A Gadolinium-Based Magnetic Ionic Liquid for Dispersive Liquid-Liquid Microextraction of Ivermectin from Environmental Water.

The recently introduced gadolinium-based magnetic ionic liquid (Gd-MIL) has been exploited as an extractant in dispersive liquid-liquid microextraction (DLLME) for preconcentration of ivermectin (IVR) from water samples followed by analysis using reversed-phase HPLC with UV detection at 245 nm. The utilized Gd-MIL extractant is hydrophobic with markedly high magnetic susceptibility. These features result in an efficient extraction of the lipophilic analyte and facilitate the phase separation under the influence of a strong magnetic field, thus promoting the method sensitivity and increasing the potential for automation. To maximize the IVR enrichment by DLLME, the procedure was optimized for extractant mass, dispersive solvent type/volume, salt addition and diluent pH. At optimized conditions, an enrichment factor approaching 70 was obtained with 4.0-mL sample sizes. The method was validated in terms of accuracy, precision, specificity and limit of quantitation. The method was successfully applied to the determination of IVR in river water samples with a mean relative recovery of 97.3% at a spiked concentration of 400 ng/mL. Compared with other reported methods, this approach used a simpler procedure with improved precision, lower amounts of safer solvents and a short analysis time.

Micellar and sub-micellar chromatography with a cocamidopropyl betaine surfactant.

We have coated a typical C18 column with the pH cationic charge controllable zwitterionic synthetic surfactant, cocamidopropyl betaine (CAPB), in order to generate a mixed mode reversed phase weak ion exchange column. As determined by the Thomas model, the column has an adsorbed surfactant capacity of 0.557 mmoles. The addition of 8.8 × 10-4 M CAPB to the totally aqueous mobile phase ensured stability of the surfactant on the column and permitted separation of the four component sulfonamide mixture with micellar liquid chromatography (MLC) in under 11 min. Comparatively, with a dilute H2SO4 mobile phase with no CAPB, the separation time for the sulfonamide mixture reached an excessive run time of an hour on the bare C18 chains. With CAPB in the mobile phase (no organic solvent present), a seven component sulfonamide mixture could be separated in less than 45 min. A five component short chain carboxylic acid mixture, separated in 20 min, was used to examine the ion exchange character of the column in pH environments of 2.3 and 4.6. Three phase MLC equilibrium analysis was also done in these pH environments with the sulfa drug and carboxylic acid mixtures to determine partition coefficients. Finally, a quite high molecular weight (70,000) anionic polystyrene sulfonate polymer was characterized by MLC with only CAPB and variable pH mobile phases; the optimal pH was determined to be 5.6. A totally aqueous mobile phase without CAPB was not suitable for profiling this polymer.

A gadolinium-based magnetic ionic liquid for supramolecular dispersive liquid-liquid microextraction followed by HPLC/UV for the determination of favipiravir in human plasma.

Favipiravir is a potential antiviral medication that has been recently licensed for Covid-19 treatment. In this work, a gadolinium-based magnetic ionic liquid was prepared and used as an extractant in dispersive liquid-liquid microextraction (DLLME) of favipiravir in human plasma. The high enriching ability of DLLME allowed the determination of favipiravir in real samples using HPLC/UV with sufficient sensitivity. The effects of several variables on extraction efficiency were investigated, including type of extractant, amount of extractant, type of disperser and disperser volume. The maximum enrichment was attained using 50 mg of the Gd-magnetic ionic liquid (MIL) and 150 µl of tetrahydrofuran. The Gd-based MIL could form a supramolecular assembly in the presence of tetrahydrofuran, which enhanced the extraction efficiency of favipiravir. The developed method was validated according to US Food and Drug Administration bioanalytical method validation guidelines. The coefficient of determination was 0.9999, for a linear concentration range of 25 to 1.0 × 105  ng/ml. The percentage recovery (accuracy) varied from 99.83 to 104.2%, with RSD values (precision) ranging from 4.07 to 11.84%. The total extraction time was about 12 min and the HPLC analysis time was 5 min. The method was simple, selective and sensitive for the determination of favipiravir in real human plasma.

