Phenyl-type and C1 stationary phases for environmentally friendlier chromatography

C1 and phenyl-type stationary phases were assessed in terms of their environmental impact on separations using as test solutes polycyclic aromatic hydrocarbons. Methanol (MeOH) and acetonitrile (ACN) mobile-phase gradients were employed. These stationary phases were examined to determine if different physical and chemical properties possessed by these surfaces decreased the organic solvent consumption, and yet maintained peak capacity. The cumulative energy demand (CED) was used to gauge the environmental impact of the separations. The separation of the polycyclic aromatic hydrocarbon test mixture using current methodologies (i.e. a C18/ACN combination) had a CED of 1.13 MJ-eq, and a peak capacity of 27 peaks (resolving 7 of 12 peak pairs with R_s>1). In comparison, a butyl phenyl stationary phase with a methanol mobile phase had a peak capacity of 26, but with a CED of 0.670 MJ-eq. Monolithic columns containing C18 and C1 phases were also tested. A monolithic C18 column with MeOH had the lowest CED at 0.675 MJ-eq, a peak capacity of 28 peaks and good resolving power (resolving ten peak pairs with R_s>1), suggesting that this is a viable option with respect to reducing environmental impact for these types of analyses.     

Effect of moisture on supercritical fluid extraction of polynuclear aromatic hydrocarbons and phenols from soil using an automated extractor

An automated supercritical fluid extraction system was evaluated with polynuclear aromatic hydrocarbons and phenols to demonstrate extraction efficiency, collection efficiency, and sample cross contamination. Results showed that 75/25 glass beads/octadecyl silica provided the highest collection efficiency for these classes of compounds. Also, the automated SFE system was used to study the effect of different percentages of water (w/w) in soil on extraction efficiency of fortified PAH and phenols at different temperatures and pressures. Results showed that the presence of (available) water in soil (>10%) does, increase extraction efficiency of higher molecular weight PAH at higher temperature. Also it was demonstrated that temperature rather than pressure had a marked effect on extraction efficiency. The extraction efficiency of phenols from soil which contained 5% of water, using pure supercritical CO₂, was higher than those obtained from dry soil or soil containing 1 % water. Extraction of phenols from soil did not show a dependence on pressure or temperature.     

Enhanced resolution of Mentha piperita volatile fraction using a novel medium‐polarity ionic liquid gas chromatography stationary phase

The evaluation of a novel medium‐polarity ionic‐liquid‐based gas chromatography column, SLB‐IL60, towards the analysis of a complex essential oil, namely, a peppermint essential oil sample, is reported. The SLB‐IL60 30 m column was subjected to bleeding measurements, by means of conventional gas chromatography with mass spectrometry. The SLB‐IL60 column was then evaluated in the analysis of pure standard compounds, chosen as typical constituents of peppermint essential oil. Resolution and peak symmetry (expressed as tailing factors at 10% of peak height) were measured and the results were compared to those obtained on the most widely used columns in such an application, namely a medium‐polarity [100% poly(ethyleneglycol)] stationary phase, and an apolar 5% diphenyl/95% dimethyl siloxane. The final part of the evaluation was dedicated to the gas chromatography with mass spectrometry analysis of a peppermint essential oil sample and again the data were compared to those obtained on the 100% poly(ethyleneglycol) and the 5% diphenyl/95% dimethyl siloxane phase. Linear retention indices were determined for all the identified components on the ionic liquid capillary.     

Expanding the Applications of the Ionic Liquids as GC Stationary Phases: Plasticizers and Synthetic Musks Fragrances

The exceptional properties of the ILs make them ideal for gas chromatography stationary phases. New stationary phases exhibiting good separation selectivity, high efficiency, and high thermal stability are in high demand. Recently, several gas chromatographic capillary columns containing IL stationary phases of various polarities have been introduced on the market. The aim of this work is to extend the applications of the ILs as GC column coatings. The effectiveness of five different commercial IL columns (SLB™-IL59, SLB™-IL76, SLB™-IL82, SLB™-IL100 and SLB™-IL111) for the analysis of two different families of emerging contaminants of environmental concern (plasticizers and synthetic musk fragrances) has been explored. The results obtained for these two families of compounds are compared with the ones obtained when using a (5 %-phenyl)-methylpolysiloxane column. For three of these IL columns, applications have not yet been described. Good resolution for the most of the studied emerging pollutants belonging to five different analytical groups (adipates, phthalates, macrocyclic musks, nitromusks and polycyclic musks) was achieved in all the IL columns.

