Needle Syringe

Mass Transfer Characteristics of Solvent Extraction into a Single Drop at the Tip of a Syringe Needle

Michael A. Jeannot and Frederick F. Cantwell*

Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2

Received for review August 12, 1996. Accepted October 22, 1996.

Abstract:

The amount of a sample compound extracted into a 1-L drop of n-octane suspended in a stirred aqueous solution from the tip of a microsyringe needle is measured by gas chromatography (GC) as a function of time. The observed extraction rate curve is first order and yields the overall mass transfer coefficient for the sample compound, o. For a given compound, o varies linearly with stirring rate. Among the four compounds malathion, 4-methylacetophenone, 4-nitrotoluene, and progesterone, at a given stirring rate, o is linearly proportional to the diffusion coefficient of the compound (Daq). This supports the film theory of convective-diffusive mass transfer, as opposed to the penetration theory. The relative standard deviation of the GC signal for 4-methylacetophenone after a 1.00 min extraction at 1500 rpm is 1.5%, which suggests that the system exhibits excellent potential as a tool for rapid analysis by solvent extraction/GC.

Automated solid phase dynamic extraction - Extraction of organics using a wall coated syringe needle

J. Lipinski A1

A1 SOFIA GmbH, Rudower Chaussee 29, 12489 Berlin, Germany e-mail: JLipinski@sofia.fta-berlin.de

Abstract:

Abstract Extractions of liquid samples were carried out using wall coated needles prepared from stainless steel capillary columns instead of syringe needles. This micro extraction technique was applied to the analysis of pesticides in water. Important parameters influencing the extraction such as sample velocity, extraction time and also the desorption parameters were investigated and optimized. Automation of this technique was realized using a conventional automatic sampler. Limits of detection were improved using the multiple extraction / desorption technique. Chromatographic data and limits of detection were compared with those obtained by solid phase micro extraction (SPME). Using a needle with a 7 wm film yielded limits of detection varying from 0.001-0.1 wg/L and were in the same range as those resulting from the extraction using a 100 wm polydimethylsiloxane (PDMS) SPME fiber. The main advantages of the needle extraction technique were the significantly higher extraction speed and the practical aspects of a stable steel needle compared to those of a fragile fiber. The extraction speed using a needle with a ¶7 wm film was up to five times higher than the speed of SPME using a 100 wm PDMS fiber. The steel needle could be stressed mechanically in a higher extent than a SPME fiber. Sample volumes and aliquots of liquid media could be handled and moved from one bottle to another using the automatic sampler.