Structure–retardation factor relationship of natural amino acids in two different mobile phases of RP-TLC

Abstract

Separation of amino acids (AAs) and their simple and inexpensive determination/identification is an interesting topic in biological and protein science, different food industries, and drug factories. Also, the presentation of the chromatographic behavior of compounds in a predictive model can be effective to estimate the structural/chemical properties of analyte and mobile phases. In this work for the first time, retardation factor (R_F) of 42 AAs in reversed-phase thin layer chromatography (RP-TLC) was modeled. Acetonitrile-sodium azide solution and 1,2 dioxane-sodium azide solution were two mobile phases which have been studied in this work. Results showed that the values of R_F are correlated with the structural properties of AAs and these properties had some similarities and differences in two noted mobile phases. For the TLC data in two mobile phases, five parametric linear models were suggested (R²_train = 0.93 and 0.97; R²_test = 0.93 and 0.99). The models were also evaluated with different statistical approaches. It was shown that increasing the sum of geometrical distances between N and O in AAs causes decreasing their R_F in RP-TLC using both mobile phases. Other structural effects of AAs on their separation in the desired RP-TLC system were also discussed.     

Extraction,separation and quantitative structure–retention relationship modeling of essential oils in three herbs

The essential oils extracted from three kinds of herbs were separated by a 5% phenylmethyl silicone (DB‐5MS) bonded phase fused‐silica capillary column and identified by MS. Seventy‐four of the compounds identified were selected as origin data, and their chemical structure and gas chromatographic retention times (RT) were performed to build a quantitative structure–retention relationship model by genetic algorithm and multiple linear regressions analysis. The predictive ability of the model was verified by internal validation (leave‐one‐out, fivefold, cross‐validation and Y‐scrambling). As for external validation, the model was also applied to predict the gas chromatographic RT of the 14 volatile compounds not used for model development from essential oil of Radix angelicae sinensis. The applicability domain was checked by the leverage approach to verify prediction reliability. The results obtained using several validations indicated that the best quantitative structure–retention relationship model was robust and satisfactory, could provide a feasible and effective tool for predicting the gas chromatographic RT of volatile compounds and could be also applied to help in identifying the compound with the same gas chromatographic RT.     

Ultra‐performance liquid chromatography of amino acids for the quality assessment of pearl powder

Pearls have been widely used as a traditional medicine, in cosmetics, and as a health food supplement in China since ancient times. However, the identification and quality assessment of pearl powder have been challenging tasks because of the similar morphological features and chemical composition of its common adulterants, especially conch powders. In this study, ultra‐performance liquid chromatography was combined with pre‐column derivatization to rapidly quantify 14 amino acids in pearl powder and its analogues. Based upon the quantification results, a quality criterion of a total amino acid content of not less than 1.10% was proposed for pearl powder. Principal component analysis indicated that leucine and phenylalanine were the amino acids characteristic for distinguishing between pearls and nacres. The area ratio of leucine to phenylalanine was demonstrated to be an effective diagnostic marker to discriminate freshwater cultured pearls, natural seawater pearls, and nacres. The proposed method, involving both the qualitative and quantitative aspects, was subsequently applied to quality assessment of pearl powders purchased commercially in various parts of China; eight out of 18 batches were deemed authentic and unadulterated. In the future, this analytical process should play a significant role in standardizing and providing quality control to the pearl powder market.     

