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   https://doi.org/10.1021/acs.analchem.9b04713  

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3. Shape-Based Peak Identity Confirmation in Liquid Chromatography

   https://doi.org/10.1021/acs.analchem.0c04432  

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4. A Dual-Mode Microwave Resonator for Liquid Chromatography Applications

   Duye Ye, Omkar (January 2021, IEEE sensors journal)

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   This work presents a microwave microfluidic sensor for high performance liquid chromatography (HPLC) applications. The sensor is based on a modified square ring loaded resonator (SRLR), where a transmission line and a ring are electrically shorted with a center gap. A microfluidic channel is bonded above the gap for liquid-under-test (LUT) measurement. When the dielectric constant of LUT is above a threshold value, two degeneration modes of the resonator are separated, resulting in two transmission-zero frequencies. The threshold dielectric constant can be easily tuned by the gap size. High sensitivity is achieved when LUT dielectric constant is close to the threshold value. These features enable the proposed resonator to be optimized for different microfluidic applications. To validate the design, three resonators with 10 µm, 30 µm and 90 µm gap sizes are built and tested with water-methanol solutions in various volume fractions. Additionally, the sensor is connected in series with HPLC system for caffeine and sucrose detection. The detection linearity is characterized by measuring water-caffeine samples from 0.77 ppm to 1000 ppm. A 0.231 ppm limit of detection (LOD) is achieved, revealing a comparable sensitivity with commercial ultraviolet (UV) detectors. The compatibility of the proposed sensor to gradient elution is also demonstrated. 

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5. Liquid chromatography enantiomeric separation of chiral ethanolamine substituted compounds

   https://doi.org/10.1002/chir.23419  

   Firooz, Sepideh Khaki; Putman, Joshua; Fulton, Brandon; Lovely, Carl J.; Berthod, Alain; Armstrong, Daniel W. (January 2022, Chirality)

   Abstract Eleven racemic ethanolamine derivatives were prepared, and their enantiomers were separated using liquid chromatography with various chiral columns. These derivatives included chiral vicinal amino alcohols, β‐hydroxy ureas, β‐hydroxy thioureas, and β‐hydroxy guanidines, all of which are present in many active pharmaceutical ingredients. The screening study was performed with six chiral stationary phase containing columns, including four recently introduced superficially porous particles bonded with two macrocyclic glycopeptides, a cyclodextrin derivative and a cyclofructan derivative. The two remaining columns contained chiral stationary phases, based on either a cellulose derivative or derivatized amylose, both bonded to fully porous particles. The cyclodextrin and cellulose‐based chiral stationary phases proved to be the most broadly effective selectors and were able to separate 8 and 7 of the 11 tested compounds, respectively. With respect to analyte structural features, marked differences in enantiorecognition were observed between compounds containing phenyl and cyclohexyl groups adjacent to the stereogenic center. Additionally, replacing a small electronegative oxygen atom by a larger and less electronegative sulfur atom induced a significant difference in chiral recognition by the cellulose derivative as well as by the vancomycin‐based chiral selectors. 

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