A dual grafted fluorinated hydrocarbon amine weak anion exchange resin polymer for adsorption of perfluorooctanoic acid from water.

Perfluorooctanoic acid (PFOA) is a persistent and recalcitrant organic contaminant of exceptional environmental concern, and its removal from water has increasingly attracted global attention due to its wide distribution and strong bioaccumulation. Adsorption is considered an effective technique for PFOA removal and more efficient PFOA sorbents are still of interest. This study developed a dual grafted fluorinated hydrocarbon amine weak anion exchange (WAX) polymeric resin (Sepra-WAX-KelF-PEI) for PFOA removal from water. This polymer was synthesized by a two-step amine grafting reaction procedure involving first the reaction of the Sepra-WAX hydrocarbon polymer with poly(vinylidinefluoride-chlorotrifluoroethylene) (Kel-F 800) and then a second reaction with polyethyleneimine (PEI). Characterization of the synthesized polymers was performed using scanning electron microscopy and elemental analysis (F and Cl) by energy dispersive X-ray spectroscopy. The PFOA adsorption performance evaluations were conducted by packed column flow analyses with on-line detection. The results show the breakthrough of the Sepra-WAX-KelF-PEI synthesized with optimum stoichiometry was two times better than the starting anion exchange polymer Sepra-WAX, and six times better than powdered activated carbon, when using the same column size. The adsorption mechanisms of this novel adsorbent including hydrophobic interaction and electrostatic interaction were also clarified in this study. The adsorption kinetic parameters of the two optimum synthesized sorbents were determined using the Thomas model, the Yoon-Nelson model, and batch isotherm studies, and compared with those found with activated carbon and the starting WAX resin. Good agreement of the batch isotherm and column studies with respect to adsorption capacities trends between all three polymers (Sepra-WAX, Sepra-WAX-KelF, and Sepra-WAX-KelF-PEI) were noted.

A gadolinium-based magnetic ionic liquid for dispersive liquid-liquid microextraction.

A hydrophobic gadolinium-based magnetic ionic liquid (MIL) was investigated for the first time as an extraction solvent in dispersive liquid-liquid microextraction (DLLME). The tested MIL was composed of trihexyl(tetradecyl)phosphonium cations and paramagnetic gadolinium chloride anions. The prepared MIL showed low water miscibility, reasonable viscosity, markedly high magnetic susceptibility, adequate chemical stability, low UV background, and compatibility with reversed-phase HPLC solvents. These features resulted in a more efficient extraction than the corresponding iron or manganese analogues. Accordingly, the overall method sensitivity and reproducibility were improved, and the analysis time was reduced. The applicability of the proposed MIL was examined through the microextraction of four sartan antihypertensive drugs from aqueous samples followed by reversed-phase HPLC with UV detection at 240 nm. The DLLME procedures were optimized for disperser solvent type, MIL mass, disperser solvent volume, as well as acid, base, and salt addition. The limits of quantitation (LOQs) obtained with the analysis of 1.2-mL samples after DLLME and HPLC were 80, 30, 40, and 160 ng/mL for azilsartan medoxomil, irbesartan, telmisartan, and valsartan, respectively. Correlation coefficients were greater than 0.9988 and RSD values were in the range of 2.48-4.07%. Under the optimized microextraction conditions and using a 5-mL sample volume, enrichment factors were raised from about 40 for all sartans using a 1.2-mL sample to 175, 176, 169, and 103 for azilsartan medoxomil, irbesartan, valsartan, and telmisartan, respectively. The relative extraction recoveries for the studied sartans in river water varied from 82.5 to 101.48% at a spiked concentration of 0.5 µg/mL for telmisartan and irbesartan and 1 µg/mL for azilsartan medoxomil and valsartan. Graphical abstract.

