New cloud vapor zone (CVZ) coupled headspace solid-phase microextraction technique

Abstract

A new cloud vapor zone (CVZ)-based headspace solid-phase microextraction (HS-SPME) technique has been demonstrated with the capability of heating the sample matrix and simultaneously cooling the sampling zone. A bi-temperature-controlled (BTC) system, allowing 10 mL of test sample heating and headspace external-cooling, was employed for the CVZ formation around the SPME-fiber sampling area. In the CVZ procedure, the heated headspace vapor undergoes a sudden cooling near the SPME to form a dense cloud of analyte-water vapor, which is helpful for adsorption or absorption of the analyte. The device was evaluated for the quantitative analysis of aqueous chlorothalonil. Parameters influencing sampling efficiency, e.g., SPME fiber coating, SPME sampling temperature and time, solution modifier, addition of salt, sample pH, and temperature, were investigated and optimized thoroughly. The proposed BTC-HS-SPME method afforded a best extraction efficiency of above 94% accuracy (less than 4.1% RSD, n=7) by using the PDMS fiber to collect chlorothalonil in the headspace at 5 degrees C under the optimized condition, i.e., heating sample solution (added as 10% ethylene glycol and 30% NaCl, at pH 7.0) at 130 degrees C for 15 min. The detection was linear from 0.01 to 80 microg L-1 with a regression coefficient of 0.9998 and had a detection limit of 3.0 ng L-1 based on S/N=3. Practical application was demonstrated by analyzing chlorothalonil in farm water samples with promising results and recoveries. The approach provided a very simple, fast, sensitive, and solvent-free procedure to collect analytes from aqueous solution. The approach can provide a new platform for other sensitive HS-SPME assays.

Use of volatile organic solvents in headspace liquid‐phase microextraction by direct cooling of the organic drop using a simple cooling capsule

“…By considering various aspects of the reported CA‐LPME setups, the useful points for their further development include (i) cooling‐assisted systems in which cooling is directly transmitted into extraction phase are most effective to create significant temperature gaps between extraction phase and sample matrix. Conversely, possible maximum temperature gap between sample matrix and extraction phase in methods with indirect cooling is not sufficiently large, (ii) in cooling‐assisted systems in which the heating zone (sample matrix) is as far as possible away from the cooling zone (extraction phase), such as cloud vapor zone solid‐phase microextraction (CVZ‐SPME) technique , the possible maximum temperature gap can be too high, and (iii) all the presented cooling‐assisted strategies are dependent on just one type of extracting phase (i.e., solid in SPME and liquid in LPME). Therefore, for further development and modification of CA‐LPME methods, five principles must be adhered to: (i) feasibility of handling various types of extraction phases, (ii) possibility of direct cooling of extraction phase, (iii) feasibility of creating distance between the heating (sample) and cooling (extraction phase) zones, (iv) being portable and applicable in field studies, and (v) using low cost and compact cooling system.…”