Determination of trace quaternary ammonium surfactants in water by combining solid-phase extraction with surface-assisted laser desorption/ionization mass spectrometry.

This study demonstrates the feasibility of combining solid-phase extraction (SPE) with surface-assisted laser desorption/ionization (SALDI) mass spectrometry to determine trace quaternary ammonium surfactants in water. The trace surfactants in water were directly concentrated on the surface of activated carbon sorbent in SPE. The activated carbon sorbent was then mixed with the SALDI liquid for SALDI analysis. No SPE elution procedure was necessary. Experimental results indicate that the surfactants with longer chain alkyl groups exhibit higher sensitivities than those with shorter chain alkyl groups in SPE-SALDI analysis. The detection limit for hexadecyltrimethylammonium bromide is around 10 ppt in SPE-SALDI analysis by sampling 100 mL of aqueous solution, while that of tetradecyltrimethylammonium bromide is about 100 ppt. The detection limit for decyltrimethylammonium bromide and dodecyltrimethylammonium bromide is in the low-ppb range.     

Carbon nanotubes as adsorbent of solid-phase extraction and matrix for laser desorption/ionization mass spectrometry

A method with carbon nanotubes functioning both as the adsorbent of solid-phase extraction (SPE) and the matrix for matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS) to analyze small molecules in solution has been developed. In this method, 10 microL suspensions of carbon nanotubes in 50% (vol/vol) methanol were added to the sample solution to extract analytes onto surface of carbon nanotubes because of their dramatic hydrophobicity. Carbon nanotubes in solution are deposited onto the bottom of tube with centrifugation. After removing the supernatant fluid, carbon nanotubes are suspended again with dispersant and pipetted directly onto the sample target of the MALDI-MS to perform a mass spectrometric analysis. It was demonstrated by analysis of a variety of small molecules that the resolution of peaks and the efficiency of desorption/ionization on the carbon nanotubes are better than those on the activated carbon. It is found that with the addition of glycerol and sucrose to the dispersant, the intensity, the ratio of signal to noise (S/N), and the resolution of peaks for analytes by mass spectrometry increased greatly. Compared with the previously reported method by depositing sample solution onto thin layer of carbon nanotubes, it is observed that the detection limit for analytes can be enhanced about 10 to 100 times due to solid-phase extraction of analytes in solution by carbon nanotubes. An acceptable result of simultaneously quantitative analysis of three analytes in solution has been achieved. The application in determining drugs spiked into urine has also been realized.     

Rapid determination of trace nitrophenolic organics in water by combining solid-phase extraction with surface-assisted laser desorption/ionization time-of-flight mass spectrometry

A rapid technique for the screening of trace compounds in water by combining solid-phase extraction (SPE) with activated carbon surface-assisted laser desorption/ionization (SALDI) time-of-flight mass spectrometry is demonstrated. Activated carbon is used both as the sorbent in SPE and as the solid in the SALDI matrix system. This eliminates the need for an SPE elution process. After the analytes have been adsorbed on the surfaces of the activated carbon during SPE extraction, the activated carbon is directly mixed with the SALDI liquid and mass spectrometric analysis is performed. Trace phenolic compounds in water were used to demonstrate the effectiveness of the method. The detection limit for these compounds is in the ppb to ppt range.     

Molecularly imprinted polymer surfaces as solid-phase extraction sorbents for the extraction of 2-nitrophenol and isomers from environmental water

The novel surface molecularly imprinted polymer (MIP) with 2‐nitrophenol (2‐NP) as the template has been prepared and used as the adsorbent for the solid‐phase extraction (SPE). The selectivity of the polymer was checked toward several selected nitrophenols (NPs) such as 2‐NP, 3‐nitrophenol (3‐NP), 4‐nitrophenol (4‐NP) and 2,4,6‐trichlorophenol (2,4,6‐TCP). Under the optimized conditions, high sensitivity (detection limits: 0.07–0.12 ng/mL) and good reproducibility of analytes (2.3–4.8% for four cycles) were achieved. Then, the method was applied for the analysis of selected phenols in spiked tap, lake and river water samples. High recoveries (>83.3%) for nitrophenols (NPs) were obtained, but lower recoveries (<63.4%) were achieved for 2,4,6‐TCP. The method was found to be linear in the range of 1–300 ng/mL with correlation coefficients (R²) greater than 0.99 and repeatability relative standard deviation (RSD) below 7.2% in all cases. For analysis of 120 mL water samples, the method detection limits (LODs) ranged from 0.10 to 0.22 ng/mL and the limit of quantification (LOQs) from 0.33 to 0.72 ng/mL. These results showed the suitability of the MIP‐SPE method for the selective extraction of a group of structurally related isomeric compounds.     

