Sorbent extraction in flow injection analysis and its application to enhancement of atomic spectrometry

The extraction of metals as their chelates from aqueous samples can be simplified, miniaturized and automated by flow injection/sorbent extraction techniques. The chelate is formed in the flow stream, sorbed on C-18 bonded silica and then eluted for transfer to the atomic absorption spectrometer. The proposed method is shown to be useful for the preconcentration of copper and lead by means of their chelation with diethyldithiocarbamate or 8-quinolinol; complexation with 1-(2- pyridylazo)-2-naphthol or 4-(2-pyridylazo)resorcinol is also possible. This approach enables organic reagents to be used directly, without immobilization, in “open” flow-injection systems for preconcentration or separation of analytes.     

Iron protoporphyrin-modified monolithic support for on-line preconcentration of angiotensin prior to CE analysis

An on-line preconcentration method using a polymeric monolithic support is proposed for the retention of the decapeptide angiotensin I and its subsequent analysis by CZE. Monolithic capillary columns were prepared in fused-silica (FS) capillaries of 150 microm id by ionizing radiation-initiated in situ polymerization and cross-linking of diethylene glycol dimethacrylate and glycidyl methacrylate, and chemically modified with iron protoporphyrin IX (Fe-ProP). Monolithic microcolumns (8 mm long) were coupled on-line to the inlet of the separation capillary (FS capillary, 75 microm id x10 cm from the inlet to the microcolumn and 27 cm from the microcolumn to the detector). Angiotensin I was released from the sorbent by a 50 mM sodium phosphate, pH 2.5/ACN, 75:25 v/v solution and then analyzed by CZE with UV absorption detection at 214 nm. The concentration LOQ (CLOQ) was 0.5 ng/mL. The Fe-ProP-derivatized monolithic microcolumn coupled to the separation capillary exhibited a high retention capacity for peptide angiotensin I, and showed as much as 10,000-fold improvement in concentration sensitivity.     

Application of the Ion Pair of 2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol and Ammonium Tetraphenylborate for Preconcentration of Trace Vanadium and Determination by Third Derivative Spectrophotometry

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浊点萃取-高效液相色谱法测定铜、钴

讨论了以5-Br-PADAP为衍生试剂,用Triton X-114非离子表面活性剂浊点萃取富集铜（Ⅱ）、钴（Ⅱ）的条件,并于ODS柱上,用内含2．0mmol·L^-1十六烷基三甲基溴化铵（CTMAB）和5mmol·L^-1 pH5．0 HAc—NaAc缓冲溶液的V（甲醇）＋V（乙腈）＋V（水）=67＋8＋25混合液作流动相．检测波长为568nm,流量为0．8mL·min^-1。,发展了浊点萃取-高效液相色谱法测定铜、钴的新方法。在选定条件下,大多数离子不干扰测定,方法灵敏度高,经浊点萃取后可提高测定响应值7—8倍,对铜、钴的检测限分别为0．5μg·L^-1,0．8μg·L^-1。方法可用于水样中钴（Ⅱ）、铜（Ⅱ）的测定,结果令人满意。     

Analysis of opioid peptides by on-line SPE-CE-ESI-MS

In this study, SPE-CE-ESI-MS is explored for the preconcentration and separation of dilute solutions of six opioid peptides. First, a CE-ESI-MS methodology was developed and validated. LODs of around 1 microg/mL were obtained for all the studied peptides. For SPE-CE-ESI-MS experiments, a home-made SPE microcartridge containing a C18 sorbent was constructed near the inlet of the separation capillary. After optimizing the on-line preconcentration methodology, LODs between 10 and 0.1 ng/mL were achieved. Repeatability, reproducibility, durability of the microcartridges and linearity of the SPE-CE-ESI-MS methodology were also investigated and compared to the values obtained by CE-ESI-MS. Finally, human plasma samples fortified with opioid peptides were analyzed by SPE-CE-ESI-MS in order to show the potential of the methodology for the analysis of biological fluids.     

