Octadecyl-bonded Silica Gel Research Articles

Determination of 41 veterinary drug residues in livestock and poultry meat using a composite purification system coupled with direct analysis in real time-tandem mass spectrometry

In a market environment where food safety problems still occur despite repeated prohibitions, food safety problems caused by veterinary drug residues and biological safety problems caused by the transfer of drug resistance have attracted much attention. Herein, a method based on a compound purification system coupled with direct analysis in real time-tandem mass spectrometry (DART-MS/MS) was established to determine 41 different types of veterinary drug residues in livestock and poultry products. First, a single-standard solution sampling method was used to optimize the selection of the best quasi-molecular ion, two daughter ions, and their cone-hole and collision voltages; qualitative and quantitative ion pairs are composed of a quasi-molecular ion and its corresponding daughter ion. The abundance ratios of the drug compounds in standard solutions of the solvent and matrix mixtures were then calculated according to the requirements of the European Union 2002/657 specification. DART-MS/MS was subsequently developed for the accurate characterization and quantitative analysis of the veterinary drugs. Finally, a composite purification pretreatment system was formed by combining the primary secondary amine (PSA) and octadecyl bonded silica gel (C18) of a QuEChERS technology with multiwalled carbon nanotubes (MWCNTs) to achieve the one-step purification of the drug compounds. The influence of the key parameters of the DART ion source on the determination of the drugs was investigated using the peak areas of the quantitative ions as the criterion. The optimum conditions were as follows: ion source temperature of 350 ℃, 12-Dip-it Samplers module, sample injection speed of 0.6 mm/s, and external vacuum pump pressure of -75 kPa. According to the differences in the dissociation constant (pKa) ranges of the 41 types of veterinary drug compounds and the characteristics of the sample matrixes, the extraction solvent, matrix-dispersing solvent, and purification method were optimized based on the recovery. The extraction solvent was 1.0% acetonitrile formate solution, and the pretreatment column included MWCNTs containing 50 mg of PSA and 50 mg of C18. The three chloramphenicol drugs showed a linear relationship in the ranges of 0.5-20 μg/L with correlation coefficients of 0.9995-0.9997,and the detection and quantification limits of three chloramphenicol drugs were 0.1 and 0.5 μg/kg, respectively. The 38 other drugs, including quinolones, sulfonamides, and nitro-imidazoles showed a linear relationship in the ranges of 2-200 μg/L with correlation coefficients of 0.9979-0.9999, and the detection and quantification limits of the 38 other drugs were 0.5 and 2.0 μg/kg, respectively. The recoveries of the 41 veterinary drugs at low, medium, and high spiked levels in chicken, pork, beef, and mutton samples were 80.0%-109.6%, with intra- and inter-day precisions of 0.3%-6.8% and 0.4%-7.0%, respectively. A total of 100 batches of animal meat (pork, chicken, beef, and mutton; 25 batches each) and known positive samples were simultaneously analyzed using the national standard method and the detection method established in this study. Sulfadiazine (89.2, 78.1, and 105.3 μg/kg) was detected in three batches of pork samples, and sarafloxacin (56.3, 102.0 μg/kg) was detected in two batches of chicken samples and no veterinary drugs were detected in the other samples; both methods yielded consistent results for known positive samples. The proposed method is rapid, simple, sensitive, environmentally friendly, and suitable for the simultaneous screening and detection of multiple veterinary drug residues in animal meat.

Simultaneous analysis of paralytic shellfish toxins and tetrodotoxins in human serum by liquid chromatography coupled to Q-Exactive high-resolution mass spectrometry

