C18 Silica Research Articles

Isolation of a High Antioxidant Non-Toxic Polar Fraction from Garcinia mangostana Fruit Pericarp by Reverse Phase Column Chromatography

The crude polar extract of mangosteen fruit pericarp not only has a moderate antioxidant activity of (55±4 μg/mL) but also has high cytotoxicity (16±0.5 μg/mL). The high cytotoxicity presumably is caused by the presence of complex cytotoxic compounds from the mangosteen pericarp. To obtain a non-toxic extract preparation with high antioxidant activity, polar crude 50% ethanol extracts of mangosteen pericarp were partially purified using reverse-phase column chromatography with Silica C18 as the stationary phase and acetonitrile-water gradient elution. Six of the ten fractions collected had high antioxidant activities, with IC50 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging antioxidant levels <50 μg/mL. Three fractions (fractions 3, 5, and 7) with the highest antioxidant activities of (16.4 ± 0.6 µg/mL), (17.8 ± 2 µg/mL) and (17.4 ± 1.8 µg/mL) respectively, were chosen for further cytotoxicity, phenolic content and High-Performance Liquid Chromatography (HPLC) analysis. The cytotoxic tests were conducted with the Brine Shrimp Lethality Assay. Fraction 3 had low cytotoxicity (LC50 485 ± 96 µg/mL) and fraction 5 was non-toxic (LC50 ≥ 1000 µg/mL), while fraction 7 still had high cytotoxicity (LC50 2.8 ± 0.8 µg/mL). The chromatogram profiles of HPLC showed that fractions 3 and 5 contained more polar compounds than the compounds present in fraction 7. It can be concluded that the reverse phase method succeeded in the isolation of a non-toxic polar fraction, that is, fraction 5, with a significantly higher (p<0.05) antioxidant activity than in the original crude polar extracts. This fraction had a high total phenolic content of 43.3 ± 0.3 g GAE per 100 g extract.

Two new sesquiterpene aryl esters from Armillaria gallica 012m

Two new sesquiterpene aryl esters, armimelleolides A and B (1 and 2), and four known ones, were isolated from the EtOAc extract of Armillaria gallica 012 m by column chromatography on silica gel, reversed-phase C18 silica gel and semi-preparative HPLC. Their structures were elucidated on the basis of spectroscopic methods, including extensive 1 D NMR, 2 D NMR and MS. All these compounds showed potential antitumor activities against at least one of the human cancer cell lines (A549, HCT-116, M231 and W256), with IC50 ranging from 2.57 to 19.94 μM.

Development of a C18 Supercritical Fluid Chromatography-Tandem Mass Spectrometry Methodology for the Analysis of Very-Long-Chain Polyunsaturated Fatty Acid Lipid Matrices and Its Application to Fish Oil Substitutes Derived from Genetically Modified Oilseeds in the Aquaculture Sector.

Lipidomics methodologies traditionally utilize either reverse phase- or hydrophilic interaction liquid chromatography-type separations; however, supercritical fluid chromatography can offer a rapid normal phase type separation while reducing the dependence on organic solvents. However, normal phase type lipid separations typically lack pronounced intraclass separation, which is problematic for complex lipidomes containing very-long-chain polyunsaturated fatty acids, especially those from genetically modified organisms. A high-strength silica C18 method was developed, which benefitted from discrete class separation, as well as displaying intraclass selectivity sufficient for profiling flesh of salmon fed with a diet supplemented with oil from the genetically engineered oilseed Camelina sativa, a terrestrial oilseed with a fish oil-type profile. Salmon fed a diet containing this Camelina oil were found to have flesh enriched in triacylglycerols and phospholipids containing 18:3, 20:5, and 22:6, whereas salmon fed the control diet were differentiated by shorter chain plant-type fatty acids integrated within complex lipids. Coupled with active scanning quadrupole technology, data acquisition was enhanced, allowing for fragmentation data to be acquired in a data independent fashion, permitting acyl chain identification of resolved isomers. Therefore, we have developed a method, which is amenable for lipidomics studies of complex lipidomes, specifically those altered by synthetic biology approaches.

