Modified Activated Carbon as Solid Phase Extraction Adsorbent for the Preconcentration and Determination of Trace As(III) in Environmental Samples by Graphite Furnace Atomic Absorption Spectrometry

A simple and selective method was developed for the preconcentration, separation, and determination of trace amounts of As(III) in an aqueous solution by solid phase extraction combined with graphite furnace atomic absorption spectrometry. Activated carbon (AC) was modified by sodium diethyldithiocarbamate (NaDDTC) and then used as a new, stable and easily prepared solid sorbent in a mini column for the extraction of As(III) in aqueous solution. Factors influencing the sorption and desorption of As(III), such as volume and concentration of eluent, sample pH, flow rate and effect of interfering ions on the recovery of As(III) have been systemically investigated. At pH 2.0 As(III) could be adsorbed quantitatively by NaDDTC‐AC, and then eluted completely with 2 mL of 3.0 mol·L^?1 HNO₃. The amount of eluted As(III) was measured using graphite furnace atomic absorption spectrometry. The detection limit of As(III) was 0.04 ng·mL^?1 with enrichment factor of 100 and the relative standard deviation (RSD, n=8) was 1.58% at 10 ng·mL^?1 level.     

Redox Speciation of Inorganic Arsenic in Water and Saline Samples by Adsorptive Cathodic Stripping Voltammetry in the Presence of Sodium Diethyl Dithiocarbamate

This paper describes a new voltammetric procedure for the inorganic speciation of As(III) and As(V) in water samples. The procedure is based on the chemical reduction of arsenate [As(V)] to arsenite [As(III)] followed by the voltammetric determination of total arsenic as As(III) at the hanging mercury drop electrode (HMDE) by adsorptive cathodic stripping voltammetry (AdCSV) in the presence of sodium diethyl dithiocarbamate (SDDC). The reduction step involved the reaction with a mixture of Na₂S₂O₅ and Na₂S₂O₃ in the concentrations 2.5 and 0.5 mg mL^?1, respectively, and the sample heating at 80 °C for 45 min. The linear range for the determination of total arsenic as As(III) in the presence of SDDC was between 5 and 150 μg L^?1 for a deposition time of 60 s (r=0.992). A detection limit of 1.05 μg L^?1 for total As was calculated for the method in water samples using a deposition time of 60 s. The detection limits of 4.2 μg L^?1 and 15.0 μg L^?1 for total As in seawater and dialysis concentrates, respectively, were calculated using a deposition time of 60 s. The relative standard deviations calculated were 2.5 and 4.0% for five measurements of 20 μg L^?1 As(V) as As(III) in water and dialysis concentrates, respectively, after chemical reduction under optimized conditions. The method was applied for the determination of As(III) and total As in samples of dialysis water, mineral water, seawater and dialysis concentrates. Recovery values between 86.0 and 104.0% for As(III) and As(V) added to the samples prove the satisfactory accuracy and applicability of the procedure for the arsenic monitoring.     

№Determination of Trace Arsenic by Solid Substrate-Room Temperature Phosphorescence Quenching Method Based on the Catalyzed Reaction of H2O2 Oxidizing 9-Hyd roxy-2,3,4,9-tet rahyd ro-1,10-anth raquinone

A new solid substrate-room temperature phosphorescence （SS-RTP） quenching method for the determination of trace As（V） has been developed, based on the facts that 9-hydroxy-2,3,4,9-tetrahydro-1,10-anthraquinone （R） can emit intense and stable SS-RTP on solid substrate, and α,α＇-dipyridyl can activate As（V） catalysis of the reaction of H2O2 oxidizing R to non-phosphorescence compound R＇, which can cause the sharp quenching of SS-RTP. Under the optimum condition, the relationship between the ΔIp of the emitting intensity and 1.60-160 fg·spot^-1 As（V） （corresponding concentration： 0.0040-0.40 ng·mL^-1, sample volume： 0.4 μL·spot^-1） conformed to Beer＇ law. The regression equation of working curve can be expressed as ΔIp= 20.46＋0.5492CAs（v） fig·spot^-1） （r= 0.9995, n = 6）. The limit detection （LD） is 0.27 fg·spot^-1 [As（V） corresponding concentration： 6.8 × 10^-13 g·mL^-1, n=11]. The samples containing 0.0040 and 0.40 ng·mL^-1 As（V） were repeatedly determined for 11 times. RSD are 3.0% and 2.7% respectively. The SS-RTP mechanism was also discussed. R was synthesized in this paper. Meanwhile, the structure was determined by NMR, IR, mass spectra and elemental analysis.     

