Extraction chromatography with bis(2-ethylhexyl)phosphoric acid for separation of tin(IV)

Tin is extracted from 0.01M hydrochloric acid on a silica-gel column impregnated with bis(2-ethylhexyl)phosphoric acid, stripped with 5M hydrochloric acid, and then determined spectrophotometrically as its Pyrocatechol Violet complex at 555 nm. Tin has been separated from several multicomponent mixtures containing arsenic, antimony, bismuth, lead and copper, and determined in various alloys.     

The influence of chelating reagents on plumbane generation: Determination of lead in the presence of PAN-S

A series of 22 chelating reagents were tested for plumbane generation. Besides nitroso R salt, the reagents Bromo Pyrogallol Red, Pyrocatechol Violet, Alizarine Red-S, 5-Br-PADAP and PAN-S could significantly enhance the lead signal. The PAN-S system has been optimized. The characteristic concentration (5 ml sample) is 1.3 ng/ml, and the RSD at the 50 ng/ml level is 3.9%. Lead spiked into tap water and natural water was determined by HG-AAS in the presence of PAN-S. Recoveries of spiked lead were between 90 and 105 %. Study of the mechanism suggests that the lead hydride might be directly generated from the chelated Pb(II) instead of the metastable Pb(IV).     

Spectrophotometric determination of bismuth and EDTA by means of the reaction of bismuth with pyrocatechol violet in the presence of septonex

The reaction of bismuth(III) with Pyrocatechol Violet in the presence of the cationic surfactant Septonex was studied and the optimal conditions for its analytical use were found (lambda = 612 nm, pH = 3.1, C(PV) = 4 x 10(-5)M, C(Sept), = 5 x 10(-4)M). The Lambert-Beer law is obeyed over the bismuth range 0.1-7.5 mug/ml. Decomposition of the Bi-PV-Septonex complex was utilized for indirect determination of ethylenediaminetetra-acetic acid at concentrations of 0.3-7.4 mug/ml.     

Additional purification of alkali or alkaline earth salts by using silica gel modified with pyrocatechol violet as a sorbent

Sorption of 14 metal ions on silica gel impregnated with a mixture of Aliquat 336 and Pyrocatechol Violet was investigated. It was found that alkali metals and calcium are not retained on the sorbent, magnesium is retained from solutions of pH > 6, contrary to other metal ions. The sorbent was used for purification of some salts from trace amounts of heavy metals and magnesium. Some metals ion mixtures have also been separated by using column extraction chromatography stepwise elution with perchloric acid solutions.     

Elaboration of the efficient technology of contact cleaning of wastewater from mineral oil

Complex investigations on development of efficient technology of contact cleaning of wastewater from oil pollution was carried out. This technology is based on processes of sorption, ion exchange, and subsequent sedimentation. It is shown that modified sorbents prepared on the basis of cellulose, polygorskite, and activated carbon effectively clean water from oil and oil products, where the degree of cleaning reaches over 98–99%. It is found that the sorption coefficient (K _a) increases with the increase in the dispersity of sorbents, and the consumption of sorbent (g/100 ml) decreases.     

Speciation of aluminium(III) in natural waters using differential pulse voltammetry with a pyrocatechol violet-modified electrode

A differential pulse voltammetric (DPV) procedure is proposed for the speciation of aluminium in natural waters using Pyrocatechol Violet chemically modified electrodes (PCV-CMEs). This novel speciation idea is based on the selective determination of different AlIII forms under two pH conditions. The labile monomeric Al fraction (mainly inorganic Al) is analysed at pH 4.8 (0.20 mol dm(-3) NaOAc-HOAc) and the total monomeric Al fraction is analysed at pH 8.5 (0.20 mol dm(-3) NH3.H2O-NH4Cl). The difference is thought to be caused by the weak competition ability of PCV to sequester AlIII from AlIII-natural organic matter complexes. This sensitive and simple speciation method has been applied successfully to aluminium speciation in natural waters sampled from different regions of China. Five fractions are measured directly or indirectly: (i) labile monomeric Al; (ii) total monomeric Al; (iii) acid reactive Al; (iv) non-labile monomeric Al; and (v) acid soluble Al. The results are in satisfactory agreement with those obtained by Driscoll's 8-hydroxyquinoline extraction-ion exchange method.     