Stabilization of Refined Olive Oil with Phenolic Monomers Fraction and Purified Hydroxytyrosol from Olive Mill Wastewater

The aim of this study was to enhance the refined olive oil (ROO) quality stabilization during storage with phenolic compound fractions obtained from C18 silica gel fractionation of olive mill waste (OMW) ethyl acetate extract. HPLC–DAD–ESI/MS analysis was used to identify the main phenolic compounds present in the obtained fractions. 16 compounds were identified belonged to four classes: simple phenols, secoiridoids, flavonoids, and lignans. In this study, Diosmetin was identified for the first time in OMW and the major compound was hydroxytyrsol. On the other hand OMW extract and its related fractions conserved their antioxidant activity until 110 min heating at 185 °C. In addition, physicochemical characteristics such as peroxide value as well as conjugated dienes (CD) and conjugated trienes (CT) were determined to evaluate the oxidation of OMW polyphenols-enriched ROO during storage. Results demonstrated that OMW monomeric fraction and hydroxytyrosol improved the quality of ROO by decreasing peroxide value and absorptions at specified wave lengths at 232 and 270 nm related to conjugated dienes and trienes formation, respectively. This study suggests that the enrichment of ROO with phenolic compounds from OMW mainly hydroxytyrosol makes the oil more functional with a higher stability. Phenolic compounds from OMW with antioxidant activity improve the stability of ROO during storage and hence would be used as a natural alternative for chemical additives.

The utility of silica hydride-based stationary phases for dual-mode ultra high performance liquid chromatography separation of synthetic cathinone positional isomers.

Emerging drugs usually mimic the effects of traditional drugs, but are not always controlled due to the chemically altered structures. Positional isomers of emerging drugs are difficult to analyze because they challenge the separation and detection techniques commonly employed by forensic laboratories. The utility of silica hydride stationary phases for the ultra-high performance liquid chromatography separation of synthetic cathinone positional isomers was studied in this manuscript. SiH phases are operable under both reversed phase and aqueous normal phase chromatographic conditions without the need to change solvent reservoirs. The separation of eight positional isomers of the synthetic cathinone, pentedrone, was investigated using five silica hydride phases, and compared to a classical dual column reversed phase, hydrophilic interaction chromatography system, and to a bimodal pentaflurophenyl column. Significant selectivity differences were observed using either a combination of a classical reversed phase C18 and NP Silica columns or the various bimodal columns. The silica hydride silica-C column, which contains no derivatized ligands attached to the silica hydride backbone, not only gave the most orthogonal separation of the bimodal columns, but provided a unique separation of all eight positional isomers (resolution ≥ 1) using the combination of reverse phase and aqueous normal phase chromatographic conditions.

A Sensitive Rapid and Environmentally Friendly UHPLC Assay Method for the Determination of Thymoquinone in Plasma Samples and Its Analytical Application.

A precise, swift and environmental-friendly reverse phase ultra-high performance liquid chromatographic assay for the determination of thymoquinone (TQ) in plasma samples using thymol (TM) as an internal standard was developed and validated. The method used a high strength silica C18 1.7μm column (100×2.1mm) with an isocratic mobile phase consisting of a blend of methanol and 20mM potassium dihydrogen ortho-phosphate (90:10v/v; pH of 4.2). The selected eluent provided a short run time (≤2min), better peak symmetry, lower limit of quantification of 10ng/mL and satisfactory values of other chromatographic parameters including resolution (Rs=1), capacity factor (k=21.5 and 14.5 for TQ and TM, respectively), selectivity (α=1.482) and number of theoretical plates (N=1653 and 784 for TQ and TM, respectively). The method was efficiently applied to a pharmacokinetic study of TQ following an intraperitoneal administration of 2mg/kg in mice. The concentrations of TQ in plasma were measurable up to 12h with Cmax of 404.08±28.91ng/mL, T1/2 of 2.31±0.10h and area under plasma concentration-time curve of 1527.00±46.61ng/mL×h.

