Parallel gradients in comprehensive multidimensional liquid chromatography enhance utilization of the separation space and the degree of orthogonality when the separation mechanisms are correlated

Comprehensive Two-Dimensional Liquid Chromatography-High-Resolution Mass Spectrometry for Complex Protein Digest Analysis Using Parallel Gradients

Despite the high gain in peak capacity, online comprehensive two-dimensional liquid chromatography coupled with high-resolution mass spectrometry (LC × LC-HRMS) has not yet been widely applied to the analysis of complex protein digests. One reason is the method's reduced sensitivity which can be linked to the high flow rates of the second separation dimension (2D). This results in higher dilution factors and the need for flow splitters to couple to ESI-MS. This study reports proof-of-principle results of the development of an RPLC × RPLC-HRMS method using parallel gradients (2D flow rate of 0.7 mL min-1) and its comparison to shifted gradient methods (2D of 1.4 mL min-1) for the analysis of complex digests using HRMS (QExactive-Plus MS). Shifted and parallel gradients resulted in high surface coverage (SC) and effective peak capacity (SC of 0.6226 and 0.7439 and effective peak capacity of 779 and 757 in 60 min). When applied to a cell line digest sample, parallel gradients allowed higher sensitivity (e.g., average MS intensity increased by a factor of 3), allowing for a higher number of identifications (e.g., about 2600 vs 3900 peptides). In addition, reducing the modulation time to 10 s significantly increased the number of MS/MS events that could be performed. When compared to a 1D-RPLC method, parallel RPLC × RPLC-HRMS methods offered a higher separation performance (FHWH from 0.12 to 0.018 min) with limited sensitivity losses resulting in an increase of analyte identifications (e.g., about 6000 vs 7000 peptides and 1500 vs 1990 proteins).

Two-dimensional liquid chromatography with reversed phase in both dimensions: A review

Two-dimensional liquid chromatography (2D-LC), and in particular comprehensive two-dimensional liquid chromatography (LC×LC), offers increased peak capacity, resolution and selectivity compared to one-dimensional liquid chromatography. It is commonly accepted that the technique produces the best results when the separation mechanisms in the two dimensions are completely orthogonal; however, the use of similar separation mechanisms in both dimensions has been gaining popularity as it helps avoid difficulties related to mobile phase incompatibility and poor column efficiency. The remarkable advantages of using reversed phase in both dimensions (RPLC×RPLC) over other separation mechanisms made it a promising technique in the separation of complex samples. This review discusses some physical and practical considerations in method development for 2D-LC involving the use of RP in both dimensions. In addition, an extensive overview is presented of different applications that relied on RPLC×RPLC and 2D-LC with reversed phase column combinations to separate components of complex samples in different fields including food analysis, natural product analysis, environmental analysis, proteomics, lipidomics and metabolomics.

Studying antigen-specific T cells through a streamlined, whole blood-based extracellular approach

Techniques currently used for the study of antigen-specific T-cell responses are either poorly informative or require a heavy workload. Consequently, many perspectives associated with the broader study of such approaches remain mostly unexplored in translational research. However, these could benefit many fields including but not limited to infectious diseases, oncology, and vaccination. Herein, the main objective of this work was to develop a standardized flow cytometry-based approach that would combine ease of use together with a relevant study of antigen-specific T-cell responses so that they could be more often included in clinical research. To this extent, a streamlined approach relying on 1/ the use of whole blood instead of peripheral blood mononuclear cells and 2/ solely based on the expression of extracellular activation-induced markers (AIMs), called whole blood AIM (WAIM), was developed and further compared to more conventional techniques such as enzyme-linked immunospot (ELISpot) and flow cytometry-based intracellular cytokine staining (ICS). Based on a cohort of 20 individuals receiving the COVID-19 mRNA vaccine and focusing on SARS-CoV-2 and cytomegalovirus (CMV)-derived antigen T-cell-specific responses, a significant level of correlation between the three techniques was found. Based on the use of whole blood and on the expression of extracellular activation-induced markers (CD154, CD137, and CD107a), the WAIM technique appears to be very simple to implement and yet allows interesting patient stratification capabilities as the chosen combination of extracellular markers exhibited higher orthogonality than cytokines that are commonly considered in ICS (IFN-γ, TNF-α, and IL-2).

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.

