Solid phase extraction and spectrophotometric determination of mercury by adsorption of its diphenylthiocarbazone complex on an alumina column

A simple method has been developed for the preconcentration of mercury based on the adsorption of its diphenylthiocarbazone complex on a neutral alumina column. The influence of acidity, eluting agents, stability of the column, sample volume and interfering ions has been investigated in detail. The adsorbed complex could be eluted using environmentally benign polyethylene glycol (PEG 400) and the concentration of mercury was determined by visible spectrophotometry at a wavelength maximum of 520nm. A detection limit of 4microgL(-1) could be achieved and the developed procedure was successfully applied for the determination of mercury in spiked water samples and city waste incineration ash (CRM176). The preconcentration factor attainable for quantitative recovery (>95%) of mercury(II) was 100 for a 1000mL sample volume.     

Spectrophotometric determination of inorganic mercury (II) after preconcentration of its diphenylthiocarbazone complex on a cellulose column

A simple and a relatively green methodology have been developed for the preconcentration of mercury based on the adsorption of its diphenylthiocarbazone complex on a cellulose column. The effects of various parameters such as effect of acidity, eluting agents, stability of the column, sample volume, interfering ions, etc. have been studied in detail. The adsorbed complex could be easily desorbed using environmentally benign polyethylene glycol-400 and the concentration of mercury was determined using visible spectrophotometry. The calibration graph was linear in the range 0-2mugmL(-1) of mercury with a detection limit of 2mugL(-1) and the validity of the proposed method was checked by studying the recovery of mercury in spiked tap water, well water and sea water samples. The highest preconcentration factor achieved for quantitative recovery (>95%) of mercury (II) was 33 for a 500mL sample volume. The method was also applied to the analysis of mercury content in city waste incineration ash (CRM176). The relative standard deviation of the method was found to be 3.5%.     

Solid phase extraction of chromium(VI) from aqueous solutions by adsorption of its diphenylcarbazide complex on a mixed bed adsorbent (acid activated montmorillonite-silica gel) column

A novel approach has been developed for the solid phase extraction of chromium(VI) based on the adsorption of its diphenylcarbazide complex on a mixture of acid activated montmorillonite (AAM)-silica gel column. The effect of various parameters such as acidity, stability of the column, sample volume, interfering ions, etc., were studied in detail. The adsorbed complex could be easily eluted using polyethylene glycol-sulfuric acid mixture and the concentration of chromium has been determined using visible spectrophotometry. The calibration graph was linear in the range 0-1microgmL(-1) chromium(VI) with a detection limit of 6microgL(-1). A highest preconcentration factor of 25 could be obtained for 250mL sample volume using glass wool as support for the mixed bed adsorbent. Chromium(VI) could be effectively separated from other ions such as nickel, copper, zinc, chloride, sulfate, nitrate, etc., and the method has been successfully applied to study the recovery of chromium in electroplating waste water and spiked water samples.     

Enhancing concentration and mass sensitivities for liquid chromatography trace analysis of clopyralid in drinking water

A theoretical treatment was developed and validated that relates analyte concentration and mass sensitivities to injection volume, retention factor, particle diameter, column length, column inner diameter and detection wavelength in liquid chromatography, and sample volume and extracted volume in solid‐phase extraction (SPE). The principles were applied to improve sensitivity for trace analysis of clopyralid in drinking water. It was demonstrated that a concentration limit of detection of 0.02 ppb (μg/L) for clopyralid could be achieved with the use of simple UV detection and 100 mL of a spiked drinking water sample. This enabled reliable quantitation of clopyralid at the targeted 0.1 ppb level. Using a buffered solution as the elution solvent (potassium acetate buffer, pH 4.5, containing 10% of methanol) in the SPE procedures was found superior to using 100% methanol, as it provided better extraction recovery (70–90%) and precision (5% for a concentration at 0.1 ppb level). In addition, the eluted sample was in a weaker solvent than the mobile phase, permitting the direct injection of the extracted sample, which enabled a faster cycle time of the overall analysis. Excluding the preparation of calibration standards, the analysis of a single sample, including acidification, extraction, elution and LC run, could be completed in 1 h. The method was used successfully for the determination of clopyralid in over 200 clopyralid monoethanolamine‐fortified drinking water samples, which were treated with various water treatment resins.     

