Determination of 13-cis-Retinoic Acid and Its Metabolites in Plasma by Micellar Electrokinetic Chromatography Using Cyclodextrin-Assisted Sweeping for Sample Preconcentration

The online preconcentration technique, cyclodextrin-assisted sweeping (CD-sweeping), coupled with micellar electrokinetic chromatography (MEKC) was established to determine 13-cis-retinoic acid (13-cis-RA), all-trans-retinoic acid (all-trans-RA) and 4-oxo-13-cis-retinoic acid (4-oxo-13-cis-RA) in human plasma. A CD-sweeping buffer (45 mM borate (pH 9.2), containing 80 mM sodium dodecyl sulfate (SDS) and 22 mM hydroxypropyl β-CD (HP-β-CD) was introduced into the capillary and, then, the sample dissolved in 70 mM borate (pH 9.2): methanol = 9:1 (v/v) was injected into capillary by pressure. The separation voltage was 23 kV. Compared to the conventional cyclodextrin-micellar electrokinetic chromatography (CD-MEKC) method, the new technique achieved 224–257-fold sensitivity enrichment of analytes. The limits of detection of 13-cis-RA, all-trans-RA were 1 ng/mL, whereas that of 4-oxo-13-cis-RA was 25 ng/mL in plasma. The linear ranges of 13-cis-RA, all-trans-RA were between 15 and 1000 ng/mL, whereas that of 4-oxo-13-cis-RA was between 75 and 1500 ng/mL. The coefficient of correlation between the concentration of analytes and peak area ratio of analytes and internal standard (2, 4-dihydroxy-benzophenone) for intra-day (n = 3) and inter-day (n = 5) analyses were both greater than 0.999. The optimized experimental conditions were successfully applied to determine 13-cis-retinoic acid and its metabolites in plasma samples from a patient during the administration of 13-cis-RA for treating acne.

A Functionalised Carbon Fiber for Flexible Extraction and Determination of Hg(II) Using Au(NP)-Thiol-CF Inductively Coupled Plasma Mass Spectrometry

This work illustrates the improvement in ultra-trace Hg(II) determination in water based on a novel flexible extraction and preconcentration technique (FEPT). This method focuses on the covalent functionalisation of carbon fibre (CF) based on (3-mercaptopropyl)trimethoxysilane. The functionalisation of CF is carried out in two steps: functionalising the surface of CF using acid treatment to obtain hydroxy and carboxyl groups on the surface, followed by a condensation reaction between the carboxyl or hydroxy groups on the carbon (CF-OH) and (3-mercaptopropyl)trimethoxysilane to form mercapto-CF (CF-SH). FTIR, EDX, SEM, XRD and UV-Vis were utilised to confirm the modification. ICP-MS is utilised to determine the Hg(II) and to assess the influence of the memory effect on the results using Au3+ solution and suspended Au nanoparticles (Au-NPs). The result shows that the Au-NPs improve Hg(II) detection and eliminate the memory effect. This study also includes appropriate parameters for contact time, eluent solution, pH, and the foreign metal and ions preconcentration factor. As a result, thiol-CF shows high Hg(II) uptake, flexibility, and stability during the analysis process, with a recovery of 98.96% ± 0.41% for 10 preconcentration factors. These features make FEPT a valuable method for extracting pollutants and overcoming the problems associated with the analysis of such samples.

Preconcentration of Pb with Aminosilanized Fe3O4 Nanopowders in Environmental Water Followed by Electrothermal Atomic Absorption Spectrometric Determination

A new preconcentration method to determine lead in environmental waters using the aminosilanized magnetite Fe3O4 powder sorbent has been developed. The preconcentration method was combined with electrothermal atomization atomic absorption spectrometry (ETAAS) and a graphite atomizer. Trace amount of sorbent (3 mg) could be applied into the preconcentration of Pb. According the preconcentration, the detection limits were 14 and 19 pg·mL−1 with bare and aminosilanized Fe3O4, respectively. The effect of interferent elements such as Al, Ca, Co, Fe, K, Mg, Na, Ni, and Zn (1000 ng·mL−1 versus Pb 1 ng·mL−1) on the preconcentration of Pb using bare magnetite was evaluated, and some elements (Al, Ni, and Zn) were found to interfere with the Pb preconcentration. The aminosilanized Fe3O4 sorbent was found to be effective in eliminating the severe interferences. The enrichment factors were 34 for the preconcentration with aminosilanized Fe3O4. The recovery of spiked Pb in the case of the sorbent with aminosilanized Fe3O4 was in the range of 75 to 110%. From the analytical data, the preconcentration technique was found to be useful for the determination of trace lead in environmental waters.

Mercapto-modified magnesium silicate micro-particles for efficient extraction and preconcentration of mercury ions from estuary waters

A quick, facile, and straightforward preconcentration technique based on the modification of magnesium silicate with mercapto-based ligands for sub-ppb determination of mercury ions in coastal seawaters.

Sweeping-micelle to solvent stacking for the on-line preconcentration and determination of organic acids in Angelica sinensis by capillary electrophoresis

A two-step on-line preconcentration technique has been applied to the analysis of organic acids in Angelica sinensis.