     

Rapid and sensitive methodology for determination of ethyl carbamate in fortified wines using microextraction by packed sorbent and gas chromatography with mass spectrometric detection

This work presents a new methodology to quantify ethyl carbamate (EC) in fortified wines. The presented approach combines the microextraction by packed sorbent (MEPS), using a hand-held automated analytical syringe, with one-dimensional gas chromatography coupled with mass spectrometry detection (GC–MS). The performance of different MEPS sorbent materials was tested, namely SIL, C2, C8, C18, and M1. Also, several extraction solvents and the matrix effect were evaluated. Experimental data showed that C8 and dichloromethane were the best sorbent/solvent pair to extract EC. Concerning solvent and sample volumes optimization used in MEPS extraction an experimental design (DoE) was carried out. The best extraction yield was achieved passing 300 μL of sample and 100 μL of dichloromethane. The method validation was performed using a matrix-matched calibration using both sweet and dry fortified wines, to minimize the matrix effect. The proposed methodology presented good linearity (R² = 0.9999) and high sensitivity, with quite low limits of detection (LOD) and quantification (LOQ), 1.5 μg L⁻¹ and 4.5 μg L⁻¹, respectively. The recoveries varied between 97% and 106%, while the method precision (repeatability and reproducibility) was lower than 7%. The applicability of the methodology was confirmed through the analysis of 16 fortified wines, with values ranging between 7.3 and 206 μg L⁻¹. All chromatograms showed good peak resolution, confirming its selectivity. The developed MEPS/GC–MS methodology arises as an important tool to quantify EC in fortified wines, combining efficiency and effectiveness, with simpler, faster and affordable analytical procedures that provide great sensitivity without using sophisticated and expensive equipment.     

Aspects of proficiency testing studies of trace elements in environmental samples with a focus on laboratory performance

Four proficiency tests of environmentally significant elements in soil and water are described. The effects of sample matrix, analyte, sample preparation procedure, extraction method efficiency and instrumental technique on laboratory performance were assessed. Participants’ performance was evaluated using z scores and E _n scores. One study included dried sediment and sediment digest as test samples. By testing both dried sediment and sediment digest in the same study, differences in laboratories’ results due to the extraction method or instrumental technique were evaluated. Cadmium and nickel were the elements with the most unsatisfactory z scores for dried sediment compared to sediment digest. The second study had as test samples river water and river water fortified with biosolid. For an evaluation of the efficiency of participants’ extraction method, the results reported for the analysis of river water were compared to the results for analysis of the same river water fortified with biosolid. No consensus could be found between participants’ results for Cr and Ni in this study as the extraction method employed by them produced results that were too variable. The last two studies included saline and fresh water samples. The analysis of fresh and saline water samples with similar analyte concentrations assisted laboratories in developing their methods for trace elements in saline water. For Cr, Pb and Se, the assigned values were reference values traceable to SI, measured using isotope dilution inductively coupled plasma mass spectrometry. Saline water containing low concentrations of analytes presented difficulties to some laboratories. Arsenic and selenium were the analytes most difficult to analyse in all types of environmental samples.     

Direct chiral liquid chromatography determination of aryloxyphenoxypropionic herbicides in soil: deconvolution tools for peak processing

In this paper, the enantiomeric separation of two aryloxyphenoxypropionic esters (fluazifop-butyl and quizalofop-ethyl) and a safener herbicide (mefenpyr-diethyl), which is widely used for protecting crop plants, has been studied by direct liquid chromatography (LC) with UV detection on an α₁-acid glycoprotein as chiral stationary phase. Optimization of separation conditions was done by factorial experimental design. Experimental factors and ranges selected were propanol (5–10%), phosphate buffer pH (6.5–7.0), and column temperature (15–25 °C). Responses were expressed in terms of enantioresolution (R _s) and adjusted retention time of the second eluted enantiomer (t _r2′). The chemometric method used to explore data was response surface analysis. Multiple response analyses were carried out to determine the combination of experimental factors which simultaneously optimize experimental responses. Under optimum conditions for enantioseparation of each herbicide, partially overlapped or fully resolved enantiomers were obtained. Deconvolution tools were employed as an integration method to fit chromatographic data and to achieve a more precise enantiomeric ratio (ER) and enantiomeric fraction (EF) values. Applicability of both direct chiral LC and peak deconvolution methods was evaluated in spiked soil samples at different R/S enantiomeric ratios. Acceptable and reproducible recoveries between 71% and 96% with precision in the range 1–6% were achieved for herbicide-spiked levels from 0.50 to 9.0 μg g^–1. In addition, parameters such as R _s, ER, and EF were calculated and compared with values obtained using the common valley drop integration method.     

