Effect of density on kinetic performance in supercritical fluid chromatography with methanol modified carbon dioxide

Lipidomics Study of Type 1 Diabetic Rats Using Online Phase Transition Trapping-Supercritical Fluid Extraction-Chromatography Coupled with Quadrupole Time-of-Flight Tandem Mass Spectrometry

Chromatography-mass spectrometry-based lipidomics represents an essential tool for elucidating lipid dysfunction mechanisms and is extensively employed in investigating disease mechanisms and identifying biomarkers. However, the detection of low-abundance lipids in biological matrices, along with cumbersome operational procedures, complicates comprehensive lipidomic analyses, necessitating the development of highly sensitive, environmentally friendly, and automated methods. In this study, an online phase transition trapping-supercritical fluid extraction-chromatography-mass spectrometry (PTT-SFEC-MS/MS) method was developed and successfully applied to plasma lipidomics analysis in Type 1 diabetes (T1D) rats. The PTT strategy captured entire extracts at the column head by converting CO2 from a supercritical state to a gaseous state, thereby preventing peak spreading, enhancing peak shape for precise quantification, and boosting sensitivity without any sample loss. This method utilized only 5 μL of plasma and accomplished sample extraction, separation, and detection within 27 min. Ultimately, 77 differential lipids were identified, including glycerophospholipids, sphingolipids, and glycerolipids, in T1D rat plasma. The results indicated that the progression of the disease might be linked to alterations in glycerophospholipid and sphingolipid metabolism. Our findings demonstrated a green, highly efficient, and automated method for the lipidomics analysis of biological samples, providing a scientific foundation for understanding the pathogenesis and diagnosis of T1D.

Inline phase transition trapping-selective supercritical fluid extraction-supercritical fluid chromatography: A green and efficient integrated method for determining prohibited substances in cosmetics

BACKGROUND

Developing an environmentally friendly and efficient integrated analytical approach is a cutting-edge topic in current analytical science. Due to the unique properties of supercritical carbon dioxide (sc-CO2), online supercritical fluid extraction-supercritical fluid chromatography (SFE-SFC) is developing rapidly and has been widely applied in many fields. However, it still faces several challenges such as peak broadening and matrix interference. In order to solve the problems, we developed an inline phase transition trapping-selective supercritical fluid extraction-supercritical fluid chromatography (PTT-SSFE-SFC)-tandem mass spectrometry (MS/MS) method in this study.

RESULTS

This method integrated extraction, purification, separation, and detection, which was applied to determine 114 prohibited substances in cosmetics within 33 min, covering ten categories. The PTT strategy trapped the extracts on the head of the column by transforming CO2 from a supercritical state to a gaseous state, preventing peak spreading and improving sensitivity. Several adsorbents were tested when analyzing aqueous samples to reduce matrix interference and absorb water. Compared with conventional online SFE-SFC, this method improved the matrix effects of 93 and 87 target substances in the toner and mask matrix, respectively. Because the integrated method reduced sample loss, it achieved high sensitivity with LODs ranging from 0.00104 μg L-1 to 3.09 μg L-1. Furthermore, compared with other reported green methods, the inline method showed advantages in automation, efficiency, sample amount, and waste volume.

SIGNIFICANCE AND NOVELTY

With the introduction of the PTT strategy and the adsorbent, the system obtained good peak shapes, high sensitivity, low matrix effect, and good recovery. Based on the results, inline PTT-SSFE-SFC-MS/MS as a green and efficient integrated method has great potential for analyzing low abundance and multiple categories of targets in complex samples.

