Separations of petroleum products involving supercritical fluid chromatography

Discrimination of plastic waste pyrolysis oil feedstocks using supercritical fluid chromatography

Advanced chemical recycling techniques provide new avenues for handling and recycling mixed plastic waste; pyrolysis is a prominent approach involving heating plastic waste in an oxygen-free environment to create pyrolysis oils. Pyrolysis oils must be thoroughly characterized before being refined into fuels and chemical feedstocks. Here, a method based on supercritical fluid chromatography with ultraviolet detection was developed to analyze plastic waste pyrolysis oils. Multiple stationary phases were examined, and 2-ethyl pyridine was chosen as the best stationary phase for resolving pyrolysis oil components. Different standards and different plastic waste pyrolysis oils were compared across the different stationary phases. Up to three columns were serially coupled to increase efficiency and column capacity. It was found that a general method using ethanol as a modifier and two 2-ethyl pyridine columns could effectively resolve plastic waste pyrolysis oils. The potential for differentiating polyethylene and polypropylene feedstocks was demonstrated using principal component analysis.

Assessment of Repeatability in Supercritical Fluid Chromatography with Electrochemical Detection Based on the ISO 11843 Part 7

The present study proposes a method for the assessment of repeatability in supercritical fluid chromatography with electrochemical detection (SFC-ECD), based on the ISO 11843 part 7 (ISO 11843-7:2018) which can theoretically provide detection limits and standard deviation (S.D.) through the stochastic properties of baseline noise without repetitive measurements of real samples. On the baseline noise of SFC-ECD, large-amplitude and periodic noises with less than 0.05 Hz were observed, and the power spectrum of the baseline noise showed 1/f fluctuation (f = frequency). It was found that the present power spectrum analysis, according to the law of error propagation, can provide suitable noise parameters to calculate S.D. of baseline noise and a relative S.D. (RSD) of peak area by ISO 11843-7. The chromatographic determinations of α-, β-, γ- and δ-tocopherol have been taken as examples. In the present SFC-ECD, the RSDs of peak areas for α-, β-, γ- and δ-tocopherol obtained by ISO 11843-7 were within 95% confidence intervals of the RSD of them obtained by repetitive measurements (n = 6). Thus, we found that ISO 11843-7 is applicable to the assessment of repeatability in SFC-ECD for determining tocopherols without repetitive measurements.

Recent applications of on-line supercritical fluid extraction coupled to advanced analytical techniques for compounds extraction and identification

In a previous review (Sánchez-Camargo et al., J. Sep. Sci. 40 (2017) 213-227), we discussed the application of on-line supercritical fluid extraction coupled to chromatographic techniques. This review includes an update of the most recent publications (from January 2016 till June 2018) on this topic, which employs advanced analytical techniques for extracting and identifying valuable analytes. Supercritical fluid extraction has been widely recognized as a green sample preparation technique, because it is efficient, environmentally friendly, powerful, and faster, offering the possibility of direct coupling to analytical instrumental techniques. Among those techniques, supercritical fluid chromatography has experienced an innovative progression in the last 10 years, and the most recent applications of supercritical fluid extraction are coupled to this advanced analytical tool. The general principles, both methodological and instrumental of on-line supercritical fluid extraction coupled to supercritical fluid chromatography are described here. Besides, applications of the mentioned coupling for analysing biological fluids, food, soil, and botanical samples are also presented and discussed. Finally, a brief description about the very recent on-line coupling of supercritical fluid extraction to ion mobility spectrometry is presented, as well as concluding remarks about the importance of using these coupled techniques in the near future.

Supercritical Fluid Chromatography of Drugs: Parallel Factor Analysis for Column Testing in a Wide Range of Operational Conditions

