Integrated Supercritical Fluid Extraction and Pre-Formulation Process of Punica granatum L. Pericarp Polar Compounds.

Pomegranate (Punica granatum L.) is a widely used fruit in the dietary supplement industry due to its richness in bioactive compounds. In this study, an experimental design was applied to optimize supercritical fluid extraction (SFE) of polar compounds of interest (ellagic acid and punicalagins), known for antioxidant and skin care properties from pomegranate's pericarp. The effects of temperature, modifier percentage, and water additive percentage added in the modifier were explored through a Box-Behnken design, followed by a study of the extraction kinetics. The results indicated that 40 °C, 20% EtOH:H2O 80:20 v:v, with an extraction duration of 60 min allowed for the highest recovery of the above-mentioned molecules (19.59 mg/g). Due to solubilization issues encountered by the extract, a screening of cosmetic solvents was carried out to solubilize SFE pomegranate extracts and a composition of Gly:H2O 80:20 v:v was selected. Furthermore, an integrated SFE pre-formulation process of pomegranate pericarp extract (PPE) was elaborated. This allowed for the recovery of the extracts in cosmetic solvent, avoiding a full evaporation. Finally, the stability of the pre-formulated extracts was evaluated and showed high stability for over 3 months at 5 °C.

Supercritical Fluid Extraction (SFE) of Polar Compounds from Camellia sinensis Leaves: Use of Ethanol/Water as a Green Polarity Modifier.

The use of bioactive plant extracts in cosmetic products is a common practice. Most of these extracts are obtained by maceration in organic solvents, and depending on which solvents are used, the polarity and the structure of the target molecules will vary. Polyphenols are polar compounds that often display antioxidant and/or antibacterial activities. To extract them, ethanol/water mixtures are usually selected as green solvents. This solid-liquid extraction (assisted or not) requires the use of high volumes of solvents and many additional steps like mixing, agitation, filtration, and evaporation. Alternatively, supercritical carbon dioxide (SC-CO2) offers many benefits for plant extraction: economical, non-toxic, and naturally concentrated extracts. However, its low polarity is not suitable to solubilize polar compounds. In this study, an experimental design was used to optimize supercritical fluid extraction (SFE) of caffeine and catechins from Camellia sinensis. Catechins are recognized for skin care use (antioxidant) and caffeine is also used for its skin care properties and to prevent excess storage of fat in cells. The temperature, modifier content, and water additive percentage were used as independent variables. The results showed that while the temperature was an insignificant parameter, a higher percentage of water (up to 20% in ethanol) and modifier favored the extraction of the polar target molecules. Additionally, the SFE results were compared with ultrasound-assisted extraction (UAE). Finally, a sequential selective extraction of caffeine from catechins is also presented.

Exploring the Sequential-Selective Supercritical Fluid Extraction (S3FE) of Flavonoids and Esterified Triterpenoids from Calendula officinalis L. Flowers.

One of the many advantages of supercritical fluid extraction (SFE) is the possibility of using it in sequential and selective approaches. This is due to the use of a dynamic extraction mode in addition to the possibility of altering the composition of the modifier during the extraction process. In this study, the optimization of Calendula officinalis L. extraction of non-polar and polar compounds was achieved using three-level Box-Behnken designs (BBD). For non-polar compounds, the factors were pressure, temperature, and EtOH percentage. As for the polar compounds, the three variables were temperature, the total modifier percentage, and H2O added in the modifier as an additive. The recovery of selectively rich extracts in triterpendiol esters and narcissin was possible using a sequential two-step SFE. The first step was performed at 80 °C and 15% EtOH, and the second at 40 °C and 30% EtOH:H2O 80:20 v:v with a total of 60 min of extraction. Additionally, the SFE extraction of non-polar compounds was scaled up on a pilot-scale extractor, demonstrating similar results. Finally, the SFE results were compared to ultrasound-assisted extraction (UAE).

Supercritical fluid chromatography for the analysis of natural dyes: From carotenoids to flavonoids.

