A stir foam composed of graphene oxide,poly(ethylene glycol) and natural latex for the extraction of preservatives and antioxidant

A stir foam composed of graphene oxide, poly(ethylene glycol) and natural latex (GO-PEG-NL) was prepared for use in micro-solid phase extraction sorbent of preservative agents and antioxidants from cosmetic products. The extracted analytes were quantified by GC-MS. Under the optimized conditions, the calibration plots are linear in the concentration ranges between 5.0 μg·L^?1 to 1.0 mg·L^?1 for benzoic acid, of 10.0 μg·L^?1 to 1.0 mg·L^?1 for 2-methyl-3-isothiazolinone (MI), and between 1.0 μg·L^?1 and 1.0 mg·L^?1 for both 3-tert-butyl-4-hydroxyanisole (BHA) and 2,6-di-tert-butyl-p-hydroxytoluene (BHT). The LODs are 1.0 μg·L^?1 for benzoic acid, 5.0 μg·L^?1 for MI and 0.5 μg·L^?1 for both BHA and BHT. The stir-foam can be easily prepared, is inexpensive and well reproducible (RSDs <3%, for n?=?6). It can be re-used for up to 12 times after which extraction efficiency has dropped to 90%. The method was successfully applied to the determination of preservatives and antioxidants in cosmetic samples. Recoveries from spiked samples ranged between 94.5?±?2.1% and 99.8?±?1.8%.

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Graphical abstract A stir foam was prepared from graphene oxide, poly(ethylene glycol) and natural latex (GO-PEG-NL) and is shown to be a most viable sorbent for the microextraction of trace amounts of preservative agents and antioxidants from cosmetic products.

     

Disposable Electrodes for Capacitive Immunosensor

Disposable electrodes were fabricated by coating chromium (5 nm) and gold (200 nm) on glass strips (5.0 mm×25.4 mm) and used in a label‐free immunosensor. Human serum albumin (HSA) and its antigen (anti‐HSA) were used as a model system. Electropolymerization of o‐phenylenediamine was used for the immobilization of anti‐HSA by covalent binding. A linear relationship was obtained in the range from 1.0×10^?14 to 1.0×10^?9 M with a limit of detection of 8.0×10^?15 M. Each modified electrode can be reused up to 30 times. The developed system was applied for human serum samples and compared to Albumin BCG method.     

Unusual enniatins produced by the insect pathogenic fungus Verticillium hemipterigenum: isolation and studies on precursor-directed biosynthesis

Two new enniatins H (3) and I (4), whose substituents on 2-hydroxycarboxylic acid moieties were different from those of known compounds, were isolated, together with known enniatins B (1) and B₄ (2), from the insect pathogenic fungus Verticillium hemipterigenum BCC 1449. Structures of these compounds were elucidated by spectroscopic means. Studies on precursor-directed biosynthesis with strain BCC 1449 led to the production and identification of three analogs, enniatins G (5), C (6) and MK1688 (7), as well as the stereochemical elucidation of 3 and 4. Enniatins 1-7 were evaluated for their antiplasmodial and antimycobacterial activities.     

One-step preparation of porous copper nanowires electrode for highly sensitive and stable amperometric detection of glyphosate

A simple and sensitive amperometric method for the detection of glyphosate based on a porous copper nanowire electrode is presented. The porous nanowires were fabricated simply by a one-step electrodeposition using hydrogen bubbles generated during the deposition to produce pores. These porous nanowires provided a 1.4 times larger surface area than a porous copper film. After the fabrication process the porous copper nanowires can be applied directly as a working electrode with the same custom-built flow cell. The detection was carried out by measuring the oxidation signal of copper; this increased with the concentration of glyphosate due to dissolution of the copper from the electrode. Under optimal conditions, the responses of the sensor were linear between 0.010–5.0 µmiol L^?1, with a limit of detection of 10.0 nmol L^?1 (S/N = 3). The large surface area of the electrode minimised the corrosion effect, as observed by the remarkably stable response (95 injections of 0.20 µmol L^?1 of glyphosate were possible). When applied in order to detect glyphosate in fresh fruit and vegetable samples, the concentrations were found in the range of non-detectable to (0.104 ± 0.005) µmiol L^?1. These results indicated that the fabrication process can be used to produce a new form of working electrode for glyphosate detection.     