Liquid chromatography of short chain carboxylic acids using a glutamic acid surfactant coated C18 stationary phase.

A C18 column was modified with the anionic amino acid surfactant lauroyl-l-glutamate (LLG) to facilitate the separation of ten short-chain aliphatic carboxylic acids (oxalic, tartaric, malic, malonic, lactic, acetic, maleic, citric, fumaric, and succinic). The developed method was proven to be fast, versatile, and environmentally friendly. After the coating of the column using 1% LLG solution and optimizing chromatographic conditions such as pH and temperature, near baseline resolution of the ten carboxylic acids within 4 min with excellent peak shape at pH = 1.8 using 100% H2O acidified with sulfuric acid was possible. Although the design of this stationary phase, with the hydrophilic group at the end of the alkyl chain, seems to be in contrast to such columns designed for a totally aqueous mobile phase that have a polar (often amide) group embedded near the silica surface, no evidence of phase collapse was noted. Linear relationships of ln retention factor (k) versus 1/Temperature (T) (van't Hoff plots) were generated for all the acids indicating a single retention mechanism was likely. As the pH of the mobile phase decreased, the analyte retention factors increased due to the increase of the fraction of the analyte with neutral charge (alpha zero). The surfactant amide linkage, being electron donating, increased the pKa of the more acidic carboxyl group of glutamic acid so both carboxyl groups were protonated (neutral) at pH 1.8. The exact nature of the retention mechanism is uncertain but there certainly seems to be a pronounced hydrophobic component due to the large difference in retention of fumaric acid and methyl fumarate at pH 1.8. In addition, eleven beverage samples were analyzed for their aliphatic carboxylic acid contents. The results showed that malic, fumaric, and citric acids were the most common carboxylic acids in natural beverages with concentrations as high as 6432 ppm of malic acid in organic apple juice, 64 ppm of fumaric acid in organic concord juice, and 6543 ppm citric acid in strawberry lemonade juice.

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

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

Solvent-terminated dispersive liquid-liquid microextraction: a tutorial.

Solvent-terminated dispersive liquid-liquid microextraction (ST-DLLME) is a special mode of DLLME in which a demulsifying solvent is injected into the cloudy mixture of sample/extractant to break the emulsion and induce phase separation. The demulsification process starts by flocculation of the dispersed microdroplets by Ostwald ripening or coalescence to form larger droplets. Then, the extractant either floats or sinks depending on its density as compared with that for the aqueous sample. The demulsifier should have high surface activity and low surface tension in order to be capable of inducing phase separation. The extraction efficiency in ST-DLLME is controlled by the same experimental variables of normal DLLME (n-DLLME) such as the type and volume of the extractant as well as the disperser. Other parameters such as pH and the temperature of the sample, the stirring rate, the time of extraction and the addition of salt are also important to consider. Along with these factors, the demulsifier type and volume and the demulsification time have to be optimized. By using solvents to terminate the dispersion step in DLLME, the centrifugation process is not necessary. This in turn improves precision, increases throughput, decreases the risk of contamination through human intervention and minimizes the overall analysis time. ST-DLLME has been successfully applied for determination of both inorganic and organic analytes including pesticides and pharmaceuticals in water and biological fluids. Demulsification via solvent injection rather than centrifugation saves energy and makes ST-DLLME easier to automate. These characteristics in addition to the low solvent consumption, the reduced organic waste and the possibility of using water in demulsification bestow green features on ST-DLLME. This tutorial discusses the principle, the practical aspects and the different applications of ST-DLLME.

Liquid chromatography with alkylammonium formate ionic liquid mobile phases and fluorescence detection.