Compact type-I coil planet centrifuge for counter-current chromatography

A compact type-I coil planet centrifuge has been developed for performing counter-current chromatography. It has a revolution radius of 10 cm and a column holder height of 5 cm compared with 37 and 50 cm in the original prototype, respectively. The reduction in the revolution radius and column length permits application of higher revolution speed and more stable balancing of the rotor which leads us to learn more about its performance and the future potential of type-I coil planet centrifuge. The chromatographic performance of this apparatus was evaluated in terms of retention of the stationary phase (S_f), peak resolution (R_s), theoretical plate (N) and peak retention time (t_R). The results of the experiment indicated that increasing the revolution speed slightly improved both the retention of the stationary phase and the peak resolution while the separation time is remarkably shortened to yield an excellent peak resolution at a revolution speed of 800 rpm. With a 12 ml capacity coiled column, DNP-DL-glu, DNP-β-ala and DNP-l-ala were resolved at R_s of 2.75 and 2.16 within 90 min at a flow rate of 0.4 ml/min. We believe that the compact type-I coil planet centrifuge has a high analytical potential.     

A dynamic soil chamber system coupled with a tunable diode laser for online measurements of δ13C, δ18O,and efflux rate of soil‐respired CO2

High frequency observations of the stable isotopic composition of CO₂ effluxes from soil have been sparse due in part to measurement challenges. We have developed an open‐system method that utilizes a flow‐through chamber coupled to a tunable diode laser (TDL) to quantify the rate of soil CO₂ efflux and its δ¹³C and δ¹⁸O values (δ¹³C_R and δ¹⁸O_R, respectively). We tested the method first in the laboratory using an artificial soil test column and then in a semi‐arid woodland. We found that the CO₂ efflux rates of 1.2 to 7.3 µmol m^?2 s^?1 measured by the chamber‐TDL system were similar to measurements made using the chamber and an infrared gas analyzer (IRGA) (R² = 0.99) and compared well with efflux rates generated from the soil test column (R² = 0.94). Measured δ¹³C and δ¹⁸O values of CO₂ efflux using the chamber‐TDL system at 2 min intervals were not significantly different from source air values across all efflux rates after accounting for diffusive enrichment. Field measurements during drought demonstrated a strong dependency of CO₂ efflux and isotopic composition on soil water content. Addition of water to the soil beneath the chamber resulted in average changes of +6.9 µmol m^?2 s^?1, ?5.0‰, and ?55.0‰ for soil CO₂ efflux, δ¹³C_R and δ¹⁸O_R, respectively. All three variables initiated responses within 2 min of water addition, with peak responses observed within 10 min for isotopes and 20 min for efflux. The observed δ¹⁸O_R was more enriched than predicted from temperature‐dependent H₂O‐CO₂ equilibration theory, similar to other recent observations of δ¹⁸O_R from dry soils (Wingate L, Seibt U, Maseyk K, Ogee J, Almeida P, Yakir D, Pereira JS, Mencuccini M. Global Change Biol. 2008; 14: 2178). The soil chamber coupled with the TDL was found to be an effective method for capturing soil CO₂ efflux and its stable isotope composition at high temporal frequency. Published in 2010 by John Wiley & Sons, Ltd.     

Determination of chlorobenzenes in water by drop-based liquid-phase microextraction and gas chromatography-electron capture detection

A drop-based liquid phase microextraction and gas chromatographic-electron capture detection (GC-ECD) method was described for the determination of chlorobenzenes including chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene and 1,2,3-trichlorobenzene in 5 ml of water. The method used 2 microl of n-hexane as extraction solvent, 5 min extraction time, a stirring rate of 600 rpm and sample ionic strength of 3 M maintained with sodium chloride at 25 degrees C (ambient temperature). The limits of detection (LODs) ranged from 0.004 microg l(-1) (for 1,3-dichlorobenzene) to 0.008 microg l(-1) (for monochlorobenzene). The dynamic linear range for all investigated chlorobenzenes was 1-50 microg l(-1). Recoveries of chlorobenzenes from fortified distilled water are over 90% for three different fortification levels (5, 15 and 45 microg l(-1)) and relative standard deviations of the recoveries are below 6%. Analysis of fortified (5 microg l(-1)) real water samples revealed that matrices had no adverse effect on extraction efficiency of proposed method. The recovery of fortified real water samples was from 90 to 94% with relative standard deviations below 6%.     