偏最小二乘分光光度法同时测定痕量铁、锰、铜、锌、钴和镍

痕量Fe^3 ,Mn^2 ,Cu^2 ,Zn^2 ,Co^2 ,Ni^2 与2－（5－溴－2－吡啶偶氮）－5－二乙氨基苯酚（5－Br-PADAP)和溴化十六烷基三甲基铵（CTMAB）在PH8．3时发生高灵敏显色反应，所形成的三元胶束络合的吸收光谱严重重叠，采用偏最小二乘法（PLS）辅助分光光度法测定了合成试样及饲料中上述6种痕量组分，结果表明，PLS法是化学计量学中一种可适用于基体较复杂的实际试样中痕量组分分光度同时测定的多元计算方法。     

Preconcentration of Rare Earth Elements in Seawater with Chelating Resin Having Fluorinated β‐Diketone Immobilized on Styrene Divinyl Benzene for their Determination by ICP‐OES

An analytical method has been developed for the preconcentration of rare earth elements (REEs) in seawater for their determination by inductively coupled plasma optical emission spectrometry (ICP‐OES). An indigenously synthesized chelating resin was used for the preconcentration of (REEs) which was based on immobilization of fluorinated β‐diketone group on solid support styrene divinyl benzene. Sample solutions (adjusted to optimized pH) were passed through a polyethylene column packed with 250 mg of the resin. Experimental conditions consisting of pH, sample flow rate, sample volume and eluent concentration were optimized. The established method has been applied for the preconcentration of light, medium and heavy REEs in coastal sea water samples for their subsequent determination by (ICP‐OES). Percentage recoveries of La, Ce, Nd, Sm, Eu, Gd, Dy, Er, Yb and Lu were ≥ 95%, a preconcentration factor of 200 times, and relative standard deviations < 5% were achieved.     

Evaluation of fritless solid‐phase extraction coupled on‐line with capillary electrophoresis‐mass spectrometry for the analysis of opioid peptides in cerebrospinal fluid

Fritless SPE on‐line coupled to CE with UV and MS detection (SPE‐CE‐UV and SPE‐CE‐MS) was evaluated for the analysis of opioid peptides. A microcartridge of 150 μm id was packed with a C₁₈ sorbent (particle size > 50 μm), which was retained between a short inlet capillary and a separation capillary (50 μm id). Several experimental parameters were optimized by SPE‐CE‐UV using solutions of dynorphin A (DynA), endomorphin 1 (End1), and methionine‐enkephaline (Met). A microcartridge length of 4 mm was selected, sample was loaded for 10 min at 930 mbar and the retained peptides were eluted with 67 nL of an acidic hydro‐organic solution. Using SPE‐CE‐MS, peak area and migration time repeatabilities for the three opioid peptides were 12–27% and 4–5%, respectively. SPE recovery was lower for the less hydrophobic DynA (22%) than for End1 (66%) and Met (78%) and linearity was satisfactory in all cases between 5 and 60 ng/mL. The LODs varied between 0.5 and 1.0 ng/mL which represent an enhancement of two orders of magnitude when compared with CE‐MS. Cerebrospinal fluid (CSF) samples spiked with the opioid peptides were analyzed to demonstrate the applicability to biological samples. Peak area and migration time repeatabilities were similar to the standard solutions and the opioid peptides could be detected down to 1.0 ng/mL.     

Column preconcentration and electrothermal atomic absorption spectrometric determination of rhodium in some food and standard samples

In the present work, an electrothermal atomic absorption spectrometric method has been developed for the determination of ultra‐trace amounts of rhodium after adsorption of its 2‐(5‐bromo‐2‐pyridylazo)‐5‐diethylaminophenol/tetraphenylborate ion associated complex at the surface of alumina. Several factors affecting the extraction efficiency such as the pH, type of eluent, sample and eluent flow rates, sorption capacity of alumina and sample volume were investigated and optimized. The relative standard deviation for eight measurements of 0.1 ng/mL of rhodium was ±6.3%. In this method, the detection limit was 0.003 ng/mL in the original solution. The sorption capacity of alumina and the linear range for Rh(III) were evaluated as 0.8 mg/g and 0.015–0.45 ng/mL in the original solution, respectively. The proposed method was successfully applied for the extraction and determination of rhodium content in some food and standard samples with high recovery values.     