Plant-derived natural dyes are used in a variety of formulated products, from food to cosmetics and pharmaceutics. In addition to their color, they also provide some bioactivity. While they are mostly analyzed with high-performance liquid chromatography, supercritical fluid chromatography was also employed for several dye families, mostly for carotenoids and chlorophylls, and more recently for anthraquinones and flavonoids. These supercritical fluid chromatography methods are described in this review. Because the dyes have different structures and structural variations (polarity, isomers, etc.), the best chromatographic system to achieve their separation is not always the same. Hydrophobic stationary phases are preferred for the most hydrophobic dyes (chlorophylls and carotenoids) while polar stationary phases are preferred for the polar dyes (anthraquinones and flavonoids). Regarding the mobile phase composition, chlorophylls and carotenoids are best eluted with moderate proportions of co-solvent in CO2 (about 40%), while the most polar glycosylated flavonoids require higher proportions of co-solvent and acidic additives. Because dyes are colorful, ultraviolet-visible detection is often sufficient, while mass spectrometry offers additional structural information. Furthermore, fundamental information can also be gained through chromatographic analysis of dyes: either solubility in supercritical fluids, in view of their extraction, or retention behavior providing an understanding of stationary phase properties.

Evaluation of the extraction and stability of chlorophyll-rich extracts by supercritical fluid chromatography.

In this study, a rapid (less than 10 min) analytical method by reverse-phase supercritical fluid chromatography was developed with an isocratic mobile phase, enabling the separation of 11 compounds, chlorophyll a and b, pheophytin a and numerous allomers or epimers. This method was used to examine the stability of chlorophyll pigments of plant extracts obtained with various extraction methods including microwave-assisted extraction (MAE), supercritical fluid extraction (SFE), pressurized liquid extraction (PLE) and ultrasound-assisted extraction (UAE), with ethanol as solvent or modifier. The effect of storage was studied for both liquid and dried extracts. Irrespective of the extraction method, the evaporation of the extracts induced partial degradation of the chlorophyll pigments. It was found that liquid extracts could be stored at 4 °C for 3 weeks without a dramatic change in allomer forms of chlorophylls. However, during this storage period, epimerization appears to be important, leading to a significant decrease in the chlorophyll b native form. Graphical abstract.

Facilitated on-line supercritical fluid extraction - supercritical fluid chromatography for nonpolar and polar compounds from milk thistle seeds.

Plant seeds, as those from milk thistle (Silybum marianum), are a valuable source of nonpolar and polar compounds with potentially interesting biological activity. The main nonpolar compounds are triglycerides, which are also the main components of all vegetable oils. In addition, specific polar compounds - flavonolignans, called silymarin, have been found in large amounts in milk thistle seeds extract. These flavonoids derivatives have different biological activity, for instance hepatoprotective effects. In order to extract and analyze both nonpolar (triglycerides) and polar compounds (flavonolignans) from milk thistle seeds through a sequential methodology, an on-line supercritical fluid extraction - supercritical fluid chromatography (SFE-SFC) method was developed. Different ways of transferring the extracts from SFE to SFC (i.e. direct on-column transfer and loop transfer) were compared, and particularly for their effect on chromatographic quality. In this respect, nonpolar and polar compounds caused different issues, especially as polar compounds required a significant portion of co-solvent in the extraction step, favoring early elution in the chromatographic column. First, on-line SFE-SFC was used for triglycerides analysis and allowed the comparison of transfer modes. Then, on-line kinetics were performed to measure defatting time before polar molecules extraction. Finally, the eventual benefit of loop transfer was also investigated for the analysis of flavonolignans, polar molecules whose analysis can be difficult by on-line SFE-SFC. The aim of this paper is to discuss the versatility of on-line SFE-SFC and how challenging the coupling can be, especially when both non-polar and polar molecules must be analyzed independently in a single sample.

Defining a generic column set for achiral supercritical fluid chromatography applied to pharmaceuticals or natural products.

