Direct immersion dual-drop microextraction for simultaneous separation and enrichment of Cr(III) and Cr(IV) in food samples prior to graphite furnace atomic absorption spectrometry detection.

Non-chromatographic speciation methods generally involve speciation conversion, which may cause sample contamination, analysis errors and tedious operations. In this work, a direct immersion dual-drop microextraction (DIDDME) was firstly developed for separation and preconcentration of Cr(III) and Cr(VI). In DIDDME, two organic drops on needle tips of microsyringes were concurrently immersed in a stirred sample solution. Each drop contains a chelating reagent for reacting with a specific species. Thus, Cr(III) and Cr(VI) were selectively extracted into different drops. This method afforded detection limits of 3.0 and 4.1 ng/L, quantification limitof 10 ng/L and 14 ng/L, linear range of 0.01-30 ng mL-1 and enrichment factors of 354-fold and 326-fold for Cr(III) and Cr(VI), respectively. Precisions like repeatability and reproducibility were assessed by calculating relative standard deviations, which were lower than 5.4 % and 6.9 %, respectively. This procedure was used successfully for quantification of Cr(III) and Cr(VI) in food samples.

A novel separation and preconcentration methodology based on direct immersion dual-drop microextraction for speciation of inorganic chromium in environmental water samples.

In this study, for the first time, a novel separation and preconcentration method of direct immersion dual-drop microextraction (DIDDME) was proposed for the species of inorganic chromium (Cr(III) and Cr(VI)) followed by graphite furnace atomic absorption spectrometry detection. The methodology is based on that two organic drops hold on the needle tips of microsyringes were concurrently immersed in a stirred sample solution. Each drop contains a chelating reagent, which can react with a specific species under the same pH value. Therefore, Cr(III) and Cr(VI) can be selectively extracted into different drops. This procedure did not require tedious and complicated pre-oxidation/pre-reduction and centrifugation/filtration operations, which may lead to the risk of sample contamination and analysis errors. Main parameters influencing separation, preconcentration and identification of the target species were investigated. An enrichment factor of 400-fold was obtained for Cr(III) and Cr(VI). Under the optimized conditions, detection limits for this method were 1.1 ng L-1 and 1.4 ng L-1 for Cr(III) and Cr(VI) with relative standard deviations of 5.1 and 6.3%, respectively. This procedure was applied for the separation, preconcentration and determination of Cr(III) and Cr(VI) in environmental water samples and certified reference materials with satisfactory results. Recoveries of spiked experiments ranged from 86.0 to 112%.

In-syringe solid phase extraction and in-syringe vortex-assisted solidified floating organic drop microextraction of Sb(III) and Sb(V) in rice wines with determination by graphite furnace atomic absorption spectrometry.

The current non-chromatographic speciation methods generally involve the conversion of different species by oxidation/reduction reactions, which may cause inherent problems such as contamination risk, time consumption and complex operations. In this work, in-syringe solid phase extraction (IS-SPE) was combined with in-syringe vortex-assisted solidified floating organic drop microextraction (IS-VA-SFODME) for the detection of Sb(V) and Sb(III) in rice wines by graphite furnace atomic absorption spectrometry. Firstly, IS-SPE involved the use of ZnFe2O4 nanotubes as the sorbent for the isolation and enrichment of Sb(V) and removal of the matrix components such as ethanol, pigment, sugars and carbohydrates. Then, IS-VA-SFODME was used for enriching Sb(III) in the original sample solution after IS-SPE. This technique exhibited good anti-interference ability and high enrichment efficiency without tedious pre-oxidation/pre-reduction and centrifugation/filtration operations, which may cause the contamination of samples. Under the selected conditions, the detection limits were 4.5 ng L-1 and 3.2 ng L-1 for Sb(III) and Sb(V) with relative standard deviations of 7.3% and 5.1%, respectively. This procedure was used with satisfactory results for the detection of Sb(III) and Sb(V) in rice wine samples and a certified reference material of water sample. Recoveries of spiked experiments ranged from 91.0 to 107%.

