Ion-pair Solid-phase Extraction Research Articles

Stability study and determination of benzene- and naphthalenesulfonates following an on-line solid-phase extraction method using the new programmable field extraction system.

Seven benzene- and naphthalenesulfonates (3-nitrobenzenesulfonate, 4-methylbenzenesulfonate, 1-hydroxy-4-naphthalenesulfonate, 1-amino-7-naphthalenesulfonate, 4-chlorobenzenesulfonate, 1-naphthalenesulfonate and 2-naphthalenesulfonate) were studied. A rapid method for quantifying aromatic sulfonated compounds from waste water samples was developed. This method consists in on-line in-field sampling and monitoring based on ion-pair solid-phase extraction with PLRP-S sorbent, using the new programmable field extraction system and ion-pair liquid chromatography with UV diode-array and electrospray mass spectrometry. Limits of detection for the studied compounds, using the SIM acquisition mode, ranged from 0.01 to 0.33 ng ml(-1). The influence of the aqueous matrix on the on-line SPE was checked by spiking ground and waste waters. Recoveries varied from 70 to 99% when 10 ml of water sample were enriched. The method was applied to the analysis of some environmental sewage samples. This study confirmed that high concentration levels of aromatic sulfonated compounds can be found in sewage samples. In addition, the stability of the seven studied sulfonated benzene and naphthalene compounds was investigated using on-line polymeric SPE pre-columns, based on the styrene-divinylbenzene polymer PLRP-S. Different storage conditions were tested to carry out the stability survey, which included storage at room temperature, at 4 degrees C and at -20 degrees C, during a period of up to 2 weeks. This study showed that the stability of aromatic sulfonic acids on disposable on-line SPE polymeric pre-columns is related to temperature and that the target compounds are more stable at lower temperatures.

Determination of aromatic sulfonates in coastal water by on-line Ion-pair solid-phase extraction/ion-pair liquid chromatography with UV detection

A method for determining aromatic sulfonates in sea water is presented. Ion-pair solid phase extraction is coupled on-line to ion-pair liquid chromatography with UV detection. In the enrichment step, the recoveries from 100 mL of sea water were higher than 65% for most analytes. Linearity was good and detection limits were between 0.02 and 1 μgL−1. The repeatability of the method, expressed as % of relative standard deviation (n=3) was between 1 and 15%. The method was checked in coastal water near the commercial port of Tarragona, where effluents from the petrochemical industry are discharged. All the samples taken were found to contain 2-naphthalenesulfonate.

Analysis of nucleotide sugars from cell lysates by ion-pair solid-phase extraction and reversed-phase high-performance liquid chromatography.

Analysis of nucleotide sugar metabolism is essential in studying glycosylation in cells. Here we describe practical methods for both extraction of nucleotide sugars from cell lysates and for their analytical separation. Solid-phase extraction cartridges containing graphitized carbon can be used for the purification of nucleotide sugars by using triethylammonium acetate buffer as a ion-pairing reagent for decreasing retention. After that they are separated by high-performance liquid chromatography using a C18 reversed-phase column and the same ion-pairing reagent for increasing retention. These new sample preparation and analysis methods enable good separation of structurally similar sugar nucleotides, compatibility with rapid evaporative concentration, and possibility to automation. Monitoring the production of GDP-deoxyhexoses in genetically engineered yeast and native bacterial cells are described here as specific applications.

Analysis of Sulfonated Naphthalene−Formaldehyde Condensates by Ion-Pair Chromatography and Their Quantitative Determination from Aqueous Environmental Samples

An ion-pair solid-phase extraction (IPE), ion-pair chromatography (IPC) procedure with fluorescence detection for the quantitative analysis of sulfonated naphthalene-formaldehyde condensates (SNFC) was developed, which provides full resolution of SNFC up to a degree of condensation n = 5 and partial resolution up to n = 15. Liquid chromatography-electrospray ionization-mass spectrometry confirmed that SNFC elute in the order of condensation. Response factors in fluorescence detection proved to be mass-constant, thereby allowing us to determine total SNFC amounts. With this IPC method, the weight- and the number-average molecular weights of these high-volume production chemicals (kiloton per annum), used as synthetic tanning agents, concrete plasticizers, and dispersants, can be determined. Recoveries in IPE range from 73 to 85% in river Rhine water and from 79 to 93% in tap water for n = 2 to n = 7 with limits of detection of 3-8 ng/L for individual homologues from 500 mL of water. The IPE-IPC procedure was applied to samples of secondary industrial effluents, river Rhine water, a river bank filtrate, and a groundwater sample. SNFC up to n = 6 were detected in the treated effluents. Total concentrations ranged from 208 micrograms/L in a secondary treated SNFC production effluent to < 1.4 micrograms/L in groundwater. These first analyses suggest a widespread occurrence of the lower oligomers of SNFC in the aquatic environment.