Paralytic shellfish toxins (PSTs) and tetrodotoxins (TTXs) are powerful neurotoxins. Previous research reported that PSTs and TTXs are found together in seafoods and may pose a serious hazard to public health. In this study, a new analytical method combining modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged, Safe) with high-performance liquid chromatography coupled to Q-Exactive Orbitrap high-resolution mass spectrometry was developed and validated for the quantification of 10 PSTs and 2 TTXs in human serum. Chromatographic separation was achieved using the HILIC TSK-Gel Amide-80 column. The mass spectrometer was operated in full scan/dd-MS2(data-dependent MS2) mode, and for quantification analysis. The dd–MS2 resolution was set to 17,500 fullwidthat halfmaximum （FWHM）. Results showed that methanol with 1 % (v/v) acetic acid extraction combined with 50 mg graphitized carbon black (GCB) and 50 mg octadecyl bonded silica gel (C18) was most suitable for purification. The mean recovery for all toxins ranged from 85.3 % to 118.2 % (RSD < 12 %). The limits of detection and quantification for human serum were in the ranges of 0.67–2.61 and 2.23–8.69 ng mL−1, respectively. The method was applied to analyze toxins in serum samples obtained from three poisoned patients in a case of poisoning caused by consumption of toxin-contaminated gastropoda (Bullacta exerata). The study has important application for rapid and accurate diagnosis of PSTs and TTXs toxin poisoning patients in clinic.

Detection of Glyamifop residues in rice and its environment by the QuEChERS method combined with HPLC–MS

Glyamifop is a new herbicide developed by Jiangsu Zhongqi Technology Co., Ltd. (Nanjing, China). No analytical method has previously been reported for determining its residual concentrations in rice and its related environmental samples. This work established a method for the determination of Glyamifop residues in various matrices using high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS) with sample pretreatment by the optimized quick, easy, cheap, effective, rugged, and safe (QuEChERS) method. All samples were extracted with acetonitrile and purified with octadecyl bonded silica gel, N-propylethylenediamine, and graphitized carbon black adsorbents. Chromatographic separation was performed on an Agilen ZORBAX Eclipse XDB-C18 column, and Glyamifop in the samples was detected by electrospray ionization mass spectrometry in positive ion mode. Results demonstrated this method has good linearity for Glyamifop assessment in all matrices over a wide concentration range (0.01–1 mg L−1), with a coefficient of determination >0.99. At levels of 0.01, 0.1, and 0.5 mg kg−1, the mean recoveries of Glyamifop in various matrices varied between 84.15% and 105.76%, with relative standard deviations of 1.3%–9.8%. The detection and quantification limits of this method in each matrix are 1.3–3.6 μg kg−1 and 4.89–12.48 μg kg−1, respectively. All matrices had a moderate matrix effect (between −21.63% and 14.21%), which could be calibrated using respective matrix standard curves. The proposed method is simple and sensitive, and appears suitable for the determination of Glyamifop residues in rice and its environment.

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.

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.

Simultaneous determination of febrifugine and isofebrifugine in Dichroa febrifuga root by HPLC method

To develop the HPLC method for simultaneous determination of febrifugine and isofebrifugine in Dichroa febrifuga root, and on the basis of this, the feasibility of quantitative analysis of multi-component by a single-marker (QAMS) model for the determination of the two alkaloids was investigated. The chromatographic separation was performed on an octadecyl bonded silica gel column with mixed solvent consisting of acetonitrile-water-glacial acetic acid-triethylamine (9∶91∶0.36∶0.745) as mobile phase at a flow rate of 1.0 mL•min⁻¹. The detection wavelength was set at 225 nm, and the column temperature was set at 30 ℃. The linear range of febrifugine and isofebrifugine were 10.7-426 ng and 10.6-424 ng, respectively. Their average recovery were 98.33% (RSD 2.7%) and 100.4% (RSD 1.8%), respectively. On the basis of this established method, febrifugine was used as the internal reference substance to calculate the relative correction factors (RCF) and the relative retention values (RRV) of isofebrifugine to febrifugine. Through a series of methodology evaluations, the two alkaloids were simultaneously assayed only by quantitative determination of febrifugine. This result played the part of demonstration role for the application of QAMS model in the determination of isomers.

Selectively Enhanced Retention of Neutral Iron(II) Complex in RP-LC with o-Hydroxy Pyrimidylazo Compounds as Precolumn Derivatizing Reagent

The diazo component of o-hydroxy heterocyclic azo compounds showed a remarkable effect on the retention of their neutral complexes of iron and nickel as a precolumn derivatizing reagent in the separation of metal ions by RP-HPLC using an octadecyl-bonded silica gel column. High resolutions of iron and nickel complexes were obtained with pyrimidyl derivatives. Acetonitrile-water or acetone-water was more suitable as a mobile phase than alcohol-water with regard to the separation of these metal ions. Thermodynamic study showed that the difference in transfer enthalpies of iron and nickel complexes from the mobile phase to the stationary phase dominated the resolution of two complexes with pyrimidyl compounds. High resolutions obtained by use of pyrimidyl compounds were ascribed to selectively enhanced retention of the iron complexes from the comparison with the retentions of the zinc complexes.