四氮杂杯[2]芳烃[2]三嗪键合硅胶固相萃取-高效液相色谱法测定河水中硝基苯酚和己烯雌酚

基于四氮杂杯[2]芳烃[2]三嗪键合硅胶吸附剂（NC-Si）,构建了固相萃取-高效液相色谱法同时测定河水中3种硝基苯酚和己烯雌酚的新方法。考察并获得了固相萃取和液相色谱分离的优化条件：将样品溶液pH调至5,以5 mL/min上样,经自制固相萃取柱净化,2 mL氨水-甲醇（2：98,v/v）洗脱;在C8柱上以甲醇-0.1%磷酸溶液为流动相进行梯度洗脱。4种目标分析物的检出限（LOD,S/N=3）为0.03~0.3 μg/L,定量限（LOQ,S/N=10）为0.1~1.0 μg/L;加标回收率为75.5%~104.2%,相对标准偏差（RSD,n=5）小于6.3%。该方法准确、可靠,可用于河水中硝基苯酚及己烯雌酚的灵敏检测。     

Disposable Screen-Printed Electrodes (Spe) Mercury-Free for Lead Detection

ABSTRACT

Strategies to modify screen-printed electrodes (SPE) for lead determination are reported. Dithizone was mixed with graphite ink to obtain a modified screen-printed strip to detect ppb levels of lead(II) (detection limit 12 μg/l) using square wave anodic stripping voltammetry (SWASV). In addition, screen-printed electrodes were also modified by casting a few μl of a Nafion® solution onto the working electrode surface. In this case, ppb levels of lead were detected (detection limit 15 μg/1), using potentiometric stripping analysis (PSA). The addition of an ionophore to Nafion® polymer was also investigated, but this did not yield a significant improvement.     

Portable Electrochemical Sensing of Indole-3-acetic Acid Based on Self-assembled MXene and Multi-walled Carbon Nanotubes Composite Modified Screen-printed Electrode

As a typical plant hormone, indole-3-acetic acid (IAA) can regulate the biological activities including division, growth and differentiation of plant cells. In this paper, a MXene and multi-walled carbon nanotubes composite was prepared by self-assembly procedure, which was modified on screen-printed electrode (SPE) to construct a wireless portable electrochemical sensor. Electrochemical investigations of IAA were studied by cyclic voltammetry and an irreversible oxidation process could be observed. The excellent electroanalytical method of IAA was realized on the modified SPE with the detection range as 0.05–125.0 μmol/L and the detection limit as 16.7 nmol/L. The sensor was used for IAA content analysis in different part of pea seedlings with satisfactory results.     

Carbon nanotube wiring for signal amplification of electrochemical magneto immunosensors: application to myeloperoxidase detection

In this work, chronoamperometric myelo-peroxidase (MPO) detection was accomplished using immunofunctionalized magnetic microparticles (MPs), disposable carbon screen-printed electrodes (C-SPEs), and a ready-to-use commercially available tetramethylbenzidine (TMB)-based enzymatic substrate. In order to reach the limit of detection (LOD) needed to study real blood serum samples, assay performance was additionally improved by exploiting CNT wiring, which amplified the signal and decreased the LOD. The optimized assay can be performed in 30 min and yields LODs of 6 and 55 ng mL^?1 in PBS and undiluted human serum, respectively, making it useful for the identification of patients at risk of cardiovascular disease. These results demonstrate that electrode nanostructuring can be accomplished “post-assay,” which favors the development of enhanced magneto immunosensors based on the exploitation of cheap and simple SPE devices.     