Analysis of free amino acids in Amur sturgeon by ultra‐performance liquid chromatography using pre‐column derivatization with 6‐aminoquinolyl‐carbamyl

A rapid, sensitive, and reliable ultra‐performance liquid chromatography (UPLC) coupled with photodiode array detection method was developed for the amino acid analysis of Amur sturgeon (Acipenser schrenckii Brandt). The method uses minimal sample volume and automated online precolumn derivitization of amino acids with fluorescent 6‐aminoquinolyl‐carbamyl reagent. The chromatographic separation was achieved by UPLC, which used a column with 1.7 μm particle packing that enabled higher speed of analysis, peak capacity, greater resolution, and increased sensitivity. Amino acid derivatives obtained under optimal conditions were separated on a Waters UPLC BEH C₁₈ column with Acetonitrile–acetate buffer as mobile phase. Matrix effects were investigated and good linearities with correlation coefficients better than 0.9949 were obtained over a wide range of 5–1000 μmol/L for all amino acids. The simple sample preparation and minimal sample volume make the method useful for the quantitation of 17 amino acids in Amur sturgeon samples. It is concluded that a rapid and robust platform based on UPLC was established, and a total of 17 amino acids of Amur sturgeon were tentatively detected. This method showed good accuracy and repeatability that can be used for the quantification of amino acids in real samples.     

Recent advances in the preparation of adsorbent layers for thin‐layer chromatography combined with matrix‐assisted laser desorption/ionization mass‐spectrometric detection

This review is focused on planar chromatography hyphenated with mass‐spectrometric detection for analysis of low‐molecular‐mass solutes. Various kinds of hyphenations are discussed with attention paid to the preparation of thin layer plates suited both for the mass‐spectrometric detection of the resolved solutes direct from thin‐layer plates and for indirect mass‐spectrometric detection of the resolved solutes, performed by scraping, extracting, purifying, and concentrating the analyte from the thin‐layer chromatography plate. Plates with monolithic layers are relatively new for thin‐layer chromatography but they can successfully be combined with mass‐spectrometric technique in a pursuit of comprehensive local sample composition information. Preparation of monolithic layers of different porosity and structure based on organic, inorganic, and composite materials is illustrated together with examples of successful separation and detection of low‐molecular‐mass solutes by means of matrix‐assisted and surface‐assisted laser desorption mass spectrometry.     

A Systematic Study of Peripherally Multiple Aromatic Ester‐Functionalized Poly(benzyl ether) Dendrons for the Fabrication of Organogels: Structure–Property Relationships and Thixotropic Property

A new class of peripherally multiple aromatic ester‐functionalized poly(benzyl ether) dendrons and/or dendrimers with different focal point substituents, surface groups, interior structures, as well as different generations have been synthesized and their structure–property relationships with respect to their gelation ability have been investigated systematically. Most of these dendrons are able to gel organic solvents over a wide polarity range. Evident dendritic effects were observed not only in gelation capability but also in thermotropic, morphological, and rheological characterizations. It was disclosed that subtle changes in peripheral ester functionalities and interior dendritic structures affected the gelation behavior of the dendrons significantly. Among all the dendrons studied, the second‐ and third‐generation dendrons G₀G₂‐Me and G₀G₃‐Me with dimethyl isophthalates (DMIP) as peripheral groups exhibited the best capability in gelation, and stable gels were formed in more than 22 aromatic and polar organic solvents. The lowest critical gelation concentration (CGC) reached 2.0 mg mL^?1, indicating that approximately 1.35×10⁴ solvent molecules could be entrapped by one dendritic molecule. Further study on driving forces in gel formation was carried out by using a combination of single‐crystal/powder X‐ray diffraction (XRD) analysis and concentration‐dependent (CD)/temperature‐dependent (TD) ¹H NMR spectroscopy. The results obtained from these experiments revealed that the multiple π–π stacking of extended π‐systems due to the peripheral DMIP rings, cooperatively assisted by non‐conventional hydrogen‐bonding, is the key contributor in the formation of the highly ordered supramolecular and fibrillar network. In addition, these dendritic organogels exhibited unexpected thixotropic‐responsive properties, which make them promising candidates with potential applications in the field of intelligent soft materials.     

