In-vessel headspace liquid-phase microextraction

Resonance light scattering combined with miniaturized Thermal-Assisted Purge-and-Trap device for screening of hydrochloride drugs

Resonance Light Scattering (RLS) is a sensitive analytical technology hindered by its susceptibility to impurities in complex samples. This study introduces a combination of RLS with a high-efficiency sample preparation device, the Miniaturized Thermal-Assisted Purge-and-Trap (MTAPT), enhancing RLS's effectiveness in complex sample analysis. Specifically, we utilized MTAPT-RLS for the indirect screening of illegal hydrochloride drug additions in health products, based on three considerations: the transformation of bound HCl in hydrochloride drugs into volatile HCl under strong acid and heat; the minimal Cl content in health products for taste purposes; and the detectability of Cl ions by RLS upon the addition of AgNO3 and a stabilizer. Employing RLS, this method quantifies Cl elements via fluorescence signals, achieving a linear response (R = 0.9984) across 5.0-80.0 μg/mL and a recovery rate of 94.1-114.0 % across three sample types. With a detection limit of 2.0 μg/mL, this approach exceeds traditional rapid detection methods in speed and sensitivity, offering substantial benefits for food safety monitoring. Additionally, we developed a smartphone-based detection system utilizing RGB signal changes captured by smartphone cameras, coupled with a custom app. This system shows a linear response (R = 0.9888) within the same concentration range and detection limit. Notably, the green light source provided the highest sensitivity, aligning with the RLS peak at approximately 520 nm. With its excellent portability, this method is well-suited for on-site rapid detection, independent of bulky analytical instruments.

Determination of Rhodamine 6G with direct immersion single-drop microextraction combined with an optical probe

The combination of an optical probe and single-drop direct immersion microextraction (DI-SDME-OP) was used for the preconcentration and subsequent spectrophotometric determination of rhodamine 6G (Rh6G). The developed method is based on the formation of an ionic associate between Rh6G and picric acid at pH 3.0 and its extraction with amyl acetate. A microdrop of the organic phase was stably placed in the hole of an optical probe immersed in the sample solution. The absorbance of the extraction phase was monitored at 534 nm. The proposed method combines in a single step several stages of the analytical procedure, such as pre-concentration, phase separation, transfer of the extraction phase to the instrument and online measurement. The sensitivity of the proposed approach is not inferior to existing microextraction methods involving the combination of liquid-phase or solid-phase extraction with spectrophotometry or HPLC with a UV-Vis detector. The evaluation of the greenness of the developed method carried out by the AGREE method (0.58 points) showed that it outperforms other similar existing techniques using this parameter. The calibration plot for the determination of Rh6G by the DI-SDME-OP method was linear over the range of 10-500 nM with a correlation coefficient of 0.9956. The limit of detection was 3.4 nM. The accuracy and applicability of the method were evaluated by the determination of Rh6G in natural waters and lipstick.

Headspace single drop microextraction based visual colorimetry for highly sensitive, selective and matrix interference-resistant determination of sulfur dioxide in food samples

Excessive intake of SO₂, a widely-used food additive, is able to cause respiratory, cardiovascular and neurological disease. For effectively monitoring SO₂ level, we have developed a headspace single drop microextraction based visual colorimetry for highly sensitive and selective sensing of SO₂ with TMB (3,3',5,5'-tetramethylbenzidine) as a classic chromogenic reagent. A combination of single drop and headspace microextraction integrated merits of high extraction efficiency, low consumption of reagents and excellent matrix interference-resistant ability. The colorimetric principle was based on oxidation of TMB, and SO₂ could compete with TMB to preferentially react with ·OH, resulting in the fading of color blue that could be easily read out by naked eye. LOD was calculated to be 0.53 μM and 5 μM by UV-vis and naked eye, respectively. The method was successfully utilized to analysis of food samples, and the experimental device was miniaturized and easy to construct, thus showing a promising potential in field analysis.

A new approach for sulfite determination by headspace liquid-phase microextraction with an optical probe

A new approach of headspace liquid-phase microextraction with an optical probe (HS-LPME-OP), which solves the problem of the extraction phase retention in the hole of the optical probe and provides the possibility of simpler, more precise and reliable online processing of the analytical signal, was used for sulfite determination. A 1 × 10^-4 M 5,5'-dithiobis-(2-nitrobenzoic) acid (DTNB) solution was used as an acceptor phase. It was placed in a plastic vial fixed in the headspace above the analyte solution. An optical probe immersed in the acceptor phase was used to monitor the analytical signal. Sulfite determination is based on the release of sulfur dioxide from the sample after the addition of ortho-phosphoric acid, followed by its extraction with an aqueous solution of DTNB at pH 7.0. The absorbance was measured at 412 nm. The calibration graph was linear in the range from 32 to 320 μg L^-1 with a detection limit of 14 μg L^-1. The developed method is sensitive, highly selective and reproducible. It was successfully applied for the sulfite determination in juice, alcoholic beverages and jam.

Online determination of sulfide using an optical immersion probe combined with headspace liquid-phase microextraction

A new design for headspace liquid phase microextraction in combination with an optical immersion probe (HS-LPME-OIP) was proposed and successfully tested for the determination of sulfide in wine and water samples. The developed method is based on the release of hydrogen sulfide from the aqueous phase after the addition of orthophosphoric acid and its extraction with an aqueous solution of 5,5′-dithiobis-(2-nitrobenzoic) acid (DTNB). The analytical signal was recorded using an optical probe immersed in a vial containing 200 μL of 0.1 mM DTNB solution. Using the optical immersion probe in combination with HS-LPME allowed to register the analytical signal online and significantly improve the reproducibility of sulfide determination compared to known microextraction approaches. In the proposed approach, the problems with drop stability, limitations in mixing rate or extraction time, too small volume of the acceptor phase and stability of the holding the acceptor phase in the hole of the optical probe were also satisfactorily solved. The calibration graph was linear in the range of 16–256 μg L⁻¹ with a correlation coefficient of 0.9992. The limit of detection was 6 μg L⁻¹.

A new design for headspace liquid phase microextraction combined with an optical probe.