Green comprehensive two-dimensional liquid chromatography (LC × LC) for the analysis of phenolic compounds in grape juices and wine

Grape juices and wines are rich in numerous groups of polyphenolic compounds which require a dedicated separation technique for such complex samples. LC × LC is considered the best technique for the analysis of such samples as it can achieve better resolution and higher peak capacity compared to 1D LC. The ever-growing demand for protecting the environment necessitates reducing or eliminating hazardous solvents to improve the environmental friendliness of analytical procedures. In this study, propylene carbonate was used as an eco-friendly mobile phase component in comprehensive two-dimensional liquid chromatography to analyze phenolic compounds in grape juices and a dealcoholized wine sample. Novel green RPLC × RPLC-DAD and RPLC × RPLC-MS methods were developed for the first time to identify phenolic compounds in five samples (two red grape juice samples, two white grape juice samples, and one dealcoholized wine sample). Four different RPLC × RPLC systems were developed; three systems were connected to a diode array detector (RPLC × RPLC-DAD), while the fourth system was connected to DAD and MS detectors (RPLC × RPLC-DAD-ESI-MS). Solvent X (propylene carbonate:ethanol, 60:40) was adopted as a green organic modifier in the first dimension (¹D) and methanol in the second dimension (²D). The practical peak capacity and the surface coverage were calculated as metrics to measure the separation performance of all proposed systems. The orthogonality values for the setups ranged from 0.64 to 0.92 when calculated by the convex hull method, and from 0.54 to 0.80 when calculated by the asterisk equations method. The practical peak capacity production rate ranged from 14.58 to 22.52 peaks/min. The results revealed that the phenolic compounds were separated efficiently with good coverage of the 2D separation space and high peak capacity. A total of 70 phenolic compounds were detected based on MS data and information from the literature.

Comprehensive two-dimensional temperature-responsive × reversed phase liquid chromatography for the analysis of wine phenolics

Phenolic compounds are an interesting class of natural products because of their proposed contribution to health benefits of foods and beverages and as a bio-source of organic (aromatic) building blocks. Phenolic extracts from natural products are often highly complex and contain compounds covering a broad range in molecular properties. While many 1D-LC and mass spectrometric approaches have been proposed for the analysis of phenolics, this complexity inevitably leads to challenging identification and purification. New insights into the composition of phenolic extracts can be obtained through online comprehensive two-dimensional liquid chromatography (LC × LC) coupled to photodiode array and mass spectrometric detection. However, several practical hurdles must be overcome to achieve high peak capacities and to obtain robust methods with this technique. In many LC × LC configurations, refocusing of analytes at the head of the ²D column is hindered by the high eluotropic strength of the solvent transferred from the ¹D to the ²D, leading to peak breakthrough or broadening. LC × LC combinations whereby a purely aqueous mobile phase is used in the ¹D and RPLC is used in the ²D are unaffected by these phenomena, leading to more robust methods. In this contribution, the combination of temperature-responsive liquid chromatography (TRLC) with RPLC is used for the first time for the analysis of phenolic extracts of natural origin to illustrate the potential of this alternative combination for natural product analyses. The possibilities of the combination are investigated through analysis of wine extracts by TRLC × RPLC-DAD and TRLC × RPLC-ESI-MS.

Three-dimensional liquid chromatography with parallel second dimensions and quadruple parallel mass spectrometry for adult/infant formula analysis

Three dimensions of chromatographic separation, using split-flow two-dimensional liquid chromatography (SF-2D-LC) with two parallel second dimensions, LC × 2LC, combined with quadruple parallel mass spectrometry (LC3MS4) is demonstrated for analysis of NIST SRM 1849a adult/infant formula. The first dimension, ¹D, was a conventional non-aqueous reversed-phase (NARP) HPLC separation using two C18 columns in series, followed by detection using an ultraviolet (UV) detector, a fluorescence detector (FLD), with flow then split to a corona charged aerosol detector (CAD), and then dual parallel mass spectrometry (MS), conducted in atmospheric pressure photoionization (APPI) and electrospray ionization (ESI) modes. The first second dimension, ²D(1), UHPLC was conducted on a 50.0 mm C30 column using a NARP-UHPLC parallel gradient for separation of short-chain triacylglycerols (TAGs) from long-chain TAGs, with detection by UV and ESI-MS. The second dimension, ²D(2), UHPLC was conducted using a 100.0 mm C30 column with a NARP-UHPLC parallel gradient for improved separation of TAG isomers, with detection by UV, an evaporative light scattering detector, and high-resolution, accurate-mass (HRAM) ESI-MS. Transferred eluent dilution was used to refocus peaks and keep them sharp during elution in both ²Ds. The separation space in the ²D(2) was optimized using multi-cycle (aka, "constructive wraparound") elution, which employed flow rate programming. In the ¹D, calibration lines for quantification of fat-soluble vitamins were constructed. A lipidomics approach to TAG identification and quantification by HRAM-ESI-MS was applied to the ²D(2). These experiments can be represented: LC1MS2 × (LC1MS1 + LC1MS1) = LC3MS4, or three-dimensional liquid chromatography with quadruple parallel mass spectrometry.

Recent forensic applications of enhanced chromatographic separation methods

This study reviews the recent applications of enhanced separation methods employed in forensic analysis utilizing gas chromatography, liquid chromatography, and supercritical fluid chromatography published between 2015 to 2020, except papers previously covered in relevant review articles. Applications of enhanced chromatographic separation methods to arson investigations, environmental forensics, sexual assault investigations, drug analysis, and toxicology are discussed. Future directions for enhanced chromatographic separation methods in forensic science are also explored.