Determination of naphthalenesulfonates in water by on-line ion-pair solid-phase extraction and ion-pair liquid chromatography with fast-scanning fluorescence detection

A fast analytical method for quantifying a mixture of 12 naphthalenesulfonates and naphthalenedisulfonates has been developed. This method consists of on-line ion-pair solid-phase extraction with PLRP-s sorbent and ion-pair liquid-chromatography using fast-scanning fluorescence spectrometer as a detection system and multivariate calibration. As complete separation is unnecessary, the compounds were analysed in isocratic conditions and the chromatographic analysis took only 25 min. Three-way partial least-squares (PLS) was used to carry out multivariate calibration for spiked tap water. In these conditions, quantification limits were between 0.01 and 3 μg l −1. Repeatability was also evaluated and relative standard deviations ( n=3) were between 0.5 and 4, depending on the compound. Finally, spiked tap and Ebro river waters were analysed to evaluate prediction capability of the method.

Positive ion electrospray ionization tandem mass spectrometry coupled to ion-pairing high-performance liquid chromatography with a phosphate buffer for the quantitative analysis of intracellular nucleotides.

A novel analytical procedure has been developed for the analysis of intracellular nucleotide triphosphates. Positive ion electrospray ionization tandem mass spectrometry (MS/MS) was interfaced to ion-pairing high-performance liquid chromatography (HPLC) utilizing a mobile phase containing 10 mM ammonium phosphate, pH 6.4, with 2 mM tetrabutylammonium hydroxide and 15% acetonitrile. The methodology was developed to support the analysis of the 5'-triphosphate anabolite of the antiviral agent (-)-FTC ((2R, 5S)-5-fluoro-1-[2-(hydroxymethyl-1,3-oxathiolan-5-yl]cytosine) in human peripheral blood mononuclear cells (PBMCs). In this procedure, all nucleotides were extracted from PBMCs with aqueous methanol, isolated with high recovery using a novel ion-pairing solid phase extraction procedure, and then analyzed directly with LC/MS/MS with a 10-min analysis time. A calibration curve was generated representing (-)-FTC 5'-triphosphate ((-)-FTCTP) concentration over the range of 0.083 to 83 picomol/10(6) cells (approximately 0.08 to 80 picomoles on-column). Linear regression analysis with 1/x(2) weighting yielded a coefficient of determination (r(2)) of greater than 0.999. The back-calculated concentrations of all calibration standards had relative errors within the range of +5 to -3%. A preliminary assessment of intra-assay precision and accuracy, analyte stability, and LC/MS system stability indicated a robust method capable of being validated with a limit of quantitation estimated conservatively at 0.08 picomol/10(6) cells (approximately 0.08 picomoles on-column; signal-to-noise (S/N) = 5). The general method developed here should be adaptable to all purine- and pyrimidine-based nucleotide applications. This report provides a detailed discussion on the key HPLC, MS, and sample preparation procedures that hold the potential for even greater nucleotide sensitivity.

On-line solid-phase extraction–ion-pair liquid chromatography–electrospray mass spectrometry for the trace determination of naphthalene monosulphonates in water

This paper presents an HPLC–MS method for the fully automated determination of a group of naphthalene monosulphonates in environmental water samples. The analytical procedure consisted of on-line ion-pair solid-phase extraction using a PLRP-S precolumn and ion-pair LC separation with triethylamine as ion-pair reagent in both cases. A mass spectrometric detector, coupled to LC through an electrospray interface and operated in negative ion mode, was used. Diagnostic ions usually corresponded to [SO3]− and/or [M−SO2H]− together with [M−H]− and/or [M−2H+Na]−. The method was applied to the trace determination of several sulphonates present in tap water, seawater and water from the Ebro river. The analytes were determined at a concentration level between 0.05 and 1 μgl−1 under selected ion monitoring acquisition by preconcentrating just 15 ml of sample. Naphthalene-1-sulphonate and naphthalene-2-sulphonate were identified and quantified in one of the samples of seawater.