Magnetic dispersive micro-solid phase extraction coupled with dispersive liquid-liquid microextraction followed by graphite furnace atomic absorption spectrometry for quantification of Se(IV) and Se(VI) in food samples.

In this work, magnetic dispersive micro-solid phase extraction (MDMSPE) coupled with dispersive liquid-liquid microextraction (DLLME) was developed for Se(IV) and Se(VI) followed by graphite furnace atomic absorption spectrometry. MDMSPE involved the use of magnetic ZnFe2O4 nanotubes for adsorbing Se(VI). The sorbent was isolated from aqueous phase by using an external magnetic field instead of tedious centrifugation or filtration. In the following step, Se(IV) in the upper aqueous phase of MDMSPE was enriched by DLLME. Samples were prepared with artificial gastric juice to avoid the inter-conversion of target species. The main factors affecting the determination of the analytes were studied in detail. the detection limits of this method were 1.0 and 1.3 pg mL-1 for Se(IV) and Se(VI) with relative standard deviations of 4.6% and 5.1% (c = 1.0 ng mL-1, n = 9), respectively. An enrichment factor of 200 was obtained. This method was used for the detection of Se(IV) and Se(VI) in food samples without any pre-oxidation or pre-reduction operation. A certified reference material of milk powder was analysed by this method, and the determined values were in good agreement with the certified values. Recoveries of spike experiments were in the range of 91.0-107%.

Determination of Mn(II) and Mn(VII) in beverage samples using magnetic dispersive micro-solid phase extraction coupled with solidified floating organic drop microextraction followed by graphite furnace atomic absorption spectrometry.

Magnetic dispersive micro-solid phase extraction (MDMSPE) was coupled with solidified floating organic drop microextraction (SFODME) for direct separation and preconcentration of Mn(II) and Mn(VII) before graphite furnace atomic absorption spectrometry determination. MDMSPE involved use of magnetic ZnFe2O4 nanotubes for adsorbing Mn(VII). Sorbent was isolated from aqueous phase by an external magnet. Mn(II) in upper solution from MDMSPE was further enriched by SFODME. This method avoids tedious pre-oxidation/pre-reduction operation and time-consuming centrifugation/filtration step. An enrichment factor of 200-fold was obtained. Detection limits of this method were 0.005 and 0.007 ng mL-1 for Mn(II) and Mn(VII) with relative standard deviations of 4.0% and 4.8% (n = 9), respectively. This method was successfully used for detection of Mn(II) and Mn(VII) in tap water, ice tea, energy drink, mineral water, sprite drink and carbonated drink. A certified reference material of water sample was analyzed with satisfactory results. Recoveries of spike experiments ranged from 92.5 to 106%.

Fibrous g-C3N4@Tio2 Nanocomposites-Based Dispersive Micro-Solid Phase Extraction for Chromium Speciation in Cow Milk by ICP-MS after Digestion Treatment with Artificial Gastric Juice.

BACKGROUND: Chromium is an interesting element because its toxicity depends on its speciation. Thus, knowledge of Cr speciation in cow milk is essential to human health. OBJECTIVE: This study aims to achieve real bioaccessible species in cow milk, including Cr(III), Cr(VI), residual, digestible, and total Cr. METHODS: Samples were treated with artificial gastric juice, followed by dispersive micro-solid phase extraction (DMSPE) combined with ICP-MS for Cr speciation. Fibrous g-C3N4@TiO2 nanocomposites (FGCTNCs) were used as a novel adsorbent for DMSPE. RESULTS: The method detection limits were 110 pg/g (Cr(III)) and 260 pg/g (Cr(VI)) for milk powder (0.1 g), and 5.1 pg/g (Cr(III)) and 13 pg/g (Cr(VI)) for liquid cow milk (2 mL). The relative standard deviations (RSDs), obtained by analyzing the standard solutions containing 1.0 ng/mL of the analytes in sequence for nine times, were 4.3% and 5.1% for Cr(III) and Cr(VI), respectively. Linearity was observed over the range of 4 magnitude orders with correlation coefficients better than 0.9961. The enrichment factor of 100 was obtained. The majority of Cr in the samples was transferred into digestion solution. The content of Cr(III) is much higher than that of Cr(VI) in the digestion solution. CONCLUSIONS: This method has the advantages of reduced solvent consumption, less adsorbent dosage, and high extraction efficiency. It may become a valuable strategy for elemental species in food samples. HIGHLIGHTS: The samples were treated with artificial gastric juice to avoid the inter-conversion of species. FGCTNCs exhibit the merits of N-rich functional groups and selective adsorption for the analytes.