When starting a method development in supercritical fluid chromatography (SFC), the first step is usually to screen several stationary phases based on previous experience or simply based on what is available in the laboratory. However, as there are now a large number of stationary phases available for SFC, the choice of an adequate set of columns to rapidly achieve a satisfying result can be difficult. In this project, 16 columns comprising a wide diversity of stationary phases and polarities ranging from the most polar (like bare silica gel) to the least polar (like octadecylbonded-silica) were compared, based on the gradient analysis of 129 probe compounds. The set mostly comprised active pharmaceutical ingredients, natural products and a few metabolites. The columns were ranked with the help of Derringer desirability functions taking account of (i) the number of compounds eluted from the column, (ii) the elution time in a suitable time frame, (iii) the average peak width, (iv) the average peak symmetry and (v) the spreading of retention along the gradient time. The five criteria selected showed no correlation. Overall, it appeared that those columns that had a high overall score were good for several reasons, like bare silica gel, propanediol-bonded silica or pentabromobenzyloxy-bonded silica. Initially, the columns had been screened with a gradient elution starting from 5% co-solvent and ending with 50% co-solvent in CO2. However, for some most retentive columns like amide-bonded silica, too many compounds remained non-eluted from the column. To examine this column more fairly, a second elution gradient was applied that ended with 100% co-solvent. This proved effective in restoring good overall performance through the elution of the most polar compounds.

Effect of dilution solvent and injection volume on the analysis of basic hydrophilic therapeutic polypeptide salts with pressurized carbon dioxide mobile phases.

The chromatographic analysis of long-chain hydrophilic therapeutic peptides, with molecular weight mostly in the 3500-4500 Da range (31-34 amino acids), is explored with pressurized CO2 in the mobile phase. The optimal method was obtained on a Torus 2-PIC column, with a gradient elution of 50-90% co-solvent in CO2, which is relevant of enhanced-fluidity liquid chromatography (EFLC). Both UV (210 nm) and mass spectrometric detection modes were employed to assess the purity of the major peak and its resolution from impurities. Ten out of the eleven peptides in this set were basic, thus they were analyzed as acetate or trifluoroacetate salts. As significant peak distortion was observed in some cases, thorough examination of dilution solvent and injection volume was conducted to improve peak shape and resolution from impurities. Finally, the best injection volume was 1 µL, as any other volume (smaller or larger) yielded distorted peaks, and the best dilution solvent composition was the same as the mobile phase co-solvent (methanol comprising 5% water and 0.1 % methanesulfonic acid). However, not all peptide salts were fully soluble in this solvent so other alternatives (including more water in the dilution solvent), offering adequate dissolution but slightly inferior chromatographic performance should be chosen in such cases.

Analysis of short-chain bioactive peptides by unified chromatography-electrospray ionization mass spectrometry. Part II. Comparison to reversed-phase ultra-high performance liquid chromatography.

In the first part of this study, a unified chromatography (UC) analysis method, which is similar to supercritical fluid chromatography (SFC) but with wide mobile phase gradients of pressurized CO2 and solvent, was developed to analyse short-chain peptides, with UV and mass spectrometry (MS) detection. In this second part, the method is compared to a reference reversed-phase ultra-high-performance liquid chromatography (RP-UHPLC) method, based on the analysis of 43 peptides, including 10 linear peptides and 33 cyclic ones. First, the orthogonality between the two methods was examined, based on the retention patterns. As the UC method was developed on a polar stationary phase (Ascentis Express OH5), the elution orders and selectivities were expected to be significantly different from RPLC on a non-polar stationary phase (ACQUITY CSH C18). Secondly, the success rate of the methods was examined, based on successful retention / elution of the peptides and the absence of observed co-elutions between the main peak and impurities. A successful analysis was obtained for 81% of the peptides in UC and 67% in RPLC. Thirdly, the performance of the methods for the intended application of impurity profiling of peptide drug candidates was assessed, based on the comparison of peak purities, the number of impurities detected and the thorough examination of impurity profiles. Excellent complementarity of the two methods for the specific task of impurity profiling, and for the separation of isomeric species was observed, with only one isomeric pair in this set remaining unresolved. The method sensitivity was however better with RPLC than UC. Finally, the operational costs in terms of solvent cost per analysis were the same between the two methods.