Speciation of arsenic in natural waters by HPLC-NAA

Neutron activation analysis (NAA) in combination with mainly high-performance liquid chromatography (HPLC) has been developed for the determination of low levels of five arsenic species, namely As(III), As(V), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), and arsenobetaine (AsB) in water samples. Organically bound arsenic (OBAs) and total arsenic have also been determined. In addition to anion-exchange HPLC, solid phase extraction and open-column cation-exchange chromatographic methods have also been used. The detection limits of the method have been found to be 0.005 ng·cm⁻³ for OBAs, 0.02 ng·cm⁻³ for AsB, DMA, MMA, As(III), and As(V) and 0.12 ng·cm⁻³ for total arsenic. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of As(III) and As(V) in water samples by flow injection online sorption preconcentration coupled to hydride generation atomic fluorescence spectrometry

A method was developed for the determination of arsenite [As(III)] and arsenate [As(V)] in water samples using flow injection online sorption coupled with hydride generation atomic fluorescence spectrometry (HG-AFS) using a cigarette filter as the sorbent. Selective determination of As(III) was achieved through online formation and retention of the pyrrolidine dithiocarbamate arsenic complex on the cigarette filter, but As(V) which did not form complexes was discarded. After reducing As(V) to As(III) using L-cysteine, total arsenic was determined by HG-AFS. The concentration of As(V) was calculated by the difference between As(III) and total arsenic. The analytes were eluted from the sorbent using 1.68 mol L^?1 HCl. With consumption of 22 mL of the sample solution, the enrichment factor of As(III) was 25.6. The detection limits (3σ/k) and the relative standard deviation for 11 replicate determinations of 1.0 ng mL^?1 As(III) were found to be 7.4 pg mL^?1 and 2.6%, respectively.     

Study on the Interaction between a Novel Ionic Liquid Probe and Anionic Surfactants Using Resonance Light Scattering Spectra and Its Analytical Application

The interaction between anionic surfactants (AS) and 1‐hexadecyl‐3‐methylimidazolium bromide [C₁₆mim]Br was studied by using resonance light scattering (RLS) technique, UV‐Vis spectrophotometry and fluorometric methods. In Britton Robinson (BR) buffer (pH 6.0), [C₁₆mim]Br reacted with AS to form supermolecular complex which resulted in enhancement in RLS intensity. Their maximum RLS wavelengths were all at 390 nm. Some important interacting experimental variables, such as the solution acidity, [C₁₆mim]Br concentration, salt effect and addition order of the reagents, were investigated and optimized. Under the optimum conditions, quantitative determination ranges were 0.001–7 μg·mL^?1 for dodecyl sodium sulfate (SDS), 0.001–6 μg·mL^?1 for sodium dodecylbenzene sulfonate (SDBS) and 0.005–7 μg·mL^?1 for sodium lauryl sulfonate (SLS), respectively, while the detection limits were 1.3 ng·mL^?1 for SDS, 1.0 ng·mL^?1 for SDBS and 5.1 ng·mL^?1 for SLS, respectively. Based on the ion‐association reaction, a highly sensitive, simple and rapid method has been established for the determination of AS.     

Diphenyl diselenide grafted onto a Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>-chitosan composite as a new nanosorbent for separation of metal ions by effervescent salt-assisted dispersive magnetic micro solid-phase extraction

Diphenyl diselenide was immobilized on chitosan loaded with magnetite (Fe₃O₄) nanoparticles to give an efficient and cost-effective nanosorbent for the preconcentration of Pb(II), Cd(II), Ni(II) and Cu(II) ions by using effervescent salt-assisted dispersive magnetic micro solid-phase extraction (EA-DM-μSPE). The metal ions were desorbed from the sorbent with 3M nitric acid and then quantified via microflame AAS. The main parameters affecting the extraction were optimized using a one-at-a-time method. Under optimum condition, the limits of detection, linear dynamic ranges, and relative standard deviations (for n?=?3) are as following: Pb(II): 2.0 ng·mL^?1; 6.3–900 ng·mL^?1; 1.5%. Cd(II): 0.15 ng·mL^?1; 0.7–85 ng·mL^?1, 3.2%; Ni(II): 1.6 ng·mL^?1,.6.0–600. ng·mL^?1, 4.1%; Cu(II): 1.2 ng·mL^?1, 3.0–300 ng·mL^?1, 2.2%. The nanosorbent can be reused at least 4 times.