Magnetic ZnFe2O4 nanotubes for dispersive micro solid-phase extraction of trace rare earth elements prior to their determination by ICP-MS.

Magnetic ZnFe2O4 nanotubes (ZFONTs) with numerous pores on their walls were synthesized and characterized. They are shown to be a viable sorbent for dispersive micro-solid phase extraction of the trivalent ions of rare earth elements (REEs), specifically of lanthanum, praseodymium, europium, gadolinium, holmium and ytterbium. The specific surface area of ZFONTs is large (57 m2⋅g-1) and much bigger than that of ZnFeO4 nanoparticles (16 m2⋅g-1). It is shown that REEs are quantitatively retained on ZFONTs in the pH range of 7.0-9.0. The separation of the sorbent from the aqueous phase was achieved by an external magnetic field. Following elution with 0.5 mol⋅L-1 HNO3, REEs were quantified by inductively coupled plasma mass spectrometry. The main parameters influencing preconcentration and determination of the REEs were studied. Under optimum conditions, detection limits for REEs range from 0.01 (Ho) to 0.75 (La) pg⋅mL-1. Relative standard deviations are less than 6.5% (for n = 9; at 1.0 ng⋅mL-1). The method was applied to the determination of trace REEs in spiked biological and environmental samples and gave satisfactory results. Graphical abstract Schematic presentation of a new adsorbent for dispersive micro-solid phase extraction (DMSPE) combined with ICP-MS. Magnetic ZnFe2O4 nanotubes with many pores on their walls were used for preconcentration and determination of rare earth elements (REEs) in environmental and biological samples.

Dual extraction based on solid phase extraction and solidified floating organic drop microextraction for speciation of arsenic and its distribution in tea leaves and tea infusion by electrothermal vaporization ICP-MS.

A dual extraction based on solid phase extraction (SPE) and solidified floating organic drop microextraction (SFODME) was developed for As species in tea leaves and tea infusion by electrothermal vaporization inductively coupled plasma mass spectrometry, including total, suspended, soluble, organic and inorganic As as well as As(III) and As(V). In SPE step, titanium dioxide nanotubes were used for preconcentration of analytes and removal of sample matrix. Elution solution from SPE was employed for further preconcentration and separation of analytes with SFODME. Under optimal conditions, detection limits of this method were 0.046 and 0.072pgmL(-1) with relative standard deviations of 6.3% and 5.8% for As(III) and As(V) (n=9, c=1.0ngmL(-1)), respectively. A preconcentration factor of 500-fold was achieved for As(III) and As(V). This method was successfully applied for analysis of speciation of arsenic and its distribution in tea leaves, tea infusion and certified reference material of tea leaves.

Solidified floating organic drop microextraction for speciation of selenium and its distribution in selenium-rich tea leaves and tea infusion by electrothermal vapourisation inductively coupled plasma mass spectrometry.