Comments on the paper "Characterization of stationary phases by a linear solvation energy relationship utilizing supercritical fluid chromatography" by C. R. Mitchell, N. J. Benz, S. Zhang.

In a recent paper published by Mitchell et al. in this journal, some results obtained in supercritical fluid chromatography and interpreted with the solvation parameter model to characterize interactions for "novel stationary phases" were surprising to us. Indeed, we had already published results for most of the stationary phases reported, but, except for polar phases, our results were not in agreement with those, despite the use of identical mobile phases in both studies. These data were disturbing because they suggest that supercritical fluid chromatography is always a normal-phase mode, while we have shown that it is a reversed-phase mode when working with non-polar stationary phases. In the process of establishing the reason for the differences between our works, we examined several different factors. This paper deals with practice of linear solvation energy relationships: choice of dead-volume marker, choice of test-solutes to adequately probe the possible interactions and appropriate column length for characterization of chromatographic systems with highly eluting mobile phases are discussed. The importance of control experiments to validate retention models and confirm their accordance with the chromatographer's experience is evidenced. Recommendations for good linear solvation energy relationship practice are suggested in order to avoid the publication of results leading to erroneous conclusions.

Selective extraction of bioactive compounds from plants using recent extraction techniques: A review.

Plant extraction has existed for a long time and is still of interest. Due to technological improvements, it is now possible to obtain extracts with higher yields. While global yield is a major parameter because it assesses the extraction performance, it can be of interest to focus on the extraction of particular compounds (specific metabolites) to enrich the sample and to avoid the extraction of unwanted ones, for instance the primary metabolites (carbohydrates, triacylglycerols). The objective then is to improve extraction selectivity is then considered. In solid-liquid extraction, which is often called maceration, the solvent has a major impact on selectivity. Its polarity has a direct influence on the solutes extracted, related to the chemical structure of the compounds, and modelling compound/solvent interactions by using various polarity or interaction scales is a great challenge to favor the choice of the appropriate extracting liquid. Technical advances have allowed the development of recent, and sometimes green, extraction techniques, such as Microwave-Assisted Extraction (MAE), Ultrasound-Assisted Extraction (UAE), Pressurized Liquid Extraction (PLE) and Supercritical Fluid Extraction (SFE). This review focuses on the specificity of these recent techniques and the influence of their physical parameters (i.e. pressure, intensity, etc.). In addition to the solvent selection, which is of prime interest, the physical parameters applied by the different techniques influence the extraction results in different ways. Besides, SFE is a versatile and green technique suitable to achieve selectivity for some compounds. Due to its properties, SC-CO2 allows tailoring conditions to improve the selectivity.

Sequential extraction of carnosic acid, rosmarinic acid and pigments (carotenoids and chlorophylls) from Rosemary by online supercritical fluid extraction-supercritical fluid chromatography.

A high degree of selectivity is required during the plant extraction process in order to obtain extracts enriched in specific compounds or to avoid the extraction of unwanted ones. Rosemary is well known for its antioxidant compounds (carnosic acid, carnosol and rosmarinic acid). The plant also contains pigments (i.e. carotenoids, chlorophylls) which may cause a colour problem during the use of the extract in cosmetic formulations, for example. Supercritical fluid extraction is considered as a selective technique for plant extraction. Due to the physico-chemical properties of supercritical fluids, related to pressure, temperature and modifier addition, it is possible to carry out sequential extraction with successive conditions to collect different fractions that are rich either in pigments or in bioactive compounds. The aim of this study was to selectively extract bioactive compounds (i.e. carnosic acid and rosmarinic acid) and pigments (carotenoids and chlorophylls) from rosemary using supercritical fluid extraction. The optimisation of the extraction method was carried out using supercritical fluid extraction online coupled with a supercritical fluid chromatography (SFE-SFC) system. Two columns of different polarities were coupled to achieve the separation of the targeted compounds every five minutes during the extraction. Four fractions were obtained: a first one rich in carotenoids obtained with pure CO2 (25°C and 20 MPa), a second rich in carnosic acid obtained with 3% polar modifier (EtOH:water 50/50 v/v), a third fraction rich in rosmarinic acid using 10% of the same modifier and a fourth fraction rich in chlorophylls with 30% of ethanol as modifier. These four samples were then analysed by UHPLC-DAD-ESI-QTOF-HRMS in order to identify other extracted compounds and to study how the selected conditions impacted their extraction.