同时测定粮谷中痕量锰铁铜锌的人工神经网络辅助分光光度法

在pH 9.5时,Mn(Ⅱ )、 Fe(Ⅲ )、 Cu(Ⅱ )和 Zn(Ⅱ )均与 2-(5-溴-2-吡啶偶氮 )-5-二乙氨基苯酚和非离子表面活性剂聚乙二醇辛基苯基醚发生高灵敏的显色反应,生成稳定的三元胶束络合物 ,其λ max分别为 566、 560、 562和 559 nm,表明吸收光谱严重重叠 ; 在相应λ max处,其表观摩尔吸光系数分别为 1.13× 105、 7.32× 104、 1.02× 105和 1.04× 105 L· mol－ 1· cm－ 1。用模拟退火－误差反向传播人工神经网络辅助分光光度法,不经分离,同时测定了模拟样和粮谷样中的痕量锰、铁、铜和锌。详细研究了该算法的最佳计算条件。虽然体系的加和性较差,但由于该算法的优良性能,仍然取得了满意结果。     

Lowering the concentration limits of detection by on-line solid-phase extraction-capillary electrophoresis-electrospray mass spectrometry

The use of solid-phase extraction coupled on-line to capillary electrophoresis using electrospray mass spectrometry detection (SPE-CE-ESI-MS) is described for the analysis of peptides in dilute solutions. A SPE microcartridge or analyte concentrator containing C(18) derivatized silica particles as the extraction sorbent was easily constructed near the inlet of the separation capillary using commercially available materials. The reversed-phase sorbent selectively retained the target peptides, enabling large volumes of the sample to be introduced (>100muL). The captured analytes were eluted in a small volume of an appropriate solution (20-50nL). This resulted in sample clean-up and concentration enhancement, with minimum sample handling. As the SPE-CE conditions were compatible with on-line ESI-MS detection, the potential for identifying and characterizing the preconcentrated analytes by SPE-CE-ESI-MS using a sheath-flow CE-ESI-MS interface is also shown. Using separation electrolytes containing N-[carbamoylmethyl]-2-aminoethanesulfonic acid (ACES) at pH 7.4, an elution plug of 80:20 (v/v) (25mM of formic acid in MeCN):H(2)O and a sheath liquid of 20mM of acetic acid in 50:50 (v/v) methanol:H(2)O the concentration limits of detection for the analyzed peptides in the positive ion mode were lowered to nanogram per milliliter levels. The systematic optimization of the operational parameters involved in the development of the SPE-CE method is described in detail, in order to promote robust and quantitative SPE-CE-ESI-MS analysis and facilitate the widespread use of the technique.     

Sensitivity enhancement for the analysis of naproxen in tap water by solid-phase extraction coupled in-line to capillary electrophoresis

SPE coupled in-line to CE, as the strategy to enhance the concentration sensitivity in CE, has been used to enrich naproxen in tap water samples. In this study, a microcartridge containing an octadecyl silica (C18) sorbent was placed near the inlet within the separation capillary column. The optimum conditions were obtained when naproxen in an acidic aqueous solution (pH 3.5) was loaded into the capillary at 930 mbar for 30 min, and 20 mM ammonium acetate in methanol/water (70:30 v/v) was used as both an elution solution and a separation BGE. Under these conditions, the sensitivity was enhanced 1820-fold with respect to normal hydrodynamic injection, and the LOD achieved was 0.2 microg/L. To show the capability of the in-line SPE-CE method, tap water samples were analysed after a pretreatment consisting in an off-line C18-SPE procedure. The recovery of this procedure was higher than 80%. Under these conditions, naproxen could be detected at a concentration of 10 ng/L; so the potential of the procedure for the sensitive analysis of this type of drugs in water samples was demonstrated. Afterwards, these results were compared with those previously obtained for naproxen in water samples using different sample stacking techniques.     

On‐line coupled capillary isotachophoresis‐capillary zone electrophoresis in hydrodynamically closed separation system hyphenated with laser induced fluorescence detection

An analytical method, based on a column coupling capillary ITP and CZE in a hydrodynamically closed separation mode hyphenated with the detection in the modular arrangement, was developed in this work. Analytical possibilities of this approach are demonstrated on the direct and ultrasensitive quantitative determination of quinine (QUI) in diluted real multicomponent ionic matrices (beverages, urine). The detection cell interface, with the rectangular arrangement of the optical channels inside, connected the separation capillary with the LIF detector via optical fibers in the on‐column detection arrangement. ITP enabled the direct large volume (30 μL) injections of the diluted real matrices with an on‐line sample pretreatment (preseparation, preconcentration) so that no external sample preparation (except for the dilution) was necessary for the separation of the analyte in the multicomponent ionic matrices. Due to the ITP sample preconcentration and intrinsic sensitivity of the LIF detection, very low concentration LOD (as low as 77 pg/mL), were reached at the same time. This was ca. two orders lower than the corresponding LOD achieved by the same 2D separation system with UV absorbance detection. Compared to the single column CE‐LIF methods applied for this model analyte and matrix, this method was found to be superior in terms of concentration LOD, with acceptable selectivity and benefits of the on‐line sample preparation. A food control and bioanalytical application clearly illustrates great practical possibilities and routine use of the proposed modular ITP–CZE–LIF technique.     