Supercritical Fluid Nanospray Mass Spectrometry: II. Effects on Ionization

Nanospraying supercritical fluids coupled to a mass spectrometer (nSF-MS) using a 90% supercritical fluid CO₂ carrier (sCO₂) has shown an enhanced desolvation compared to traditional liquid eluents. Capillaries of 25, 50, and 75 μm internal diameter (i.d.) with pulled emitter tips provided high MS detection sensitivity. Presented here is an evaluation of the effect of proton affinity, hydrophobicity, and nanoemitter tip size on the nSF-MS signal. This was done using a set of primary, secondary, tertiary, and quaternary amines with butyl, hexyl, octyl, and decyl chains as analytes. Each amine class was analyzed individually to evaluate hydrophobicity and proton affinity effects on signal intensity. The system has shown a mass sensitive detection on a linear dynamic range of 0.1-100 μM. Results indicate that hydrophobicity has a larger effect on the signal response than proton affinity. Nanospraying a mixture of all amine classes using the 75 μm emitter has shown a quaternary amine signal not suppressed by competing analytes. Competing ionization was observed for primary, secondary, and tertiary amines. The 75 and 50 μm emitters demonstrated increased signal with increasing hydrophobicity. Surprisingly, the 25 μm i.d. emitter yielded a signal decrease as the alkyl chain length increased, contrary to conventional understanding. Nanospraying the evaporative fluid in a sub-500 nm emitter likely resulted in differences in the ionization mechanism. Results suggest that 90% sCO₂ with 9.99% methanol and 0.01% formic acid yielded fast desolvation, high ionization efficiency, and low matrix effect, which could benefit complex biological matrix analysis.

Supercritical Fluid Nanospray Mass Spectrometry

Supercritical fluids are typically electrosprayed using an organic solvent makeup flow to facilitate continuous electrical connection and enhancement of electrospray stability. This results in sample dilution, loss in sensitivity, and potential phase separation. Premixing the supercritical fluid with organic solvent has shown substantial benefits to electrospray efficiency and increased analyte charge state. Presented here is a nanospray mass spectrometry system for supercritical fluids (nSF-MS). This split flow system used small i.d. capillaries, heated interface, inline frit, and submicron emitter tips to electrospray quaternary alkyl amines solvated in supercritical CO₂ with a 10% methanol modifier. Analyte signal response was evaluated as a function of total system flow rate (0.5-1.5 mL/min) that is split to nanospray a supercritical fluid with linear flow rates between 0.07 and 0.42 cm/sec and pressure ranges (15-25 MPa). The nSF system showed mass-sensitive detection based on increased signal intensity for increasing capillary i.d. and analyte injection volume. These effects indicate efficient solvent evaporation for the analysis of quaternary amines. Carrier additives generally decreased signal intensity. Comparison of the nSF-MS system to the conventional SF makeup flow ESI showed 10-fold signal intensity enhancement across all the capillary i.d.s. The nSF-MS system likely achieves rapid solvent evaporation of the SF at the emitter point. The developed system combined the benefits of the nanoemitters, sCO₂, and the low modifier percentage which gave rise to enhancement in MS detection sensitivity.

Development and validation of ultra-high performance supercritical fluid chromatography method for quantitative determination of six compounds in Guizhi Fuling capsule and tablet samples

A fast and simple ultra-high performance supercritical fluid chromatography method has been developed for the determination of six analytes, namely (paeonol, coumarin, cinnamic alcohol, cinnamic acid, paeoniflorin, and amygdalin) in Guizhi Fuling capsule and tablet samples. The influence of the key chromatographic parameters for the separation purposes was evaluated. The optimal column was Trefoil CEL1 column. The optimal mobile phase was a gradient mixture of carbon dioxide and methanol at flow rate of 1.0 mL/min. The back pressure of the system was set to 1.38 × 10⁷  Pa and the temperature to 45°C. The six compounds were separated within 11 min by the proposed ultra-high performance supercritical fluid chromatography method with satisfactory resolution. Method validation confirmed that the procedure is accurate with the recovery rates from 87.04 to 104.30%, intraday precision values less than 4.81% and interday precision less than 5.22%, and linear with R² higher than 0.9967. Therefore, this work provides a simple and novel method for the simultaneous analysis of six compounds in Guizhi Fuling capsule and tablet samples.