A configuration for cooling assisted organic solvent coated thin film microextraction after dispersive liquid-liquid microextraction method: A microextraction method for ultra-trace analyzing of volatile sample

A combination of the dispersive liquid-liquid microextraction (DLLME) method based on the total
vaporization procedure and cooling-assisted organic solvent-coated thin film microextraction
(TFME) was applied for extracting chlorpyrifos (as the model compound). Based on the high
thermal conductivity, a nickel foam thin film with the dimensions of 5.0 mm × 5.0 mm was used
as a substrate for holding the organic solvent. Supporting thin film by organic solvent increases
the thickness and contact area of the film relative to TFME or single drop microextraction (SDME)
alone, resulting in a dramatic increase in the extraction efficiency. To protect the organic solvent
and enhance the analyte distribution coefficient between the film and the vapor phase, a cooling
system was applied. The proposed design was effective due to condensing the target analyte only
on the uniform cooled thin film and not on the other regions in the extraction chamber. A corona
discharge ionization source-ion mobility spectrometer was employed to identify the analyte. After
optimizing the effective parameters, the limits of quantification (S/N = 10) and detection (S/N =
3) were calculated 0.1 and 0.03 μg L􀀀 1, respectively, and the dynamic range was measured between
0.1 and 7.0 μg L􀀀 1, with a determination coefficient of 0.9997. For three concentration
levels of 0.1, 3.0, and 7.0 μg L􀀀 1, the relative standard deviations (n = 3) as the repeatability
index were to be 6 %, 5 %, and 4 % for intra-day and 9 %, 6 %, and 5 % for inter-day, respectively.
The enrichment factor was also calculated to be 3630 for the analyte concentration of 1.0
μg L􀀀 1. Well water, potato, and agricultural wastewater were analyzed as the real samples and the
relative recovery values were measured between 92 % and 99 %. The accuracy of the proposed
technique was validated by the European Standards EN 12393 method. In this approach, two
steps of analyte extraction (DLLME and TFME) were used consecutively, resulting in better preconcentration
and reduced matrix interference during cleaning-up.