In-syringe magnetic stirring assisted dispersive liquid–liquid micro-extraction with solvent washing for fully automated determination of cationic surfactants

Abstract

An automated simple analyzer system for the extraction of cationic surfactants as an ion-pair with disulfine blue dye is described based on the technique in-syringe magnetic stirring-assisted dispersive liquid-liquid micro-extraction.The use of chloroform as an extraction solvent denser than water required to operate the syringe pump 10 upside-down. The remaining air cushion inside the syringe allowed emptying the syringe completely and reducing the dead volume significantly compared to prior works. Since the stirring bar placed inside the syringe to obtain a closed yet size-adaptable mixing chamber remains at the same position, the former magnetic stirring bar driver was simplified. The new system configuration further enabled automated insyringe washing of the organic phase with water and barium acetate solution to minimize interferences. 15 High signal repeatability with < 5 % RSD was achieved both for extraction as well as for double organic phase washing. Only 220 µL of extraction solvent and 4 mL of sample were required for simple extraction achieving a detection limit below 30 nmol L -1 and a linear response up to 1 µmol L -1 of cetyltriamethylammonium bromide. The time of analysis was 240 s for simple extraction. Considerable reduction of interferences was achieved by extract washing requiring up to 545 s. Analyte recovery in real 20 water samples was 95.6 ± 7.0 % applying extract washing.

The Automation Technique Lab-In-Syringe: A Practical Guide

“…Such systems have been used repeatedly ones combining LIS-DLLME either with mixing chambers or in-syringe stirring. Spectrophotometric detection has been used mostly taking advantage of analyte-selective chromogenic reactions or ion-pair formation [17,18] including utilization of liquid waveguide capillary cells [14], in-syringe detection [13], or fluorescence measurement [15,16].…”

“…renewed stirring and consequent solvent dispersion will prolong the procedural time by pausing for phase separation. This step can also be used for solvent washing for which a lower stirring rate can be advantageous to avoid long phase separation times [18]. Recently, we demonstrated DLLME with back-extraction converting the syringe into a flowthrough chamber that was enabled by a channel in the syringe piston ( Figure 2D).…”

“…Here, mixing by turbulence suffices while renewed stirring and consequent solvent dispersion will prolong the procedural time by pausing for phase separation. This step can also be used for solvent washing for which a lower stirring rate can be advantageous to avoid long phase separation times [18].…”

“…Nonetheless, this arrangement enabled the reproducible performance of automated DLLME procedures into solvents denser than water while previous works had all used floating solvents. The classical assay of total cationic surfactants, requiring chloroform, was miniaturized and automated this way [18]. Noteworthy is that it was possible to use a much simpler stir-driver since the magnetic bar was not displaced with the syringe piston but remained at the bottom, near the syringe inlet.…”

Temperature-assisted ionic liquid-based dispersive liquid–liquid microextraction with following back-extraction for HPLC/UV–Vis determination of 3-indole acetic acid in pea plants

“…Auxins are a group of plant hormones that have an essential role in the coordination of many growth processes in the 1 3 Table 1 A comparison table for temperature-assisted IL- Karst [15] 1 3 assistance [22], ultrasound assistance [23], and magnetic stirring assistance [24,25]. It is remarkable that in these methods an organic solvent is used as an extractant.…”