Microliter Volume Determination of Cosmetic Mercury with a Partially Crosslinked Poly(4‐vinylpyridine) Modified Screen‐Printed Three‐Electrode Portable Assembly

We successfully demonstrated microliter (μL) volume determination of Mercury (Hg) using an in‐built screen‐printed three electrodes containing partially crosslinked poly(4‐vinlylpyridine) (designated as pcPVP) modified carbon‐working, carbon‐counter, and Ag⁺‐quasireference electrodes (SPE/pcPVP) in a pH 4 acetate buffer solution with 2 M KCl by using the square wave anodic stripping voltammetric (SWASV) technique. Instrumental and solution phase conditions were systematically optimized. Experiments were carried out by simply placing a 500 μL‐droplet of Hg containing real sample mixed with the base electrolyte on the SPE/pcPVP surface. The SPE/Ag⁺ quasi‐reference system shifted the Hg‐SWASV detection potential ca. 250 mV positive, but the quantitative current values were appreciably similar to that of a standard Ag/AgCl reference electrode. Under optimal condition, the calibration graph is linear in the window of 100–1000 ppb of the Hg droplet system with a detection limit of 69.5 ppb (S/N=3). Finally real sample assays were demonstrated for prohibited cosmetic Hg containing skin‐lightening agents in parallel with ICP‐OES measurements.     

Fifty years of solid-phase extraction in water analysis--historical development and overview

The use of an appropriate sample handling technique is a must in an analysis of organic micropollutants in water. The efforts to use a solid phase for the recovery of analytes from a water matrix prior to their detection have a long history. Since the first experimental trials using activated carbon filters that were performed 50 years ago, solid-phase extraction (SPE) has become an established sample preparation technique. The initial experimental applications of SPE resulted in widespread use of this technique in current water analysis and also to adoption of SPE into standardized analytical methods. During the decades of its evolution, chromatographers became aware of the advantages of SPE and, despite many innovations that appeared in the last decade, new SPE developments are still expected in the future. A brief overview of 50 years of the history of the use of SPE in organic trace analysis of water is given in presented paper.     

Comparison of different liquid chromatography methods for the determination of corticosteroids in biological matrices

Various extraction techniques can be combined with column liquid chromatography (LC) and ultraviolet (UV) or mass spectrometric (MS) detection for the determination of synthetic corticosteroids in biological matrices. Target analysis of low concentrations of 25 microg/kg of dexamethasone in feed can be performed by combining immunoaffinity chromatography (IAC) and LC with UV detection. A straightforward multi-analyte procedure is obtained by tandem solid-phase extraction (SPE) and subsequent LC-UV. However, the limits of detection for feed samples are then relatively poor, viz. 100 microg/kg. A multi-analyte method which meets modern demands of about 5 microg/kg detection limit requires one-step SPE combined with LC-MS analysis. As regards urine corticosteroids can be determined down to a level of 0.5 microg/l by either SPE-LC-MS- MS or SPE(IAC)-LC-MS.     

Construction and performance characterization of screen printed and carbon paste ion selective electrodes for potentiometric determination of naphazoline hydrochloride in pharmaceutical preparations

This paper describes the development of screen-printed (SPE) and carbon paste (CPE) sensors for the rapid and sensitive quantification of naphazoline hydrochloride (NPZ) in pharmaceutical formulations. This work compares the electroactivity of conventional carbon paste and screen-printed carbon paste electrodes towards potentiometric titration of NPZ. The repeatability and accuracy of measurements performed in the analysis of these pharmaceutical matrices using new screen printed sensors were evaluated. The influence of the electrode composition, conditioning time of the electrode and pH of the test solution, on the electrode performance were investigated. The drug electrode showed Nernstain responses in the concentration range from 1 × 10(-6) to 1 × 10(-2) mol L(-1) with slopes of 57.5 ± 1.3 and 55.9 ± 1.6 mV per decade for SPE and CPE, respectively, and was found to be very precise and usable within the pH range 3-8. These sensors exhibited a fast response time (about 3 s for both SPE and CPE, respectively), a low detection limit (3.5 × 10(-6) and 1.5 × 10(-6) M for SPE and CPE, respectively), a long lifetime (3 and 2 months for SPE and CPE, respectively) and good stability. The selectivity of the electrode toward a large number of inorganic cations, sugars and amino acids was tested. It was applied to potentiometric determination of NPZ in pure state and pharmaceutical preparation under batch conditions. The percentage recovery values for the assay of NPZ in tablets (relative standard deviations ≤0.3% for n = 4) were compared well with those obtained by the official method.     

Solid-phase extraction for metabolomic analysis of high-salinity samples by capillary electrophoresis-mass spectrometry

Environmental samples such as soil solutions contain inorganic ions such as NH4(+), K(+), Na(+), NO3(-), and PO4(3-) in high concentrations, which must be removed prior to capillary electrophoresis-mass spectrometry analysis to obtain accurate results. However, the separation of these inorganic ions from ionic metabolites, which are the target compounds in capillary electrophoresis-mass spectrometry analysis, is difficult because the physicochemical properties of the inorganic ions are similar to those of the ionic metabolites. In this study, we used various solid-phase extraction (SPE) columns for the purification of the samples containing inorganic ions in high concentrations. We found that cation-exchange SPE columns successfully filtered out the inorganic ions while retaining most of the organic compounds, which were easily collected with high recovery rates. In addition, 17 cationic metabolites in the soil solution were quantified by CE-MS analysis following the SPE purification process. The results suggest that our method can be used to analyze other environmental samples containing inorganic ions in high concentrations.     

