Liquid chromatography of polyglycerol fatty esters and fatty ethers on porous graphitic carbon and octadecyl silica by using evaporative light scattering detection and mass spectrometry

Analysis of human biological samples using porous graphitic carbon columns and liquid chromatography-mass spectrometry: a review

Liquid chromatography-mass spectrometry (LC-MS) has emerged as a powerful analytical technique for analyzing complex biological samples. Among various chromatographic stationary phases, porous graphitic carbon (PGC) columns have attracted significant attention due to their unique properties-such as the ability to separate both polar and non-polar compounds and their stability through all pH ranges and to high temperatures-besides the compatibility with LC-MS. This review discusses the applicability of PGC for SPE and separation in LC-MS-based analyses of human biological samples, highlighting the diverse applications of PGC-LC-MS in analyzing endogenous metabolites, pharmaceuticals, and biomarkers, such as glycans, proteins, oligosaccharides, sugar phosphates, and nucleotides. Additionally, the fundamental principles underlying PGC column chemistry and its advantages, challenges, and advances in method development are explored. This comprehensive review aims to provide researchers and practitioners with a valuable resource for understanding the capabilities and limitations of PGC columns in LC-MS-based analysis of human biological samples, thereby facilitating advancements in analytical methodologies and biomedical research.

A rapid and sensitive method for characterization and quantification of polyglycerol esters by supercritical fluid chromatography coupled to high-resolution mass spectrometry (SFC-HRMS)

Polyglycerol esters of fatty acids (PGEs), a very complex mixture of various isomers, are widely used as green surfactants in different industrial fields such as in cosmetic, pharmaceutic and food industries. However, no study related to the purification and the absolute quantification of these compounds has been described yet. In this study, we developed a rapid and efficient method for characterization and quantification of PGEs using Supercritical Fluid CO₂ coupled to High-Resolution Mass Spectrometry (SFC-HRMS). The SFC conditions were first considered including the stationary phase, the nature of mobile phase, the column temperature, the back-pressure regulator. The MS parameters (drying-gas temperature, capillary voltage, nozzle voltage, fragmentor voltage) were then investigated to get the best sensitivity for the PGE analysis. The MS/MS-based structural characterization of targeted PGE, triglycerol mono-oleate (PG3+1C18:1), was established and is helpful to study complex mixtures of PGEs with numerous isobaric PGEs. PG3+1C18:1 was then purified at lab scale and used as standard for quantification. This enabled to develop a rapid quantification method for PG3+1C18:1 within 12 min with good linearity (R² = 0.9997) as well as sensitivity (picogram level). The validated method was then successfully applied to quantify PG3+1C18:1 in commercial products in order to evaluate their composition.

Enzymatic Synthesis of Polyglycerol Fatty Acid Esters and Their Application as Emulsion Stabilizers

Polyglycerol ester is considered an excellent kind of food emulsifier. The aim of the current study was to synthesize polyglycerol fatty acid esters (PGFEs) with different-sized long-chain fatty acids (i.e. long-carbon fatty acid polyglycerol esters, L-PGFEs; medium-carbon fatty acid polyglycerol esters, M-PGFEs; and short-carbon fatty acid polyglycerol esters, S-PGFEs), using Lipozyme 435 as a catalyst in a solvent-free system. Thereafter, the physicochemical properties of the newly synthesized PGFEs and their potential applications as food emulsifiers were investigated. The maximum esterification efficiencies of L-PGFEs, M-PGFEs, and S-PGFEs were 69.37, 67.34, and 71.68%, respectively, at the optimum conditions: a reaction temperature of 84.48 °C, a reaction time of 6 h, a molar ratio of polyglycerol to fatty acid of 1.35:1, and 1.41 wt % enzyme usage (based on the total substrate mass). A high-performance liquid chromatograph equipped with an evaporative light-scattering detector (HPLC-ELSD) and an electrospray-ionization mass spectrometer (ESI-MS) were employed to identify the synthesized products. The results demonstrated that the main components of these PGFEs were dimeric glycerides (68.3%), triglycerides (13.13%), and a small amount of tetraglycerides (3.18%). The properties of the PGFEs were characterized by physical and chemical methods. Compared with M-PGFEs and S-PGFEs, L-PGFEs had the best physicochemical properties without any obvious odor. Further, the emulsion capabilities of these different long-chain PGFEs were evaluated via examining the particle sizes and storage stabilities and comparing them with those of glycerin monostearate (GMS). The results showed that the emulsions prepared with L-PGFEs had the best stability and the smallest particle sizes (16.8 nm) compared with those of M-PGFEs, S-PGFEs, and GMS, and they were not prone to oil-droplet coalescence or the separation of oil and water. From the current study, the newly synthesized PGFEs with long-chain fatty acids showed the best advantages as a food emulsifier compared with M-PGFEs, S-PGFEs, and even glycerin monostearate.