Ion-pair solid-phase extraction of biogenic amines before micellar electrokinetic chromatography with laser-induced fluorescence detection of their fluorescein thiocarbamyl derivatives.

Extraction conditions by ion-pair solid-phase extraction of biogenic amines from soy sauce samples were studied. The type of surfactant used as ion-pair reagent, the mode of extraction and the pH were factors studied to enhance the extraction efficiency. High recoveries were obtained using dodecylbenzenesulfonic acid as ion-pair reagent. Octanesulfonate and decanesulfonate did not provide satisfactory recoveries. A dynamic ion-pair solid-phase extraction method was also tested for comparison. The extracted amines were derivatized with fluorescein isothiocyanate, separated by micellar electrokinetic chromatography and detected by laser-induced fluorescence (MEKC-LIF). Because of sample clean-up after extraction and the very high number of theoretical plates obtained with the MEKC-LIF method, identification and quantification of biogenic amines in soy sauce samples could be accomplished. Biogenic amines in soy sauce samples could be separated and quantified with detection limits of the order of 0.1 microg/mL, depending on the sample source.

Quantitative determination of pamoic acid in dog and rat serum by automated ion-pair solid-phase extraction and reversed-phase high-performance liquid chromatography

Pamoic acid is used as a counter ion to obtain long-acting pharmaceutical formulations of certain basic drugs. In order to investigate the pharmacokinetics of pamoic acid, a simple, sensitive and reliable method has been established for the quantitative determination of pamoic acid in serum from dog and rat. The method uses ion-pair solid-phase extraction followed by ion-pair reversed-phase high-performance liquid chromatograpy. The influence on recovery of the addition of different agents (tetrabutylammonium acetate, methanol, sodium hydroxide) to the serum samples prior to solid-phase extraction was studied and the analytical method was validated. The method was found to be valid for accurate, precise and selective determination of pamoic acid in the tested concentration range of 5–200 ng/ml serum. The overall performance of the HPLC method was found to be satisfactory for the purpose of determining concentrations of pamoic acid in serum samples from pharmacokinetic studies with pamoic acid in dogs and rats.

Determination of Naphthalenesul-Phonates in Water by On-Line Ion-Pair Solid-Phase Extraction and Ion-Pair Liquid Chromatography with Diode-Array UV Detection

Ion-pair solid-phase extraction was on-line coupled to a chromatographic system with a PLRP-s precolumn and the results were compared with those obtained when C18 sorbents are used. After optimization, the method was used to determine these compounds in two river waters. A sample of 20 ml of river water was preconcentrated with good recovery values for all the compounds studied and detected at 220 nm with detection limits between 0.25 and 0.1 μ1−1. Some of the compounds were provisionally determined by diode-array UV detection.

Effect of Aromatic Solvents Dissolved in an Aqueous Phase on Ion-pair Solid-phase Extraction

The effect of aromatic solvents dissolved in an aqueous phase at the 10–3 mol dm–3 level on the distribution of an ion pair between octadecylsilane (ODS)-modified silica gel and cellulose nitrate was studied systematically. Bis[2-(5- chloro-2-pyridylazo)-5-diethylaminophenolato]cobalt(III) ion and dodecanesulfonate ion were the cation (C+) and anion (A–) studied. The extent of distribution was expressed in terms of the ion-pair extraction constant, Kex, which is defined as Kex = [C+·A–]s/[C+][A–], where the subscript s denotes the solid phase and no subscript the aqueous phase. In the ODS–silica gel system, nitrobenzene (NB), p-methylnitrobenzene (p-MNB), p-ethylnitrobenzene (p-ENB) and o-, m- and p-xylene enhanced the Kex value by more than two orders of magnitude. Other aromatic solvents such as toluene, chlorobenzene and benzene also enhanced Kex. Non-aromatic solvents, such as chloroform, dichloromethane and octan-2-ol had no effect on the extraction. The solvent effect cannot be described in terms of a model of ion-pair solvent extraction. The effect was interpreted through mutual interactions of key constituents of the solid phase, organic solvent and ion pair. The key structual fragments present in an effective solvent are a phenyl group and nitro and alkyl groups on the phenyl group. In the proposed model, the alkyl group on the phenyl group interacts with the octadecyl group on the ODS–silica gel through a hydrophobic force, and the negatively polarized nitro group and/or π electrons in the benzene ring of the solvent adsorbed on the ODS interact with the ion pair through electrostatic forces. In the cellulose nitrate system, the solvent effects were small even in the case of NB, p-MNB and p-ENB. The effect must be saturated by the nitro group originally present in the matrix of cellulose nitrate.