Application of a Chiral Stationary Phase Based on 3,4,9,10-Perylenetetracarboxylic Acid to the Separation of Enantiomers under the Conditions of Gas and Liquid Chromatography

A chiral stationary phase is proposed on the basis of 3,4,9,10-perylenetetracarboxylic acid (3,4,9,10-perylentetracarbonacid, PTCA). The PTCA molecule itself is not chiral; however, it can form chiral supramolecular structures. Symmetry breaking during the self-assembly of PTCA supramolecular structures was carried out similarly to the Viedma ripening process. The obtained stationary phases with PTCA multilayers on an inert solid support and C18 silica were used to separate racemates in gas and liquid chromatography, respectively. It was found that the proposed stationary phases exhibit enantioselectivity with respect to pairs of enantiomers bearing a hydroxyl group at an asymmetric carbon atom. Enantiomers of butanol-2, pentanol-2, and 1-methoxy-propanol-2 were separated by gas chromatography. The separation of menthols was achieved in the normal-phase HPLC mode. It was shown that the separation of the last named compounds is possible up to a concentration of 0.04 mg/mL inclusive.

Innovations in Extractive Phases for In-Tube Solid-Phase Microextraction Coupled to Miniaturized Liquid Chromatography: A Critical Review.

Over the past years, a great effort has been devoted to the development of new sorbents that can be used to pack or to coat extractive capillaries for in-tube solid-phase microextraction (IT-SPME). Many of those efforts have been focused on the preparation of capillaries for miniaturized liquid chromatography (LC) due to the reduced availability of capillary columns with appropriate dimensions for this kind of system. Moreover, many of the extractive capillaries that have been used for IT-SPME so far are segments of open columns from the gas chromatography (GC) field, but the phase nature and dimensions are very limited. In particular, polar compounds barely interact with stationary GC phases. Capillary GC columns may also be unsuitable when highly selective extractions are needed. In this work, we provide an overview of the extractive capillaries that have been specifically developed for capillary LC (capLC) and nano LC (nanoLC) to enhance the overall performance of the IT-SPME, the chromatographic separation, and the detection. Different monolithic polymers, such as silica C18 and C8 polymers, molecularly imprinted polymers (MIPs), polymers functionalized with antibodies, and polymers reinforced with different types of carbon nanotubes, metal, and metal oxide nanoparticles (including magnetic nanoparticles), and restricted access materials (RAMs) will be presented and critically discussed.

Determination of Monoaromatic Hydrocarbons in Water Samples by Nano-Liquid Chromatography using a Composite Carbon Nanotubes- Lauryl Polymethacrylate Capillary Monolithic Column

Background: This work reports a green analytical method for the determination of organic environmental pollutants using nano-liquid chromatography with a self-made column for rapid, sensitive, inexpensive and efficient analysis of BTX pollutants in water. The applications of monolithic nanoscale columns for quantitative analysis of environmental real samples are very limited in the literature. Methods: A capillary column containing a composite of multi-walled carbon nanotubes incorporated into a lauryl methacrylate-co-ethylene dimethacrylate porous monolithic polymer was fabricated for the determination of BTX pollutants in real water samples. Results: Baseline separation was accomplished at 0.4 µL/min flow rate with UV-detection set at 208 nm. Under the optimum conditions, the calibration curves were validated over the range of 1.0-500 µg/L with R2 more than 0.9992. The detection limits of benzene, toluene, o-xylene and m/p-xylene were 0.25, 0.05, 0.075 and 0.05 µg/L, respectively. After a simple extraction process with a theoretical preconcentration factor equal to 200, the recovery values in Milli-Q, tap and sea water samples were found to be ranged from 84.85 to 97.84% with %RSD less than 7.5. Furthermore, we reported a comparison between our prepared composite column with a commercial C18 silica based column which is the most used in such analytical field. Each column demonstrated its advantages from different analytical aspects. Conclusion: The application of monolithic columns and nano-scale LC for routine analysis of environmental samples is very promising as the use of monolithic capillary columns offers several advantages over conventional scale particulate packed columns.

