Inorganic Interferences Research Articles

Simultaneous determination of environmental endocrine disruptors bisphenol A and 4-nitrophenol bleached from food-contacting materials using the spin-ladder compound La2Cu2O5 modified glassy carbon electrode

Environmental endocrine-disrupting chemicals, Bisphenol A (BPA) and 4-Nitrophenol (4-NP), pose significant risks to reproductive health in both animals and humans. Here, we introduce the first utilization of the 4-leg spin ladder compound La2Cu2O5 as an electrode material for electrochemical sensor. Nanostructured La2Cu2O5 was synthesized via a straightforward Sol-Gel method and thoroughly characterized using X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and powder X-ray diffraction. La2Cu2O5 nanoparticles modified glassy carbon electrode (GCE) exhibited a significant electrocatalytic activity towards the oxidation of BPA and 4-NP in phosphate buffer saline (pH 7.0). Square wave voltammetry studies revealed lowest detection limits of 3 nM for BPA and 2.6 nM for 4-NP over a wider concentration range of 0.01–500 μM. Notably, this study marks the first utilization of La2Cu2O5 for simultaneous electrochemical detection of BPA and 4-NP, demonstrating its potential in this field. Furthermore, the sensor exhibited good sensitivity, reproducibility, and selectivity towards BPA and 4-NP, even in the presence of similar potential organic and inorganic interferents. Additionally, the newly developed sensor enabled simultaneous quantification of BPA and 4-NP in real samples such as packaged milk, river water, and plastic bottles, achieving recovery rates above 95%. Importantly, our results underscore the leaching of BPA into water from thin and thick plastics at elevated temperatures (40 °C–80 °C), emphasizing the utility of the proposed sensor for rapid and simultaneous detection of BPA and 4-NP in environmental and food matrices.

Continuous precision separation of gold using a metal–organic framework/polymer composite

Critical metals of environmental and economic relevance can be found within complex mixtures, such as mine tailings, electronic waste and wastewater, at trace amounts. Specifically, gold is a critical metal that carries desired redox active properties in various applications, including modern electronics, medicine and chemical catalysis. Here we report the structuring of sub-micron Fe-BTC/PpPDA crystallites into larger 250 μm or 500 μm granules for continuous packed bed experiments for the precision separation of gold. The Structured Fe-BTC/PpPDA is highly crystalline and porous with a BET surface area of 750 m2 g−1. Further, the hybrid nanocomposite material maintains its selectivity for gold ions over common inorganic interferents. The structuring approach reported prevents excessive pressure drop and ensures stability over time and operation in a packed bed column. Further, we demonstrate that the Structured Fe-BTC/PpPDA can concentrate at least 42 wt% of gold under a dynamic continuous flow operation. These findings highlight the potential of Structured Fe-BTC/PpPDA for practical applications in industry, particularly in the selective capture of gold from complex mixtures.

Multi-analyte fluorescence sensing based on a post-synthetically functionalized two-dimensional Zn-MOF nanosheets featuring excited-state proton transfer process

Covalent post-synthetic modification of metal–organic frameworks (MOFs) represents an underexplored but promising avenue for allowing the addition of specific fluorescent recognition elements to produce the novel MOF-based sensory materials with multiple-analyte detection capability. Here, an excited-state proton transfer (ESPT) active sensor 2D-Zn-NS-P was designed and constructed by covalent post-synthetic incorporation of the excited-state tautomeric 2-hydroxypyridine moiety into the ultrasonically exfoliated amino-tagged 2D Zn-MOF nanosheets (2D-Zn-NS). The water-mediated ESPT process facilitates the highly accessible active sites incorporated on the surface of 2D-Zn-NS-P to specifically respond to the presence of water in common organic solvents via fluorescence turn-on behavior, and accurate quantification of trace amount of water in acetonitrile, acetone and ethanol was established using the as-synthesized nanosheet sensor with the detection sensitivity (<0.01% v/v) superior to the conventional Karl Fischer titration. Upon exposure to Fe3+ or Cr2O72−, the intense blue emission of the aqueous colloidal dispersion of 2D-Zn-NS-P was selectively quenched even in the coexistence of common inorganic interferents. The prohibition of the water-mediated ESPT process and local emission, induced by the coordination of ESPT fluorophore with Fe3+ or by Cr2O72− competitively absorbs the excitation energy, was proposed to responsible for the fluorescence turn-off sensing of the respective analytes. The present study offers the attractive prospect to develop the ESPT-based fluorescent MOF nanosheets by covalent post-synthetic modification strategy as multi-functional sensors for detection of target analytes.