Determination of Copper by Faas After Preconcentration with Lead-4-Methylpiperidinedithiocarbamate on Microcrystalline Naphthalene By Solid Phase Extraction

ABSTRACT

By using the Pb-4-methylpiperidinedithiocarbamate complex (Pb(4-MPDC)₂) on microcrystalline naphthalene in a column a method was developed for the preconcentration of copper in water samples prior to its determination by FAAS. In this method, copper in liquid phase quantitatively replaces lead on the Pb(4-MPDC)₂-naphthalene solid phase in the column, forming solid Cu(4-MPDC)₂ complex.

Afterwards, copper on Cu(4-MPDC)₂-naphthalene can be easily eluted by potassium cyanide into the aqueous phase, and the Cu is measured by FAAS. The optimum experimental parameters such as pH, flow rate, sample volume, Pb(4-MPDC)₂-naphthalene ratio, concentration of the potassium cyanide solution and effect of matrix ions for the preconcentration of copper were investigated. The obtained recovery was nearly 100 %, when the enrichment factor was 100 for standard solutions and spiked water samples. The proposed method has been employed for the determination of copper in various standard metal alloys and natural water samples.     

Determination of benzene, toluene, ethylbenzene and xylene in river water by solid-phase extraction and gas chromatography.

A rapid and reproducible method is described that employs solid-phase extraction (SPE) using dichloromethane, followed by gas chromatography (GC) with flame ionization detection for the determination of benzene, toluene, ethylbenzene, xylene and cumene (BTEXC) from Buriganga River water of Bangladesh. The method was applied to detect BTEXC in a sample collected from the surface, or 5 cm depth of water. Two-hundred milliliters of n-hexane-pretreated and filtered water samples were applied directly to a C18 SPE column. BTEXC were extracted with dichloromethane and the BTEX concentrations were obtained to be 0.1 to 0.37 microg ml(-1). The highest concentration of benzene was found as 0.37 microg ml(-1) with a relative standard deviation (RSD) of 6.2%; cumene was not detected. The factors influencing SPE e.g., adsorbent types, sample load volume, eluting solvent, headspace and temperatures, were investigated. A cartridge containing a C18 adsorbent and using dichloromethane gave a better performance for the extraction of BTEXC from water. Average recoveries exceeding 90% could be achieved for cumene at 4 degrees C with a 2.7% RSD.     

Solid phase extraction using a sulfoxide adsorbent for preconcentration and separation of Hg(II) in natural water followed by ICP-MS measurements

A separation and preconcentration method based on solid-phase extraction using sulfoxide adsorbent was developed for the determination of Hg(II) in natural water samples by inductively coupled plasma mass spectrometry (ICP-MS). The sulfoxide adsorbent was packed into a commercially available syringe-driven column (with a bed volume of 1.0 mL), which permitted off-line sample loading and on-line elution/measurement. The optimized operating conditions were as follows: sample condition for Hg(II) adsorption, 0.5% HCl; sample-loading flow rate, 10 mL min(-1); eluent for recovering Hg(II), 1% cysteine water solution. A test using multi-element mixed solution showed that most trace elements in natural water, except for Bi, could be completely separated from Hg(II). The recoveries of Hg(II) were 99.0 ± 3.2 and 100.7 ± 4.3%, respectively, when 0.64 and 0.16 ng mL(-1) of Hg(II) were added into the test sample. The detection limit of Hg(II) using a quadrupole ICP-MS after 10-fold preconcentration was 1.5 pg mL(-1). The blank value was 2.8 ± 0.5 pg mL(-1).     

Synthesis of cross-linked chitosan modified with the glycine moiety for the collection/concentration of bismuth in aquatic samples for ICP-MS determination.