Fluorescence detection of various pharmaceuticals and the amino acid tryptophan (low molecular weight organic compounds) as well as the enzyme lactate dehydrogenase LDH (high molar mass compound) has been studied in aqueous solutions using alkyl ammonium formate ionic liquids as the primary solvent component. It was expected that the high viscosity of such ionic liquid-water mixtures would enhance fluorescence. Pharmaceuticals such as riboflavin and naproxen showed no such enhancement in the presence of ethylammonium formate (EAF) or isopropylammonium formate (IPAF) but the fluorescence of warfarin was substantially enhanced by a factor of 4 with 80% EAF and a factor of 7 with 70% IPAF. However, this improved fluorescence using alkylammonium formates did not seem to be general for other coumarin compounds except for bromadiolone which showed a similar fluorescence enhancement using EAF. Enhancement of tryptophan fluorescence was also seen for both EAF and IPAF. During the reversed phase elution of LDH on a polymeric HPLC column, remarkable enhancements in LDH peak intensity and activity were observed by incorporating 6% PEG 8000 in the organic mobile phase that contained either 20% acetonitrile or IPAF. Using higher concentrations of PEG 8000 is not recommended, not only because of the high viscosity, but also because the stabilizing effect of PEG 8000 is gradually reduced at higher concentrations.

Hydrophilic interaction liquid chromatography of hydroxy aromatic carboxylic acid positional isomers.

Hydrophilic interaction liquid chromatography (HILIC) has become increasingly popular as an alternative to reversed phase LC due to its ease of separating complex polar compound mixtures and the compatibility of the mobile phase with mass spectrometry (MS). Using a plain silica column (150  mm × 4.6  mm), we have shown a mixture containing three hydroxybenzoic acid isomers plus syringic and vanillic acid and three hydroxycinnamic acid isomers plus ferulic and sinapic acid can be separated using a mobile phase comprised of 90% acetonitrile (MeCN) and 10% 20 mM ammonium acetate at pH 6 in under 45 min. This method is appropriate when using UV detection at 275 nm. However, for improved MS compatibility, a buffer concentration of 10 mM is recommended but this greatly decreases the analyte retention factors. A second more nonpolar organic solvent component in the mobile phase (particularly pentane which has not been previously considered for HILIC) is found to offset this loss in retention. The optimum mobile phase is found to be 90% MeCN, 5% 10 mM ammonium acetate pH 6, and 5% pentane with resolution of eight of the ten compounds with a separation time of 30 min. Using UV detection, we have shown that detection limits range from 36 to 133 pmole and quantitation limits are spread from 94 to 376 pmole for six of the analytes. Upon testing this method on two other silica columns from different manufacturers, it is found that while resolution is similar, further optimization of the mobile phase is recommended.

Solidification of floating organic droplet in dispersive liquid-liquid microextraction as a green analytical tool.

Dispersive liquid-liquid microextraction (DLLME) is a special type of microextraction in which a mixture of two solvents (an extracting solvent and a disperser) is injected into the sample. The extraction solvent is then dispersed as fine droplets in the cloudy sample through manual or mechanical agitation. Hence, the sample is centrifuged to break the formed emulsion and the extracting solvent is manually separated. The organic solvents commonly used in DLLME are halogenated hydrocarbons that are highly toxic. These solvents are heavier than water, so they sink to the bottom of the centrifugation tube which makes the separation step difficult. By using solvents of low density, the organic extractant floats on the sample surface. If the selected solvent such as undecanol has a freezing point in the range 10-25°C, the floating droplet can be solidified using a simple ice-bath, and then transferred out of the sample matrix; this step is known as solidification of floating organic droplet (SFOD). Coupling DLLME to SFOD combines the advantages of both approaches together. The DLLME-SFOD process is controlled by the same variables of conventional liquid-liquid extraction. The organic solvents used as extractants in DLLME-SFOD must be immiscible with water, of lower density, low volatility, high partition coefficient and low melting and freezing points. The extraction efficiency of DLLME-SFOD is affected by types and volumes of organic extractant and disperser, salt addition, pH, temperature, stirring rate and extraction time. This review discusses the principle, optimization variables, advantages and disadvantages and some selected applications of DLLME-SFOD in water, food and biomedical analysis.