Quantitative bioanalytical assay for the selective RET inhibitors selpercatinib and pralsetinib in mouse plasma and tissue homogenates using liquid chromatography-tandem mass spectrometry

Selpercatinib and pralsetinib are potent and selective tyrosine kinase inhibitors targeting the rearranged during transfection (RET) receptor in various types of cancer. In this study, a bioanalytical assay was developed and fully validated for selpercatinib and pralsetinib in mouse plasma and partially in eight mouse tissue homogenates using liquid chromatograph-tandem mass spectrometry. Samples were pre-treated by protein precipitation with acetonitrile using erlotinib as internal standard. Separation of the analytes was performed on an ethylene bridged octadecyl silica C18 column by gradient elution using ammonium hydroxide (in water) and methanol. Analytes were detected by positive electrospray ionization in selected reaction monitoring mode. A linear concentration range of 2–2000 ng/ml was used for the validation of the assay for both inhibitors. The precision values (within–day and between–day) ranged between 3.4 and 10.2% for selpercatinib and 3.1–14.6% for pralsetinib in all matrices. Furthermore, data obtained for accuracy were between 91.7 and 109.3% and 85.1–114.1% for selpercatinib and pralsetinib, respectively. No significant matrix effects or extraction losses were observed and both analytes were stable under all investigated conditions. Finally, a pilot study for selpercatinib in mice was conducted employing this method, followed by a successful incurred sample reanalysis.

A novel high performance liquid chromatography method development and validation of fluconazole by ezchrom software

The current research explains the development of a new method and its subsequent validation by a novel HPLC method in fluconazole tablets. Inertsil Octadecyl silica C18 column having dimensions of length 150 mm, diameter 4.6 mm, particle size 5 μm was exploited for the method development, and the mobile phase embodies buffer pH 4 and acetonitrile in the combo of 40:60. Wavelength exploited for the segregation was 289 nm. The volume of injection was preserved at 20 µl. The new developed method has been established to demonstrate linearity in the range of 10 to 30 µg /ml correspondingly. Average recovery established to be 101.571, 100.315, and 99.021, the standard deviation was established to be 0.93834, 0.986418, and 0.989741, and % R.S.D was established to be 0.92382, 0.98331, and 0.999526. The percentage recovery was established to be within prescribed restrictions. The limit of detection was established to be 0.0080. The limit of quantitation was established to be 0.0051. In assay studies, an average assay was found to be 95.966, and standard deviation and % RSD of the assay was found to be 0.6021 and 0.6274, respectively. The method was found to be specific as there was no intrusion from impurities and excipients. Extensive diversity of mobile phase combos was utilized for the research and flow rate preserved at 1.3 ml/min all through the process. After carefull and systemic investigation of various research articles and review articles, it is observed that H.P.L.C method development and validation of fluconazole has been done in various pharmaceutical dosage forms, but till now a smaller amount of work is executed on dosage forms of solid nature, and hence there is huge prospective for research to be done in this area for new methodology to be developed in pharmaceutical dosage form of solid nature by means of dissimilar mobile phase combos and different strategy adopted by use of chromatography software which avoids the problems and demerits associated with present methods

VALIDASI DAN ANALISIS KADAR AKRILAMIDA PADA KOPI TUNGKAL DENGAN METODE KROMATOGRAFI CAIR KINERJA TINGGI (KCKT)