Optimization of a solid phase extraction procedure for prostaglandin E 2, F 2α and their tissue metabolites

The primary prostaglandins PGE 2 and PGF 2α are metabolized in tissues by a series of enzymatic and non-enzymatic reactions. To measure metabolic rates and individual reaction rates it is necessary to extract the parent prostaglandins and metabolites before the separation and quantification of each compound is achieved. Here we have established and optimized a solid phase extraction (SPE) procedure to recover PGE 2, PGF 2α and their six enzymatic and non-enzymatic tissue metabolites from aqueous solutions including urine, plasma and tissue homogenate. We have used octadecyl-bonded silica gel as the stationary phase and methanol–water mixtures as binary mobile phases. The volumes and concentrations of the washing and elution solutions were optimized individually for each PG. Recoveries of all PG standards were quantitative except for PGEM, which was recovered at 80% efficiency. Biological matrix components interfered with the extraction in a PG- and matrix-specific fashion. Inclusion of 1% formic acid in the loading mixture raised recoveries from urine, plasma and tissue homogenate to ≥90%. This SPE method is the first that has been optimized by systematic elution studies for PGE 2, PGF 2α and the complement of their tissue metabolites. The procedure is simple, robust and can serve as an effective pre-purification step before downstream separation and quantification of each tissue metabolite of PGE 2 and PGF 2α from complex biological matrices.

TLC analysis of non-steroidal anti-inflammatory drugs and videodensitometric determination of fenbufen in tablets

The chromatographic separation of fenbufen, ibuprofen, ketoprofen, diclofenac sodium, mefenamic acid, and tiaprofenic acid has been investigated. Normal-phase chromatography on silica gel by the ascending and horizontal techniques, and reversed-phase chromatography on octadecyl-bonded silica gel (RP-18) in horizontal chambers, were performed with suitable mobile phases. The substances were identified by UV illumination at λ = 254 nm and by use of dyeing reagents. Reversed phase chromatography with phosphate buffer, pH 5.73–10% CTMA-Br in methanol, 3.5 + 6.5 ( v/v ), as mobile phase enabled better separation of the six drugs than normal-phase mode. A simple videodensitometric TLC method on silica gel RP-18 was developed and validated for quantitative determination of fenbufen in tablets. The limits of detection and quantification were determined by videodensitometry at λ = 254 nm. A calibration plot was constructed in the range 2.0–12.0 μg/5-μL spot and was linear with a good correlation coefficient (0.992...

Normal- and reversed-phase thin-layer chromatography of seven oral antidiabetic agents

The chromatographic behavior of seven oral antidiabetic drugs — chlorpropamide, tolbutamide, glibenclamide, metformin, pioglitazone, rosiglitazone, and repaglinide — has been investigated. Normal-phase chromatography was performed on silica gel and alumina layers with mixtures of chloroform, diethyl ether, and ethyl acetate as mobile phases. For more effective resolution aqueous ammonia or acetic acid was added to the mobile phases. Silica gel enabled better separation than alumina. Reversed-phase chromatography was performed on octadecyl-bonded silica gel (RP-18) with mixtures of acetonitrile or 2-propanol with phosphate buffer as mobile phases. The effect of pH on the separation of the drugs was also examined. For separation of these drugs reversed-phase chromatography was more effective than use of normal-phase mode.

Recovery of gangliosides from aqueous solutions on styrene-divinylbenzene copolymer columns

An investigation was made using a styrene-divinylbenzene copolymer as a solid phase sorbent to recover gangliosides from aqueous solutions. A comparison with octadecyl-bonded (C18) silica gel showed that the general procedure used to purify gangliosides on C18 silica gel could be used with the copolymer. The yield of gangliosides depended on various parameters such as the composition of the conditioning solution, the salt concentration of the loading solution, and the amount of applied gangliosides per gram of copolymer. In optimal conditions, the recovery of gangliosides and other lipids present in the upper phases of partition was higher than 95%. Using radiolabeled gangliosides, it was found that gangliosides present in serum-containing medium could also be quantitatively recovered on copolymer, provided the medium was diluted with an equal volume of methanol prior to its application onto the column. The major advantage of the copolymer is its high stability in acidic or alkaline conditions that allows multiple cycles of cleaning and reconditioning of the sorbent without alteration of its chromatographic properties.