Radiation induced depolymerization of hyaluronic acid (HA) in aqueous solutions at pH 7.4

The separation of the trivalent metal ions Am(III) and Eu(III) by extraction chromatography employing TBP impregnated macroporous XAD-4 resin as the stationary phase was examined; some parameters affecting the distribution ratio (K_d) and the column resolution (R_s) of Am(III) and Eu(III) were investigated. These parameters are the effect of TBP loading, aqueous nitrate concentrations, and flow rate. Both K_d andR_s increase with the TBP loading.     

Electrochemical Determination of Ascorbic Acid in Room Temperature Ionic Liquid BPPF6 Modified Carbon Paste Electrode

A room temperature ionic liquid N‐butylpyridinium hexafluorophosphate (BPPF₆) was used as a binder to make an ionic liquid modified carbon paste electrode (IL‐CPE), which showed good characteristics such as simple preparation procedure, fast electrochemical response and good conductivity. The electrochemical oxidation of ascorbic acid (AA) on the new IL‐CPE was carefully studied. The oxidation peak potential of AA on the IL‐CPE appeared at 109 mV (vs. SCE), which was about 338 mV decrease of the overpotential compared to that obtained on the traditional carbon paste electrode (CPE) and the oxidation peak current was increased for about four times. The electrochemical parameters of AA on the IL‐CPE were calculated with the charge transfer coefficient (α) and the electrode reaction rate constant (k_s) as 0.87 and 0.800 s^?1, respectively. Based on the relationship of the oxidation peak current and the concentration of AA a sensitive analytical method was established with cyclic voltammetry. The linear range for AA determination was in the range from 1.0×10^?5 to 3.0×10^?3 mol/L with the linear regression equation as I_p (μA)=?2.52–0.064C (μmol/L) (n=13, γ=0.9942) and the detection limit was calculated as 8.0×10^?6 mol/L (3σ). The proposed method was free of the interferences of coexisting substances such as dopamine (DA) and amino acids etc., and successfully applied to the vitamin C tablets determination.     

Validation of a chiral capillary electrochromatographic method for metoprolol on a teicoplanin stationary phase

Summary A chiral capillary electrochromatographic (CEC) method for determination of the enantiomeric purity of either enantiomer of metoprolol has been validated. High resolution and efficiency separations (R _s =2.5 and 80000 plates m⁻¹, respectively) were achieved by use of a teicoplanin chiral stationary phase in the polar organic mode. Method validation showed that detection linearity, robustness, accuracy, and repeatability were adequate. The method was also shown to be sufficiently sensitive for the determination of a minor enantiomer; the limit of quantitation (LOQ) was determined to be 0.09% of the peak area of the enantiomer under investigation. A similar commercial column was subsequently evaluated by use of the validated method and found to yield results for metoprolol comparable with those obtained on the homepacked columns. Acceptable separations on this commercial column were also obtained for other β-blocking drugs; those for alprenolol were particularly noteworthy (R _S =3.8 and 265000 plates m⁻¹).     

A Validated LC Method for Determination of the Enantiomeric Purity of Darifenacin in Bulk Drug and Extended Release Tablets

A new and accurate chiral liquid chromatographic method has been developed for the determination of enantiomeric purity of darifenacin [(S)-enantiomer] in bulk drugs and extended release tablets. Normal phase chromatographic separation was performed on an immobilized cellulose based chiral stationary phase (Chiralpak-IC) with n-hexane:ethanol:diethylamine (50:50:0.3, v/v/v) as mobile phase at a flow rate of 1.0 mL min⁻¹. The elution time was ~15 min. The resolution (R _s ) between the enantiomers was greater than four and interestingly the (R)-enantiomer was eluted prior to darifenacin in the developed method. The limit of detection (LOD) and limit of quantification (LOQ) for the (R)-enantiomer were 0.02 μg and 0.07 μg, respectively, for a 10 μL injection volume. The method was extensively validated in terms of linearity, precision and accuracy and satisfactory results were obtained. Robustness studies were also conducted. The sample solution stability of darifenacin was determined and the compound was found to be stable for a study period of 48 h.