Solid Phase Extraction of Neutral Analytes through Silica Gel Coated with Layers of Au Nanoparticles Self‐Assembled with Alkanethiols

In this study, we used Au nanoparticle (NP)‐coated silica gel as a solid phase extraction sorbent for the preconcentration of neutral analytes (steroid drugs). The sorbent was fabricated using two alkanethiol self‐assembly processes: one to deposit the Au NPs onto a 3‐aminopropyltrimethoxysilane‐modified silica gel and the other to functionalize the surfaces of the Au NPs. A large volume of the steroid solution was passed through the silica gel to facilitate adsorption mediated by hydrophobic interactions between the steroids and the hydrophobic moieties on the silica gel surface. Extraction of the steroids was accomplished by flushing the silica gel with a low‐polarity solvent. In this preliminary study, we found that the particle size of the silica gel and the number of layers of Au NPs coated on the silica gel both affected the preconcentration performance for the steroids. When using six layers of Au NPs coated on 5–20‐μm silica gel, the detection limits for steroids were below 80 ng L^?1; the preconcentration efficiency was over 170‐fold higher than that of the original steroid solution. Our findings provide further evidence that nanotechnology has much to benefit analytical science.     

Separation of aromatic sulphonic acids by CZE in coated and non‐coated capillaries

Capillary zone electrophoresis (CZE), besides ion‐pairing mode HPLC and salting‐out HPLC, is well‐suited for the analysis of aromatic sulphonic acids widely used as intermediates in the production of synthetic dyes and optical brighteners. The separation selectivity in CZE of many aromatic acids, including positional isomers, can be controlled by the type and concentration of a cyclodextrin additive. The influence of the concentration of β‐cyclodextrin in the working electrolyte on the separation of the positional isomers of naphthalene (poly‐)sulphonic acids, and their amino‐ and hydroxy derivatives, by CZE was studied, both in non‐coated fused silica capillaries and in capillaries coated with polyacrylamide. The migration time scale was calibrated using 4‐alkylbenzenesulphonic acids as the calibration standards. Limiting mobilities of the free acid anions and of their complexes with β‐cyclodextrin were calculated and the effect of the inclusion guest‐host complex formation on the CZE separation was quantitatively characterized. The migration order in coated capillaries is reversed with respect to CZE in non‐coated fused silica capillaries, the separation selectivity is different and the separation of polysulphonic acids such as naphthalene tri‐ and tetrasulphonic acids is significantly accelerated.     

Synthesis and application of vinylpyridine containing ion‐imprinted copolymer gel microbeads for Cu(II) solid‐phase extraction

The influence of polymer matrix on the extraction efficiency for Cu(II) and selectivity against metal ions such as Ni(II), Cd(II), Pb(II) of Cu(II) imprinted copolymer gels was described. The functional monomers investigated include the weakly basic 4‐vinylpyridine (4‐VP) and its mixure with the acidic and hydrogen binding methacrylic acid. Copolymer gels were prepared by dispersion cross‐linking copolymerization using Cu(II)–4‐(2‐pyridylazo)resorcinol complex, Cu(II), or 4‐(2‐pyridylazo)resorcinol as templates. The chemical structure and morphology of the Cu(II)‐imprinted microbeads are defined using elemental analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. Extraction efficiencies of newly synthesized sorbents were studied by batch procedure. The prepared copolymer gel with 4‐VP as monomer and Cu(II)–4‐(2‐pyridylazo)resorcinol complex has higher capacity and selectivity toward Cu(II) than the copolymer gels prepared using the mixture of methacrylic acid and 4‐VP. This new sorbent can be used as an effective SPE material for the highly selective preconcentration and separation of Cu(II) in sea water samples. It shows high mechanical and chemical stability.     