Prediction of soil adsorption coefficients from retention parameters on three reversed-phase liquid chromatographic columns.

Reversed-phase high-performance liquid chromatographic (RP-HPLC) retention parameters, which are determined by the intermolecular interactions in retention process, can be considered as the chemical molecular descriptors in linear free energy relationships (LFERs). On the basis of the characterization and comparison of octadecyl-bonded silica gel (ODS), cyano-bonded silica gel (CN), and phenyl-bonded silica gel (Ph) columns with linear solvation energy relationships (LSERs), a new multiple linear regression model using RP-HPLC retention parameters on ODS and CN columns as variables for estimation of soil adsorption coefficients was developed. It was tested on a set of reference substances from various chemical classes. The results showed that the multicolumn method was more promising than a single-column methpd was for the estimation of soil adsorption coefficients. The accuracy of the suggested model is identical with that of LSERs.

Analysis of glyphosate and its metabolite, aminomethylphosphonic acid, in agricultural products by HPLC

An analytical method for residues of the herbicide glyphosate [GLY: N-(phosphonomethyl)-glycine] and its metabolite (AMPA: aminomethylphosphonic acid) in agricultural products is described. GLY and AMPA were extracted with water (soybeans extract was moreover treated with acetone), and purified by application to a dual mini-cartridge column (octadecyl-bonded silica gel and cation-exchange silica gel) system. GLY was derivatized with 9-fluorenylmethylchloroformate, and determined by HPLC with fluorescence detection. AMPA determination was performed by HPLC employing postcolumn fluorogenic labeling with o-phthalaldehyde-mercaptoethanol. The detection limits for GLY and AMPA were 0.04 microgram/g (soybean: 0.08 microgram/g), and both recoveries from samples to which the compounds were added at the 0.2 microgram/g level (soybean: 1.0 microgram/g) were more than 65%.

Evaluation of the Gibbs free energies of tris(β-diketonato) chromium (III),-cobalt(III), and bis(β-diketonato)palladium(II) in reversed-phase liquid chromatography on octadecyl-bonded silica gel with acetonitrile-water mobile phases

To clarify the mechanism of retention of several β-diketonates of chromium(III), cobalt(III), and palladium(II) in reversed-phase liquid chromatography (RPLC), their capacity factors (k) were measured on an octadecyl-bonded silica gel (ODS) stationary phase with acetonitrile-water binary mobile phases. The values obtained were compared with the liquid-liquid parition coefficients (P) of the metal β-diketonates in the dodecane/(acetonitrile-water mixture) system. This comparison showed that with regard to the distribution of the metal β-diketonates the nature of the stationary phase was similar to, but not identical with, that of dodecane. When the Gibbs free energies of the metal β-diketonates in the stationary phase were calculated, the values showed that the cavity-formation free energy for each metal β-diketonate in the stationary phase was close to that in dodecane, and the interaction free energy was almost equal to the sum of the energies of interaction with the alkyl moiety and with acetonitrile. This implies that acetonitrile molecules from the mobile phase penetrate the alkyl moiety of ODS.

SELECTIVITY OF PHENYLHEXYL-BONDED SILICA GEL FOR LIQUID CHROMATOGRAPHY

The selectivity of a computer-designed phenylhexyl-bonded silica gel was studied from the chromatographic behavior of alkylbenzenes and polycyclic aromatic hydrocarbons. The retention capacity of this phenyl phase for alkylbenzenes was equivalent to a pentyl-bonded phase, and that for polycyclic aromatic hydrocarbons was equivalent to an octyl-bonded phase. The phenylhexyl-bonded silica gel demonstrated the selectivity for the separation of antibacterial drugs, even though the separation time was the same as that on an octadecyl-bonded silica gel.