Multiwalled carbon nanotubes/cryogel composite, a new sorbent for determination of trace polycyclic aromatic hydrocarbons

A new cost-effective sorbent, multiwalled carbon nanotubes/poly (vinyl alcohol) cryogel composite (MWCNTs/PVA), was prepared under frozen conditions for the extraction and preconcentration of trace polycyclic aromatic hydrocarbons (PAHs) in water samples. This was followed by high performance liquid chromatography (HPLC) with fluorescence detection. The proposed method provided a high enrichment factor with an extremely high extraction efficiency (89–98%) of three spiked levels of three standard PAHs with relative standard deviations of less than 8%. The low detection limits of the method were 5, 8 and 5 ng L^{− 1} for benzo(a)anthracene, benzo(b)fluoranthene and benzo(a)pyrene, respectively. This method was successfully applied for the determination of the three PAHs in real water samples where they were found in the range of 7 to 22 ng L^{− 1}. The major advantages of MWCNTs/PVA over the commercial C₁₈ is that it can be operated at a higher loading flow rate without sorbent clogging and requires a shorter time for completion without any loss of extraction efficiency.     

A new polyethylene glycol fiber prepared by coating porous zinc electrodeposited onto silver for solid-phase microextraction of styrene

A new polyethylene glycol fiber was developed for solid-phase microextraction (SPME) of styrene by electrodepositing porous Zn film on Ag wire substrate followed by coating with polyethylene glycol sol-gel (Ag/Zn/PEG sol-gel fiber). The scanning electron micrographs of fibers surface revealed a highly porous structure. The extraction property of the developed fiber-to-styrene residue from polystyrene packaged food was investigated by headspace solid-phase microextraction (HS-SPME) and analyzed with a gas chromatograph coupled with flame ionization detection (GC-FID). The new Ag/Zn/PEG sol-gel fiber is simple to prepare, low cost, robust, has high thermal stability and long lifetime, up to 359 extractions. Repeatability of one fiber (n = 6) was in the range of 4.7-7.5% and fiber-to-fiber reproducibility (n = 4) for five concentration values were in the range 3.4-10%. This Ag/Zn/PEG sol-gel fiber was compared to two commercial SPME fibers, 75 μm carboxen/polydimethylsiloxane (CAR/PDMS) and 100 μm polydimethylsiloxane (PDMS). Under their optimum conditions, Ag/Zn/PEG sol-gel fiber showed the highest sensitivity and the lowest detection limit at 0.28 ± 0.01 ng mL⁻¹.     

Development of an on-column affinity smart polymer gel glucose sensor

An on-column affinity smart polymer gel glucose sensor was developed as a non-enzymatic glucose sensor. A copolymer of 3-acrylamidophenylboronic acid and acrylamide, the so called "smart polymer", was synthesized in situ in a 5 cm long capillary tube with a detection window to provide the on-column detection. The optical density of this semitransparent affinity smart polymer gel, coated inside the tube, decreased with increasing glucose concentration and was detected using a UV-vis detector at 500 nm. The capillary tube was incorporated into a flow injection system. Under optimum conditions, a linear dynamic range of 0.5-16.0mM with a limit of detection of 0.5mM (S/N ≥ 3) was obtained. A single coated affinity smart polymer gel had good stability for up to 250 consecutive injections with relative standard deviation of less than 5%. The analysis time for each injection was 6 min. Ten glucose samples prepared in distilled water were analyzed by the developed method and the results compared well with those obtained from the conventional dinitrosalicylic acid (DNS) method (P>0.05). Real urine samples with known glucose levels were analyzed and the developed sensor provided comparable results to those from the normal strip test technique. Acceptable percentage recoveries, ranging from 88 ± 2% to 103 ± 4% from the spiked urine sample, were obtained.     

Integrated explosive preconcentrator and electrochemical detection system for 2,4,6-trinitrotoluene (TNT) vapor

This article reports on an integrated explosive-preconcentration/electrochemical detection system for 2,4,6-trinitrotoluene (TNT) vapor. The challenges involved in such system integration are discussed. A hydrogel-coated screen-printed electrode is used for the detection of the thermally desorbed TNT from a preconcentration device using rapid square wave voltammetry. Optimization of the preconcentration system for desorption of TNT and subsequent electrochemical detection was conducted yielding a desorption temperature of 120 °C under a flow rate of 500 mL min⁻¹. Such conditions resulted in a characteristic electrochemical signal for TNT representing the multi-step reduction process. Quantitative measurements produced a linear signal dependence on TNT quantity exposed to the preconcentrator from 0.25 to 10 μg. Finally, the integrated device was successfully demonstrated using a sample of solid TNT located upstream of the preconcentrator.     

Fabrication of Nanoporous Copper Film for Electrochemical Detection of Glucose

A nanoporous copper film was fabricated on a copper wire by electrodeposition of copper/zinc alloy and chemically etching of zinc. The surface morphology was investigated by SEM. When applied to detect glucose in an amperometric flow injection system the porous copper electrode provided 12 times higher sensitivity than solid copper. It could be continuously used up to 50 times (%RSD=5.7). Different preparations of the porous film provided reproducible responses (P<0.05). Detection of glucose in E. coli cultivation medium compared well with spectrophotometric technique (P<0.05). This simple technique can produce a nanoporous electrode with good performances and can easily be applied to other metals and analytes.