氮氧化硅反相色谱固定相材料的制备及色谱分离性能评价

硅胶是目前高效液相色谱(HPLC)固定相中应用最为广泛的基质材料,其流动相的最佳使用范围为pH 2～8。在高pH(pH＞8)的流动相条件下,流动相中的氢氧根会进攻硅胶基质表面残余的硅醇基,导致硅胶基质固定相骨架溶解。在前期的研究中,我们将高温氨气处理多孔硅胶微球得到的氮氧化硅材料用作HPLC固定相,氮氧化硅在高pH流动相条件下表现出了较硅胶更高的稳定性。本文利用元素分析对氮氧化硅材料的氮化程度及含氮量进行系统的表征,并考察了氮氧化硅材料在不同pH条件下的静态稳定性。利用十八烷基二甲基氯硅烷试剂对氮氧化硅材料表面进行疏水性修饰,并以元素分析和核磁共振波谱对表面键合氮氧化硅材料进行了表征。考察了不同碳链的烷基苯、酸性化合物、碱性化合物在疏水改性的C₁₈氮氧化硅反相色谱固定相上的色谱分离性能。进一步分别以酸、碱和中性化合物为分析对象,比较了C₁₈-SiON1050(10)与C₁₈-SiO₂色谱保留的差异。     

Quantifying silica in filter-deposited mine dusts using infrared spectra and partial least squares regression

The feasibility of measuring airborne crystalline silica (α-quartz) in noncoal mine dusts using a direct-on-filter method of analysis is demonstrated. Respirable α-quartz was quantified by applying a partial least squares (PLS) regression to the infrared transmission spectra of mine-dust samples deposited on porous polymeric filters. This direct-on-filter method deviates from the current regulatory determination of respirable α-quartz by refraining from ashing the sampling filter and redepositing the analyte prior to quantification using either infrared spectrometry for coal mines or x-ray diffraction (XRD) from noncoal mines. Since XRD is not field portable, this study evaluated the efficacy of Fourier transform infrared spectrometry for silica determination in noncoal mine dusts. PLS regressions were performed using select regions of the spectra from nonashed samples with important wavenumbers selected using a novel modification to the Monte Carlo unimportant variable elimination procedure. Wavenumber selection helped to improve PLS prediction, reduce the number of required PLS factors, and identify additional silica bands distinct from those currently used in regulatory enforcement. PLS regression appeared robust against the influence of residual filter and extraneous mineral absorptions while outperforming ordinary least squares calibration. These results support the quantification of respirable silica in noncoal mines using field-portable infrared spectrometers.

Separation and identification of some common isomeric plant triterpenoids by thin-layer chromatography and high-performance liquid chromatography

Chromatographic separation of 10 triterpenoids (α-amyrin, β-amyrin, δ-amyrin, lupeol, lupenon, lupeol acetate, cycloartenol, cycloartenol acetate, ursolic acid, oleanolic acid) and 2 sterols (stigmasterol and β-sitosterol) was studied. The chromatographic techniques included silica gel and reversed-phase (C₁₈ RP) thin-layer chromatography (TLC) and C₁₈ RP high-performance liquid chromatography (HPLC) using UV and mass spectrometric (MS) detection with atmospheric pressure chemical ionization (APCI). The TLC separation of the isomeric triterpenols lupeol, α-amyrin, β-amyrin and cycloartenol was achieved for the first time using C₁₈ RP-HPTLC plates. Cycloartenol could be separated from related compounds only on C₁₈ RP-TLC but not on the C₁₈ RP-HPLC. δ-Amyrin isolated from the tomato fruit surface extract could be separated from other amyrins only by HPLC. Tandem mass spectrometry allowed discrimination between the isomers lupeol, α-amyrin, β-amyrin, δ-amyrin, cycloartenol and between lupeol acetate and cycloartenol acetate. The combination of 3 TLC methods and 2 HPLC methods enables qualitative determination of all 12 compounds and proves to be useful for the analysis of plant extracts. It is recommended that TLC screening on silica gel and C₁₈ RP be performed before HPLC analysis.     

