Using an Optical Probe as the Microdrop Holder in Headspace Single Drop Microextraction: Determination of Sulfite in Food Samples

Abstract

A novel headspace single-drop microextraction method (HS-SDME) for determination of sulfite in the form of sulfur dioxide was developed. An optical probe was used as the droplet holder in the HS-SDME procedure, and the analytical signal (absorbance) was monitored online during the extraction process. The method is based on the conversion of sulfite to volatile sulfur dioxide by acidification of the analyzed solution. The liberated SO was absorbed by 25 μL of an aqueous mixed reagent solution placed on the optical probe tip and containing Fe(III), 1,10-phenantroline, and an acetic buffer solution of pH 5.6. During the extraction process, Fe(III) reduces to Fe(II) and the Fe(II) formed then reacts with 1,10-phenantroline to form a colored complex. Absorbance was measured at 510 nm. The calibration plot was linear in the range 0.032-0.320 mg L of sulfite (as SO), with a correlation coefficient of 0.9989. The limit of detection (LOD), calculated as three times the standard deviation of the blank test (n = 10), was found to be 8 μg L. The method was applied for analysis of real food samples, such as wine, jam, and juice.

A two-in-one device for online monitoring of direct immersion single-drop microextraction: an optical probe as both microdrop holder and measuring cell

“…In comparison with our previous work, in which HS-SDME was reported, 23 the xing of the extraction phase in DI-SDME has a particular feature: the organic solvents should be xed on the probe aer immersion of the optical probe into the sample solution (Video 1 †); otherwise the organic solvent will spread away from the optical probe tip, due to its low surface tension in comparison with water solvents (surface tension of 72 and 25.8 dyn cm À1 for water and amyl acetate, respectively).…”

“…22 Very recently, we demonstrated the applicability of the optical probe as a microdrop holder in headspace single drop microextraction (HS-SDME). 23 The usefulness of the recently developed approach was presented for sulte determination in food samples. The method based on sulte conversion to volatile sulfur dioxide followed by absorption into a drop of an aqueous mixed reagent solution placed on the optical probe tip, and online measuring of the absorbance of the formed colored complex.…”

Surface nanodroplet-based nanoextraction from sub-milliliter volumes of dense suspensions

“…The simple setup also enables in-situ analysis in tandem with analytical instruments such as a UV-vis spectrometer. 39,40 However, the single drop extraction is not compatible with slurry samples as the droplet can easily detach from the needle upon collision with the particles or from the high shear stress generated during the stirring motion. 41 Although the droplet can be protected with a hollow fibers membrane, 41,42 blockage and fouling of pores by the particles can occur and lower the extraction performance.…”

Development of a New Kinetic Spectrophotometric Method for the Determination of Chromium with an Optical Probe

“…In the literature, an optical probe has been used for monitoring the extraction efficiency only several times in the recent years, for example, as in the following articles. 24–26…”

“…The method is based on the conversion of sulfite to volatile sulfur dioxide, which was absorbed by 25 µL of an aqueous mixed reagent solution placed on the optical probe tip. 25…”