Ultra high efficiency/low pressure supercritical fluid chromatography (UHE/LP-SFC) for triglyceride analysis: Identification, quantification, and classification of vegetable oils.

Triglycerides of vegetable oils have been extensively studied. Non-aqueous reversed-phase liquid chromatography and silver-ion chromatography are most frequently used to achieve their separation. In previous works, we presented the use of supercritical fluid chromatography with long columns (75 cm) packed with fused-core particles to provide ultra-high-performance separations, with a low-toxicity fluid (carbon dioxide) compared to the usual liquid-phase methods. In the present paper, we describe the quantification of triglycerides with supercritical fluid chromatography and evaporative light-scattering detection. Thanks to the isocratic elution mode, this quantification can be simplified, assuming (a) identical response coefficients for compounds having a close structure, (as only triglycerides are quantified), and (b) constancy of the response coefficient along the analysis (no elution gradient). Therefore, the relative concentrations of triglycerides were easily assessed. Only one calibration curve for one reference compound (in this case triolein) was required. The resulting relative concentrations are in good accordance with the numerous publications available. Relative quantification with UV detection at 210 nm is also proposed, facilitated by the very low UV absorption of carbon dioxide and with a calibration curve taking account of the variation of UV response according to double bond number. Nineteen vegetable oils are compared. The identification of triglycerides was carried out based on previous knowledge of these oils, but also with the help of a Goiffon retention diagram, based on the relationship between the logarithm of retention factor and the total double bond number. Finally, cluster analyses were computed, based on evaporative light-scattering detection or UV quantification data. They allow a quick comparison of the triglyceride content between the oils, in the goal to exchange one by the other for certain applications, or to compare a new oil to well-known ones.

Changes in secoiridoids content and chemical characteristics of cultivated and wild Algerian olive oil, in term of fruit maturation.

Wild varieties in nature are known to be better adapted to climate change and more resistant to arid conditions common in some regions of the world. Oil samples of two cultivated varieties, Chemlal and Lemli, and one sylvestris variety were collected at four different harvesting periods in the semi-arid region of Bouira, Algeria. The aim of this study was to determine the influence of the genetic and maturity factors on the quality indices (acidity, peroxides value, and the parameters K232, K270), fatty acids profile, phenolic composition, and antioxidant activity of monovarietal olive oils. The study showed that early harvest dates of the fruits produced oils richer in pigments and phenolic compounds, with high antioxidant activity registered in both wild and cultivated varieties. Moreover, all oil samples showed high values of secoiridoids exceeding 60-90% of total biophenols, with higher values found in oleaster oils, which are correlated with high resistance to oxidation attacks. UHPLC-DAD and UHPLC-HRMS analyses showed that the secoiridoids composition is dominated by a profile rich in several isomers of oleuropein and ligstroside aglycons, which in turn represent more than 60% of the total secoiridoids in olive and Oleaster oils. Furthermore, chemometric analysis on the data allowed a better appreciation of the sensitivity of the virgin olive oil composition to the changes in genetic and ripening factors. According to the principal component analysis, phenolic and fatty acid profiles were the most important components contributing to the discrimination between olive oil samples.

Characterization of stationary phases in supercritical fluid chromatography including exploration of shape selectivity.

