Determination of l-norvaline and l-tryptophan in dietary supplements by nano-LC using an O-[2-(methacryloyloxy)-ethylcarbamoyl]-10,11-dihydroquinidine-silica hybrid monolithic column

Chromatographic speed classification for liquid chromatography using average theoretical peak time (ATPT)

BACKGROUND

The development of analytical techniques in the field of liquid chromatography has brought new frontiers in performance and analytical speed for the technique. The proper evaluation of the analytical boundaries achieved with those developments was not addressed in the literature, since different liquid chromatography (LC) techniques have not yet received any classification regarding their chromatographic speed. Defining chromatographic analysis speed based simply on analysis time is an outdated concept since it is sample and analyte-dependent. In this context, the application of the Average Theoretical Peak Time concept (ATPT) is proposed as a unified metric for chromatographic speed classification.

RESULTS

This metric was evaluated using PCA analysis in a group of more than 50 publications, which generated the classification of LC methods in normal, high, hyper, and ultra-high-speed separations using ATPT. Normal speed (ATPT values greater than 18000 ms/peak) was found in HPLC, nano-LC, SFC, and CEC methods. Therefore, high-speed methods (ATPT values between 4000 and 18000 ms/peak) were found in UHPLC techniques, while LC × LC methods presented higher ATPT values between 1000 and 4000 ms/peak being classified as hyper-speed separations. ATPT can also be used as an optimization parameter, since older methods show higher ATPT values, while recent published papers show lower values of this metric. This behavior is justified due to the improvement of the LC methods over the years.

SIGNIFICANCE

This work fulfills the gap in chromatographic definitions and metrics, regarding analytical speed in one-dimensional and multidimensional liquid chromatographic techniques and shows that ATPT metrics is a robust parameter that can be used to classify the separation speed as well as a metric to evaluate the LC Method optimization. It also corrects the historical application of separation time as a metric for chromatographic speed.

Nano liquid chromatography, an updated review

Low flow chromatography has a rich history of innovation but has yet to reach widespread implementation in bioanalytical applications. Improvements in pump technology, microfluidic connections, and nano-electrospray sources for mass spectrometry have laid the groundwork for broader application, and innovation in this space has accelerated in recent years. This article reviews the instrumentation used for nano-flow liquid chromatography , the types of columns employed, and strategies for multi-dimensionality of separations, which is key to the future state of the technique to the high-throughput needs of modern bioanalysis. An update of the current applications where nano-LC is widely used, such as proteomics and metabolomics, is discussed. But the trend towards biopharmaceutical development of increasingly complex, targeted, and potent therapeutics for the safe treatment of disease drives the need for ultimate selectivity and sensitivity of our analytical platforms for targeted quantitation in a regulated space. The selectivity needs are best addressed by mass spectrometric detection, especially at high resolutions, and exquisite sensitivity is provided by nano-electrospray ionization as the technology continues to evolve into an accessible, robust, and easy to use platform.

Chiral Monolithic Silica-Based HPLC Columns for Enantiomeric Separation and Determination: Functionalization of Chiral Selector and Recognition of Selector-Selectand Interaction

This review draws attention to the use of chiral monolithic silica HPLC columns for the enantiomeric separation and determination of chiral compounds. Properties and advantages of monolithic silica HPLC columns are also highlighted in comparison to conventional particle-packed, fused-core, and sub-2-µm HPLC columns. Nano-LC capillary monolithic silica columns as well as polymeric-based and hybrid-based monolithic columns are also demonstrated to show good enantioresolution abilities. Methods for introducing the chiral selector into the monolithic silica column in the form of mobile phase additive, by encapsulation and surface coating, or by covalent functionalization are described. The application of molecular modeling methods to elucidate the selector–selectand interaction is discussed. An application for enantiomeric impurity determination is also considered.

Fabrication of edge-curled petals-like covalent organic frameworks and their properties for extracting indole alkaloids from complex biological samples

In this study, a functionalized covalent-organic framework (COF) was first synthesized using porphyrin as the fabrication unit and showed an edge-curled, petal-like and well-ordered structure. The synthesized COF was then introduced to prepare porous organic polymer monolithic materials (POPMs). Two composite POPM/COF monolithic materials with rod shapes, referred to as sorbent A and sorbent B, were prepared in stainless steel tubes using different monomers. Sorbents A and B exhibited relatively uniform porous structures and enhanced specific surface areas of 153.14 m²/g and 80.01 m²/g, respectively. The prepared composite monoliths were used as in-tube solid-phase extraction (SPE) sorbents combined with HPLC for the on-line extraction and quantitative analytical systems. Indole alkaloids (from Catharanthus roseus G. Don and Uncaria rhynchophylla (Miq.) Miq. Ex Havil.) contained in mouse plasma were extracted and quantitatively analyzed using the online system. The two composite multifunctional monoliths showed excellent clean-up ability for complex biological matrices, as well as superior selectivity for target indole alkaloids. Method validation showed that the RSD values of the repeatability (n=6) were ≤ 3.46%, and the accuracy expressed by the spiked recoveries was in the ranges of 99.38%–100.91% and 96.39%–103.50% for vinca alkaloids and Uncaria alkaloids, respectively. Furthermore, sorbents A and B exhibited strong reusability, with RSD values ≤ 5.32%, which were based on the peak area of the corresponding alkaloids with more than 100 injections. These results indicate that the composite POPM/COF rod-shaped monoliths are promising media as SPE sorbents for extracting trace compounds in complex biological samples.

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Edge-curled petals-like COF was synthesized using porphyrin as the fabrication unit.

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In-tube monolithic POMP/COF composite SPE sorbents with rod-shape were fabricated.

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The in-tube sorbents were used to extract hence indole alkaloids from complex samples.

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The two homemade sorbents show strong reusability of more than 100 times.

Sensitive Electrochemical Detection of Tryptophan Using a Hemin/G-Quadruplex Aptasensor

In this study, we design an electrochemical aptasensor with an enzyme-free amplification method to detect tryptophan (Trp). For the amplified electrochemical signal, the screen-printed electrode was modified with dendritic gold nanostructures (DGNs)/magnetic double-charged diazoniabicyclo [2.2.2] octane dichloride silica hybrid (Fe3O4@SiO2/DABCO) to increase the surface area as well as electrical conductivity, and the hemin/G-quadruplex aptamer was immobilized. The presence of Trp improved the catalytic characteristic of hemin/G-quadruplex structure, which resulted in the efficient catalysis of the H2O2 reduction. As the concentration of Trp increased, the intensity of H2O2 reduction signal increased, and Trp was measured in the range of 0.007–200 nM with a detection limit of 0.002 nM. Compared with previous models, our sensor displayed higher detection sensitivity and specificity for Trp. Furthermore, we demonstrated that the proposed aptasensor successfully determined Trp in human serum samples, thereby proving its practical applicability.