Agriculture Reference
In-Depth Information
homogeneous extraction is better than the other methods. For octachlorobiphenyl,
nonachlorobiphenyl, and decachlorobiphenyl, ASE is better than homogeneous
extraction and oscillation extraction, but considering other environmental pollutants,
homogeneous extraction is better than ASE and oscillation extraction as it is fast, easy,
and can avoid the in
uence of the high temperature of ASE extraction. Thus,
homogeneous extraction was selected.
5.3.4 Comparison of Sample Cleanup
Under the above-mentioned conditions, less fat can be dissolved by homogeneous
extraction with acetonitrile. As SPE is simple, highly ef
cient, and uses less solvent,
GPC is compared with SPE. Three SPE methods are selected.
Accurately weigh 5 g sample, add standard solution of 2 LOQ, add 35ml
acetonitrile, and homogeneously extract twice.
+
1. Transfer the concentrate with 2 ml acetonitrile
1, v/v) to NH
2
-
Carb cartridge cleanup, repeat three times, and then elute with 25 ml acetoni-
trile
-
toluene (3
1, v/v). Evaporate the eluate to about 1ml using a rotary
evaporator with a water bath at 45
-
toluene (3
+
C. Add 5 ml
n
-hexane for solvent exchange,
repeat twice, and then evaporate the eluate to about 1ml using a rotary
evaporator for detection.
2. Transfer the concentrate with 5ml acetonitrile to neutral Al
2
O
3
cartridge
cleanup, repeat two times, and then elute with 10 ml acetonitrile. Concentrate
the eluate and transfer the concentrate with 2ml acetonitrile
°
1,
v/v) to NH
2
-Carb cartridge cleanup, repeat three times, and then elute with
25ml acetonitrile
-
toluene (3
+
1, v/v). Evaporate the eluate to about 1 ml using
a rotary evaporator with a water bath at 45
-
toluene (3
+
C. Add 5ml
n
-hexane for solvent
exchange, repeat twice, and then evaporate the eluate to about 1 ml using a
rotary evaporator for detection.
3. Transfer the concentrate with 5ml acetonitrile to C18 cartridge cleanup, repeat
two times, and then elute with 10ml acetonitrile. Concentrate the eluate and
transfer it with 2ml acetonitrile
°
1, v/v) to NH
2
-Carb cartridge
cleanup, repeat three times, and then elute with 25ml acetonitrile
-
toluene (3
+
-
toluene
(3
1, v/v). Evaporate the eluate to about 1ml using a rotary evaporator with a
water bath at 45
+
C. Add 5 ml
n
-hexane for solvent exchange, repeat twice, and
then evaporate the eluate to about 1 ml using a rotary evaporator for detection.
°
+
Seven pesticides and seven PAHs cannot be detected by C18
NH
2
-Carb and
Al
2
O
3
+
NH
2
-Carb cleanup. It may be that these chemicals are adsorbed on the
cartridge and thus are not completely eluted and have low recovery or no recovery.
The results are shown in Figure 5.4.
Figure 5.4 shows that the recoveries of GPC cleanup and NH
2
-Carb cartridge
cleanup are better. The TIC plots of GPC cleanup and NH
2
-Carb column cleanup
show that GPC cleanup has low noise, good cleanup effect, and causes low pollution