Achiral packed column supercritical fluid chromatography (SFC) has shown an important regain of interest in academic and industrial laboratories in the recent years. In relation to this increased concern, major instrument manufacturers have designed some stationary phases specifically for SFC use. SFC stationary phases have been widely examined over the last two decades, based on the use of linear solvation energy relationships (LSER), which relate analyte retention to its properties and to the interaction capabilities of the chromatographic system. The method provides some understanding on retention mechanisms (normal phase, reversed phase or mixed-mode) and the possibility to compare stationary phases on a rational basis, especially through a spider diagram providing a visual classification. The latter can be used as a primary tool to select complementary stationary phases to be screened for any separation at early stages of method development, before optimization steps. In this context, the characterization of the 14 columns from the Shim-pack UC series (Shimadzu Corporation, Kyoto, Japan), which are dedicated to SFC and more broadly to unified chromatography (UC), was performed, using the LSER methodology. As in previous works, seven descriptors, including five Abraham descriptors (E, S, A, B, V) and two descriptors describing positive and negative charges (D- and D+) were first employed to describe interactions with neutral and charged analytes. Secondly, two more descriptors were introduced, which were previously employed solely for the characterization of enantioselective systems and expressing shape features of the analytes (flexibility F and globularity G). They brought additional insight into the retention mechanisms, showing how spatial insertion of the analytes in some stationary phases is contributing to shape separation capabilities and how folding possibilities in flexible molecules is unfavorable to retention in other stationary phases.

Analysis of short-chain bioactive peptides by unified chromatography-electrospray ionization mass spectrometry. Part I. Method development.

A method to analyse short-chain bioactive peptides (MW < 800 Da) and their impurities was developed with a unified chromatography (UC) analysis, including a wide mobile phase gradient ranging from supercritical fluid to near-liquid conditions, with UV and electrospray ionization mass spectrometry detection (ESI-MS). Four stationary phases and three mobile phase compositions were examined. Ten model peptides were first selected to identify the best operating conditions, including five linear tripeptides and five cyclic pentapeptides, with log P values ranging from -5.9 to 3.6, and including isomeric species. Derringer desirability functions were designed to identify optimal operating conditions based on 7 criteria, namely the number of peaks detected (including all impurities resolved), the proportion of the chromatogram occupied by target peaks, the least favourable resolution observed between the main peptide and impurities, peak shape features (asymmetry and peak width at half height), and finally the signal-to-noise ratio observed both with UV (210 nm) and ESI-MS in positive ionization mode. The optimum conditions were obtained on Ascentis Express OH5 stationary phase, with a mobile phase composed of carbon dioxide and methanol, comprising 2% water and 20 mM ammonium hydroxide. The final gradient program ranged from 5 to 80% co-solvent in CO2, with a reversed flow rate gradient ranging from 3.0 to 1.5 mL/min. Back-pressure was set at 120 bar and the column oven temperature at 60°C. Optimal conditions were applied to a large set of 76 peptides (34 linear tripeptides and 42 cyclic pentapeptides) and provided adequate scattering of the peaks in the retention space, together with some separation of isomeric species, particularly for the cyclic peptides.

Chiral separation of phosphine-containing alpha-amino acid derivatives using two complementary cellulosic stationary phases in supercritical fluid chromatography.

Enantiomeric separations of six amino-acid derivatives have been studied using packed-column supercritical fluid chromatography with two polysaccharide-based enantioselective stationary phases: cellulose tris(3,5-dimethylphenylcarbamate) and cellulose tris(3-chloro-4-methylphenylcarbamate) (Lux Cellulose-1 and -2). The effect of analyte structure on retention and separation was studied. Varied mobile phase compositions were investigated: alcohol modifier percentage was increased from 3 to 40% but smaller amounts were most effective in separating these compounds. Besides, ethanol was preferred to methanol or isopropanol as it proved to be a good compromise to achieve sufficient resolution in a reasonable analysis time. Moreover, a carbon dioxide-ethanol mixture allows performing analyses in safe and green conditions. The effect of temperature at constant mobile phase composition was explored between 10 and 40 degrees C. In most cases, increasing the temperature improved the chiral separation, up to an optimum temperature. The results are discussed in line with the structure variation of the racemic derivatives analyzed and the two columns are compared. The two columns were shown to provide complementary selectivities for the investigated solutes: whereas Lux 1 provided separation for five of the six racemates, Lux 2 could resolve the last racemic mixture. Finally, optimized conditions of separation are defined.