Solid-phase extraction of polar compounds with a hydrophilic copolymeric sorbent

A new synthesized copolymer based on N-vinylimidazole-divinylbenzene (VIm-DVB) was tested as a sorbent for the solid-phase extraction (SPE) of polar analytes. In the on-line SPE, this synthesized sorbent enabled 100 ml of sample to be preconcentrated with recoveries as high as 80% for oxamyl, phenol (Ph) and derivates, bentazone and (4-chloro-2-methylphenoxy)acetic acid (MCPA). For the off-line SPE, 1000 ml of sample was extracted and recoveries were higher than 92% for all compounds with the exception of oxamyl (83%) and methomyl (78%). The VIm-DVB sorbent gives better recoveries than the previously synthesized 4-vinylpyridine-divinylbenzene (VP-DVB) resin and similar to such highly crosslinked commercial sorbents as LiChrolut EN or Oasis HLB. Real water samples were used to validate the on-line SPE method. Linearity was good and detection limits were between 0.1 and 0.2 microg l(-1).     

Cellulose fibrous sorbents with conformationally flexible aminocarboxylic groups for preconcentration of metals

New cellulose fibrous sorbents, containing a diethylenetriamine tetraacetate groups, are proposed for the preconcentration of heavy metals. Quantitative extraction of heavy metals from river and sea water is achieved in a wide pH range (3–8) at a high solution flow rate (up to 100–150 volumes of sorbent per minute). Quantitative desorption of metals is achieved with a very small volume of the acid.     

Multielement Preconcentration and Removal of Trace Metals by Solid-Phase Extraction

ABSTRACT

The solid phase extraction of trace amounts of some metal ions from their mixtures using cation exchanger Dowex 50Wx4, cellulose sorbent with phosphonic acid groups Cellex P, chelating resin Chelex 100 and SIO₂-TPP sorbent which contains porphyrin ligand covalently attached to aminopropyl silica gel was investigated. With respect to multielement preconcentration Cellex P and Chelex 100 seem to be the best sorbents; the recovery test for Al, Be, Cd, Ni, Pb and Zn were > 90%. Additionally, Cellex P appeared to be suitable for enrichment of Co and Mn. Silica-TPP sorbent could be applied as a selective collector for Mo(VI) and V(IV).     

Novel poly-glutamic acid functionalized microfiltration membranes for sorption of heavy metals at high capacity

Various sorbent/ion exchange materials have been reported in the literature for metal ion entrapment. We have developed a highly innovative and new approach to obtain high metal pick-up utilizing poly-amino acids (poly-l-glutamic acid, 14,000 MW) covalently attached to membrane pore surfaces. The use of microfiltration (0.2–0.6 μm) membrane-based sorbents containing multiple functional groups is a novel technique to achieve high metal sorption under convective flow conditions. For our studies, both commercial membranes and laboratory prepared cellulose membranes containing aldehyde groups were used for the attachment of poly-amino acids. Cellulose membranes were prepared by converting cellulose acetate microfiltration membranes to cellulose (using alkali treatment), subsequent oxidation of hydroxyl groups to aldehyde using sodium periodate, and attachment of poly-l-glutamic acid via Schiff base chemistry. Extensive experiments (pH 3–6) were conducted (under convective flow mode) with the derivatized membranes involving the heavy metals: lead, cadmium, nickel, copper, and selected mixtures with calcium in aqueous solutions. Metal sorption results were found to be a function of derivatization (aldehydes) density of membranes and degree of attachment of the polyfunctional groups, number of functional groups per chain, membrane surface area, and the type of metals to be sorbed. We have obtained metal sorption capacities as high as 1.5 g metal/g membrane. Of course, depending on the desired goals the membrane containing metal could be regenerated or stabilized for appropriate disposal.     

