C18-bonded Silica Research Articles

Effectiveness of fullerene as a sorbent for the determination of trace amounts of cobalt in wheat flour by electrothermal atomic absorption spectrometry

A flow injection system for the on-line preconcentration of ultratrace levels of cobalt by sorption with ammonium pyrrolidinedithiocarbamate on a C 60 fullerene column was developed. The eluate volume is reduced and dispersion minimized by using a nitrogen (or air) stream to carry the eluent (IBMK) for elution of the adsorbed chelate, which is collected in a 500 µl PTFE autosampler cup. The analytical figures of merit for the determination of cobalt are as follows: limit of detection (3σ), 8 ng l –1 ; precision (RSD), 4% for 0.2 ng ml –1 ; preconcentration factor, 40 (using 25 ml of sample and 500 µl of IBMK). Similar experiments involving C 18 -bonded silica as sorbent revealed ethanol to be the most suitable eluent under these conditions. The results obtained in the determination of cobalt in wheat flour testify to the usefulness of the proposed method.

The Determination of Cd, Cu and Pb in Potable Water and Plant Material by Flame-AAS after on-Line Preconcentration of DDTP-NH4 Metal Complexes on a C18 Column

ABSTRACT An on-line preconcentration method, based on complex formation with ammonium diethyldithiphosphate (DDTP-NH4) and sorption on a C18-bonded silica reversed phase sorbent, for the determination of Pb, Cd and Cu in potable water and biological samples was investigated. Preconcentration factors of 25; 38 and 86 and detection limits of 7, 3" acceptdate="and 7 μg/L for Pb, Cd and Cu, respectively, were obtained, with sample throughputs of 26, 38" acceptdate="and 29 samples/h. The system was efficient at low pH ranges and good agreement between found and certified values was observed in the analysis of certified reference materials.

Preconcentration of Trace Cadmium from Seawater Using a Dynamically Coated Column of Quaternary Ammonium Salt on C18-Bonded Silica Gel and Determination by Graphite-Furnace Atomic Absorption Spectrometry

A dynamically coated column of C18-bonded silica gel with methyltricaprylylammonium chloride was used for the selective preconcentration of Cd from water samples under acidic conditions. The complete adsorption of Cd occurred from seawater with no additional reagent, and was found from non-saline waters containing 0.05 - 5 M HCl. The interfering matrix ions were not retained and pass through the column. The sorbed Cd was eluted with 4 ml of 0.1 M HNO3 for a subsequent measurement by graphite-furnace AAS. The technique has been successfully applied to seawater and riverwater certified reference materials. The preconcentration process is simple and minimizes the contamination of blanks. The detection limit (3 σ) is 0.2 ng l-1 of Cd based on a 75-fold preconcentration.

Concentration of Some Metal Ions Using 2-(5-Bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol and C18-Bonded Silica Gel

A simple and reliable concentration method of trace metals in aqueous solution is proposed. 2-(5-Bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol is used to form water-soluble metal chelates. The chelated metal ions are concentrated from dilute solution by adsorption onto a C18-bonded silica gel column. The adsorbed chelates are eluted with methanol and 1.0 mol dm-3 HCl and determined by ICP-AES or flame AAS. The proposed method is applied to the determination of heavy metal impurities in some commercial sodium salt reagents.

Determination of trace elements in sea-water by inductively coupled plasma mass spectrometry after preconcentration by formation of water-soluble complexes and their adsorption onC18-bonded silica gel