Solidified floating organic drop microextraction was combined with electrothermal vapourisation inductively coupled plasma mass spectrometry for Se species in Se-rich tea leaves and tea infusion, including total, suspended, soluble, organic and inorganic Se as well as Se(IV) and Se(VI). Ammonium pyrrolidinedithiocarbamate was used as both chelating reagent and chemical modifier in this study. Se(IV) and Se(VI) were separated at pH range of 2.0-5.0. An enrichment factor of 500 was obtained for Se(IV) from this method. Under the optimum conditions, the detection limits for Se(IV) and Se(VI) were 0.19 and 0.26pgmL(-1), respectively. The relative standard deviations were less than 5.5% (c=0.1ngmL(-1), n=9). This method was applied for Se species, its content and distribution in Se-rich tea leaves and tea infusion with satisfactory results. The recoveries of spike experiments are in the range of 92.2-106%. A certified reference material of tea leaves was analyzed by this method, and the results were in agreement with certified values.

Speciation of chromium and its distribution in tea leaves and tea infusion using titanium dioxide nanotubes packed microcolumn coupled with inductively coupled plasma mass spectrometry.

Titanium dioxide nanotubes (TDNTs) were used as a solid phase extraction adsorbent for chromium species by a packed microcolumn coupled with inductively coupled plasma mass spectrometry (ICP-MS), including total, suspended and soluble chromium as well as Cr(III) and Cr(VI) in tea leaves and tea infusion. The experimental results indicated that Cr(III) was quantitatively retained on TDNTs in the pH range of 5.0-8.0, while Cr(VI) remained in the solution. The total chromium was determined after reducing Cr(VI) to Cr(III). The concentration of Cr(VI) is calculated by the difference between total chromium and Cr(III). Under optimal conditions, the detection limits of this method were 0.0075ngmL(-1) for Cr(III). The relative standard deviation was 3.8% (n=9, c=1.0ngmL(-1)). This method was applied for the analysis of the speciation of chromium and its distribution and content in tea leaves, tea infusion and a certified reference material of tea leaves with satisfactory results.

Solid-phase extraction of Cu, Co and Pb on oxidized single-walled carbon nanotubes and their determination by inductively coupled plasma mass spectrometry.

A novel method using a microcolumn packed with single-walled carbon nanotubes (SWNTs) as a new adsorption material was developed for the preconcentration of trace Cu, Co and Pb in biological and environmental samples prior to their determination by inductively coupled plasma mass spectrometry (ICP-MS). SWNTs oxidized with concentrated nitric acid have been proved to possess an exceptional adsorption capability for the analytes due to their surface functionalization. The adsorption behaviors of the analytes on SWNTs under dynamic conditions were studied systematically. The main factors influencing the preconcentration and determination of the analytes (pH, sample flow rate and volume, eluent concentration and interfering ions) have been examined in detail. Under the optimum conditions, the detection limits for Cu, Co and Pb were 39, 1.2 and 5.4 pg mL(-1), respectively; the relative standard deviations (RSDs) were found to be less than 6.0% (n=9, c=1.0 ng mL(-1)). This method was validated using a certified reference material of mussel, and has been successfully applied for the determination of trace Cu, Co and Pb in real water sample with the recoveries of 96.0-109%.

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%.

[Determination of gold in geological sample by inductively coupled plasma mass spectrometry after carbon nanofibers separation and preconcentration].

A novel method for the determination of Au by inductively coupled plasma mass spectrometry (ICP-MS) is described. Au can be separated and preconcentrated with a micro-column packed with carbon nanofibers as an adsorption material. The adsorption and elution behaviors of Au3+ on carbon nanofibers were systematically investigated under dynamic conditions. The experimental results showed that the studied ions can be adsorbed quantitatively at pH 2.0, and the analytes adsorbed on the column can be eluted with H2NCSNH2-HCl solution at pH 1.0. Under the optimum conditions, the detection limits for Au is 0.15 ng x mL(-1), and the relative standard deviation (RSD) is 8.5% (n = 6). The proposed method has been applied to the determination of trace Au in geological standard material with satisfactory results.

Use of a microcolumn packed with modified carbon nanofibers coupled with inductively coupled plasma mass spectrometry for simultaneous on-line preconcentration and determination of trace rare earth elements in biological samples.