A chelating resin, cross-linked chitosan modified with the glycine moiety (glycine-type chitosan resin), was developed for the collection and concentration of bismuth in aquatic samples for ICP-MS measurements. The adsorption behavior of bismuth and 55 elements on glycine-type chitosan resin was systematically examined by passing a sample solution containing 56 elements through a mini-column packed with the resin (wet volume; 1 ml). After eluting the elements adsorbed on the resin with nitric acid, the eluates were measured by ICP-MS. The glycine-type chitosan resin could adsorb several cations by a chelating mechanism and several oxoanions by an anion-exchange mechanism. Especially, the resin could adsorb almost 100% Bi(III) over a wide pH region from pH 2 to 6. Bismuth could be strongly adsorbed at pH 3, and eluted quantitatively with 10 ml of 3 M nitric acid. A column pretreatment method with the glycine-type chitosan resin was used prior to removal of high concentrations of matrices in a seawater sample and the preconcentration of trace bismuth in river water samples for ICP-MS measurements. The column pretreatment method was also applied to the determination of bismuth in real samples by ICP-MS. The LOD of bismuth was 0.1 pg ml(-1) by 10-fold column preconcentration for ICP-MS measurements. The analytical results for bismuth in sea and river water samples by ICP-MS were 22.9 +/- 0.5 pg ml(-1) (RSD, 2.2%) and 2.08 +/- 0.05 pg ml(-1) (RSD, 2.4%), respectively.     

Solid phase extraction of trace amounts of uranium(VI) from water samples using 8-hydroxyquinoline immobilized on surfactant-coated alumina

A simple and reliable method has been developed for the determination of uranium(VI). The method is based on the separation and preconcentration of uranium(VI) using a column packed with 8-hydroxyquinoline immobilized on surfactant coated alumina prior to its spectrophotometric determination with arsenazo III. The effect of pH, sample flow rate and volume, elution conditions, and foreign ions on the sorption of uranium(VI) has been investigated. A preconcentration factor of 200 was achieved by passing 1000 mL of sample through the column. The relative standard deviation for 10 replicate analyses at the 100 ng/mL level of uranium(VI) was 2.1% and the detection limit was 0.12 ng/mL. The method was success-fully applied to the determination of uranium in natural water samples. The accuracy was assessed through recovery experiments and the analysis of a certified reference material.     

Solid phase extraction of trace amounts of uranium(VI) from water samples using 8-hydroxyquinoline immobilized on surfactant-coated alumina

A simple and reliable method has been developed for the determination of uranium(VI). The method is based on the separation and preconcentration of uranium(VI) using a column packed with 8-hydroxyquinoline immobilized on surfactant coated alumina prior to its spectrophotometry determination with Arsenazo III. The effect of pH, sample flow rate and volume, elution conditions, and foreign ions on the sorption of uranium(VI) has been investigated. A preconcentration factor of 200 was achieved by passing 1000 mL of sample through the column. The relative standard deviation for 10 replicate analyses at the 100 ng/mL level of uranium(VI) was 2.1% and the detection limit was 0.12 ng/mL. The method was successfully applied to the determination of uranium in natural water samples. The accuracy was assessed through recovery experiments and the analysis of a certified reference material.     

Selective solid phase extraction and preconcentration of trace mercury(II) with poly-allylthiourea packed columns

A new method for selective solid-phase extraction and preconcentration of trace mercury(II) from aqueous solution was developed by using poly-allylthiourea as a new extractant. The procedure is based on the retention of analyte in the form of thiourea complex on a mini column of polymer resin. The effects of pH, eluent type, eluent concentration, sample volume, sample flow rate, and foreign ions on the recovery of the analyte were investigated using model solutions. At optimal pH value, the extraction capacity of the new sorbent was 1.13 mmol g^?1. The adsorption behavior of mercury(II) on the sorbent can be described by a Langmuir adsorption isotherm equation. The method was validated by analyzing a certified reference material with the results being in agreement with those quoted by manufacturers. The method was applied to the determination of trace inorganic mercury(II) in natural water samples and vegetables with satisfactory results.     

一种以含硅藻土的复合材料为介质的支撑液液萃取柱的制备及其应用

以含硅藻土的复合材料为支撑介质,开发了一种独特的支撑液液萃取柱;以一系列酸性、碱性和中性水溶液样品为模型化合物,结合高效液相色谱法(HPLC)对该萃取柱进行了系统评价,同时将其用于复杂基质样品的分析。结果表明: 经该支撑液液萃取柱预处理的苯甲酸、对硝基苯胺和对羟基苯甲酸甲酯水溶液的萃取回收率分别为90.6%、98.1%和97.7%,远超过对应样品经传统液液萃取法处理后的回收率（分别为71.9%、81.9%和83.9%）。对于复杂基质样品的分析,如雪碧中的防腐剂苯甲酸以及牛血清中的中性药物醋酸地塞米松、碱性药物马来酸氯苯那敏及酸性药物吲哚美辛等,样品的加标回收率均在80%和110%之间,相对标准偏差(RSD)均小于15%,符合生物样品的分析要求,且未出现传统液液萃取技术中常见的问题(如乳化现象)。所开发的支撑液液萃取柱具有快速、简单、耐受性好、易于实现自动化和高通量的特点,具有广泛的应用前景。     