A simple and reliable preconcentration method was developed for the determination of seven trace metals (Mn, Fe, Ni, Cu, Zn, Cd and Pb) in sea-water by ICP-MS. The method is based on the formation of water-soluble complexes in an aqueous sample followed by adsorption of the complexes onto a C18-bonded silica gel column. The chelating reagent used was 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol (5-Br-PAPS). By passage of 100 ml of sea-water sample, after addition of 5-Br-PAPS and adjustment of the pH to 8.3, quantitative adsorption of the metal complexes onto the column took place while the major matrix ions in sea-water passed through the column. A similar but separate sample work-up at pH 4.5 provided acceptably low blank values for Fe. The metals were subsequently eluted with 4.0 ml of 1.0 M HNO3. All seven elements were determined with an all-argon plasma, whereas ultratrace levels of Fe were determined with a nitrogen–argon mixed-gas plasma to reduce the isobaric interference by 40Ar16O on 56Fe. The detection limits of the method, based on a 25-fold preconcentration, range from 0.08 ng l–1 for Cd to 16 ng l–1 for Fe. The precision and accuracy of the method were demonstrated by analyzing coastal and open-ocean sea-water certified reference materials.

Trace Enrichment of Phenolic Compounds from Aqueous Samples by Dynamic Ion-Exchange Solid-Phase Extraction

A novel trace enrichment procedure for ionogenic compounds in environmental aqueous samples, dynamic ion-exchange solid-phase extraction (DIE-SPE), is proposed and evaluated using 15 phenols as model compounds and GC/MS for detection. The procedure is based on the fact that the long-carbon-chain ionic surfactants, such as cetyltrimethylammonium bromide (CTAB), can be steadily adsorbed on the surface of C18-bonded silica, and the ionized functional groups of the adsorbed surfactant molecules can then act as ion-exchange sites to attract the ionized organic analytes from aqueous samples. At the same time, the bonded silica still remains its function as reversed-phase material. Therefore, the mechanism of DIE-SPE has two aspects, i.e., ion exchange and hydrophobic interaction. Sample pH, the loading amount of surfactant on the solid phase, and volume and matrixes of the sample were studied as the factors that affected the extraction efficiency. When applied to the trace enrichment of ionogenic compounds, DIE...

Fullerene: a Sensitive and Selective Sorbent for the Continuous Preconcentration and Atomic Absorption Determination of Cadmium

Ultratrace levels of cadmium were quantitatively sorbed on a C 60 fullerene mini-column to form neutral chelates, which were eluted with 200 µl of isobutyl methyl ketone and transferred to an atomic absorption spectrometer. Two chelating reagents, viz. , ammonium pyrrolidinedithiocarbamate (APDC) and 8-hydroxyquinoline, were tested in a simple flow system. The adsorption constant was dramatically increased for the APDC reagent and C 60 fullerene, and cadmium was selectively separated from co-existing copper, lead, zinc and iron, among other metals. Similar experiments were performed in parallel by using C 18 -bonded silica as sorbent. The concentration factor achieved was 110 and the detection limit was 0.3 ng ml -1 Cd. For analytical validation, cadmium was determined in certified reference biological samples; only the APDC method with C 60 fullerene as sorbent provided accurate results.

The Use of Hydrophilic Counterion for Superior Retention and Separation of Anionic Metal Chelates in Reversed-Phase Partition High Performance Liquid Chromatography

Abstract It has been found that hydrophilic ions, such as protonated tris(hydroxymethyl)aminomethane (H+THMAM), are eminently suitable as counterion for reversed-phase partition high performance liquid chromatography. The anionic metal chelates with 2,2′-dihydroxyazobenzene were separated on C18-bonded silica packing with an aqueous methanol mobile phase (pH 7.9) containing THMAM, and detected spectrophotometrically.

Optimization by orthogonal array design of solid phase extraction of organochlorine pesticides from water

A two-level orthogonal array design (OAD) to optimize the solid phase extraction of organochlorine pesticides is described. Parameters including eluting solvents, SPE cartridges packed with C18-bonded silica from different manufacturers, duration of air drying, pH, salinity and humic acid have been examined using OAD. This systematic approach was then used to optimize the relevant parameters required for off-line solid phase extraction of organochlorine pesticides from water. The optimized parameters were employed to perform extraction of the pesticides from natural waters.