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Graphical abstract Fe₃O₄-chitosan composite was modified with diphenyl diselenide as a sorbent for separation of metal ions by effervescent salt-assisted dispersive magnetic micro solid-phase extraction.

     

Determination of arsenic at the picogram level by atomic absorption spectrometry with miniaturized suction-flow hydride generation

A continuous-flow hydride generator is modified and miniaturized for the determination of picogram amounts of arsenic by atomic absorption spectrometry. A 300-μl sample is dropped into a teflon cup and pumped into an alkaline sodium tetrahydroborate stream, which is acidified in a reaction coil. The evolved hydride is swept with argon through a phase separator into an electrically-heated quartz absorption cell and the absorbance is recorded. To eliminate differences in sensitivity between arsenic(III) and arsenic(V) without prereduction by potassium iodide, it is important that arsenic(V) be mixed with tetrahydroborate prior to mixing with hydrochloric acid. The method has a detection limit of 0.08 ng As ml^?1 (24 pg) and the calibrations is linear up to 50 ng As ml^?1. The relative standard deviation for 10 replicate measurements is 5.4% for 0.5 ng As ml^?1. The addition of potassium iodide and hydroxylamine is confirmed to be effective in minimizing some interferences. The sampling rate is 90 h^?1. Results for NBS biological and steel reference materials demonstrate applicability of the technique.     

Synthesis hexagonal ß-Ni(OH)2 nanosheets for use in electrochemistry sensors

A new method for the determination of inorganic arsenic species (As(III) and As(V)) was developed by dispersive liquid-liquid microextraction (DLLME) separation and graphite furnace atomic absorption spectrometry (GFAAS) detection. In the pH range of 3–5, As(III) complexes with ammonium pyrrolidinedithiocarbamate (APDC) and then can be extracted into carbon tetrachloride droplets formed by injecting the binary solution of carbon tetrachloride (extraction solvent) and methanol (dispersive solvent) into the sample solution. As(V) is not extracted at the same pH conditions and remained in the aqueous phase. After extraction and phase separation by centrifugation, the enriched As(III) in the sedimented phase was determined by GFAAS. Total inorganic arsenic was determined after reduction of As(V) to As(III) with sodium thiosulfate and potassium iodide, and As(V) was calculated by difference. Under optimized conditions, the detection limits of this method for As(III) were 36 ng L^?1 with an enrichment factor of 45, and the relative standard deviation (R.S.D.%) was 3.1% (n?=?11, c?=?1.0 ng mL^?1). The method has been applied to the speciation of As(III) and As(V) in natural water samples with satisfactory results.     

Highly sensitive inhibitory kinetics fluorescence method for determination of arsenic

A new and highly sensitive inhibitory kinetic fluorescence method for the determination of arsenic (III) has been established based on its inhibitory effect on the oxidation reaction of Acridine red (ADR) by KBrO₃ in sulphuric acid medium. The reaction has been followed by measuring the enhancement of fluorescence at 550?nm. It relies on the linear relationship where the change in the fluorescence (ΔF) versus added As(III) amounts in the range of 0–0.450?µg?mL^?1 is plotted, under the optimum conditions. The sensitivity of the proposed method, i.e. the limit of detection, is 2.1?×?10^?2?ng?mL^?1. The method is featured with good accuracy and reproducibility for arsenic (III) determination. This method was successfully applied for the quantitative determination of arsenic (III) in food products samples, and the relative standard deviations and the recoveries were in ranges of 2.31–2.83% and 90.0–107.2%, respectively. A review of recently published catalytic or inhibiting kinetic methods for the determination of arsenic (III) has also been presented for comparison. The mechanism of reaction was studied.     