Extension of the C18 stationary phase knowledge by using the carotenoid test.

The carotenoid test for octadecylsiloxane-bonded stationary phases used in RPLC was developed some years ago. Additional experiments have now been performed with varied stationary phases. The effect of the bonding density and of the pore diameter on steric selectivity, polar surface activity and hydrophobicity was determined by using YMC series (J'Sphere and Pack ODSA). The test was also extended to estimate the phase evolution of several classical or hybrid silicas. The high loading phases were also studied, as well as the fused core silicas. The effect of the particle size reduction on the three previous phase properties was investigated in the goal to determine in which way this parameter could also modify the chemical properties of the phases.

Supercritical Fluid Chromatography development of a predictive analytical tool to selectively extract bioactive compounds by supercritical fluid extraction and pressurised liquid extraction.

Selective extraction is a great concern in the field of natural products. The interest is to apply specific conditions favouring the solubility of targeted secondary metabolites and avoiding the simultaneous extraction of unwanted ones. Different ways exist to reach selective extractions with suited conditions. These conditions can be determined from experimental studies through experimental design, but a full experimental design takes time, energy, and uses plant samples. Prediction from varied solubility models can also be applied allowing a better understanding of the final selected conditions and eventually less experiments. The aim of this work was to develop and use a chromatographic model to determine optimal extraction conditions without the need for numerous extraction experiments. This model would be applied on the selective extraction of the desired antioxidant compounds in rosemary leaves (rosmarinic and carnosic acids) vs chlorophyll pigments to limit the green colour in extracts. This model was achieved with Supercritical Fluid Chromatography (SFC) and then applied to Supercritical Fluid Extraction (SFE) and Pressurised Liquid Extraction (PLE) assays. SFC models predicted low solubility of chlorophylls for low (5%) and high (100%) percentage of solvent in carbon dioxide. Also, low solubility was predicted with acetonitrile solvent compared to methanol or ethanol. This was confirmed with different extractions performed using SFE with different percentages of solvent (5, 30, and 70%) and with the three solvents used in the SFC models (acetonitrile, methanol and ethanol). Also extractions using PLE were carried out using the same neat solvents in order to confirm the SFC models obtained for 100% of solvent. Globally, extractions validated the SFC models. Only some differences were observed between ethanol and methanol showing the complexity of plant extraction due to matrix effect. For all these extracts, the content of carnosic acid and rosmarinic acid was also monitored and selective extraction conditions of bioactive compounds could be determined.

Development of an analytical method for chlorophyll pigments separation by reversed-phase supercritical fluid chromatography.

Chlorophyll pigments give the green colour to plants, which is a quality attribute of food and vegetables. However, the chemical structure of native chlorophyll can change during varied processes (drying, freezing, extraction) applied to plants, which produce degradation compounds that could have a brown and unwanted colour. Systematic experiments have been conducted in supercritical fluid chromatography with a C18 stationary phase to understand and model the chromatographic behaviour of the compounds with respect to the nature of the modifier (MeOH, ACN, and MeOH/ACN 50/50) and its percentage, from 10% to 100%. Specific retention changes were observed, which provide numerous analytical conditions to achieve compound separation. The chromatographic profile of the extract containing native chlorophyll a, b and numerous phytylated chlorophyll derivatives (pheophytin a, a', b, b'; hydroxypheophytin a, a', b, b'; pyropheophytin and lactone derivatives) is strongly impacted by the nature of the modifier and, because of the complexity of the extract, the optimal conditions obtained are unusual for supercritical fluid chromatography. An original method development using an optimization criterion was discussed for the analyses of samples, leading to a fast analytical method with a very low backpressure and a flow rate gradient, but a simplest and rapid method is also suggested for samples displaying fewer derivatives.