On-line preconcentration of pharmaceutical residues from large volume water samples using short reversed-phase monolithic cartridges coupled to LC-UV-ESI-MS

A simplified preconcentration method for a range of ultra-trace level pharmaceuticals in natural waters has been developed. Solid phase extraction was performed on-line using a micro-reversed-phase monolithic silica column, allowing for very rapid trace enrichment from large volume (500 ml) samples with minimal sample handling. Acceptable recoveries of >70% were obtained for the majority of compounds investigated and the monolithic columns could be washed and conditioned on-line with no sample carryover and used reproducibly for up to eight extractions each. The on-line SPE-LC-UV method was coupled to electrospray ionisation ion trap mass spectrometry (ESI-MS) to increase both selectivity and specificity. Detection limits were determined in spiked river and tap water samples and found to lie in the low ng/l region using sample volumes of 500 ml, loaded at a flow rate of 10 ml/min, and therefore, were suitable for ultra trace analysis.     

Anion exchanger as a reaction/separation medium-absorptiometric determination of trace amounts of boron in waters by on-line complexation with chromotropic acid presorbed on the anion-exchange column

A novel method of on-line absorptiometric determination for trace amounts of boron was developed based on the complexation with chromotropic acid presorbed on an anion-exchange column. On-line reaction and separation were achieved by controlling pH conditions in solutions to accelerate the 1:2 complex formation in the concentration process at pH 3 and to stabilize the complex in the separation process at pH 8. About 75% of the boron introduced into the stream was kinetically collected as the 1:2 complex on the column under the experimental conditions. The 1:2 complex was satisfactorily separated from excess reagent and matrix components by changing the concentration of NaClO4 in the eluent and its peak height on the chromatogram monitored at 350 nm was used for calibration. The sensitivity could be enhanced by increasing the sample amount introduced and the detection limits (3sigma) were 162 ng dm(-3) and 45 ng dm(-3) of boron, when 5.0 cm3 and 13.4 cm3 of the samples were used, respectively. The method has been successfully applied to the determination of boron in samples of river water, tap water and ion-exchanged water.     

Determination of chlorophenols in red wine using ionic liquid countercurrent chromatography as a new pretreatment method followed by high‐performance liquid chromatography

A countercurrent chromatography method for the enrichment and cleanup of chlorophenols from food samples was successfully established by using an ionic‐liquid‐modified two‐phase solvent system composed of dichloromethane containing 2% 1‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide and water. The column was firstly filled with the organic stationary phase, and then a large volume of sample was pumped into the column after it was equilibrated with pure water at the rotation speed. Finally, the trace amounts of chlorophenols extracted and enriched in the stationary phase were eluted out by an alkaline mobile phase and determined by high‐performance liquid chromatography. Under optimized conditions, the enrichment and cleanup of the chlorophenols can be fulfilled online with enrichment factors (34–65) and high recoveries (84.69–95.23%). The method has been applied to the determination of chlorophenols in real red wine samples with the limits of detection in the range of 1.89–4.21 μg/L. The present method is highly suitable for the pretreatment of large volume of aqueous sample for the determination of trace amounts of contaminants in food and environmental samples.     

Method for the simultaneous determination of traces of atrazine,pyrazon and lindane for monitoring potable water supplies

When groundwater reservoirs situated in agriculturally used areas are assigned as future potable water supplies, it has to be provided that traces of plant protection agents used in this area can be monitored in this groundwater. A method is described for the simultaneous quantitative determination of atrazine, pyrazon and lindane in potable water at the (sub-)ppb level. An adsorption column filled with Amberlite XAD-2 microporous resin advantageously replaces other preconcentration techniques. The concentrated eluate is analyzed by capillary gas chromatography without further purification. The recovery is 80% for atrazine and lindane at the 0.1 ppb level and 40% for pyrazon (1 ppb). The method was tested using tap water from the public water supply network. The complete procedure including sample preparation, preconcentration by adsorption on a macroporous resin, elution with diethyl ether, evaporation to dryness, addition of internal standard solution and capillary gas Chromatographic analysis is carried out in less than three hours (sample volume: 11).     