Speciation of inorganic arsenic in environmental waters using magnetic solid phase extraction and preconcentration followed by ICP-MS

A new method was developed for the speciation of inorganic arsenic in environmental water by using selective magnetic solid-phase extraction followed by inductively coupled plasma mass spectrometry. It is found that As(V) selectively adsorbed on amino-modified silica-coated magnetic nanoparticles (MNPs) in the pH range from 3 to 8, while As(III) is not be retained. The As(V)-loaded MNPs can be separated easily from the aqueous sample solution by simply applying an external magnetic field. The adsorbed As(V) was quantitatively recovered from the MNPs using using 1 M nitric acid. Total inorganic As was extracted after the permanganate oxidation of As(III) to As(V). Parameters affecting the separation were investigated systematically, and the optimal separation conditions were established. Under the optimal conditions, the limit of detection is 0.21 ng L^?1, and the precision is 6.8% (at 10 ng L^?1, for n?=?7). The method was applied to the speciation of inorganic arsenic in environmental water of tobacco growing area.

Inorganic arsenic speciation analysis of water samples by trapping arsine on tungsten coil for atomic fluorescence spectrometric determination

Arsine trapping on resistively heated tungsten coil was investigated and an analytical method for ultratrace arsenic determination in environmental samples was established. Several chemical modifiers, including Re, Pt, Mo, Ta and Rh, were explored as permanent chemical modifiers for tungsten coil on-line trapping and Rh gave the best performance. Arsine was on-line trapped on Rh-coated tungsten coil at 640 °C, then released at 1930 °C and subsequently delivered to an atomic fluorescence spectrometer (AFS) by a mixture of Ar and H₂ for measurement. In the medium of 2% (v/v) HCl and 3% (m/v) KBH₄, arsine can be selectively generated from As(III). Total inorganic arsenic was determined after pre-reduction of As(V) to As(III) in 0.5% (m/v) thiourea-0.5% (m/v) ascorbic acid solution. The concentration of As(V) was calculated by difference between the total inorganic arsenic and As(III), and inorganic arsenic speciation was thus achieved. With 8 min on-line trapping, the limit of detection was 10 ng L⁻¹ for As(III) and 9 ng L⁻¹ for total As; and the precision was found to be <5% R.S.D. (n = 7) for 0.2 ng mL⁻¹ As. The proposed method was successfully applied in total arsenic determination of several standard reference materials and inorganic arsenic speciation analysis of nature water samples.     

Determination of inorganic arsenic(III) in ground water using hydride generation coupled to ICP-AES (HG-ICP-AES) under variable sodium boron hydride (NaBH4) concentrations

The determination of inorganic arsenic species in ground water matrices using hydride generation coupled online to ICP-AES (HG-ICP-AES) is suggested on the fact that the As(III)-species shows significantly higher signal intensities at low sodium boron hydride (NaBH₄) concentrations than the As(V)-species. The sodium boron hydride concentration used for the determination of As(III) without any considerable interferences of As(V) was at 13.2 mmol/L NaBH₄ (0.05 wt/v%), whereas the concentration for the total As determination was at 158.4 mmol/L NaBH₄ (0.6 wt/v%). The interferences of As(V) during the As(III) measurements were very small: at concentrations below 100 μg/L of total arsenic, the interferences of As(V) were smaller than 2%. An amount of As(III) higher than 10% of the total As amount could be determined exactly and reliably. The total amount of arsenic is measured after reducing the sample with 20 mmol/L L-cysteine (C₃H₇NO₂S). Finally, the amount of the As(V)-species is calculated by the difference between the As(III)-species and the total arsenic. Therefore, this analytical method requires the absence of organic arsenic species, but if they still appear, they could be frozen out with liquid nitrogen after the hydride generation system. The linearity of calibration reaches from 2 μg/L up to 1000 μg/L with a detection limit routinely of about 1 μg/L for each species. The advantages of this method in comparison to AAS measurements are the higher extent of the linear calibration range (3 orders of magnitude) and a higher sensitivity. Additional merits of the method developed are easy handling and high sampling rates.     