Acrylamide is a chemical compound found in roasted coffe at temperature above 120⁰C. potential to couse cancer in humans. The coffee used by processed at home in the village of Betara sub-district, Tanjung Jabung Barat, Kuala Tungkal, Jambi. The purpose of this study is to compare acrylamide content traditional coffee powder with the high performance liquid chromatography method (HPLC). The phase of motion used acetonitril : phosphate acid (80:20 v/v), using C18 or oktadesil silica (ODS) with size 250 nm × 4,6 mm,injection volume 20 μl, detector genesys 10S UV-Vis at wavelength 203 nm. Acrylamide is ground coffee was identified at retention time (tR) ± 5,825 minute. This method is proven valid with linearity y = 20717x + 28752, correlation coefficient (r) = 0,998%, the limit of detection 0, 32109 ppm and the limit of quantitation 1,07031 ppm, orecision with <2%. Acrylamide levels in coffee powder 1 to 4 respectively are 72,065 μg/g sample (1), 66,922 μg/g sample (2), 60,215 μg/g sample (3), and 61,422 μg/g sample (4). The four coffee samples showed that the acrylamide levels of each sample exceeded the safe limit of consumption of acrylamide released by FDA is 2 μg/g.

Method Development and Estimation of Phenylenediamine in Gastric contents, Blood and Urine

PhenylenediamineA method for detecting and estimating Paraphenylenediamine (PPD) in the biological samples has been developed and validated using High- Performance Liquid Chromatography (HPLC) with UV/VIS detector. The method quantitatively measured the PPD in the biological samples. The mobile phase was composed of 10: 90 (Acetonitrile: Ammonium acetate 25 Mm v/v) of pH 4.5. The isocratic separation was carried out at C18 silica gel column at 1ml/minute of flow rate. The spectrophotometric detection was carried out at 240 nm. The process was validated, and the limit of detection for PPD was found to be 10μg. The accuracy and precision of the process were within limits. The linearity of the process found to be upto 1000 ppm. The extraction of PPD was carried out with chloroform and Sodium Hydroxide. The stock solution of PPD was freshly prepared due to oxidation potential. Aniline was used as an internal standard. The sample negative and sample positive were run to ensure the validity of the process. The estimation of the PPD was performed by drawing the calibration curve of different calibrators of PPD. The determination of PPD was carried out in gastric contents, Blood, and Urine. The extracted samples were prepared and run at HPLC for the detection. The pretreatment of the samples was not required, and the method proved to be accurate, precise, and specific.

Micellar and sub-micellar liquid chromatography of terephthalic acid contaminants using a C18 column coated with Tween 20.

The tremendous amounts of terephthalic acid (TPA) produced globally require consistent monitoring of its contaminants during the different stages of production for quality control purposes. In this paper, a simple, robust and green liquid chromatography method has been developed using an isocratic 100% aqueous mobile phase at pH 2 (dilute sulfuric acid) to separate TPA contaminants (mono-, di-, and tri-carboxylic aromatic acids) on a C18 stationary phase coated with Tween 20 (polyoxyethylene(20)sorbitan monolaurate). After optimization of all chromatographic conditions, near baseline separation of the nine carboxylic acids under investigation was achieved with a 2.5 mL/min flow rate on a 5 micron C18 silica column (100 x 4.6 mm) in under 20 min. The modified stationary phase showed an excellent capability to separate structural isomers in a reasonable time, markedly better that the bare C18 stationary phase. Plots of ln retention factor versus 1/temperature showed the expected linear relationship for the di- and tri-carboxylic aromatic acids (single retention mechanism likely) but a quadratic fit for the mono-carboxylic aromatic acids (dual retention mechanism likely). Due to the stability of the surfactant modified stationary phase, future potential mass spectrometry compatibility was shown through the alternative use of trifluoroacetic acid in the 100% H2O (no Tween) mobile phase but still with UV detection. The developed method with 0.001% (vol/vol) Tween in the mobile phase was successfully used to analyze two different types of TPA industrial samples for all nine components plus revealing some other impurity peaks. The lowest limit of detection was 0.010 nmoles for o-phthalic acid and p-toluic acid (PTA), while the highest was 0.065 nmoles for 4-carboxybenzaldehyde (CBA). The concentrations of these important contaminants, PTA and CBA, in the mother liquor sample were 3348mg/L and 1806mg/L, respectively, while their respective concentrations in the purified TPA powder were 135mg/kg and 17.7mg/kg.