近红外光谱法快速分析有机肥料中有机质、总养分和pH值

建立了近红外光谱法结合偏最小二乘(PLS)法测定126种有机肥料中有机质、总养分和p H值的快速方法。采用K–S法分类,选取S–G平滑、S–G导数、多元散射校正和均值平均化4种前处理方法对粉碎后样品的近红外光谱信息进行预处理,以PLS法建立定量分析模型。结果表明,有机肥料中总养分的RC,SEC,RP,SEP,RPD分别为0.990,1.272%,0.985,1.084%,5.9;p H值的RC,SEC,RP,SEP,RPD分别为0.910,0.344%,0.737,0.428%,2.9。有机质项目根据国标方法分为小于40%、小于55%和大于55%3种样品进行分析,3种样品的RP分别为1.000,0.989,1.000;RPD分别为18.9,17.5,8.8。对比国标方法,有机质和总养分的测定精度满足实验室精确分析要求,p H值测定法可用于定量分析。NIR–PLS法实现了对有机肥料进行无损快速的检测分析。     

Development of superparamagnetic high-magnetization C18-functionalized magnetic silica nanoparticles as sorbents for enrichment and determination of methylprednisolone in rat plasma by high performance liquid chromatography

In this study, a novel extraction and enrichment technique based on superparamagnetic high-magnetization C₁₈-functionalized magnetic silica nanoparticles (C₁₈-MNPs) as sorbents was successfully developed for the determination of methylprednisolone (MP) in rat plasma by high performance liquid chromatography (HPLC). The synthesized silica-coated magnetite modified with chlorodimethyl-n-octadecylsilane was about 320 nm in diameter with strong magnetism and high surface area. It provided an efficient way for extraction and concentration of MP in the samples through hydrophobic interaction by the interior C₁₈ groups. Moreover, MP adsorbed with C₁₈-MNPs could be simply and rapidly isolated through placing a strong magnet on the bottom of container, and then easily eluted from C₁₈-MNPs by n-hexane solution. Extraction conditions such as amounts of C₁₈-MNPs added, adsorption time and desorption solvent, were investigated. Method validations including linear range, detection limit, precision, and recovery were also studied. The results showed that the proposed method based on C₁₈-MNPs was a simple, accurate and high efficient approach for the analysis of MP in the complex plasma samples.     

Solid phase extraction/programmed temperature vaporizer (PTV) injection in GC-analysis of toxaphene and PCBs in aqueous samples

Summary A high-resolution gas-chromatographic (HRGC) method with electron capture detection is described for the sensitive determination of PCBs and toxaphene in water in the lower ng/l range. The required low detection limits are guaranteed by isolation of the target compounds and concentration from the filtered water sample by solid phase extraction with specific C₁₈ silica gel (200–250 m) alone or combined with the injection of larger extract volumes into a programmed temperature vaporizer (PTV) operating in the solvent venting mode. The bonded silica gel was prepared by reaction of the surface silanol groups with octadecyltrichlorosilane. A C₁₈ silica of reproducible coverage was received. Practical aspects of the use of the solid phase extraction in combination with the PTV injection technique are discussed. The recoveries for toxaphene and PCBs were 85 and 78%.     

HPLC Determination of α-Amino Acids in Phytoplanktonic Marine Cells

Abstract

A procedure for the quantitative determination of 17 amino acids in a marine matrix using HPLC is reported. Pre-column derivatization with o-phthalaldehyde, separation on C₁₈-bonded silica with phosphate buffer (pH 7.2)-acetonitrile as eluent and fluorescence detection have been used. The good variation coefficient (average 2% with working curves in real matrix) and the low detection limit (1-5 fmoles) make the procedure suitable for the determination of total or free amino acids in matrix cultures.     

Rapid screening for ethyl carbamate in stone-fruit spirits using FTIR spectroscopy and chemometrics