Re-evaluation of polyglycerol esters of fatty acids (E 475) as a food additive

The EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS) provides a scientific opinion re-evaluating the safety of polyglycerol esters of fatty acids (PEFA) (E 475) when used as a food additive. In 1978, the Scientific Committee on Food (SCF) endorsed an acceptable daily intake (ADI) of 25 mg/kg body weight (bw) per day previously established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA). Absorption of intact PEFA in the gastrointestinal tract was extremely low. PEFA was rapidly and almost fully hydrolysed to polyglycerols and fatty acids in the gastrointestinal tract. The safety of polyglycerols and specific fatty acids has recently been assessed and no adverse effects were identified in the available studies. No adverse effects of PEFA at any dose have been observed in short-term, subchronic or chronic toxicity studies. A no observed adverse effect level (NOAEL) of 9,000 mg/kg bw per day was identified from subchronic studies and of 2,500 mg/kg bw per day from chronic studies, the highest doses tested. No genotoxic potential of PEFA was identified from the limited information available. The reproductive toxicity studies showed no adverse effects of PEFA but had major limitations. Clinical chemistry and urinalysis, from a clinical study with limited information, did not reveal any adverse effects in volunteers receiving up to 300 mg/kg bw per day for 3 weeks. The highest exposure to PEFA used as a food additive was 2.6 and 6.4 mg/kg bw per day in children at the mean and the 95th percentile, respectively, for the non-brand loyal scenario. Considering all the above, the Panel concluded that the food additive PEFA (E 475) was not of safety concern at the reported uses and use levels and that there was no need for a numerical ADI. The Panel recommended some modifications of the EU specifications for E 475.

Analysis of triacylglycerols on porous graphitic carbon by high temperature liquid chromatography

The retention behaviour of several triacylglycerols (TAGs) and fats on Hypercarb, a porous graphitic carbon column (PGC), was investigated in liquid chromatography (LC) under isocratic elution mode with an evaporative light scattering detector (ELSD). Mixtures of chloroform/isopropanol were selected as mobile phase for a suitable retention time to study the influence of temperature. The retention was different between PGC and non-aqueous reversed phase liquid chromatography (NARP-LC) on octadecyl phase. The retention of TAGs was investigated in the interval 30-70 degrees C. Retention was greatly affected by temperature: it decreases as the column temperature increases. Selectivity of TAGs was also slightly influenced by the temperature. Moreover, this chromatographic method is compatible with a mass spectrometer (MS) detector by using atmospheric pressure chemical ionisation (APCI): same fingerprints of cocoa butter and shea butter were obtained with LC-ELSD and LC-APCI-MS. These preliminary results showed that the PGC column could be suitable to separate quickly triacylglycerols in high temperature conditions coupled with ELSD or MS detector.

Rapid analysis of triterpenic acids by liquid chromatography using porous graphitic carbon and evaporative light scattering detection

An original system which uses Porous Graphitic Carbon as support and a mixture of organic solvents as mobile phase is proposed for the analysis of triterpenic acids by liquid chromatography. The separation of betulinic acid, ursolic acid, oleanolic acid, and 18alpha- and 18beta-glycyrrhetinic acids was carried out within a short time and monitored by evaporative light scattering detection as universal detection method. Molecular modelling studies show that the main contribution to the selectivity comes from the electrostatic interaction characterised by the dipole moment of the products.

Temperature-programmed packed capillary liquid chromatography coupled to evaporative light-scattering detection and electrospray ionization time-of-flight mass spectrometry for characterization of high-molecular-mass hindered amine light stabilizers

High-molecular weight-hindered amine light stabilizers (HMW-HALSs) are of utmost importance in modern polyolefin stabilization technology and in-depth knowledge about their chemical composition, particularly the oligomers, is essential for development of new and more efficient stabilizers. In the present study, the applicability of temperature-programmed packed capillary LC coupled to miniaturized ELSD and positive mode ESI-TOF-MS for analysis of HMW-HALSs is demonstrated through extensive characterization of two state-of-the-art stabilizers, i.e., HALS-1 and HALS-2. Both stabilizers were individually separated on a 320 microm i.d. x 35 cm long Hypersil 3 microm ODS-100 column using a temperature program from 30 to 120 degrees C and a quaternary mixture of ethylacetate, acetonitrile, triethylamine (TEA) and acetic acid (45.0:44.9:10.0:0.1 (v/v/v/v)) as the mobile phase. The effect of using various amounts of ethylacetate, acetonitrile and triethylamine in the mobile phase on the chromatographic separation is demonstrated. Furthermore, the LC-ESI-TOF-MS analyses revealed that HALS-1 (oligomeric) was highly complex and consisted of at least five different mass series, while HALS-2, which was assumed to be monomeric, contained two different mass series. Chemical structures for nearly all species of both stabilizers are proposed.

