Development and evaluation of plunger-in-needle liquid-phase microextraction

In this work, a novel, simple and fast one-step liquid-phase microextraction (LPME) approach, termed plunger-in-needle LPME was developed. In this method, the stainless steel plunger wire of a commercially available plunger-in-needle microsyringe was simply etched by immersion in hydrofluoric acid to form a microporous structure, and was used as the extractant solvent holder. The extractant solvent could be easily held within the pores created by the etching. When the plunger wire with the extractant solvent was exposed to the sample solution, analytes directly diffused from the sample solution to the solvent. After extraction, the plunger wire was directly introduced into the injection port of a gas chromatography–mass spectrometry (GC–MS) system for analysis of the analytes after thermal desorption. Polycyclic aromatic hydrocarbons (PAHs) were used as model analytes to evaluate the extraction performance of this new approach to LPME. Parameters affecting the extraction efficiency were investigated in detail. Under the optimized conditions, the method detection limits for 10 PAHs were in the range of 0.003 and 0.136 μg/L (at a signal/noise ratio of 3), with relative standard deviations of between 2.9% and 9.6% on the same etched plunger wire. The linearities of the calibration plots were from 0.05 to 50 or from 1 to 50 μg/L, depending on the PAHs. When this method was applied for the spiked river water sample, the relative recoveries ranged from 70.1% to 106.4%. The proposed method integrates the extraction and extract introduction into one device, without extraneous sorbent needed, which makes the procedure fast and simple. It is also an environmentally friendly approach as the organic solvent consumed is almost negligible.