (8.19%)
-150n
-150n
-100n
-100n
-50.0n
-50.0n
-1.7e-005
0
-2.00e-5
-1e-006
0
-1.00e-6
0
2.00e-5
c (g/L)
4.00e-5
1.00e-6
c (g/L)
2.00e-6
0
I (A )
I (A)
Figure 3.69: DPCSV curve and standard addition graph to determine the form of selenium in the aqueous phase after removing fat with 10ml of n-hexane (5 times)
Se-cyst
c = 14.738 µg/L
+/- 0.272 µg/L (1.84%)
Se(IV)
c = 0.873 µg/L
+/- 0.025 µg/L (2.88%)
-250n
-150n
-200n
-125n
-150n
-100n
-75.0n
-100n
-50.0n
-50.0n
-1.5e-005
0
-2.00e-5-1.00e-5 0 1.00e-52.00e-53.00e-54.00e-5
c (g/L)
-8.7e- -25.0n
007
0
-1.00e-6 0
1.00e-6
c (g/L)
2.00e-6
I (A)
I (A)
Figure 3.70: DPCSV curve and standard addition graph to determine the form of selenium in the aqueous phase after removing fat with 10ml of n-hexane (6 times)
The summary of the results obtained is presented in Table 3.48.
Table 3.48: Research results on the influence of the number of extractions and the volume of n-hexane extraction solvent on the recovery of two forms of Se-Cyst and Se(IV)
Number of extractions
Selenium form | Extract with 5ml n-hexane | Extract with 10ml n-hexane | |||
Amount found (µg/l) | Recovery (%) | Amount found (µg/l) | Recovery (%) | ||
1 time | Se-Cyst | 19,421 | 97.11 | 20,238 | 101.19 |
Se(IV) | 0.000 | 0.00 | 0.000 | 0.00 | |
2 times | Se-Cyst | 20,513 | 102.57 | 20,319 | 101.60 |
Se(IV) | 0.000 | 0.00 | 0.335 | 33.50 | |
3 times | Se-Cyst | 20,486 | 102.43 | 20,941 | 104.71 |
Se(IV) | 0.000 | 0.00 | 1,155 | 115.50 | |
4 times | Se-Cyst | 20,212 | 101.06 | 19,606 | 98.03 |
Se(IV) | 0.126 | 12.60 | 1,103 | 110.30 | |
5 times | Se-Cyst | 19,904 | 99.52 | 17,316 | 86.58 |
Se(IV) | 0.640 | 64.00 | 1,014 | 101.40 | |
6 times | Se-Cyst | 21,671 | 108.36 | 14,738 | 73.69 |
Se(IV) | 0.850 | 85.00 | 0.873 | 87.30 | |
7 times | Se-Cyst | 20,800 | 104.00 | ||
Se(IV) | 0.901 | 90.10 | |||
8 times | Se-Cyst | 16,283 | 81.42 | ||
Se(IV) | 1,097 | 109.70 | |||
9 times | Se-Cyst | 15,270 | 76.35 | ||
Se(IV) | 1,012 | 101.20 | |||
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The research results show that if 5ml of n-hexane is used to extract fat, after 8 extractions, the Se-Cyst content decreases by 19%, while the Se(IV) content increases and remains stable after 9 extractions. If 10ml of n-hexane is used, the Se(IV) content decreases by 19%.