Mild pre-heating of organic cation-exchanged clays enhances their interactions with nitrobenzene in aqueous environment

Aqueous sorption kinetics and equilibrium isotherms of nitrobenzene were studied on two series of sorbents that were prepared by (i) replacing inorganic exchangeable cations in Wyoming bentonite with tetraethylammonium (TEA) and benzyltrimethylammonium (BTMA) and (ii) heating synthesized complexes in air at different temperatures (between 150 and 420°C). The aim of this work was to examine recently observed enhancement of aqueous sorption of a probe organic sorbate on organoclays after mild thermal pre-treatment of sorbents. Thermal pre-treatment of TEA- and BTMA-clays at 150°C results in the maximal enhancement of nitrobenzene–sorbent interactions as compared with treatment of original bentonite and its exchange complexes formed with long-chain quaternary ammonium (n-hexadecyltrimethylammonium, HDTMA). Based on C, N content data and FTIR spectra of TEA- and BTMA-clay complexes, no indications of decomposition of organic matter were found in organoclays heated at 250°C (and below this temperature). Suppressed hydration of pre-heated sorbents resulting in a lessening of water–organic sorbate competition for sorption sites is considered to be responsible for thermally induced enhancement of nitrobenzene–sorbent interactions. In the HDTMA-based organoclays, the long-chain aliphatic groups of the quaternary ammonium can additionally interact with clay surface thus competing with organic sorbate–sorbent surface interactions and, in this way, mitigating the enhancement of nitrobenzene sorption on thermally treated sorbents.     

Solid-Phase Extraction of Trace Amounts of Selenomethionine

Abstract

Preconcentration and separation of trace amounts of selenomethionine was investigated using several solid sorbents. The best results were obtained with copper-treated Chelex 100 chelating resin. Selenomethionine from 100 ml of solution adsorbed on 0.2 g of the resin was eluted with 8 ml of 1.5 mol/l ammonia solution and determined by electrothermal atomic absorption spectrometry. The column chromatography with Cu-Chelex and functionalized cellulose sorbent Cellex T was applied to separate organic and inorganic selenium forms.     

Inorganic Oxides with Immobilized Ferrozine and Ferene for the Sorption–Spectroscopic Determination of Iron(II)

Sorbents based on inorganic oxides sequentially modified with polyhexamethylene guanidine, ferrozine, and ferene S are proposed for the preconcentration and determination of iron(II). Upon sorption from solutions with pH 2.5–7.0, colored iron(II) complexes with ferrozine and ferene S, having broad bands with maxima at 560 and 600 nm in the diffuse reflectance spectrum, respectively, formed on the sorbent surface. Procedures for the sorption–photometric determination of iron(II) using diffuse reflectance spectroscopy were developed. The limits of detection for iron(II), calculated by the 3s criterion were 0.005 and 0.006 μg per 0.1 g for sorbents based on silica with immobilized ferrozine and ferene S, respectively. The linearity of calibration curves remains up to 5 and 10 μg per 0.1 g for sorbents based on silicon and aluminum oxides, respectively. The procedures were tested in the determination of the total iron concentration in bottled drinking waters and alcoholic drinks.     

The effect of organic sorbates on water associated with environmentally important sorbents: estimating and the LFER analysis