Ethyl carbamate (EC, urethane, C₂H₅OCONH₂) is a known genotoxic carcinogen of widespread occurrence in fermented food and beverages with the highest concentrations being found in stone-fruit spirits. Time-consuming procedures requiring extraction and gas chromatographic–mass spectrometric determination are regarded as reference procedures for the analysis of EC in alcoholic beverages. In this study, the rapid method of Fourier transform infrared (FTIR) spectroscopy in combination with partial least-squares (PLS) regression using selected wavelength bands is applied for the first time to the screening analysis of EC in stone fruit spirits (analysis time only 2 min). Apart from the actual content of EC in the sample, additional information was available from the FTIR spectra. This included data concerning the EC precursor hydrocyanic acid (HCN) and the maximum EC concentration which could be formed during storage. The PLS procedure was validated using an independent set of samples (Q² = 0.71–0.76, SEP = 0.42–0.67). The method was found to lack the accuracy required for a quantitative determination; it could only be used semi-quantitatively in the context of a screening analysis. If a rejection level of 0.8 mg L^–1 is applied as cut-off, overall correct classification rates of 85–91% for the calibration set and 77–85% for the validation set were achieved. False negative results can be avoided by lowering the cut-off to 0.6 mg L^–1. Through use of FTIR screening, 60–70% of all samples can be classified as negative and removed, leaving only conspicuous analysis results exceeding cut-off to be confirmed by complex and labour-intensive reference analyses.     

Rapid radiochemical separation in neutron activation analysis : Part 1. The use of C18-bonded silica gel and selective complexation for determinations of manganese,copper and zinc in biological materials

A rapid radiochemical separation method based on the removal of metal ions by columns of C₁₈-bonded silica gel after selective complexation by 8-quinolinol, ammonium pyrolidinedithiocarbamate or cupferron is described for the determination of manganese, copper and zinc in neutron-activated biological materials. The removal of the metal ions, either by adsorption or by a combination of filtration and adsorption on columns of C₁₈-bonded silica gel, was investigated to optimise the separation procedure. Analysis of several National Bureau of Standards and International Atomic Energy Agency biological reference materials demonstrated the effectiveness of this technique. The method is simple and reliable and readily adaptable in all radiochemical laboratories. Furthermore, columns of C₁₈-bonded silica gel have been successfully recycled a number of times without deterioration.     

Factors affecting the reversed-phase liquid chromatographic separation of polycyclic aromatic hydrocarbon isomers

Reversed-phase liquid chromatography (LC) on C₁₈ stationary phases provides excellent selectivity for the separation of polycyclic aromatic hydrocarbons (PAH). Recent studies have shown that several factors affect selectivity for the LC separation of PAH including phase type (monomeric or polymeric), pore diameter and surface area of the silica substrate, and surface density of the C₁₈ ligands. In this paper the separation of eleven PAH isomers of molecular weight 278 is used to further illustrate the effect of stationary phase characteristics and shape of the solute (length-to-breadth ratio, L/B) on retention and selectivity. Only polymeric C₁₈ phases with a high C₁₈ surface coverage provided separation of all eleven isomers and the elution order of these isomers generally followed increasing L/B values. The effect of solute nonplanarity on reversed-phase LC retention was investigated on both monomeric and polymeric phases using a series of planar and nonplanar PAH pairs. For each solute pair, the nonplanar solute eluted earlier than the planar solute, the largest selectivity factors being observed on the C₁₈ phase with the highest percent carbon load. Based on these studies, a model is proposed to describe the retention of PAH on polymeric C₁₈ phases.     

Artificial neural network combined with principal component analysis for resolution of complex pharmaceutical formulations

A chemometric approach based on the combined use of the principal component analysis (PCA) and artificial neural network (ANN) was developed for the multicomponent determination of caffeine (CAF), mepyramine (MEP), phenylpropanolamine (PPA) and pheniramine (PNA) in their pharmaceutical preparations without any chemical separation. The predictive ability of the ANN method was compared with the classical linear regression method Partial Least Squares 2 (PLS2). The UV spectral data between 220 and 300 nm of a training set of sixteen quaternary mixtures were processed by PCA to reduce the dimensions of input data and eliminate the noise coming from instrumentation. Several spectral ranges and different numbers of principal components (PCs) were tested to find the PCA-ANN and PLS2 models reaching the best determination results. A two layer ANN, using the first four PCs, was used with log-sigmoid transfer function in first hidden layer and linear transfer function in output layer. Standard error of prediction (SEP) was adopted to assess the predictive accuracy of the models when subjected to external validation. PCA-ANN showed better prediction ability in the determination of PPA and PNA in synthetic samples with added excipients and pharmaceutical formulations. Since both components are characterized by low absorptivity, the better performance of PCA-ANN was ascribed to the ability in considering all non-linear information from noise or interfering excipients.     