High Performance Liquid Chromatography of Mono- and Oligosaccharides Derivatized withP-Aminobenzoic Ethyl Ester on a C18-Bonded Silica Column

Abstract This report examines a behavior of mono- and oligosaccharide-ABEE derivatives in RP-HPLC. Sugar-ABEE derivatives are saparated by reverse-phase partition chromatography rather than normal-phase partition chromatography. Reducing sugars are derivatized with p-aminobenzoic ethyl ester(ABEE) for the UV detection at 254 nm. C18-bonded silica column is used for the separation of sugar-ABEE derivatives in an isocratic mode. RP-HPLC is performed by using ternary mixture as a mobile phase and column temperature is maintained at 45°C. Sugar-ABEE derivatives are separated well within a short run time(ca. 25 min) by reverse-phase partition chromatographic mode, and CIS-bonded silica column is very stable during the analysis. The (1→6)-linkage type of dihexose-ABEE derivatives has shorter retention time than (1→4)-linkage type. β-Anomeric configuration of [Glc-β-(1→4)Glc]-oligomer has shorter retention time than α-anomer in RP-HPLC. Column temperature and ionic strength slightly affect the elution behavior of sugarABBEE derivatives.

High Performance Liquid Chromatographic Isolation and Characterization of (Pheophytin)Mercury(II)

Abstract Mercury-substituted chlorophylls, i.e., (pheophytin a)mercury(ll) and (pheophytin b)mercury(ll), were separated by reversed-phase HPLC with a C18-bonded silica column and a mobile phase of acetone-methanol. Their spectroscopic and chromatographic characteristics strongly suggest that both (pheophytin a)mercury(ll) and (pheophytin b)mercury(ll) form 1: 1 (metal ion: chlorin ring) complexes.

Multiresidue analysis of polar pesticides in surface and drinking water by on-line enrichment and thermospray LC-MS

In the search for a fast and robust sample handling and preparation step to analyse various pesticides at trace levels in aqueous samples, an on-line trace enrichment has been combined with our thermospray LC-MS method [1] allowing both selective identification and a quantification down to the lower ng/L level. 51 polar pesticides were investigated by applying solid phase extraction to 50–100 ml aqueous samples using small cartridges filled with 40 mg adsorbent. Prior to their liquid chromatographic separation, the enriched analytes were eluted from the solid phase with the initial methanol/water gradient composition of the HPLC onto the analytical column using column switching techniques. A base-deactivated C18 material and the two styrene-divinylbenzene copolymers PLRP-S and PRP-1 were tested for enrichment in combination with a C8-bonded silica analytical column. The method developed was evaluated with respect to recoveries, precision, limits of detection and linearity. Furthermore, it was applied to various environmental samples. Apart from a few compounds of higher polarity, most of the pesticides show recoveries >60% (often >80%) with relative standard deviations between 1–15%. Overall method detection limits are in the range of 1–100 ng/L allowing, with one exception, a ready verification of the pesticide limit of 100 ng/L set in the EU drinking water guideline [2].

An Evaluation of Column-to-Column Retention Variability for Compounds Related to Panadiplon (U-78,875) Using Three Different Reverse-Phase HPLC Separation Modes

Abstract In order to assess the potential for substituting one brand of column for another in the analysis of multiple analytes, panadiplon (U-78,875) and eight of its related compounds were examined with respect to relative retention and peak shape on six different reversed-phase C8-bonded silica columns in the isocratic and gradient separation modes, and on six different bare silica columns in the dynamically modified silica (DMS) mode. No two columns in any separation mode showed identical retention behavior for all nine analytes. Gradient chromatography demonstrated generally more uniform relative retention for all columns than either the isocratic or the DMS mode, which is largely attributable to a reduction in time available for partitioning as a consequence of increasing solvent strength. DMS may offer improvements over isocratic reversed-phase HPLC in reproducibility for multiple analytes containing either alkyl homology or single, strongly interactive groups. In general, gradient chromatography p...