Micellar liquid chromatography of terephthalic acid impurities.

The production of terephthalic acid (TPA) by oxidation of p-xylene is an important industrial process because high purity TPA is required for the synthesis of polyethylene terephthalate, the primary polymer used to make plastic beverage bottles. Few separation methods have been published that aim to separate TPA from eight major aromatic acid impurities. This work describes a "green" micellar liquid chromatography (MLC) method using a C18 column (100×2.1mm, 3.5µm), an acidic 1% sodium dodecyl sulfate (SDS) mobile phase, and a simple step flow rate gradient to separate TPA and eight impurities in less than 20min. The resulting chromatogram shows excellent peak shape and baseline resolution of all nine acids, in which there are two sets of isomers. Partition coefficients and equilibrium constants have been calculated for the two sets of isomers by plotting the reciprocal of the retention factor versus micelle concentration. Quantitation of the nine analytes in an actual industrial TPA sample is possible. Limits of detection for all nine acids range from 0.180 to 1.53ppm (2.16-19.3 pmoles) and limits of quantitation range from 0.549 to 3.45ppm (6.48-43.0 pmoles). In addition, the method was tested on two other reversed phase C18 columns of similar dimensions and particle diameter from different companies. Neither column showed quite the same peak resolution as the original column, however slight modifications to the mobile phase could improve the separation.

Kinetic sorption of contaminants of emerging concern by a palygorskite-montmorillonite filter medium.

Kinetic sorption of bisphenol A (BPA), carbamazepine (CMZ) and ciprofloxacin (CIP) by three palygorskite-montmorillonite (Pal-Mt) granule sizes was studied. For BPA, CMZ and CIP, apparent sorption equilibrium was reached within about 3, 5 and 16 h, respectively. The highest and the lowest sorption capacities were by the small and the large granule sizes, respectively. Experimental results were compared to various sorption kinetics models to gain insights regarding the sorption processes and achieve a predictive capacity. The pseudo-second order (PSO) and the Elovich models performed the best while the pseudo-first order (PFO) model was only adequate for CMZ. The intraparticle-diffusion (IPD) model showed a two-step linear plot of BPA, CMZ and CIP sorption versus square root of time that was indicative of surface-sorption followed by IPD as a rate-limiting process before equilibrium was reached. Using the pseudo-first order (PFO) and the pseudo-second order (PSO) rate constants combined with previously-established Langmuir equilibrium sorption models, the kinetic sorption (ka) and desorption (kd) Langmuir kinetic rate constants were theoretically calculated for BPA and CIP. Kinetic sorption was then simulated using these theoretically calculated ka and kd values, and the simulations were compared to the observed behavior. The simulations fit the observed sorbed concentrations better during the early part of the experiments; the observed sorption during later times occurred more slowly than expected, supporting the hypothesis that IPD becomes a rate-limiting process during the course of the experiment.

Ion-Exclusion High-Performance Liquid Chromatography of Aliphatic Organic Acids Using a Surfactant-Modified C18 Column.

Ion exclusion chromatography (IELC) of short chain aliphatic carboxylic acids is normally done using a cation exchange column under standard HPLC conditions but not in the ultra-HPLC (UHPLC) mode. A novel IELC method for the separation of this class of carboxylic acids by either HPLC or UHPLC utilizing a C18 column dynamically modified with sodium dodecyl sulfate has been developed. The sample capacity is estimated to be near 10 mM for a 20 µL injection or 0.2 µmol using a 150 × 4.6 mm column. The optimum mobile phase determined for three standard mixtures of organic acids is 1.84 mM sulfuric acid at pH 2.43 and a flow rate of 0.6 mL/min. Under optimized conditions, a HPLC separation of four aliphatic carboxylic acids such as tartaric, malonic, lactic and acetic can be achieved in under 4 min and in <2 min in the UHPLC mode at 2.1 mL/min. A variety of fruit juice and soft drink samples are analyzed. Stability of the column as measured by the retention order of maleic and fumaric acid is estimated to be ∼4,000 column volumes using HPLC and 600 by UHPLC. Reproducible chromatograms are achieved over at least a 2-month period. This study shows that the utility of a C18 column can be easily extended when needed to IELC under either standard or UHPLC conditions.