Determination of chlorogenic acid,polyphenols and antioxidants in green coffee by thin‐layer chromatography,effect‐directed analysis and dot blot – comparison to HPLC and spectrophotometry methods

The great prevalence of thin‐layer chromatography over high‐performance liquid chromatography is connected with the possibility of analyzing many samples in parallel. Therefore, the method is often used in screening and/or effect directed analysis to compare composition and chemical/biological properties of many samples in one run. It was already proved, that high performance thin‐layer chromatography, in many cases, can replace high‐performance liquid chromatography for quantitative analysis. The main aim of the paper is to show that simple thin‐layer chromatography can also be used as a quantitative or at least as a semi‐quantitative method, even when it concerns effect directed analysis e.g. direct bioautography. Chlorogenic acid content was measured in four methanol extracts of various green coffees and in one extract of black coffee using thin‐layer chromatography with ultraviolet detection and thin‐layer chromatography with effect directed detection. High‐performance liquid chromatography was used as a reference method. Additionally, total contents of polyphenols and antioxidants were estimated using thin‐layer chromatography or dot‐blot on chromatography plates. These results were compared to spectrophotometric methods. It was proved that thin‐layer chromatography can be used as a quantitative (using densitometry) or semi‐quantitative method (using other detection methods including effect directed detection) as well as for estimating total antioxidants or polyphenols content.     

Derivatization coupled to headspace programmed‐temperature vaporizer gas chromatography with mass spectrometry for the determination of amino acids: Application to urine samples

A new method based on headspace programmed‐temperature vaporizer gas chromatography with mass spectrometry has been developed and validated for the determination of amino acids (alanine, sarcosine, ethylglycine, valine, leucine, and proline) in human urine samples. Derivatization with ethyl chloroformate was employed successfully to determine the amino acids. The derivatization reaction conditions as well as the variables of the headspace sampling were optimized. The existence of a matrix effect was checked and the analytical characteristics of the method were determined. The limits of detection were 0.15–2.89 mg/L, and the limits of quantification were 0.46–8.67 mg/L. The instrumental repeatability was 1.6–11.5%. The quantification of the amino acids in six urine samples from healthy subjects was performed with the method developed with the one‐point standard additions protocol, with norleucine as the internal standard.     

Development of a highly sensitive high‐performance thin‐layer chromatography method for the screening and simultaneous determination of sofosbuvir,daclatasvir, and ledipasvir in their pure forms and their different pharmaceutical formulations

The combination of sofosbuvir and daclatasvir or sofosbuvir and ledipasvir is now widely used as an ideal treatment for hepatitis C virus infection. For this purpose, a simple, sensitive, accurate, economic, and precise high‐performance thin‐layer chromatography was developed and validated for the determination of sofosbuvir, daclatasvir, and ledipasvir in their pure form as well as their different pharmaceutical products. The method used Merck high‐performance thin‐layer chromatography aluminum plates precoated with silica gel 60 F254 as a stationary phase and mobile phase consisting of methylene chloride/methanol/ethyl acetate/ammonia (25%) (6:1:4:1, v/v/v/v). This system was found to give compact symmetric peaks of sofosbuvir, daclatasvir, and ledipasvir with retardation factors of 0.27 ± 0.01, 0.50 ± 0.007, and 0.68 ± 0.008, respectively. The densitometric scanner was set at 275 nm using a deuterium lamp. The calibration curves were linear over the range of 100–3000 ng/spot for sofosbuvir, and daclatasvir, and range of 50–3000 ng/spot for ledipasvir. The detection limits were 22.5, 31.90, and 15.80 for sofosbuvir, daclatasvir, and ledipasvir. The quantitation limits were 67.50, 95.60, and 47.50 for sofosbuvir, daclatasvir, and ledipasvir. The proposed method was validated according to International Conference on Harmonization (ICH) guidelines and the results were acceptable.     