Electrodes supported on ion-exchange membranes as sensors in gases and low-conductivity solvents

An electroanalytical sensor is proposed that is suitable for the detection of electroactive analytes present in gases or low-conductivity solvents where supporting electrolytes cannot be introduced. It consists of a porous working electrode supported on one surface of a cationic ion-exchange membrane (Nafion 417), the other surface of which is in contact with an electrolyte solution containing the counter and reference electrodes. Such an ion-exchange membrane replaces a conventional supporting electrolyte dissolved in the analyte sample and can be regarded as a solid polymer electrolyte (SPE) confined in the close neighbourhood of the working electrode. Alternative procedures followed for coating SPE membranes with various materials (Pt, Au, C or Hg) are described, together with the general properties displayed by the resulting composite electrodes in analyte-free gaseous or liquid media. These assemblies have been used as both voltammetric and amperometric sensors for electroactive analytes present in gases and in aqueous or organic solvents with no supporting electrolyte. The results indicate that their performance is similar to that expected on conventional electrodes, the only difference being a slightly lower degree of reversibility for the electrode processes investigated. Detection limits for some analytes were calculated and the use of SPE electrodes as sensors suitable for the continuous monitoring of electroactive analytes dispersed in gases or non-conductive liquids is reported. Preliminary attempts to use these assemblies for the determination of trace metals in low-conductivity solvents by anodic stripping voltammetry are discussed.     

Real‐Time Nitrophenol Detection Using Single‐Walled Carbon Nanotube Based Devices

Single‐walled carbon nanotube (SWNT) based devices have been developed for the real‐time detection of nitrophenols in aqueous solution. SWNTs are assembled to electrodes using AC dielectrophoresis technique. The SWNT devices exhibit not only high sensitivity to nitrophenol compounds, but also good reusability. Charge transfer between nitro group and SWNTs, and the metal‐nanotube interface modification are hypothesized to be the possible origins of conductance change. These results indicated that the SWNT devices can be utilized as a simple, low cost, sensitive, and reusable platform for real‐time detection of nitrophenol compounds.     

High-performance liquid chromatographic analysis with electrochemical detection for residues of explosives in water samples around a former ammunition plant

Electrochemical detection (ED) in the oxidative and reductive mode was applied to the analysis of nitroaromatics, nitramines, aminoaromatics and nitrophenols in groundwater samples from the surroundings of a former ammunition plant. Settings for working potential and eluent composition were optimized in terms of detection limit, linearity and selectivity. The results were compared with those obtained by UV detection and the advantages of combined UV-ED detection for the analysis of complex samples are shown.     

固相萃取吸附材料在植物激素样品前处理中的应用新进展

植物激素在植物生长过程中具有重要作用,调节植物生长、发育及抗逆的各个过程。植物激素超微精准定量分析一直是植物生理学研究的瓶颈问题。植物激素的准确、高效检测目前大多是基于液相色谱-串联质谱联用技术。样品前处理是植物激素色谱-质谱分析中必不可少的一个步骤,直接影响后续检测方法的灵敏度和准确性。在植物激素各种前处理方法中,固相萃取(SPE)技术应用非常广泛。在萃取小柱基础上发展了多种新形式(分散固相萃取、磁性固相萃取、固相微萃取等,称之为SPE相关方法)。在上述SPE相关方法中,吸附材料的选择均是关键因素,决定了样品前处理过程的目标物提取、净化和富集效果。碳基材料(包括碳纳米管、石墨烯、碳氮化合物等)和有机骨架材料(包括金属有机骨架、共价有机材料)拥有结构可设计、比表面积大、稳定性良好等特性,非常适合作为吸附材料。分子印迹聚合物和超分子化合物依靠主-客体特异性分子识别作用,能显著提高样品前处理方法的选择性。本文重点针对植物激素样品前处理中的SPE技术,综述了近5年来上述几类功能化吸附材料的最新应用进展,并对其发展趋势进行展望。     