The Influence of Water–Acetonitrile Solvent Composition on Thermodynamic Characteristics of Adsorption of Aromatic Heterocycles on Octadecyl-Bonded Silica Gels

The thermodynamics of adsorption of some substituted 1,3,4-oxadiazoles and 1,2,4,5-tetrazines from water–acetonitrile solutions with acetonitrile volume fraction varying within a range of 0.35–0.90 on chemically modified Luna C18 and Discovery C18 silica gels has been studied within a temperature range of 313.15–333.15 K. The thermodynamic characteristics of the adsorption of these compounds on Luna C18 and Discovery C18 silica gels have been determined as depending on solution composition. In the case of Discovery C18, the character of the dependences of different thermodynamic characteristics of the adsorption on liquid phase composition is similar to that of the corresponding dependences previously observed for modified Ascentis®Phenyl silica gel. A similarity has also been found for the dependences of the thermodynamic characteristics of the adsorption on Luna C18 and modified Diasfer-110-C18 silica gel studied previously. The mechanism of the liquid-phase adsorption of 1,3,4-oxadiazoles and 1,2,4,5-tetrazines on Luna C18 is changed within a range of acetonitrile volume fractions of 0.60–0.75, as it is in the case of Diasfer-110-C18. At acetonitrile volume fractions of higher than 0.75, the studied heterocycles are adsorbed on Luna C18 surface dynamically modified with acetonitrile without a direct interaction with the grafted layer of the chemically modified silica gel. At the same time, the mechanism of their adsorption on Discovery C18 remains unchanged while acetonitrile concentration is increased in the liquid phase.

Automated on-line liquid-liquid extraction in a multisyringe flow injection analysis manifold for migration studies in food-contact materials: analysis of 4,4´-dihydroxybiphenyl

ABSTRACTPackaging may represent a source of food contamination, as different organic compounds and degradation compounds may migrate from packaging to foodstuff. For fatty foods, rectified olive oil is the common simulant, which implies time-consuming and laborious liquid-liquid extraction (LLE) procedures to isolate the contaminant(s) from the oil. Here we propose a Multisyringe Flow Injection Analysis manifold to automate this sample treatment, using the monomer 4,4´-dihydroxybiphenyl as the contaminant. The LLE procedure, using water as extractant, was fully automated. After the on-line LLE, the resulting extract was pumped through a fluorescence detector, inside which a flow-cell filled with C18 silica gel solid support was placed. The analyte was pre-concentrated on the solid support (in which the analytical signal was directly recorded), so improving the sensitivity of the system. Under optimum conditions, the method detection limit is 0.05 mg kg−1, well within the specific migration limit of 6 mg kg−1. The method developed was compared with the standard CEN test method (off-line LLE and HPLC determination) observing savings in sample and reagents of 90% and a 7-fold increase in sample throughput.

The dispersive micro-solid phase extraction method for MS-based lipidomics of human breast milk

A simple and rapid microextraction method ensuring high lipidome coverage was developed for liquid chromatography mass spectrometry (LC-MS)-based lipidomics of human breast milk. The dispersive microsolid phase extraction (D-µ-SPE) technique, coupled with the design of experiment (DoE) method, enabled the study of the influence of several conditions (desorption solvent, stationary phase ratio, and sorption and desorption time) on the lipid extraction process of various lipid classes. The D-µ-SPE-based method, which used a mixture of C18 and zirconia-coated silica gel as the sorbent, allowed for the extraction of a wide range lipid classes characterized by different concentration levels. The developed method simplified the extraction procedure for lipidomics without loss of good reproducibility (70% of the MFs had peak volume%RSD <20% for all the tested stationary phases). The highest lipidome coverage was achieved when 100 µL of the human breast milk (HBM) sample was extracted using 27 mg of C18 mixed with 3 mg of zirconia-coated silica gel as the sorbent and methanol:2-propanol: ammonium hydroxide (14:81:5 v/v/v) mixture as the desorption solvent. The sorption and desorption time did not influence the number of extracted molecular features. The advantages of the present method over the traditional SPE and liquid-liquid extraction (LLE) commonly used in lipidomics are the possibility of mixing sorbents with various sorption mechanisms, which ensures high lipidome coverage, and the use of a small number of materials, including the sorbent and organic solvent.