Novel potentiometric carbon paste electrodes for trace detection of uranyl(II) ions in petroleum water samples

Two different phosphine sulfide derivatives have been explored as electroactive materials to modify carbon paste electrodes for the accurate detection of uranyl(II) ions. The optimized electrodes based on triphenylphosphine sulfide (L1) and triisobutylphosphine sulfide (L2) responded linearly towards uranyl(II) ions within the range of 1.0 × 10-7 – 1.0 × 10-1 M. Good sensitivity (29.32 ± 0.53 and 27.99 ± 0.61 mV per decade) and detection capability up to 7.9 × 10-8 and 1.0 × 10-7 M uranyl(II) were observed for L1- and L2-based electrodes, respectively. The effect of solution temperature on uranyl(II) determination was studied within 10–60 °C. Selectivity studies showed that the electrodes are capable to discriminate uranyl(II) ions over a large number of possible co-existing inorganic interferents. Moreover, they exhibited speedy response, thermal and long-term stability, and significant reusability. Petroleum water samples spiked with uranyl(II) ions were analyzed utilizing the developed electrodes where good recovery and accuracy were achieved, demonstrating the real-life applicability of the developed electrodes.

Ion Exchange MIEX® GOLD Resin as a Promising Sorbent for the Removal of PFAS Compounds

Per- and polyfluoroalkyl substances (PFASs) are synthetic compounds, which have been widely produced, used, and recently identified as extremely toxic chemicals, and are responsible for serious environmental and human health risks. In this study, the removal efficiency of MIEX® GOLD resin was tested against six PFAS compounds including perfluorobutanoic acid (PFBA), perfluorobutanesulfonic acid (PFBS), perfluorohexanoic acid (PFHxA), perfluorohexanesulfonic acid (PFHxS), perfluorooctanoic acid (PFOA), and perfluorooctanesulfonic acid (PFOS). The removal of PFASs and the regeneration of resin (NaCl-saturated methanol) were achieved via adsorption and desorption mechanisms. In all cases, the removal efficiency was greater than 99% where the volume ratio of 1 ppm PFAS to resin was maintained at 50-bed volume. Furthermore, the adsorption capacity of MIEX® GOLD resin was studied for PFOA and PFHxS and achieved 1.05 ± 0.01 g PFOA adsorption and 1.01 ± 0.04 g PFHxS adsorption per gram of resin. In addition, a detailed study on the interference of natural organic matter (NOM) and inorganic matter was carried out against PFHxA, PFOA, and PFOS. The presence of 10 ppm NOM (5 ppm tannic acid + 5 ppm humic acid) and 25 ppm inorganic matter (5 ppm nitrate + 20 ppm sulfate) showed no noticeable interference in the removal of selected PFAS compounds. Compared to sulfonic acid-containing PFASs, the interference of organic and inorganic matter on carboxylic acid-containing PFASs was slightly higher. The regeneration of PFAS-adsorbed resin was studied using a mixed solution containing 70% methanol and saturated NaCl. Desorption of PFHxS, PFOS, and PFOA was found to be 98.3, 100, and 43.3%, respectively. The results again indicate that the resin regeneration is strongly affected by the functional group of PFASs; i.e., resin with sulfonic acid-containing PFAS is much easier to regenerate than carboxylic acid-containing PFAS compounds. All the PFAS analyses were performed by using mass spectroscopy and liquid chromatography–mass spectroscopy. In conclusion, this study confirms the remarkable efficiency of MIEX® GOLD resin in removing PFAS compounds, even in the presence of a high concentration of organic and inorganic interferences, and its capacity to be regenerated for repeated usage. These advantages make MIEX® GOLD a promising product for the remediation of PFAS-contaminated water. This study in the broader sense proves that MIEX® GOLD is a promising adsorbent and provides the ground for future study to treat contaminated groundwater.

Microplastic isolation method for wastewater and sludge samples by removal of excess organic and inorganic interferences

The isolation of microplastics from other organic and inorganic contents is a major hurdle to the effective quantification and characterization of microplastics in wastewater and biosolids samples. As a result, a well-established and standardized isolation method is vital for the analysis of microplastics. In this study, we evaluated biological hydrolysis, enzymatic hydrolysis, wet peroxidation and ethylenediaminetetraacetic acid treatment for microplastics isolation and demonstrated that the integration of these processes can effectively remove organic and inorganic contents to provide a clear microscope view for microplastics identification from wastewater and sludge samples. To the best of our knowledge, this study is the first to introduce biological hydrolysis and ethylenediaminetetraacetic acid treatment for the isolation of microplastics from environmental samples. The results reported could facilitate the establishment of a standardized procedure for microplastic isolation from wastewater and biosolid samples.