RP-LC Determination and Pharmacokinetic Study of Ferulic Acid and Isoferulic Acid in Rat Plasma After Taking Traditional Chinese Medicinal-Preparation: Guanxinning Lyophilizer

A sensitive, simple, and accurate method for determination and pharmacokinetic study of ferulic acid and isoferulic acid in rat plasma was developed using a reversed-phase column liquid chromatographic (RP-LC) method with UV detection. Sample preparations were carried out by protein precipitation with the addition of methanol, followed by evaporation to dryness. The resultant residue was then reconstituted in mobile phase and injected into a Kromasil C₁₈ column (250 × 4.6 mm i.d. with 5 μm particle size). The mobile phase was methanol-1% formic acid (33:67, v/v). The calibration plots were linear over the range 5.780–5780 ng·mL^?1 for ferulic acid and 1.740–348.0 ng·mL^?1 for isoferulic acid. Mean recoveries were 85.1% and 91.1%, respectively. The relative standard deviations (RSDs) of within-day and between-day precision were not above 15% for both of the analytes. The limits of quantification were 5.780 ng·mL^?1 for ferulic acid and 1.740 ng·mL^?1 for isoferulic acid. This RP-LC method was used successfully in pharmacokinetic studies of ferulic acid and isoferulic acid in rat plasma after intravenous injection of Guanxinning Lyophilizer.     

A FIA-system for As(III)/As(V)-determination with electrochemical hydride generation and AAS-detection

A flow-injection system with electrochemical hydride generation and atomic absorption detection for As(III)/As(V) determination is described. A simple electrolytic flow-through cell has been developed and optimized. Several cathode materials like Pt, Ag, Cu, C and Pb have been tested. The influence of the electrolysis current, concentration of sulfuric acid, carrier stream, flow rate, sample volume and interferences by other metals on the arsenichydride generation have been studied. For the determination of total inorganic arsenic, As(V) is reduced to As(III) on-line by postassium iodide or L-cysteine at 95 degrees C. The influence of the temperature and the reduction medium on this pre-reduction step has been tested. The calibration curve is linear in the range of 5 to 50 microg/L for As(III) and total inorganic arsenic and shows a higher sensitivity than in case of reduction with sodium tetrahydroborate. The detection limit is 0.4 microg/L for As(III) and 0.5 microg/L for total inorganic arsenic at a sample volume of 1 mL.     

A Highly Sensitive Electrochemical Impedance Spectroscopy Immunosensor for Determination of 1‐Pyrenebutyric Acid Based on the Bifunctionality of Nafion/Gold Nanoparticles Composite Electrode

A simple, highly sensitive and label‐free electrochemical impedance spectroscopy (EIS) immunosensor was developed using Nafion and gold nanoparticles (nano‐Au/Nafion) composites for the determination of 1‐pyrenebutyric acid (PBA). Under the optimal conditions, the amount of immobilized antibody was significantly improved on the nano‐Au/Nafion electrode due to the synergistic effect and biocompatibility of Nafion film and gold nanoparticles composites. The results showed that the sensitivity and stability of nano‐Au/Nafion composite electrode for PBA detection were much better than those of nano‐Au modified glassy carbon electrode (nano‐Au/GCE). The plot of increased electron transfer resistances (R_ets) against the logarithm of PBA concentration is linear over the range from 0.1 to 150 ng·mL^?1 with the detection limit of 0.03 ng·mL^?1. The selectivity and accuracy of the proposed EIS immunosensor were evaluated with satisfactory results.     

Second‐order Scattering and Frequency Doubling Scattering Spectra of Thallium(III)‐Methotrexate System and Its Analytical Application

In pH 4.9 Britton-Robinson buffer solution, methotrexate (MTX) reacted with thallium(III) to form a 3∶1 chelate. This resulted in great enhancement of second-order scattering (SOS) spectra and frequency doubling scattering (FDS) spectra and appearance of new SOS and FDS spectra. Their maximum wavelengths were located at 520 and 390 nm, respectively. The increments of scattering intensities (ΔI) were directly proportional to the concentrations of MTX in the ranges of 0.022—2.0 μg•mL－1 (SOS method) and 0.008—2.5 μg•mL－1 (FDS method). The methods exhibited high sensitivities. The detection limits for MTX were 7.4 ng•mL－1 (SOS method) and 2.3 ng•mL－1 (FDS method), respectively. The optimum conditions of the reaction, the influencing factors and the effects of coexisting substances were investigated. A highly sensitive, simple and fast method for the determination of MTX has been developed. The method can be applied satisfactorily to the determination of MTX in human serum samples. In this work, the charge distribution of MTX was calculated by a CNDO quantum chemistry method. In addition, the reaction mechanism was discussed.     