Optimization of microfabricated nanoliter-scale solid-phase extraction device for detection of gel-separated proteins in low abundance by matrix-assisted laser desorption/ionization mass spectrometry

A nano-scale solid-phase extraction (SPE) device was developed for the detection of gel-separated proteins in low abundance by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) with a simplified microfabrication technology. By using SU-8 photoresist instead of epoxy glue to connect the microchannel and transfer capillary, polymeric contaminant signals in MS analysis were significantly reduced. Micro SPE columns with different capacities and geometric characteristics were investigated in order to increase the detection sensitivity and decrease spot size for MALDI-TOF-MS analysis. It is shown that enhancements in sensitivities for the detection of proteins in low abundance were correlated with the reduction in column capacity and increase in column aspect ratio. Fifty nanoliters of matrix solution were sufficient to elute the sample completely from the optimized micro SPE column with 3.5 nL capacity. The mass spectrum of a 5 fmol in-gel tryptic digest of bovine serum albumin (BSA), processed by the micro SPE column, demonstrated that 29 peptides matched the protein giving a sequence coverage of 51%, which was better than that obtained from analysis of 25 fmol of the same sample prepared by the dried-droplet method. With the micro SPE column treatment of 2 microL of digestion supernatant of a gel spot of the IQGAP1 protein, 15 peptides were detected from the mass spectrum with the highest individual score of 111, while, with a ZipTip procedure, only nine peaks were detected with the highest individual score of 71. Analytical results demonstrated that this approach greatly improved the sequence coverage and identification specificity for the tested protein. It can serve as a very useful tool in proteomics studies, especially for low abundance proteins.     

Determination of Cadmium,Nickel, Lead,and Zinc in Fish Tissue by Flame and Graphite Furnace Atomic Absorption after Extraction with Pyrrolidine Dithiocarbamate and Activated Carbon

A solid phase extraction (SPE) technique using an activated carbon column was developed for the extraction of trace levels of Cd, Ni, Pb, and Zn in aqueous solution which was obtained from the digestion of fish tissue. Ammonium pyrrolidin edithiocarbamate (APDC) was used to form metallic complexes that could be retained in a SPE column which was packed with powder activated carbon. The analytes were eluted from the column by nitric acid in acetone. The metal concentrations were determined by flame and graphite atomic absorption spectroscopy. The effects of flow rate, APDC concentration, and pH were investigated. The proposed method was validated. The method detection limits were 11.7, 13.4, 10.1, and 25.3 µg kg^?1 for Cd, Ni, Pb, and Zn, respectively. The recoveries and RSDs were within the range of 81.9–101.1% and 0.6–6.0%, respectively. The method has potential merit for heavy metal determination in fish tissue.     

Hemimicelle capped functionalized carbon nanotubes-based nanosized solid-phase extraction of arsenic from environmental water samples

The end functionalization of CNTs can introduce oxygen-containing negatively functional groups such as -COOH, -OH, or -CO on their surface site. If cationic surfactant such as cetyltrimethylammonium chloride (CTAC) was added to the functionalized CNTs, then interactions such as hydrophobic and ionic may lead to formation of hemimicelle/admicelle aggregates on the CNTs, a new kind of adsorbents, namely, the hemimicelle capped CMMWCNTs, is obtained. The application of the hemimicelle capped carbon nanotubes-based nanosized solid-phase extraction (SPE) adsorbents in environmental analysis is reported for the first time using arsenic as model target. The effect of adsorption and desorption conditions for arsenic including the amount of surfactant, initial pH of sample solution, the ultrasonic time of sample solution, the amount of electrolyte, flow rate, eluent and its amount were investigated and optimized prior to its determination by atomic fluorescence spectrophotometry (AFS). Arsenic can be quantitatively retained on the hemimicelle capped CMMWCNTs at pH 5-6 from sample volume up to 500 mL and then eluted completely with 2 mol L⁻¹ HNO₃ in the presence of 10 mg L⁻¹ CTAC. The method detection limit for arsenic determination with AFS detection was 2 ng L⁻¹, and the relative standard deviation (RSD, n = 11) was 5.3% at the 0.5 μg L⁻¹ level. The recoveries of arsenic in the spiked environmental water samples ranged from 94% to 104.29% with 500 mL of water sample. The proposed method has been applied successfully to the analysis of arsenic in aqueous environmental samples, which demonstrates the hemimicelle capped CMMWCNTs can be an excellent SPE adsorbents for arsenic pretreatment and enrichment from real water samples.