Tetraphenylporphyrin Decorated Bi2MoO6 Nanocomposite: Its Twin Affinity of Oxygen Reduction Reaction and Electrochemical Detection of 4-Nitrophenol.

A selective electrode for oxygen reduction reaction (ORR) and electrocatalytic reduction of 4-nitrophenol (p-NP) was fabricated on a glassy carbon electrode using organic-inorganic Bi2MoO6/H2TPP nanocomposites with different weight percentages of tetraphenylporphyrin, synthesized by the solvothermal process. Materials thus synthesized were characterized through UV-Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) analysis. The electrocatalytic performance of the modified electrode toward ORR in the 0.1 M KOH solution, the onset potential Eonset (0.942 V), E1/2 (0.704 V) vs RHE, Jd (-5.545 mA cm-2), and n = 4 physicochemical parameters were well appreciable. It exhibits good catalytic activity toward ORR through a four-electron pathway with excellent stability and high active site density, and thus, the in situ Porphy-decorated metal oxide system facilitates the electron transport process. High selectivity and efficacy for the oxygen reduction reaction (ORR) are a significant measure for several energy-converting applications. The decorated electrode, glassy carbon electrode (GCE)/Bi2MoO6/3 wt % Porphy, serves as an electrochemical sensor that exhibited good sensitivity (0.4683 μAμM-1 cm-2), good reproducibility, a low detection limit (0.0940 μM), and long-term stability in the aqueous phase without any appreciable effect in the presence of some common organic and inorganic interferences for the detection of p-NP in a linear concentration range of 0.5-350 μM. Therefore, the material performs as an effective electrode for both the ORR and the electrocatalytic reduction of p-NP with real matrix samples at room conditions.

Electrochemical detection of 4-nitrophenol on nanostructured CuBi2O4 with plausible mechanism supported by DFT calculations

In this report, copper bismuth oxide (CuBi2O4), a ternary oxide is used for the electrochemical detection of 4-nitrophenol (4-NP). 4-NP is an organic pollutant which is extremely toxic and hazardous to environment. Herein, CuBi2O4 nanorods are prepared hydrothermally followed by electrode fabrication using drop casting method. Structural, morphological studies of CuBi2O4 and electrochemical characterizations pertaining to its performance for electrochemical detection of 4-NP are performed. The electrode has displayed the sensitivity of 56.16 μA μΜ−1 cm−2 with limit of detection (LoD) of 0.61 μM. It displayed high selectivity against several organic and inorganic interferences. The feasibility of CuBi2O4 modified electrode for real water samples is tested and obtained good recovery values. The detailed mechanism involved in the electrochemical detection of 4-NP is proposed and validated with computational studies. Density functional theory (DFT) calculations are performed on the optimized molecules involved in the electrochemical detection of 4-NP confirming CuBi2O4 acting as electron donor while 4-NP as electron acceptor. Further, natural bond orbital (NBO) calculations of 4-NP show a charge of − 0.251 a.u. on -NO2 group and + 0.251 a.u. on the rest of the molecule indicating 4-NP undergoes facile nucleophilic attack. The electrostatic potential (ESP) mapping of 4-NP blue shaded regions justifies its favorable behavior towards nucleophilic attack. Apart from this, UV-Vis spectroscopy is used to study the catalytic reduction of 4-NP using NaBH4. This study reveals that CuBi2O4 is promising material for the electrochemical detection of 4-NP. Also, further modifications of CuBi2O4 can be explored for electrochemical sensing and catalytic performance.