A new triterpenoid from the leaves of Rhodomyrtus tomentosa (Ait.) Hassk

A new triterpenoid, 2α, 3β, 23α, 29-tetrahydroxyolean-11, 13 (18)-dien-28, 19β-olide, named as rhodotomoside A (1), together with six known triterpenoids (2–7), were isolated from the leaves of Rhodomyrtus tomentosa (Ait.) Hassk by column chromatography on silica gel, reversed-phase C18 silica gel and semi-preparative HPLC. Their structures were elucidated on the basis of spectroscopic methods, including extensive 1D NMR, 2D NMR and MS spectra. The inhibition rates of α-glucosidase of compound 1 was 77.82%, and exhibited inhibitory activity against α-glucosidase with IC50 value at 0.213 ± 0.016 mg/mL.

On the Differences in the Mechanisms of Adsorption of Aromatic Heterocycles from Water–Acetonitrile Solutions on Octadecyl-Bonded Silica Gels

Adsorption of some 1,3,4-oxadiazoles and 1,2,4,5-tetrazines from water–acetonitrile solutions on Luna C18 and Discovery C18 silica gels with grafted octadecyl groups has been studied in a wide range of compositions at temperatures of 313.15–333.15 K. The comparative analysis of the liquid-phase adsorption of the heterocycles has revealed a number of differences between the mechanisms of binding molecules of the studied compounds by the surfaces of these octadecyl-derivatives of silica gel. The log–log dependences of the retention factor on the molar fraction of acetonitrile in the solutions are strictly linear only for adsorption on Luna C18 silica gel, which is characterized by an increased hydrophobicity. For the adsorption of the studied heterocycles on Discovery C18 silica gel, the concentration dependences of the retention at low and high acetonitrile concentrations in the solution are described by quadratic functions and characterized by higher retention values as compared with those for the linear dependence because of the lower hydrophobicity of this silica gel. It has been found that the surface layer of Luna C18 modified silica gel is enriched with acetonitrile molecules to a higher extent than the surface layer of Discovery C18 silica gel. It has been shown that one adsorbed molecule of 1,3,4-oxadiazoles and 1,2,4,5-tetrazines displaces three and two molecules of pre-adsorbed acetonitrile from the surfaces of Luna C18 and Discovery C18 silica gels, respectively. Linear correlation equations have been proposed for calculating the retention of the studied heterocycles on Luna C18 and Discovery C18 silica gels from mobile phases of arbitrary compositions at different temperatures of chromatographic columns.

Micro solid-phase extraction for the analysis of per- and polyfluoroalkyl substances in environmental waters

Growing concern over the environmental and health impacts of per- and polyfluoroalkyl substances (PFASs) has led to the development of increasingly stringent regulatory guidelines. To meet these guidelines for the determination of PFASs in surface-water, solid-phase extraction (SPE) is commonly implemented for clean-up and pre-concentration of samples. In this paper a micro-SPE method for the clean-up and pre-concentration of PFASs from surface-water was developed. A micro-SPE packing phase was created to retain 13 long and short chain PFAS after examining combinations of four 3 µm particle size sorbents, with the optimal phase consisting of a 50:50 mixture of C18 and aminopropyl silica. Micro-SPE achieved similar results to conventional SPE methods while reducing sample preparation time to 5 min and using only 2 mL of sample. The method was validated using spiked recoveries (100 ng L−1) from PFAS contaminated surface-water samples with recoveries ranging from 86% to 111% and relative standard deviations below 18%. Concentrations of the PFASs in the samples ranged from below the limit of quantification to 898 ± 15 ng L−1. Automation of sample preparation, including the micro-SPE extraction, was also demonstrated. These results show the potential for automated micro-SPE to replace conventional SPE, with the decreases in sample preparation time, sample and solvent volumes crucial for incorporation into routine analyses in commercial laboratories.