Comparison of flow cell position in the DV-SIA system; alternative for concentration factor enhancement

IVANA SRÁMKOVÁ; CAROLINA ACEBAL; HANA SKLENÁROVÁ; PETR CHOCHOLOUS; LUKÁS ZAHÁLKA; FERNANDEZ BAND, BEATRIZ S.; PETR SOLICH

Thessaloniki

Conferencia; 12th International Conference on Flow Analysis (Flow Injection XII); 2012

The DV-SIA system was designed in 2010 by ?krlíková et al. in order to avoid difficulties caused by performing liquid-liquid extraction in common SIA system [1]. This type of SIA configuration, where extraction and detection units are separated, enables to use variety of samples and immiscible solvents without potential problems resulting from different affinity to the PTFE tubing and bubble formation. Dispersive micro-extraction methods bring advantage of higher analyte pre-concentration using only small amount of extraction mixture and providing low detection and quantitation limits. Acebal et al. introduced a DV-SIA manifold for determination of thiocyanate ions in human saliva samples [2]. The ion associate of thiocyanate and Astra Phloxine dye was pre-concentrated in the extraction unit. Before the actual spectrophotometric detection at 550 nm was carried out, a portion of the organic layer in the extraction unit (containing the analyte) was used to fill the respective port of the detection unit and to wash the tubing, then another part of the organic layer was aspirated and propelled to the flow cell of the detector. In the above mentioned works, the extraction solvent volume had to meet two requirements: 1. to be small enough to provide high pre-concentration factor, 2. to be large enough for steps performed in the detection unit. Although the limits of detection and quantitation (20 µmol.L-1 and 70 µmol.L-1, respectively) were sufficient and the volume of organic phase was small (350 µL for extraction), alternated position of the flow cell could even improve these parameters. In the suggested manifold, the extraction unit was directly linked with the flow cell inlet, so the organic layer with the analyte ion associate was propelled to the flow cell by one step (pump aspiration). Performing dispersive liquid-liquid micro-extraction in the adapted DV-SIA system has also improved the pre-concentration factor, since the volume of extractant was decreased as there was no need to wash the tubing of the detection unit. Additionally, skipping the washing steps shortened the analysis time.