High‐density extraction solvent‐based solvent de‐emulsification dispersive liquid–liquid microextraction combined with MEKC for detection of chlorophenols in water samples

For the first time, the high‐density solvent‐based solvent de‐emulsification dispersive liquid–liquid microextraction (HSD‐DLLME) was developed for the fast, simple, and efficient determination of chlorophenols in water samples followed by field‐enhanced sample injection with reverse migrating micelles in CE. The extraction of chlorophenols in the aqueous sample solution was performed in the presence of extraction solvent (chloroform) and dispersive solvent (acetone). A de‐emulsification solvent (ACN) was then injected into the aqueous solution to break up the emulsion, the obtained emulsion cleared into two phases quickly. The lower layer (chloroform) was collected and analyzed by field‐enhanced sample injection with reverse migrating micelles in CE. Several important parameters influencing the extraction efficiency of HSD‐DLLME such as the type and volume of extraction solvent, disperser solvent and de‐emulsification solvent, sample pH, extraction time as well as salting‐out effects were optimized. Under the optimized conditions, the proposed method provided a good linearity in the range of 0.02–4 μg/mL, low LODs (4 ng/mL), and good repeatability of the extractions (RSDs below 9.3%, n = 5). And enrichment factors for three phenols were 684, 797, and 233, respectively. This method was then utilized to analyze two real environmental samples from wastewater and tap water and obtained satisfactory results. The obtained results indicated that the developed method is an excellent alternative for the routine analysis in the environmental field.     

Three‐phase hollow fiber liquid‐phase microextraction based on a magnetofluid for the analysis of aristolochic acids in plasma by high‐performance liquid chromatography

A new and fast sample preparation technique based on three‐phase hollow fiber liquid‐phase microextraction with a magnetofluid was developed and successfully used to quantify the aristolochic acid I (AA‐I) and AA‐II in plasma after oral administration of Caulis akebiae extract. Analysis was accomplished by reversed‐phase high‐performance liquid chromatography with fluorescence detection. Parameters that affect the hollow fiber liquid‐phase microextraction processes, such as the solvent type, pH of donor and acceptor phases, content of magnetofluid, salt content, stirring speed, hollow fiber length, extraction temperature, and extraction time, were investigated and optimized. Under the optimized conditions, the preconcentration factors for AA‐I and AA‐II were >627. The calibration curve for two AAs was linear in the range of 0.1–10 ng/mL with the correlation coefficients >0.9997. The intraday and interday precision was <5.71% and the LODs were 11 pg/mL for AA‐I and 13 pg/mL for AA‐II (S/N = 3). The separation and determination of the two AAs in plasma after oral administration of C. akebiae extract were completed by the validated method.     

The determination of capreomycin in human plasma by LC–MS/MS using ion‐pairing chromatography and solid‐phase extraction

A bioanalytical method was developed and validated for the quantification of capreomycin (Cm) analogs, Cm IA and Cm IB, in human plasma. This implemented ion‐pairing solid phase extraction, followed by ion‐pairing high‐performance liquid chromatography, with tandem mass spectrometry detection. Chromatographic separation was achieved using a Discovery C₁₈, 5 μm, 4.6 × 50 mm analytical column. An isocratic mobile phase consisting of water and acetonitrile with 0.1% formic acid and 4mm heptafluorobutyric acid (80:20; v/v) was used at a flow‐rate of 500 μL/min. An AB Sciex API 3000 mass spectrometer at unit resolution, in multiple reaction monitoring mode, was used for detection. Electrospray ionization was used for ion production. The method was successfully validated for the range 469–30,000 ng/mL for Cm IA and for Cm IB, with cefotaxime as the internal standard. The within‐ and between‐day precision determinations for Cm IA and IB, expressed as the percentage coefficient of variation, were < 20.0% at the lower limit of quantification (LLOQ) and < 8.2% at all other test concentrations. Recovery of both analogs was > 72.3% and reproducible at the low, medium and high end of the calibration range. No significant matrix effects were observed for the analyte. The assay performed well when applied to clinical samples generated from children in a clinical multidrug resistant tuberculosis research study in South Africa.