Ion-pair solid-phase extraction with membranes: group contributions and steric effects of ions on the extraction behaviour

The group contribution of the components of organic ions and the effect of the position of the charge in the ions on ion-pair solid-phase extraction with a membrane filter (MF) were studied in terms of extraction constant. The extraction constants for many combinations of MFs made of several materials, anionic surfactants and cationic dyes having various substituents were determined. The results were compared with those obtained in solvent extraction. The extraction constant Kex is defined as Kex=[C+·A–]s/([C+][A–]), where the subscript s denotes solid or solvent phase and no subscript denotes aqueous phase. Cellulose nitrate (CN), cellulose acetate (CA), poly ether sulfone (PS) and polytetrafluoroethylene (PTFE) were the materials of the MFs. Crystal Violet ion (CV+) and bis[2-(5-X-2-pyridylazo)-5-diethylaminophenolato]-cobalt(III) ion {[Co(5-X-PADAP)2]+, ×= H, Cl, CF3} were the cations. Alkylsulfonates, alkylcarbonates, alkylsulfates and alkylbenzenesulfonates with different alkyl groups were the anions. The magnitude of the contribution of several components of organic ions for solid-phase extraction was found to be fixed and smaller than that for solvent extraction for any combinations of MFs, cations and anions. Although the extractabilities of CV+ and [Co(5-Cl-PADAP)2]+ are almost same in solvent extraction, in solid-phase extraction with CN, CA and PS MFs CV+ is much more extractable than [Co(5-Cl-PADAP)2]+. In solid-phase extraction with PTFE, the situation is the converse, that is, [Co(5-Cl-PADAP)2]+ is more extractable than CV+. Probably CV+, a planer cation where the positive charge distributes on the surface on the ion, interacts strongly with the negatively polarized site of the membrane material through electrostatic forces. On the other hand, [Co(5-Cl-PADAP)2]+, a steric cation where the positive charge is at the centre of the ion, interacts with PTFE essentially through hydrophobic forces.

High-performance liquid chromatographic determination of spectinomycin in swine, calf and chicken plasma using post-column derivatization

An HPLC method for the determination of spectinomycin in swine, calf and chicken plasma at 0.1 μg/ml or higher is described. The clean-up is based upon ion-pair solid-phase extraction on a High Hydrophobic C 18 column treated with sodium dioctyl suflosuccinate. After elution with methanol, spectinomycin is chromatographed on a Spherisorb SCX column using 0.1 M sodium sulphate solution (pH 2.6)-acetonitrile (80:20, v/v) as mobile phase. Fluorescence detection is at an excitation wavelength of 340 nm and an emission wavelength of 460 nm after post-column oxidation with sodium hypochlorite followed by derivatization with o-phthaldialdehyde. Mean recoveries were 99 ± 2% ( n = 6), 99 ± 2% ( n = 7) and 104 ± 2% ( n = 6) for swine, calf and chicken plasma, respectively, at the 0.1 μg/ml level.

Preconcentration and Determination of Cadmium and Lead by Ion-Pair Solid Phase Extraction on Silica Gel Followed by Flame Atomic Absorption Spectrometry

The ion-pair formation between the metal complex with 4-(4'-nitrophenylazo)-1-naphthol and cetyltrimethylammonium bromide and its sorption on silica gel form the basis for preconcentration of cadmium and lead, which are subsequently determined on-line by flame AAS. The method was applied to the quantitation of cadmium and lead in potable and surface waters, with limits of determination (10s) of 0.5 and 2 μg l-1, respectively.