Retention mechanisms involved in supercritical fluid chromatography (SFC) are influenced by interdependent parameters (temperature, pressure, chemistry of the mobile phase, and nature of the stationary phase), a complexity which makes the selection of a proper stationary phase for a given separation a challenging step. For the first time in SFC studies, Parallel Factor Analysis (PARAFAC) was employed to evaluate the chromatographic behavior of eight different stationary phases in a wide range of chromatographic conditions (temperature, pressure, and gradient elution composition). Design of Experiment was used to optimize experiments involving 14 pharmaceutical compounds present in biological and/or environmental samples and with dissimilar physicochemical properties. The results showed the superiority of PARAFAC for the analysis of the three-way (column × drug × condition) data array over unfolding the multiway array to matrices and performing several classical principal component analyses. Thanks to the PARAFAC components, similarity in columns' function, chromatographic trend of drugs, and correlation between separation conditions could be simply depicted: columns were grouped according to their H-bonding forces, while gradient composition was dominating for condition classification. Also, the number of drugs could be efficiently reduced for columns classification as some of them exhibited a similar behavior, as shown by hierarchical clustering based on PARAFAC components.

Exploring the complexity of oil sands process-affected water by high efficiency supercritical fluid chromatography/orbitrap mass spectrometry

RATIONALE

Approximately 1 billion m(3) of oil sands process-affected water (OSPW) is currently stored in tailings ponds in Northern Alberta, Canada. The dissolved organic compounds in OSPW have been termed a supercomplex mixture of bitumen-derived substances and continuing efforts to understand its underlying chemical composition are important for evaluating its environmental hazards.

METHODS

Packed column supercritical fluid chromatography (SFC) was applied to OSPW analysis for the first time. By combining four columns in series (each 25 cm × 4.6 mm I.D., 5.0 µm bare silica) approximately 80,000 plates were achieved on a 1 m column. Using a simple fixed restrictor, the SFC eluent was coupled directly to ultrahigh-resolution orbitrap mass spectrometry (SFC/Orbitrap-MS).

RESULTS

SFC/Orbitrap-MS, with positive and negative atmospheric pressure chemical ionization (APCI +/-), revealed the partial or full chromatographic separation of isomers for a wide array of chemical species, including naphthenic acids (Cn H2n + Z O2 ) and unknown sulfur- and nitrogen-containing molecules. For smaller compounds (e.g. naphthenic acids where n ≤10), or for larger structurally constrained compounds (e.g. C16 naphthenic acid with 9 double-bond equivalents), apparent baseline resolution of many isomers was possible. Isomer-specific MS/MS experiments furthermore allowed characterization of functional groups in novel species. For example, in APCI+ mode, up to 16 isomers of C6 H11 ON were revealed to have amide and amino functionalities.

CONCLUSIONS

This combination of high efficiency chromatography and ultra-high mass resolution detection resulted in a powerful method with capabilities for characterizing or 'fingerprinting' unknown species with little interference. The method has great promise for environmental monitoring and forensics in the oil sands region, as well as for further studies on the composition of dissolved organic compounds in OSPW.

A rapid and highly specific method to evaluate the presence of 2-(2-phenylethyl) chromones in agarwood by supercritical fluid chromatography-mass spectrometry

The detection and structural characterization of the major constituents of agarwood, 2-(2-phenylethyl)chromones, are important to quality control and the establishment of the authenticity of agarwood samples. However, a highly specific and rapid method for the evaluation of 2-(2-phenylethy)chromones in agarwood has not been reported to date. In this study, we developed a method using super- critical fluid chromatography in combination with mass spectrometry (SFC-MS). Tropylium ions, the characteristic product ions of 2-(2-phenylethyl)chromones in tandem mass spectrometric experiments, were selected for the targeted detection of 2-(2-phenylethyl) chromones. This method used precursor ion scans for tropylium ions with different possible substitutions on a triple-quadrupole mass spectrometer. To evaluate the usefulness of the developed method, a diethyl ether extract from a Chinese agarwood "Qi-Nan" sample was first separated using SFC, and the elutes were later subjected to precursor ion scans, which searched for 15 common substituted tropylium ions to evaluate the 2-(2-phenylethyl)chromones. In the precursor ion scans, a total of 29 2-(2-phenylethyl)chromones were detected and investigated further using tandem mass spectrometry (MS/MS) to obtain more detailed structural information. By comparing the retention times and m/z values of the precursor ions with reference standards, nine of the detected compounds were unequivocally identified. The remaining compounds were tentatively identified by analyzing the MS/MS spectra. This method provides a rapid and efficient method for evaluating the 2-(2-phenylethyl)chromones present in a sample, which aids in quality control and the establishment of the authenticity of the agarwood sample.