The effect of organic sorbates on the water associated with naturally occurring sorbents is of significant interest since it probes the hydration of a sorbate-specific microenvironment and its role in a compound partitioning between various environmental compartments. This effect was described in a thermodynamically strict way by converting the sorption isotherms of organic vapors on variously hydrated sorbents into the derivatives relating the change in the amount of water associated with a sorbent to the change in the amount of an organic sorbate. Further, these derivatives were analyzed by means of the Linear Free Energy Relationship (LFER). The analysis included the sorption data for various organic vapors on such environmentally important sorbents as quartz, metal oxides, calcite, clay minerals and humic acid. From the LFER analysis it followed that (i) organic sorbate polarizability contributions from n- and π-electrons resulted in driving water into the sorbent phase; (ii) the increasing volume of the organic compounds involved expelling water molecules; (iii) the increasing hydrogen-bond acidity and basicity of organic sorbates resulted in expelling water from inorganic surfaces but in enhancing hydration of the humic phase. In contrast to inorganic surfaces, when sorbed on strongly hydrated humic acid, the majority of organic sorbates containing oxygen, nitrogen or sulfur atoms drive water into the sorbent phase. Several molecules of water may need to be cosorbed by a humic sorbent for each sorbed molecule of an organic compound thus supporting the possibility of the concomitant participation of a number of water molecules in organic sorbate–humic matter interactions.     

The miniaturised process for lead removal from water samples using novel bioconjugated sorbents

ABSTRACT

In the present study, novel bioconjugated sorbents (peptide and oligo-nucleotide on the cobalt aluminate nanomaterials) were used to remove lead through miniaturised process and the concentration of lead was measured by inductively coupled plasma mass spectrometry. For this aim, lead was collected on sorbent in mini tube, and the influences of experimental conditions (e.g. pH of sample, amount of sorbent, concentration of eluent, foreign ions) and retention parameters on the recovery of the lead element were examined. After the optimisation of experimental parameters, a successful separation was obtained at pH 7.5 with high (>95%) quantitative recovery and high precision (<10% relative standard deviation). Using the proposed bioconjugated sorbents, the lead in sea water and tap water samples could be practically and easily removed with 95% confidence level. The detection limits of this method for lead using oligonucleotide and peptide on the cobalt aluminate nanomaterials were 0.14 and 0.12 µg/L (3σ, N = 10) with sample-matched blanks. This method can be widely used as promising and cost-effective nanomaterials to remove lead from water systems.     

Removal of heavy metal ions from aqueous solutions using low-cost sorbents obtained from ash

This study’s main objective was the development of effective low-cost sorbents for the removal of heavy metal ions from aqueous solutions. The influence of different factors on the sorption capacity of ash and modified ash as low-cost sorbents obtained by different methods was investigated. The synthesis of new ash-based materials was carried out at ambient temperature (20°C), 70°C, and 90°C, respectively, in an alkaline medium with NaOH concentrations of 2 M and 5 M, respectively, corresponding to a mixture with solid/liquid ratios of 1: 3 and 1: 5, respectively. The prepared materials (sorbents) were characterised by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), X-ray diffraction, and BET surface measurement. Adsorption isotherms were determined using the batch equilibrium method. The results showed that these types of new materials displayed a good capacity to remove copper, nickel, and lead ions (29.97 mg of Cu²⁺ per g of sorbent, 303 mg of Ni²⁺ per g of sorbent, and 1111 mg of Pb²⁺ per g of sorbent) from aqueous solutions. The modified materials were prepared using an alkaline attack (a recognised method used in previous studies), but Romanian ash from a thermal power plant was studied for the above purpose for the first time. Hence, the factors which affect the sorption capacity of the prepared low-cost sorbents were determined and their behaviour was explained, taking into account the composition and structure of the new materials.     

Flow-injection determination of total organic fluorine with off-line defluorination reaction on a solid sorbent bed