A sequential injection method for the determination of aluminum in drinking water using fluorescence enhancement of the aluminum-morin complex in micellar media

A robust and simple sequential injection (SI) method for the assay of aluminum ions in natural water is described. The method is based on the enhancement of the fluorescence of the aluminum-morin complex in the presence of a non-ionic surfactant (Tween-20). The fluorescence of the complex is monitored at an emission wavelength of 495 nm with excitation at 425 nm. The pH, morin concentration and the aspirated sample volume were optimized simultaneously using a chemometric method. The optimum operating conditions are: 150 μl aspirated sample volume, 20 μM morin concentration, a pH of 4.5 and 0.8% Tween-20. Using these optimum conditions a linear calibration curve was obtained from 50 to 1000 ppb. The detection limit was 3 ppb and the maximum relative standard deviation (n=5) of the method was 2.9%. The method was successfully applied for the determination of aluminum ions in natural water samples.     

Rapid prediction and optimization of concentration conditions for preparative fractions by solid-phase extraction

SPE is an effective tool for concentrating preparative fractions isolated from a complex sample. To guarantee high efficiency and recovery of concentration, the concentration conditions could be optimized by predicting the breakthrough volume (V(B)). In this study, a method of predicting V(B )of unknown compounds in preparative fractions at any isocratic mobile phase composition with the analytical retention parameters a and c is described. The a and c values and the relationship between half peak width (W(1/2)) and retention time of a model analyte were measured using the analytical elution mode on an SPE column, and the V(B )and retention volume (V(R)) predicted with the a and c values were validated with breakthrough experiments. However, it is impossible to measure the a and c values of multiple compounds in a complex system directly on an SPE column with a low number of theoretical plates. The correlation of the a and c values between the SPE and analytical columns was developed so that the analytical data could be transferred to the SPE column. With the calculated a and c values, we could optimize the concentration conditions on the basis of the predicted V(B )and the volume of the preparative fraction.     

Trace analysis of pesticide residues in water by high-speed narrow-bore capillary gas chromatography-mass spectrometry with programmable temperature vaporizer

A method for the rapid trace analysis of 17 residual pesticides in water by narrow-bore capillary (I.D. 100 microm) gas chromatography-mass spectrometry (GC-MS) using a programmable temperature vaporizer (PTV) was discussed. The method consisted of a large-volume injection (40 microl) by a PTV, high-speed analysis using a narrow-bore capillary column and MS detection. The PTV with solvent vent mode was very useful for large-volume injection into a narrow-bore capillary column because the injected solvent volume could be reduced to less than 2 microl. The analysis time was 8.5 min [less than 50% of the analysis time using conventional columns (I.D. 250 microm)]. A 10-ml volume of river water was extracted by dichloromethane (4 ml), and then the extract was condensed to 1 ml. This extract was analyzed. Mean recoveries for river water spiked at 100 pg/ml ranged from 83.4 to 96.7%. The limit of detections of the 17 pesticides ranged from 1 to 100 pg/ml.     

Application of counter-current chromatography as a new pretreatment method for the determination of polycyclic aromatic hydrocarbons in environmental water

Counter‐current chromatography (CCC) was investigated as a new sample pretreatment method for the determination of trace polycyclic aromatic hydrocarbons (PAHs) in water environmental samples. The experiment was performed with a non‐aqueous binary two‐phase solvent system composed of n‐heptane and acetonitrile. The CCC column was first filled with the upper stationary phase, and then a large volume of water sample was pumped into the column while the CCC column was rotated at 1600 rpm. Finally, the trace amounts of PAHs extracted and enriched in the stationary phase were eluted out by the lower mobile phase and determined by gas chromatography–flame ionization detector (GC‐FID) or gas chromatography–mass spectrometry (GC‐MS). The enrichment and cleanup of PAHs can be fulfilled online by this method with high recoveries (84.1–103.2%) and good reproducibility (RSDs: 4.9–12.2%) for 16 EPA PAHs under the optimized CCC pretreatment conditions. This method has been successfully applied to determine PAHs in lake water where 8 PAHs were detected in the concentration of 40.9–89.9 ng/L. The present method is extremely suitable for the preparation of large volume of environmental water sample for the determination of trace amounts of organic pollutants including PAHs as studied in this paper.