In-syringe SIL-DLLME procedure
The commercial NWPP sheet (40 cm×50 cm×2 mm) was washed
with deionized water and acetone and then dried at the room
temperature. The sheet was divided into 10 layers, and the thickness
of each layer was approximately 0.2 mm. Then, the NWPP sheet was
cut into small pieces (1 cm×0.8 cm×0.2 mm) with a weight of approximately
2.5 mg. Finally, the NWPP-based syringe needle was prepared
by stuffing a small piece of NWPP into the needle. The prepared
NWPP-based syringe needle allowed water to pass through smoothly
and prevented the leakage of the solidified extractant. The preparation
of the NWPP-based syringe needle is shown in Fig. 1.
Accurately weighed [N8881]Cl (0.04 g) was placed into a 20 mL
plastic syringe, and 20 mL sample solution was added. The syringe was
sealed with a plunger and screw cap. After the syringe was manually
shaken, the ionic liquid, [N8881]Cl, was uniformly scattered in the
solution, and the mixture was placed into a constant temperature water
bath (55 °C) for 5 min. Then, an aliquot of 1 mL of KPF6
(0.0364 g mL−1
) aqueous solution was quickly added into the syringe.
The extractant, [N8881]PF6, immediately formed and made the solution
emulsified and cloudy. The resulting mixture was then cooled in an ice
bath for another 5 min. Pulled out the plunger from the syringe, and
50 mg of NaCl was added to the solution from the large opening end of
the barrel. Then the syringe was resealed by the plunger and shaken
manually until the NaCl completely dissolved in the aqueous sample.
The solution was clear, and the solidified extractant quickly separated
from the water phase. The mixture was filtered through the prepared
NWPP-based needle, and all the water was discharged from the syringe
by pushing the plunger. A 60 μL volume of acetonitrile was added to
the syringe barrel to dissolve the solidified extractant, and the diluted
solution was collected. These dilution steps were repeated two more
times until all the eluents were merged together. The volume of the
final eluent was measured by a microsyringe. And then the eluent was
transferred into an HPLC vial for analysis. The procedure is schematically
illustrated in Fig. 2.