Rapid High-Performance Liquid Chromatographic Determination of Physostigmine in Plasma

Abstract

A new method is described for the quantitative determination of physostigmine in human plasma. The drug is isolated from human plasma utilizing a C₁₈ SEP PAK Cartridge, and quantified by liquid chromatography with ultraviolet detection. The average recovery is 54.3 ± 4.3% (S.D.) with a day to day coefficient of variation of 4%.     

Near-infrared spectroscopy quantitative determination of Pefloxacin mesylate concentration in pharmaceuticals by using partial least squares and principal component regression multivariate calibration

Pefloxacin mesylate, a broad-spectrum antibacterial fluoroquinolone, has been widely used in clinical practice. Therefore, it is very important to detect the concentration of Pefloxacin mesylate. In this research, the near-infrared spectroscopy (NIRS) has been applied to quantitatively analyze on 108 injection samples, which was divided into a calibration set containing 89 samples and a prediction set containing 19 samples randomly. In order to get a satisfying result, partial least square (PLS) regression and principal components regression (PCR) have been utilized to establish quantitative models. Also, the process of establishing the models, parameters of the models, and prediction results were discussed in detail. In the PLS regression, the values of the coefficient of determination (R²) and root mean square error of cross-validation (RMSECV) of PLS regression are 0.9263 and 0.00119, respectively. For comparison, though applying PCR method to get the values of R² and RMSECV we obtained are 0.9685 and 0.00108, respectively. And the values of the standard error of prediction set (SEP) of PLS and PCR models are 0.001480 and 0.001140. The result of the prediction set suggests that these two quantitative analysis models have excellent generalization ability and prediction precision. However, for this PFLX injection samples, the PCR quantitative analysis model achieved more accurate results than the PLS model. The experimental results showed that NIRS together with PCR method provide rapid and accurate quantitative analysis of PFLX injection samples. Moreover, this study supplied technical support for the further analysis of other injection samples in pharmaceuticals.     

Synthesis of monodisperse silica microspheres and modification with diazoresin for mixed‐mode ultra high performance liquid chromatography separations

Monodisperse silica particles with average diameters of 1.9–2.9 μm were synthesized by a modified Stöber method, in which tetraethyl orthosilicate was continuously supplied to the reaction mixture containing KCl electrolyte, water, ethanol, and ammonia. The obtained silica particles were modified by self‐assembly with positively charged photosensitive diazoresin on the surface. After treatment with ultraviolet light, the ionic bonding between silica and diazoresin was converted into covalent bonding through a unique photochemistry reaction of diazoresin. Depending on the chemical structure of diazoresin and mobile phase composition, the diazoresin‐modified silica stationary phase showed different separation mechanisms, including reversed phase and hydrophilic interactions. Therefore, a variety of baseline separation of benzene analogues and organic acids was achieved by using the diazoresin‐modified silica particles as packing materials in ultra high performance liquid chromatography. According to the π–π interactional difference between carbon rings of fullerenes and benzene rings of diazoresin, C₆₀ and C₇₀ were also well separated by ultra‐high performance liquid chromatography. Because it has a small size, the ∼2.5 μm monodisperse diazoresin‐modified silica stationary phase shows ultra‐high efficiency compared with the commercial C₁₈‐silica high‐performance liquid chromatography stationary phase with average diameters of ∼5 μm.     

Comparison of different sorbents for multiresidue solid-phase extraction of 16 pesticides from groundwater coupled with high-performance liquid chromatography

A procedure based on solid-phase extraction (SPE) followed by high-performance liquid chromatography (HPLC) with diode array detection has been developed for the simultaneous analysis of 16 widely used pesticides in groundwater samples. The compounds analysed were: aldicarb, atrazine, desethylatrazine, desysopropylatrazine, carbofuran, 2,4-D, dicloran, fenitrothion, iprodione, linuron, metalaxyl, metazachlor, phenmedipham, procymidone, simazine and vinclozolin. Five different SPE sorbents, C₁₈ bonded silica (Isolute SPE C18 (EC)), graphitised carbon black (Superclean Envi-Carb), highly cross-linked polystyrene-divinylbenzene (Lichrolut EN), divinylbenzene-N-vinylpyrrolidone (Oasis HLB) and surface modified styrene-divinylbenzene (Strata X), were compared. HPLC separation and quantification of the selected pesticides was carried out under isocratic conditions by means of a new reversed-phase column (Gemini from Phenomenex) based on C₁₈ bonded to organic-silica particles. Oasis HLB and Strata X provided the best results in the preconcentration of 1-l samples, yielding average recoveries higher than 70%, except for phenmedipham that rapidly degrades in groundwater. Detection limits of the target pesticides provided by the proposed SPE-HPLC procedure were between 0.003 and 0.04 μg l⁻¹.     