Ion-pair solid-phase extraction of cimetidine from plasma and subsequent analysis by high-performance liquid chromatography

An improved method is described for the solid-phase extraction of cimetidine from plasma or serum with subsequent analysis by HPLC. New aspects of the method include protein precipitation with metaphosphoric acid (5%, w/v), followed by selective adsorption of cimetidine and the internal standard ranitidine on the surface of a solid-phase phenyl (PH Bond Elut) column, using octanesulfonate as an ion-pairing agent. Separation was achieved on a LiChrosorb RP-18 column with a mobile phase consisting of acetonitrile—0.01 M phosphate buffer pH 3.0 containing 0.005 M octanesulfonate (22:78, v/v). The intra-assay coefficient of variation varied between 0.7 and 4.0%. The procedure provides cleaner and more stable samples and a better recovery (90 ± 2.3%) and sensitivity (limit of detection 5 ng/ml and limit of quantitation 25 ng/ml) as compared with previous methods.

Analysis of sulphonated polyphenols, synthetic tanning agents in heavily polluted tannery wastewaters

A method is presented for the analysis of sulphonated polyphenols, acting as synthetic tanning agents, in heavily polluted tannery wastewater. It consists of ion-pair solid-phase extraction (RP-18) with tetrabutylammonium bromide followed by reversed-phase ion-pair liquid chromatography on a C 18 stationary phase with UV detection. The detection limit is 15 μg/1. The influence of the wastewater matrix on extraction and the effects of pH and temperature on the HPLC separation are discussed. The procedure is not affected by the high contents of dissolved organic carbon and inorganic salts of tannery wastewater. The tannery effluents investigated contained around 40 mg/1 of sulphonated polyphenols. These compounds appear to be refractory against both anaerobic and aerobic biological wastewater treatment. They might, thus, contribute to the dissolved organic sulphur content of surface waters.

Determination of aromatic sulfonic acids in industrial waste water by ion-pair chromatography

A method for the identification and quantification of aromatic sulfonic acids in industrial waste water has been developed. The preparation of the samples comprises a clean-up step and an enrichment step, utilizing i) reversed-phase extraction and ii) ion-pair solid phase extraction. The aromatic sulfonic acids are separated by ion-pair chromatography with diode-array detection. An advantage of the developed ion-pair chromatographic method is the separation of linear alkylbenzenesulfonic acids (LAS), lignosulfonic acids and aromatic sulfonic acids in one chromatographic run. Also described is an optimized clean-up procedure for collected fractions of a preparative chromatographic run to identify monosulfonic acids with GC/MS after methylation. The detection limits for aromatic sulfonic acids in industrial waste waters are at the μg/l level.

Determination of paraquat in rat brain by high-performance liquid chromatography

The applications of a method based on ion-pair solid-phase extraction and reversed-phase HPLC are reported. The method was used to measure paraquat concentrations in discrete brain areas at different times after its systemic administration in rats. In addition, the method was employed in the determination of paraquat levels in whole-brain samples from rats of various ages systemically treated with several doses of the herbicide.

High-performance liquid chromatographic determination of spectinomycin in swine, calf and chicken plasma

A rapid clean-up procedure based on ion-pair solid-phase extraction (SPE) for the high-performance liquid chromatographic (HPLC) determination of spectinomycin in swine, calf and chicken plasma at a limit of detection of 50 ng/ml is described. After dilution with water and adjustment of the pH to approximately 5.6, the plasma is applied to a high-hydrophobic C 18 SPE column treated with sodium dioctylsulphosuccinate. Spectinomycin is eluted with methanol and derivatized with 2-naphthalene sulphonyl chloride prior to chromatography. The HPLC set-up consists of a dual-column system using two Chromspher silica columns and dichloromethane—acetonitrile—ethyl acetate—acetic acid, in different ratios, as mobile phases. Detection is performed at 250 nm. Quantification is carried out using external standards prepared in blank cleaned plasma. Mean recoveries were 83 ± 3% ( n = 5), 93 ± 6% ( n = 5) and 92 ± 6% ( n = 6) for swine, calf and chicken plasma, respectively, at the 0.1 μg/ml level.

Determination of glycyrrhetinic acid in human plasma by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) method has been developed for measuring 18β-glycyrrhetinic acid (GRA) in human plasma in the range of 0.1–3 μg/ml. The acetate ester of GRA is added to the plasma as an internal standard, plasma proteins are denatured with urea to release GRA, and the GRA and the internal standard are extracted in an ion-pairing solid-phase extraction process. An isocratic, reversed-phase HPLC separation is used, followed by ultraviolet absorbance detection at 248 nm. The results from the analysis of five GRA-fortified plasma pools show a mean relative standard deviation of 7% and are accurate to within 10%. With evaporative concentration of the extract, the limit of detection for GRA in plasma is approximately 10 ng/ml.