In this work, a new method was developed for the determination of trace rare earth elements (REEs) in biological samples by inductively coupled plasma mass spectrometry (ICP-MS) after preconcentration on a microcolumn packed with modified carbon nanofibers (CNFs). CNFs oxidized with nitric acid have been proved to possess an exceptional adsorption capability for REEs due to their surface functionalization. The effects of the experimental parameters, including pH, sample flow rate and volume, elution solution and interfering ions, on the recoveries of the analytes have been investigated systematically. A 100-fold enrichment factor was obtained. The adsorption capacity of CNFs was found to be 18.1, 19.3, 23.6, 17.6, 22.3 and 19.5 mg/g for La, Ce, Sm, Eu, Dy and Y, respectively. Under the optimum conditions, the detection limits of this method ranged from 0.2 pg/mL (Dy) to 1.2 pg/mL (Ce) with an enrichment factor of 15-fold, and the relative standard deviations (RSDs) for the determination of REEs at the 1.0 ng/mL level were less than 4% (n = 9). This method was applied to the analysis of trace REEs in a real sample of human hair with recoveries of 95-115%. In order to validate the proposed method, a certified reference material of human hair (GBW 07601) was analyzed with satisfactory results.

Direct inductively coupled plasma-atomic emission spectrometry analysis of trace elements in muscle tissues of hairtail using electrothermal vaporization with slurry sampling.

A procedure for direct determination of trace elements in muscle tissue of hairtail was developed using inductively coupled plasma-atomic emission spectrometry and electrothermal vaporization with slurry sampling. Due to use of polytetrafluoroethylene as the chemical modifier, the vaporization behaviors of analytes from the slurry and the aqueous standard solutions were very similar. In this case, the aqueous standards could be used for the calibration of slurry samples. The main factors influencing this method were studied systematically. The detection limits for Cr, Ni, Zn, Cd, and Pb were 3.1, 10.5, 176, 6.9, and 83 ng/mL, respectively, and the relative standard deviations were less than 10%. The proposed method was applied to the determination of trace Cr, Ni, Zn, Cd, and Pb in hairtail samples with satisfactory accuracy and precision. A certified reference material of mussel (GBW 08571) was analyzed, and good agreement was obtained between the results from the proposed method and certificate values.

[Slurry sampling for direct determination of trace cadmium in amber by graphite furnace atomic absorption spectrometry].

A method for the direct determination of trace cadmium in amber by graphite furnace atomic absorption spectrometry (GFAAS) with slurry sampling was described. Palladium nitrate was used as a matrix modifier to eliminate the interference. Slurry stability and the influences of the matrix modifier, ashing/atomization temperature and coexistent ions on analytical signals were investigated in detail. Under the optimized experimental conditions, the detection limit of this method was 9.4 ng x g(-1) with a precision of 6.1%.

Application of low temperature electrothermal vaporization ICP-AES for determination of refractory yttrium with 1-(2-pyridylazo)-2-naphthol as chemical modifier.

A low temperature electrothermal vaporization inductively coupled plasma atomic emission spectrometry (ETV-ICP-AES) method was developed for the determination of the refractory yttrium, using 1-(2-pyridylazo)-2-naphthol (PAN) as chemical modifier. The trace yttrium was vaporized as PAN complex into plasma from a graphite furnace at a comparatively low temperature of 1200 degrees C. The operation conditions were optimized, and the vaporization behavior of Y-PAN chelate and the main factors affecting the determination were investigated in detail. Under the optimized conditions, the detection limit of Y was 0.7ngml(-1), and the relative standard deviation (R.S.D.) for 0.1mugml(-1) Y was 4.5% (n=9, v=10mul). The linear range of calibration curve covered three orders of magnitude. The recommended approach has been applied for analysis of three biological samples with satisfactory results. The accuracy of the method was demonstrated by analyzing two standard reference materials.