     

Lipophilicity of Some Preservatives Estimated by RP-TLC Using Stationary Phases with Different Polarity

Lipophilcity of some preservatives was determined by reversed phase high performance thin layer chromatography (RP-HPTLC) using methanol–water mixtures in different volume proportions as mobile phase on three stationary phases of different polarity: RP-18F_254s, RP-18WF_254s and CNF_254s plates. The R _M values decreased linearly with increasing methanol concentration in the mobile phase in all cases. The regression determination coefficients obtained for all stationary phases were excellent (higher than 0.98 in most cases). The chromatographic behavior of the preservatives on the RP-HPTLC plates used in this study is similar and in a very good agreement with their polarity. Good chromatographic regularities found for retention factors and by applying principal component analysis for all three types of stationary phases indicate that the same lipophilic interactions are dominants in all cases. The relationships between different RP-HPTLC retention parameters (R _M0 , b, scores of R _F -PC1/R _F and scores of R _M -PC1/R _M ) and various calculated log P values of the same preservatives show highly significant correlations for all types of stationary phases.     

Evaluation of Alkyl Bonded Silica and Solvent Phase Modifiers for the Efficient Elution of Basic Drugs on HPLC

Abstract

Nine representative drugs were used to evaluate the effects of alkyl bonded stationary phases containing type A and type B silica and the effects of an amine modifier on the efficiency of high performance liquid chromatographic elution of basic and acidic drugs. The theoretical plate count and asymmetry factor of the eluted peaks were compared to that of acetophenone as a reference to the maximal efficiency of each system evaluated. Zorbax^R C₈ was used as the stationary phase prepared from type A silica and Zorbax RX^R was used as the stationary phase prepared from the type B silica. The theoretical plate count and asymmetry factor of acetophenone was observed to be the same on both columns when analyzed in an acidic aqueous/acetonitrile mobile phase. An improvement in the efficiency and peak shape of the amine containing compounds was observed using the Zorbax RX^R stationary phase as compared to the efficiency and peak shape of these compounds on the Zorbax^R C₈ stationary phase. Interestingly, the acidic compounds salicylic acid and mefenamic acid showed better peak shapes on the Zorbax RX^R column than on the Zorbax C₈. For all drugs studied the theoretical plate count and asymmetry factor was better on both the Zorbax^R C₈ and the Zorbax RX^R stationary phases when the amine modifier triethylamine was used in the mobile phase. Except for salicylic acid, the theoretical plate count and asymmetry factor for each drug was similar on the Zorbax^R C₈ and the Zorbax RX^R columns when the amine modifier     

Chemometrics-Assisted Optimization of Beta-/Gamma-Tocol Separation on a C<Subscript>30</Subscript> Stationary Phase in Reversed-Phase LC

This paper presents a chemometrics-assisted optimization study to improve the separation of tocopherol (-T) and tocotrienol (-TT) homologues on a C₃₀ stationary phase in reversed-phase HPLC. The HPLC settings were optimized using a central composite design and the response surface methodology. Flow rate, column temperature, and mobile phase composition were chosen as independent variables. Peak resolution (R_s), analysis time (t_R), and peak symmetries of the tocopherol isomers were chosen as response variables. Optimum performance in terms of R_s was obtained at a flow rate of 0.31 mL min^?1, a temperature of 8.70 °C, and % B content (methyl tert-butyl ether: methanol: water, 80:18:2, v/v/v) in the mobile phase of 38.12%. The analysis of variance and regression analysis gave adjusted R² values of 0.9841 for R_s, 0.9850 for t_R-(α-T), 0.9853 for t_R-(β-T), and 0.9204 for the peak symmetry of β-T. This confirms the good agreement of experimental data with predicted values. The close eluting peaks of β-/γ-tocol could be baseline separated at the optimized conditions at a minimized analysis time. Empirical second-order polynomial models were derived that gave statistically high significances (P?<?0.0001). Hence, the models can be successfully employed to predict the optimum separation conditions of co-eluting peaks of β-/γ-tocols. The optimized method was successfully applied to determine the individual tocol homologues in various cold pressed edible oils. Total contents ranged from 15 to almost 2600 mg tocol kg^?1 oil.     

Chiral phenethylamine synergistic tricarboxylic acid modified β-cyclodextrin immobilized on porous silica for enantioseparation

In this work, a series of chiral phenethylamine synergistic tricarboxylic acid modified β-cyclodextrin bonded stationary phase for high performance liquid chromatography (HPLC) were synthesized via a simple one-pot synthesis approach. Various racemates (aryl alcohols, flavanones, triazoles, benzoin, etc.) were well separated on the tricarboxylic acid modified chiral stationary phases in both normal and reversed modes with good reproducibility and stability, and the influence of mobile phase composition on resolution (R_s) were deeply investigated. The RSD values of R_s for repeatability and column-to-column were below 1.28% and 3.05%, respectively. Hence, the fabrication of tricarboxylic acid modified chiral stationary phase (CSPs) is a new efficient strategy to improve the application of β-cyclodextrin as CSPs in the field of chromatography.