Sol−Gel Capillary Microextraction

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Abstract
Sol−gel capillary microextraction (sol−gel CME) is introduced as a viable solventless extraction technique for the preconcentration of trace analytes. To our knowledge, this is the first report on the use of sol−gel-coated capillaries in analytical microextraction. Sol−gel-coated capillaries were employed for the extraction and preconcentration of a wide variety of polar and nonpolar analytes. Two different types of sol−gel coatings were used for extraction: sol−gel poly(dimethylsiloxane) (PDMS) and sol−gel poly(ethylene glycol) (PEG). An in-house-assembled gravity-fed sample dispensing unit was used to perform the extraction. The analysis of the extracted analytes was performed by gas chromatography (GC). The extracted analytes were transferred to the GC column via thermal desorption. For this, the capillary with the extracted analytes was connected to the inlet end of the GC column using a two-way press-fit fused-silica connector housed inside the GC injection port. Desorption of the analytes from the extraction capillary was performed by rapid temperature programming (at 100 °C/min) of the GC injection port. The desorbed analytes were transported down the system by the helium flow and further focused at the inlet end of the GC column maintained at 30 °C. Sol−gel PDMS capillaries were used for the extraction of nonpolar and moderately polar compounds (polycyclic aromatic hydrocarbons, aldehydes, ketones), while sol−gel PEG capillaries were used for the extraction of polar compounds (alcohols, phenols, amines). The technique is characterized by excellent reproducibility. For both polar and nonpolar analytes, the run-to-run and capillary-to-capillary RSD values for GC peak areas remained under 6% and 4%, respectively. The technique also demonstrated excellent extraction sensitivity. Parts per quadrillion level detection limits were achieved by coupling sol−gel CME with GC-FID. The use of thicker sol−gel coatings and longer capillary segments of larger diameter (or capillaries with sol−gel monolithic beds) should lead to further enhancement of the extraction sensitivity.