Simultaneous separation and quantitation of four antiepileptic drugs—a study with potential for use in patient drug level monitoring

The purpose of this study was to illustrate the applicability of high-performance liquid chromatography (HPLC) coupled with evaporative light scattering detector (ELSD) in simultaneously separating and quantitating four commonly used antiepileptic drugs (AEDs). A mixture of the four AEDs were separated using a C8 column using volatile mobile phases and were detected using ELSD. Optimal instrumental conditions were obtained by assessing the effect of various critical experimental parameters such as evaporator tube temperature, carrier gas flow rate, photomultiplier gain on separation efficiency, accuracy, reproducibility and sensitivity of measurement on all four AEDs. A novel, rapid, accurate, sensitive, reproducible and robust HPLC-ELSD method for simultaneous separation and quantitation of four commonly used AEDs was developed. The physical basis of the results obtained as a consequence of varying several critical experimental parameters has been explained. This study illustrates the potential for use of HPLC-ELSD in drug level monitoring of patients undergoing mono- or polytherapy for epilepsy.

Eluotropic strength in non-aqueous liquid chromatography with porous graphitic carbon

Porous graphitic carbon is an attractive packing for the chromatographic analysis of highly hydrocarbonaceous compounds with non-aqueous mobile phase. An eluotropic-strength scale of 10 pure organic solvents was established using the methylene selectivity from the fatty acid methyl ester homologous series (chain length between 18 and 31 carbon atoms). Eight binary mobile phases combining a weak solvent: methanol or acetonitrile with a strong solvent: toluene, chloroform, dichloromethane or tetrahydrofuran at different volume fractions phi of strong solvents (ranging from 0.3 to 1.0) were tested and their eluotropic strengths were then compared with those of pure solvents. The curves of the eluotropic strength versus the volume fraction of the strong solvent followed two different trends: linear or curved. The knowledge of the pure solvent strength is not sufficient to predict the eluotropic strength of solvent in the mixture. Then modelling of the eluotropic strength for binary mobile phases was envisaged in order to provide a prediction tool. This model was assessed for the establishment of the composition of eight iso-eluotropic mobile phases. Good assessment was found except in the case of toluene with acetonitrile where the difference between the predicted and the real value was the highest.

Structure-retention diagrams of ceramides established for their identification

Molecular species analysis of ceramides was carried out using porous graphitic carbon with gradient elution: chloroform-methanol from 45:55 to 85:15 with a slope at 2.7%/min. These conditions gave a linear relationship between retention data and structure of ceramides. It was demonstrated that linearity occurred when a high slope value of linear gradient elution was used. Thereby the linear diagram was evolved by plotting the adjusted retention time against the total number of carbon atoms of ceramide molecules. Each line represents one ceramide class. Such a Structure-Retention Diagram describes ceramide retention and thus constitutes an identification method using only retention data. This Structure-Retention Diagram was assessed and compared to another obtained from octadesyl-grafted silica in terms of their reproducibility, precision and ability to provide ceramide identification. Better identification was obtained using the results from both Structure-Retention Diagrams. This approach with a two-dimensional separation system allowed to take advantage of the specificity of both identification models.

Recent advances in the application of mass spectrometry in food-related analysis

A review is presented on recent applications of mass spectrometry (MS)-based techniques for the analysis of compounds of food concern. Substances discussed are naturally occurring compounds in food products such as lipids, oligosaccharides, proteins, vitamins, flavonoids and related substances, phenolic compounds and aroma compounds. Among xenobiotics, applications of MS techniques for the analysis of pesticides, drug residues, toxins, amines and migrants from packaging are overviewed. Advances in the analysis of trace metals of nutritional and toxicological interest by MS with inductively coupled plasma (ICP) source are presented. The main features of mass spectrometry combined with separation instruments are discussed in food-related analysis. Examples of mass spectrometry and tandem MS (MS-MS) are provided. The development and application of matrix-assisted laser desorption ionization (MALDI) and electrospray (ESI) to the analysis of peptides and proteins in food is discussed. This survey will attempt to cover the state-of-the-art up from 1999 to 2001.