Speciation of inorganic mercury(II) and methylmercury by vesicle-mediated high-performance liquid chromatography coupled to cold vapour atomic absorption spectrometry

A novel high-performance liquid chromatography (HPLC) separation coupled to cold vapour atomic absorption spectrometry (CVAAS) detection for the speciation of inorganic mercury(II) and methylmercury is described. The mercury species can be successfully separated within 8 min by using a vesicular mobile phase of didodecyldimethylammonium bromide (DDAB) in acetate buffer containing 5% v/v of modifier, methyl cyanide (acetonitrile), and 0.005% v/v of 2-mercaptoethanol. The stationary phase is a C18-bonded silica column previously modified by the passing of a solution of DDAB. Detection limits of 0.1–0.2 µg l–1 of mercury were achieved after off-line preconcentration of the aqueous samples using C18 Sep-pack cartridges modified with 2-mercaptoethanol solutions. This vesicle-enhanced HPLC–CVAAS approach has been applied to the speciation of inorganic mercury(II) and methylmercury in spiked sea-water and human urine. Recoveries obtained ranged between 91–103% both for the inorganic and organic mercury species.

On-Line Dialysis-Column Liquid Chromatography for the Determination of Polar Pesticides in Water Samples Containing Humic Substances

Abstract The potential of the on-line combination of dialysis, for the removal of interfering humic substances from environmental samples, and trace enrichment on a precolumn packed with C18-bonded silica for the determination of polar pesticides by column liquid chromatography with UV detection is investigated, using six phenylurea herbicides as model compounds. The influence of the membrane material, thickness and molecular weight cut-off value, the configuration of the system-i.e. planar or hollow-fibre membranes-and, especially, the sample volume on analyte recovery and removal of humic Substances is studied. Systems which allow the determination of the test compounds at the 1.0 μg/1 level in river and lake water and at the 0.1 μg/l level in tap water are presented.

Simultaneous Determination of Thiuram, Iprodione and Bensulide (Pesticides for Golf Course Use) in the Environmental Waters by Solid-Phase Extraction/HPLC.

A simultaneous analysis for thiuram, iprodione and bensulide in environmental water was performed by the procedures including solid-phase extraction and high performance liquid chromatography (HPLC). To 1000 ml of sample water, two grams of ethylenediamine tetraascetic acid disodium dihydrate (EDTA·2Na·2H2O) was added. The sample solution was passed through Sep-Pak ENVtC18 cartridge which was previously washed with acetonitrile containing 50 mM EDTA·2 Na. The cartridge was washed with acetonitrile-H2O (3 : 7) and the sample was eluted with acetonitrile. The eluant was analysed by HPLC on a column of C18-bonded silica gel (Nucleosil 120-5C18) with acetonitrile-methanol (60 : 40) as mobile phase. The recoveries of thiuram, iprodione and bensulide added to environmental waters were 91-96%, 101-105% and 100-104%, respectively. Addition of EDTA·2Na to the sample water was effective for analysing thiuram.

Determination of aluminum in the human serum of a dialysis patient by ion-pair reversed-phase partition high-performance liquid chromatography

An ion-pair reversed-phase partition high-performance liquid chromatography-spectrophotometric method is described for the determination of aluminum in human serum, based on its complexation with 2,2'-dihydroxyazobenzene. The chelate is separated on C18-bonded silica packing by using an aqueous methanol mobile phase containing tetrabutylammonium bromide and is detected with 0.005 AU full-scale at 510 nm. The proposed system offers a simple, sensitive, and selective method. The detection limits defined as twice the standard deviation of the blank signal, are 0.2 micrograms L-1 in pure solution and 6 micrograms L-1 in serum. The sample solution is prepared from 0.4 mL of serum after protein precipitation with hydrochloric acid and methanol. There was good agreement between the values obtained by this method and graphite furnace atomic absorption spectrophotometry. The aluminum concentrations in 121 patients on hemodialysis were 6-201 micrograms L-1.