High-Performance Liquid Chromatographic Determination of Mn(II), Co(II), Zn(II), Ni(II), Cu(II) As Coproporphyrin-I Complexes

The mobilities of 3,8,13,18-tetrametyl-21H,23H-porphine-2,7,12,17-tetrapropionic acid or coproporphyrin-I (CPI) and five metal-CPI complexes were measured by reversed-phase high performance liquid chromatography (RP-HPLC) on a octadecyl-bonded silica gel (C18 silica) with developing solvent (69:31 v/v) methanol-buffer at pH 7 (buffer ionic strength 0.270 mol L−1. 0.018 mol L−1 boric, phosphoric and acetic acid, and 0.036 mol L−1 sodium hydroxide), and 0.050 mol L−1 of NaCl, with UV detection at 374 and 458 nm.

Rapid analysis of guanidino compounds in serum from nephritic patients using column-switching with isocratic elution.

The rapid method for baseline separation of ten guanidino compounds in serum from nephritic patients was designed using a single eluent with a column switching system. A porous graphitic carbon column and an octadecyl-bonded silica gel columns were used, (50 mm x 4.6 mm i.d.). Separation was completed within 15 min. The stable baseline permitted highly sensitive detection with excellent reproducibility. The system was applied to analyze guanidino compounds in sera from 175 nephritic patients. The hemodialysis process could not completely eliminate guanidino compounds, and the degree of removal varied between patients. The correlation among metabolites indicated the differences in disease.

Adsorption Equilibria of 1,10-Phenanthroline and Its Fe(II) Complex on Octadecyl-Bonded Silica Gel

Abstract Adsorption of 1,10-phenanthroline (phen) and its iron(II) complex (Fe(II)-phen) on octadecyl-bonded silica (ODS) gel from aqueous solution was studied by a batch method. The adsorption isotherms of phen and Fe(II)-phen were Langmiur type. Equilibrium constants for the adsorption reaction were estimated from the adsorption data in the system containing a small amount of adsorbates, in which the adsorption isotherm obeyed Henry’s law. It was clear that the adsorbed species of phen was not only the basic type but also the acidic type: protonated phen. The adsorption behavior in trace amounts (1.79 × 10−5 mol dm−3; 1 ppm) of Fe(II)-phen was analyzed by their equilibrium parameters. The distribution constants of Fe(II)-phen between ODS gel and aqueous solution were determined. The effect of co-existent anions on the adsorption of Fe(II)-phen was discussed from the obtained constants.

Unusual Maxima in HPLC Retention of an Homologous Series Consisting of Longer Alkyl Chain Substitutions

A series of compounds were studied which had increasing alkyl chain length between an aromatic group and a tertiary amine. In this homologous series, a maximum in retention versus alkyl chain length was found for a wide range of mobile phases using either a silica gel column or a cyanopropyl-bonded silica gel column. One nonaqueous mobile phase using an octadecyl-bonded silica gel column also showed this maximum. The selectivity between E and Z geometric isomers found with the shorter chain analogues decreased with increasing chain length greater than about pentyl, with eventual complete loss of resolution. A few normal-phase solvents produced a reversal of the usual E−Z elution order. 1H NMR assignments are described for the individual geometric isomers. NMR studies and ab initio calculations indicate that a folded conformation in solution is possible for the longer chain analogues. The unusual retention patterns are most likely due to a combination of localized adsorption and analyte solution conformation effects.

Determination of chlorophylls by reversed-phase high-performance liquid chromatography with isocratic elution and the column-switching technique

A reversed-phase high-performance liquid chromatographic (HPLC) system was designed for the separation and determination of chlorophylls and their degradation products. Two separation columns packed with octadecylbonded silica gel (ODS) and octadecyl-bonded vinyl alcohol copolymer (ODP) were employed with the aid of a column-switching technique. The ODS column (1 cm) functioned for the seperation of very hydrophobic compounds, such as chlorphyll a, chlorophyll b, pheo phytin a and pheophytin b, and the ODP column (15 cm) for separating the compounds of low hydrophobicity, such as chlorophyll c 1, chlorophyll c 2, pheoporphyrin c 1, pheoporphyrin c 2, pheophorbide a and pheophorbide b. The HPLC system could cope with a variety of hydrophobicities of chlorophyll pigments by means of isocratic elution with methanol-phosphate buffer (pH 3) (92:8, v/v). Application to several seaweed samples was demonstrated.