Micellar and sub-micellar ultra-high performance liquid chromatography of hydroxybenzoic acid and phthalic acid positional isomers.

Micellar liquid chromatography (MLC) has been used primarily for the separation of neutral analytes of varying polarities, most commonly phenols and polyaromatic hydrocarbons, but does not seem to have been used to study aromatic hydroxy acids in detail. We have studied the separation of hydroxybenzoic acid mixtures, including monohydroxybenzoic and dihydroxybenzoic acid positional isomers by MLC. Sodium dodecylsulfate (SDS) is investigated as the modifying surfactant on a C18 ultra-high performance liquid chromatography (UHPLC) column (100 × 2.1mm, 1.8 µm). The addition of only SDS (no organic solvent) to the mobile phase reduced the influence of hydrophobic interactions while improving the retention times, resolution, and peak shapes, even at concentrations below the critical micellization concentration (CMC). The UHPLC separation of 7 hydroxybenzoic acids, including 6 dihydroxybenzoic acid positional isomers and one trihydroxybenzoic acid, is achieved with high efficiency using 0.1% SDS in 1.84 mM sulfuric acid (pH 2.43) mobile phase, in less than 6 min with a flow rate of 0.3 mL min(-1), and in less than four min with a flow rate of 0.7 mL min(-1). Six monohydroxybenzoic acid isomers are also effectively separated by MLC, using a 0.5% SDS mobile phase modifier, in less than 20 min with a flow rate of 0.3 mL min(-1), and in less than 14 min with a flow rate of 0.7 mL min(-1). The 3 phthalic acid isomers could be separated using a similar mobile phase and flow rates in less than 6 and 4 min. Solute-micelle equilibrium constants and partition coefficients are calculated for 6 monohydroxybenzoic acids based on a plot of MLC retention factor vs. mobile phase micelle concentration. All aromatic acid isomers studied can be classified as binding solutes in the MLC retention mechanism. Less effective separations are observed with shorter chain surfactants, leading to higher retention times and poor peak shapes. It is concluded that increasing chain length led to more efficient MLC separations, and SDS is the preferred modifying surfactant for the examined separation.

Ion chromatography for the separation of heparin and structurally related glycoaminoglycans: A review.

The global crisis resulting from adulterated heparin in late 2007 and early 2008 revived the importance of analytical techniques for the purity analysis of heparin products. The utilization of ion chromatography techniques for the separation, detection, and structural determination of heparin and structurally related glycoaminoglycans, including their corresponding oligosaccharides, has become increasingly important. This review summarizes the primary HPLC approaches, particularly strong anion exchange, weak ion exchange, and reversed-phase ion-pair, used for heparin purity analysis as well as structural characterization. Strong anion exchange HPLC has been studied most extensively and currently offers the best separation of crude heparin and heparin-like compounds. Weak anion exchange HPLC has been shown to provide shorter analysis times with lower salt concentrations in the mobile phase but is not as widely developed for the separation of all glycoaminoglycans of interest. Reversed-phase ion-pair HPLC offers fast and effective separations of oligosaccharides derived from glycoaminoglycans that can be coupled to mass spectrometry for structural analysis. However, this method generally does not provide sufficient retention of intact glycoaminoglycans.

Sorption-desorption of carbamazepine by palygorskite-montmorillonite (PM) filter medium.