Improving the sensitivity of the determination of ceftiofur by capillary electrophoresis in environmental water samples: in-line solid phase extraction and sample stacking techniques

This paper describes two different approaches for increasing the sensitivity for the analysis of ceftiofur by capillary electrophoresis (CE). Two different techniques based on the introduction of an enlarged volume of sample, namely large volume sample stacking (LVSS) and in-line solid phase extraction (SPE) were studied and compared. LVSS allowed the on-column electrophoretic preconcentration of ceftiofur without modification of the separation capillary. In-line SPE-CE was developed by using a home-made microcartridge that was filled with a reversed-phase sorbent (C₁₈). The microcartridge was coupled in-line near the inlet of the separation capillary. LVSS and in-line SPE-CE allowed automated operation and improved sensitivity for the analysis of ceftiofur with respect to conventional CE. When environmental water samples were analyzed, an additional pretreatment step based on off-line SPE was necessary in both cases to further decrease the detection limits. In terms of sensitivity for the determination of ceftiofur in river water samples, the combination of off-line SPE with in-line SPE-CE was found the most sensitive with a detection limit of 10 ng L⁻¹, whereas the method based on the use of off-line SPE with LVSS presented a detection limit of 100 ng L⁻¹.     

Carbon Nanofibers as Solid‐Phase Extraction Adsorbent for the Preconcentration of Trace Rare Earth Elements and Their Determination by Inductively Coupled Plasma Mass Spectrometry

Abstract

Systematic investigations were carried out into the sorption of rare earth elements (REEs) on carbon nonofibers (CNFs) by inductively coupled plasma mass spectrometry (ICP‐MS). The experimental parameters for preconcentration of REEs, such as pH, sample flow rate and volume, eluent concentration, and interfering ions on preconcentration of REEs have been examined in detail. The studied metal ions can be adsorbed quantitatively on CNFs in a pH range from 2.0 to 5.0, and then eluted completely with 0.5 mol l^?1 HNO₃. Based on the above facts, a novel method using a microcolumn packed with carbon nanofibers as an adsorption material was developed for the separation and preconcentration of REEs prior to their determination by ICP‐MS. The proposed method has been successfully applied to the determination of light (La), medium (Eu and Gd) and heavy (Yb) rare earth elements in real sample with the recovery more than 90%. In order to validate this method, two certified reference materials of tea leaves (GBW 07605) and mussel (GBW 08571) were analyzed, and the determined values are in good agreement with the certified values.     

Application of 1-(2-Pyridylazo)-2-naphthol Anchored SiO2 Nanoparticles for the Preconcentration of Trace Pb2+ from Different Water and Food Samples

SiO₂‐PAN nanoparticles has been synthesized by reacting silica nanoparticles with 3‐aminopropyltriethoxysilane, formaldehyde and 1‐(2‐pyridylazo)‐2‐naphthol and characterized by FT‐IR and SEM which were used as new sorbent for the preconcentration of trace amount of Pb²⁺ from various samples. Conditions of the analysis such as preconcentration factor, effect of pH, sample volume, shaking time, elution conditions and effects of interfering ions for the recovery of analyte were investigated. The adsorption capacity of the nanometer SiO₂‐PAN was found to be 168.34 μmol/g at optimum pH and the detection limit (3δ) was 0.63 µg/L. The extractant showed rapid kinetic sorption. The adsorption equilibrium of Pb²⁺ on the nanometer SiO₂‐PAN was achieved within 15 min. Adsorbed Pb²⁺ was easily eluted with 6 mL of 4 mol·L^?1 hydrochloric acid. The maximum preconcentration factor was 50. The method was applied to determine trace amounts of Pb²⁺ in different samples (water and food samples).     

In-capillary preconcentration of pirimicarb and carbendazim with a monolithic polymeric sorbent prior to separation by CZE

CZE was assayed for the separation of carbamate pesticides susceptible to protonation (Pirimicarb, Carbendazim). Different electrophoretic media with high organic contents were explored, adequate separation and resolution being achieved when a BGE based on ACN with acetic acid in the presence of SDS as an ionic additive was used. With a view to increasing the sensitivity of the method, an in-capillary SPE step prior to the electrophoretic separation was developed. We employed a monolithic polymer formed in situ within the capillary as a medium for analyte retention. The synthesized monolithic bed exhibited high porosity and allowed samples to be loaded at flow rates of about 65 microL/min by applying a pressure of 12 bar. A 5-cm length of monolithic sorbent was used to preconcentrate the target analytes from aqueous samples. The analytes retained were eluted from the polymeric phase directly in the separation capillary with the same electrophoretic medium used for their further separation by CZE. For a 15-min preconcentration time, the in-line SPE-CZE approach proposed here permitted the determination of these pesticides in drinking water at a concentration level of 0.1 microg/L, as demanded by current EU legislation.