Considering recent reports on widespread occurrence and concerns about perfluoroalkyl substances (PFAS) in environmental and biological systems, analysis of these compounds have gained much attention in recent years. Majority of analyte-specific methods are based on a LC/MS/MS or a GC/MS detection, however many environmental or biological studies would benefit from a total organic fluorine (TOF) determination. Presented work was aimed at developing a method for TOF determination. TOF is determined as an amount of inorganic fluoride obtained after defluorination reaction conducted off-line using sodium biphenyl reagent directly on the sorbent without elution of retained analytes. Recovered fluoride was analyzed using flow-injection system with either fluorimetric or potentiometric detection. The TOF method was tested using perfluorocarboxylic acids (PFCA), including perfluorooctanoic acid (PFOA), as model compounds. Considering low concentrations of PFAS in natural samples, solid-phase extraction as a preconcentration procedure was evaluated. Several carbon-based sorbents were tested, namely multi-wall carbon nanotubes, carbon nanofibres and activated carbon. Good sorption of all analytes was achieved and defluorination reaction was possible to carry out directly on a sorbent bed. Recoveries obtained for PFCAs, adsorbed on an activated carbon sorbent, and measured as TOF, were 99.5 ± 1.7, 110 ± 9.4, 95 ± 26, 120 ± 32, 110 ± 12 for C4, C6, C8, C10 and C12-PFCA, respectively. Two flow systems that would enable the defluorination reaction and fluoride determination in a single system were designed and tested.     

Pyrocatecholsulphonphthalein complexan as an analytical reagent

Pyrocatecholsulphonphthalein complexan (PSC) has been synthesized from Pyrocatechol Violet (PV), iminodiacetic acid and formaldehyde by Mannich condensation. Its acid dissociation equilibria have been studied potentiometrically. Some characteristic properties of Xylenol Orange (XO) and PV are found in PSC, which is slightly superior to XO and PV in sensitivity as a chromogenic reagent for bismuth. The spectrophotometric characteristics of some metal ion-PSC complexes are reported.     

Flow injection sorbent extraction with dialkyldithiophosphates as chelating agent for the determination of cadmium, copper and lead by flame atomic absorption spectrometry

Using octadecyl functional groups (C₁₈) bonded to silica gel as sorbent and methanol as eluent, the flow injection sorbent extraction features of dialkyldithiophosphates (RO)₂P(S)S⁻ as the chelating agent for cadmium, copper and lead was investigated in respect of the effects of pH, alkyl substituent group, reagent concentration and masking agent, with flame atomic absorption spectrometric detection. The elements are quantitatively extracted with the short-alkyl-chain reagents (R up to propyl) in acidic medium. The extractability decreases with the number of carbon atoms in the alkyl groups of the reagents and with the reagent concentration when the alkyl groups are larger than butyl, but masking agents increase the extractability. An explanation proposed for this effect is the formation of polynuclear chelates. Diethyldithiophosphate can be used for the selective determination of cadmium, copper and lead in digested solid environmental samples. With 20 s sample loading at 8.7 ml min⁻¹, the enhancement factors are 35 for cadmium and copper or 26 for lead; the detection limits (3σ) are 0.8, 1.4 and 10.0 μg 1⁻¹ for cadmium, copper and lead, respectively.     

On-line preconcentration of inorganic mercury and methylmercury in sea-water by sorbent-extraction and total mercury determination by cold vapour atomic absorption spectrometry

A comparative study of three mercury chelate forming reagents [diethyldithiocarbamate, pyrrolidin-1-yldithioformate and diphenylthiocarbazone (dithizone)] has been carried out for the preconcentration of ultratrace amounts of inorganic mercury and methylmercury in silica C(18) minicolumns as the solid sorbent. Sample flow injection in-line sorbent extraction was coupled with continuous cold vapour atomic absorption spectrometry (CVAAS) for detection. Results showed the superiority of the carbamate type reagents over the dithizone for the on-line formation and preconcentration of the corresponding mercury chelates. Using diethyldithiocarbamate (DDC) as reagent, aqueous sample volumes of 100 ml can be preconcentrated with 100% efficiency for both inorganic mercury and methylmercury. Quantitative release of the retained DDC chelates was obtained for volumes of eluent (ethanol) of 50 microl. Following the proposed procedure, detection limits of 16 ng/l. of mercury were achieved for sample volumes of 25 ml. The relative standard deviation was +/- 3.4% at 0.5 microg/l. Hg(II) levels. The method has been successfully applied to the determination of low levels of mercury in sea-water.