Palygorskite-montmorillonite (PM) was studied as a potential sewage treatment effluent filter material for carbamazepine. Batch sorption experiments were conducted as a function of granule size (0.3-0.6, 1.7-2.0 and 2.8mm) and different sewage effluent conditions (pH, ionic strength and temperature). Results showed PM had a mix of fibrous and plate-like morphologies. Sorption and desorption isotherms were fitted to the Freundlich model. Sorption is granule size-dependent and the medium granule size would be an appropriate size for optimizing both flow and carbamazepine retention. Highest and lowest sorption capacities corresponded to the smallest and the largest granule sizes, respectively. The lowest and the highest equilibrium aqueous (Ce) and sorbed (qe) carbamazepine concentrations were 0.4 mg L(-1) and 4.5 mg L(-1), and 0.6 mg kg(-1) and 411.8 mg kg(-1), respectively. Observed higher relative sorption at elevated concentrations with a Freundlich exponent greater than one, indicated cooperative sorption. The sorption-desorption hysteresis (isotherm non-singularity) indicated irreversible sorption. Higher sorption observed at higher rather than at lower ionic strength conditions is likely due to a salting-out effect. Negative free energy and the inverse sorption capacity-temperature relationship indicated the carbamazepine sorption process was favorable or spontaneous. Solution pH had little effect on sorption.

Separation of Aliphatic and Aromatic Carboxylic Acids by Conventional and Ultra High Performance Ion Exclusion Chromatography.

An ion exclusion chromatography (IELC) comparison between a conventional ion exchange column and an ultra-high performance liquid chromatography (UHPLC) dynamically surfactant modified C18 column for the separation of an aliphatic carboxylic acid and two aromatic carboxylic acids is presented. Professional software is used to optimize the conventional IELC separation conditions for acetylsalicylic acid and the hydrolysis products: salicylic acid and acetic acid. Four different variables are simultaneously optimized including H2SO4 concentration, pH, flow rate, and sample injection volume. Thirty different runs are suggested by the software. The resolutions and the time of each run are calculated and feed back to the software to predict the optimum conditions. Derringer's desirability functions are used to evaluate the test conditions and those with the highest desirability value are utilized to separate acetylsalicylic acid, salicylic acid, and acetic acid. These conditions include using a 0.35 mM H2SO4 (pH 3.93) eluent at a flow rate of 1 mL min-1 and an injection volume of 72 µL. To decrease the run time and improve the performance, a UHPLC C18 column is used after dynamic modification with sodium dodecyl sulfate. Using pure water as a mobile phase, a shorter analysis time and better resolution are achieved. In addition, the elution order is different from the IELC method which indicates the contribution of the reversed-phase mode to the separation mechanism.

The ionic liquid isopropylammonium formate as a mobile phase modifier to improve protein stability during reversed phase liquid chromatography.

The room temperature ionic liquid isopropylammonium formate (IPAF) is studied as a reversed phase HPLC mobile phase modifier for separation of native proteins using a polymeric column and the protein stability is compared to that using acetonitrile (MeCN) as the standard organic mobile phase modifier. A variety of important proteins with different numbers of subunits are investigated, including non-subunit proteins: albumin, and amyloglucosidase (AMY); a two subunit protein: thyroglobulin (THY); and four subunit proteins: glutamate dehydrogenase (GDH) and lactate dehydrogenase (LDH). A significant enhancement in protein stability is observed in the chromatograms upon using IPAF as a mobile phase modifier. The first sharper peak at about 2min represented protein in primarily the native form and a second broader peak more retained at about 5-6min represented substantially denatured or possibly aggregated protein. The investigated proteins (except LDH) could maintain the native form within up to 50% IPAF, while a mobile phase, with as low as 10% MeCN, induced protein denaturation. The assay for pyruvate using LDH has further shown that enzymatic activity can be maintained up to 30% IPAF in water in contrast to no activity using 30% MeCN.