GC Determination of Cisplatin in Serum and Urine of Cancer Patients after Chemotherapy as Platinum (II) Pyrrolidinedithiocarbamate Chelate

A gas chromatographic procedure has been developed for determination of cisplatin from pharmaceutical preparation, serum and urine after chemotherapy of cancer patients as platinum(II) pyrrolidinedithiocarbamate chelate. The elution was carried from the column DB-1701 (30 m × 0.32 mm i.d.) coupled with FID detection. Cu(II), Ni(II), Co(III), Mn(II), Fe(III), Zn(II) and VO(II) when present together with Pt(II) separated completely and did not affect the determination of platinum. The linear calibration curve for platinum (II) was within 1–30 μg mL^?1 with a detection limit of 300 ng mL^?1. The amount of cisplatin detected from serum and urine was 250–325 and 20–116 ng mL^?1 with relative standard deviations (RSD) of 0.8–1.2%, and 0.9–1.2%. The % recovery of Pt from serum and urine by standard addition was 98 and 98.2% with RSD 1.4 and 1.1%.     

Speciation analysis of inorganic arsenic in natural water by carbon nanofibers separation and inductively coupled plasma mass spectrometry determination

In this paper, carbon nanofibers (CNFs) as a novel solid phase extraction sorbent were developed for speciation preconcentration and separation of inorganic arsenic species As(III) and As(V) prior to determination by inductively coupled plasma mass spectrometry (ICP-MS). It was found that during all the steps of the separation, As(III) was selectively sorbed on the microcolumn packed with CNFs within a pH range of 1.0-3.0 in the presence of ammonium pyrroinedithiocarbamate (APDC), while As(V) was passed through the microcolumn without the retention. Various experimental parameters affecting the separation and determination of As(III) and As(V) have been investigated in detail. Under the optimized conditions, the detection limits of this method for As(III) were 0.0045 ng mL⁻¹ with an enrichment factor of 33 and 0.24 ng mL⁻¹ for As(V), and the relative standard deviations for As(III) and As(V) were 2.6% and 1.9% (n = 9, c = 1.0 ng mL⁻¹), respectively. In order to verify the accuracy of the method, a certified reference of water sample was analyzed, and the results obtained were in good agreement with the certified values. The proposed method was applied for the analysis of inorganic arsenic species in groundwater and lake water with the recovery of 92-106%.     

Quantification of Imidacloprid in Honeybees: Development of a Chemiluminescent ELISA

A Chemiluminescent Enzyme-Linked Immuno-Sorbent Assay (CL-ELISA) for determination and quantification of the fungicide imidacloprid in honeybees was developed in an indirect competitive format. The assay was optimized by determining: the optimal coating conjugate concentration and anti-imidacloprid antiserum dilution, the effect of the incubation time on the competitive step, and the tolerance to organic solvents. The IC₅₀ and the limit of detection (LOD) values were 14.8 ng mL^?1 and 0.11 ng mL^?1, respectively, similar to those of colorimetric ELISA with a calibration range of 0.1–2600 ng mL^?1. Cross reactivity of some related compounds such as three imidacloprid metabolites, 6-chloro nicotinic acid, 5-hydroxy-imidacloprid, and imidacloprid olefin, and one other chloronicotinoid insecticide, acetamiprid, were tested. The assay was then applied to honeybee extracts obtained by using the liquid-liquid extraction. The calibration curves in honeybee extracts from the liquid-liquid procedure gave an IC₅₀ of 23.7 ng mL^?1 and a LOD 1.6 ng mL^?1. The average recovery value from honeybee extracts spiked with 100 and 1000 ng mL^?1 of imidacloprid were 73% and 76%, respectively. Finally, the assay was applied to honeybee samples collected during monitoring activities in Italy; it was found that only five of the 27 samples were positives, with low concentrations of imidacloprid ranging between 1.2 and 15.4 ng g^?1.