Analyte focusing by micelle collapse for liquid extraction surface analysis coupled with capillary electrophoresis of neutral analytes on a solid surface

Abstract

Liquid extraction surface analysis (LESA) has an advantage of directly sampling analytes on a surface, thus avoiding unnecessary dilution by homogenization of the bulk sample commonly practiced in solid sample analysis. By combining LESA with CE, the additional advantage of separating analytes before detection can be accomplished. For neutral molecules, MEKC needs to be used. Since the detection sensitivity of CE in general suffers from the small capillary dimension, analyte focusing by micelle collapse was employed for enhanced extraction in LESA and sample preconcentration for MEKC. In addition, using a commercial CE instrument, the LESA process was performed much faster and more reliably compared to our first demonstration of LESA‐CE using a homemade CE setup. Three neutral water‐insoluble pesticides sprayed on an apple skin were directly extracted, preconcentrated, and analyzed by the automated LESA‐analyte focusing by micelle collapse‐MEKC with high sensitivity in 10 min. The relative standard deviations of the migration times and peak heights were 0.8–2.1 and 1.2–3.0%, respectively when ametryn was used as an internal standard. The limits of detection obtained with UV absorbance at 200 nm were 1.8–6.4 ppb.

Practical sample pretreatment techniques coupled with capillary electrophoresis for real samples in complex matrices

“…Note that in LPME as in most extraction procedures, the extraction efficiency for an analyte strongly depends on its distribution coefficient. It is thus necessary for quantification to take some measures such as using an internal standard [17,18] or standard addition [19].…”

“…However, for a home-made CE setup, LESA-CE requires a skilled operator and long operation times (≥ 30 min) to handle liquids by gravity. Thus, an automated LESA-CE methods using commercial CE equipment with pressure controlled liquid handling was demonstrated [18]. With less manual interventions, LESA-CE was much faster and more reliable.…”

“…By using a high conductivity solvent containing SDS micelles to form a liquid microjunction, LESA and AFMC were synergistically coupled for the analysis of neutral pesticides on apple skin. The micellar solvent not only improved the surface extraction efficiency but also enabled on-line preconcentration of the injected extract by AFMC [18]. MSS is performed via reversal of the electrophoretic mobility of charged analytes at the boundary stacking zone between the micelle-and organic solvent-rich zones [58].…”