Study of RP HPLC Retention Behaviours in Analysis of Carotenoids

For determination of selected carotenoids, various types of columns for high-performance liquid chromatography (HPLC) with different properties have been used. The characteristics of the laboratory-used packing material containing monomeric alkyl-bonded phases (C₁₈, C₃₀) and phenyl as well as phenyl-hexyl stationary phases were studied. The retention data of the examined compounds were used to determine the hydrophobicity and silanol activity of stationary phases applied in the study. The presence of the polar and carboxyl groups in the structure of the bonded ligand strongly influences the polarity of the stationary phase. Columns were compared according to methylene selectivity using a series of benzene homologues. The measurements were done using a methanol–water mobile phase. Knowledge of the properties of the applied stationary phase provided the possibility to predict the RP HPLC retention behaviours in analysis of carotenoids including lutein, lycopene and β-carotene. The composition of the mobile phase, the addition of triethylamine and the type of stationary phase had been taken into account in designing the method of carotenoid identification. Also a monolithic column characterised by low hydrodynamic resistance, high porosity and high permeability was applied. The presented results show that the coverage density of the bonded ligands on silica gel packings and length of the linkage strongly influence the carotenoid retention behaviours. In our study, the highest retention parameters for lutein, lycopene and β-carotene were observed for C₃₀ and C₁₈ stationary phase. This effect corresponds with pore size of column packing greater than 100 Å and carbon content higher than 11 %.     

Evaluation of capillary gas chromatography columns for the determination of free volatile amines after solid-phase microextraction

Summary Gas-liquid chromatographic capillary columns coated with 14% diphenyldimethylpolysiloxane, base-deactivated 5% diphenyldimethylpolysiloxane, or poly(ethylene glycol), and deactivated porous polymer for capillary gas-solid chromatography were evaluated for analysis of low-molecular-weight (C₁−C₉) amines. Solid-phase microextraction with a polydimethylsiloxane fiber was used for headspace sampling and for introduction of the sample into the gas chromatograph. As expected, basic of aliphatic gaseous or volatile aliphatic amines (carbon number: C₁−C₄). A thick (e. g. 3 μm) film of 5% diphenyldimethylpolysiloxane enabled determination of analytes in a wider molecular-weight range (C₃−C₉) with acceptable efficiency and resolution.     

Comparison of several sorbents for continuous in situ derivatization and preconcentration of low-molecular mass aldehydes prior to liquid chromatography–tandem mass spectrometric determination in water samples

A comparative study of six SPE conventional and non-conventional sorbent materials (silica RP-C₁₈, LiChrolut EN, Amberlite XAD-2, C₆₀ fullerene, multiwall carbon nanotubes and graphitized carbon black) was carried out for the in situ derivatization/preconcentration of eight aldehydes with 2,4-dinitrophenylhydrazine. Although two of the sorbents, LiChrolut EN and RP-C₁₈, turned out to be the most suitable for ultratrace analysis of the aldehydes, LiChrolut EN showed higher capacity for 2,4-dinitrophenylhydrazine trapping (higher efficiency for the in situ derivatization reaction) and superior performance in terms of sensitivity (likely a result of its increased sample breakthrough volume). The LiChrolut EN-based method combined with LC–MS/MS allowed the determination of aldehydes over the linear range of 0.02–15 μg l⁻¹, with limits of detection at 6–24 ng l⁻¹ and precision of 3.2–7.2%. The method was applied to determine low-molecular mass aldehydes in water samples. These results indicate that the method proposed is a straightforward and sensitive tool for the determination of these aldehydes in water samples providing better results than those LC–MS/MS reported alternatives in terms of the limit of detection, sample requirements for analysis and cost.