Spectrometry: Speciation of Parts PER Billion of Metal Ions Using Silica and C18-Bonded Silica Columns and Graphite Furnace Atomic Absorption Spectrometry

Abstract It is demonstrated that silica gel columns will quantitatively adsorb free Cu2+ and Pb2+ ions at pH > 8. These are eluted with 0.1 M HNO3 but not with methanol. Negatively charged EDTA chelates are not adsorbed. Neutral APDC chelates are partially adsorbed on silica columns, but are quantitatively adsorbed on C18-bonded columns, and are eluted with methanol. The metal ions are partially adsorbed on C18-bonded columns, due to residual silanol groups. A microcolumn (1 mm i.d., 5 cm length) manifold system is described for automatic delivery of eluant (0.12 ml) to a heated atomic absorption graphite atomizer, using either methanol or 0.1 M HNO3 in methanol eluant, allowing speciation and measurement of parts per billion of metals. These studies demonstrate that by using a mixed column or sequential columns of silica gel and C18-bonded silica, cationic and neutral metal species could be adsorbed, followed by sequential elution and measurement using methanol and then 0.1 M HNO. Negatively charged spec...

Determination of plasma leukotrienes in antigen-induced bronchoconstrictive guinea pigs

Convenient extraction and radioimmunoassay methods for measurement of leukotrienes C 4 and D 4 (LTC 4 and LTD 4) in biological fluids are described. LTC 4 or LTD 4 in plasma was extracted with acetonitrile, and extract was washed with dichloromethane then and adjusted to pH 3.5 or 6.0 respectively. Each leukotriene was partially purified by using a C18-bonded silica cartridge and quantified by radioimmunoassay. Amounts of LTC 4 and LTD 4 in the range of 0.025–1.6 ng could be assayed in plasma. This procedure was employed to examine the increase in plasma LTC 4 (0.249 ± 0.036 ng/ml) and LTD 4 (1.399 ± 0.235 ng/ml) of guinea pigs during intravenous challenge-induced anaphylactic bronchoconstriction, and the suppression of the increase of bronchoconstriction and leukotrienes by the administration of 5-lipoxygenase inhibitors such as E6080 (6-hydroxy-2-(4-sulfamoylbenzyl-amino)-4,5,7-trimethylbenzothiazole hydrochloride), AA861 (2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone) and phenidone. On the other hand, LTC 4 and LTD 4 were not detected in plasma after an inhaled challenge, though significant bronchoconstriction was provoked. It was concluded that the present study validates a new technique for quantitating plasma leukotrienes on the basis of pH and a suitable method for evaluating the pharmacological efficacy of 5-lipoxygenase inhibitors.

Determination of Atrazine and Hydroxyatrazine Residues in Soil by Ion-Pair, Reversed-Phase High Performance Liquid Chromatography

Abstract An improved method is presented for the determination of atrazine and hydroxyatrazine in soils. the method involves performing an initial extraction of the soil sample with a mixture (90:10 v/v) acetonitrile-aqueous 0.1 M hydrochloric acid. After centrifugation, the extract is concentrated onto a disposable strong cationic exchange, sulfonic acid-bonded, solid phase extraction (SPE) cartridge, and interfering soil substances are removed by rinsing. the atrazine and hydroxyatrazine are eluted with a 50:50 (v/v) acetonitrile-aqueous 0.1 M K2HP04 solution. The analysis was performed using a reversed-phase, high performance liquid chromatographic column of C18-bonded silica with an ion-pairing solvent system (50:50 v/v) acetonitrile-water containing 0.020 M n-heptanesulfonic acid and 0.10 M phosphoric acid. This isocratic solvent system provided an excellent separation of not only atrazine, simazine and propazine but also of hydroxyatrazine, hydroxysimazine and various dealkylated products of atrazin...