A reusable Gemini surfactant-based electrochemical sensor for As(III) detection

ABSTRACT KSA is one of the rising Gulf regions with many industrial developments, including petrochemicals, mining, agriculture, and pharmaceuticals. These activities have a direct impact on the climate and water resources. A Gemini surfactant has been used for enabling the electrochemical detection of As(III) at the indium tin oxide (ITO) electrode. Monitoring of As(III) in the presence of Gemini surfactant compared either in the presence of cetyltrimethylammonium bromide (CTAB) surfactant or in the absence of any surfactant was studied. The results showed that the cyclic voltammetry (CV) response of 70 ppb of As(III) at bare ITO in the absence of any surfactant shows a background response. In contrast, 1 mM of CTAB showed a weak oxidation peak at 630 mV without any cathodic peak. On the other hand, the capability of monitoring As(III) species in the presence of Gemini surfactant in neutral pH showed high sensitivity with a low limit of detection of 0.88 ppb. The calibration plot was fit using a linear, exponential Langmuir model. Thus, the bare ITO electrode itself could not detect the As(III); while, the use of the Gemini surfactant enhances the electrochemical activity of ITO towards the As(III). The efficiency of this Gemini surfactant is higher than that of CTAB. The presented sensor showed high reversibility that could conduct without a decrease in the sensor activity. Furthermore, this sensor’s selectivity was verified based on the detection of As(III) in the existence of a high concentration of various organic and inorganic interferences.

A New Sensing Strategy for Determination of Tamoxifen Using Fe3O4/Graphene-Ionic Liquid Nanocomposite Amplified Paste Electrode

Monitoring tamoxifen as an anticancer drug with high side effects is so important in the chemotropic process. In this regard, a fast and simple electrochemical sensor was fabricated using a carbon paste electrode (CPE) modified with 1-octyl-3-methylimidazolium chloride (OMIC) and Fe3O4/graphene nanocomposite and utilized for tamoxifen monitoring. Fe3O4/graphene nanocomposite (Fe3O4-GR) was synthesized by a one-pot synthesis approach, following by then characterized by FESEM and EDS methods. The Fe3O4-GR/OMIC/CPE offered catalytic activity on the redox reaction of tamoxifen and enhanced its oxidation current about 4.59 times. Moreover, the high electrical conductivity of mediators aided the reducing the oxidation potential of tamoxifen (about 80 mV) compared with the unmodified electrode. In addition, Fe3O4-GR/OMIC/CPE showed a linear dynamic range of 0.01 µM – 150 µM with a detection limit of 7.0 nM for sensing of tamoxifen using the square wave voltammetric method. Furthermore, Fe3O4-GR/OMIC/CPE displayed a superior ability for sensing tamoxifen in real samples with an acceptable recovery range. In brief, Fe3O4-GR/OMIC/CPE provided good selectivity for sensing f tamoxifen in an aqueous solution in the presence of organic and inorganic interferences.

Potentiometric Surfactant Sensor Based on 1,3-Dihexadecyl-1H-benzo[d]imidazol-3-ium for Anionic Surfactants in Detergents and Household Care Products.

A 1,3-dihexadecyl-1H-benzo[d]imidazol-3-ium-tetraphenylborate (DHBI-TPB) ion-pair implemented in DHBI-TPB surfactant sensor was used for the potentiometric quantification of anionic surfactants in detergents and commercial household care products. The DHBI-TPB ion-pair was characterized by FTIR spectroscopy and computational analysis which revealed a crucial contribution of the C–H∙∙∙π contacts for the optimal complex formation. The DHBI-TPB sensor potentiometric response showed excellent analytical properties and Nernstian slope for SDS (60.1 mV/decade) with LOD 3.2 × 10−7 M; and DBS (58.4 mV/decade) with LOD 6.1 × 10−7 M was obtained. The sensor possesses exceptional resistance to different organic and inorganic interferences in broad pH (2–10) range. DMIC used as a titrant demonstrated superior analytical performances for potentiometric titrations of SDS, compared to other tested cationic surfactants (DMIC > CTAB > CPC > Hyamine 1622). The combination of DHBI-TPB sensor and DMIC was successfully employed to perform titrations of the highly soluble alkane sulfonate homologues. Nonionic surfactants (increased concentration and number of EO groups) had a negative impact on anionic surfactant titration curves and a signal change. The DHBI-TPB sensor was effectively employed for the determination of technical grade anionic surfactants presenting the recoveries from 99.5 to 101.3%. The sensor was applied on twelve powered samples as well as liquid-gel and handwashing home care detergents containing anionic surfactants. The obtained results showed good agreement compared to the outcomes measured by ISE surfactant sensor and a two-phase titration method. The developed DHBI-TPB surfactant sensor could be used for quality control in industry and has great potential in environmental monitoring.

Ultraviolet-transparent low-index layers for antireflective coatings.

Nanostructured low-index layers are useful as the last layers of antireflective (AR) coatings because they can broaden their spectral ranges and improve the performance for oblique light incidence. Structuring of evaporated organic layers by plasma opens a route to produce inorganic interference stacks and low-index layers in the same vacuum process. The organic material uracil has been investigated as a template material for AR nanostructures. An additional plasma-treatment step was added to the manufacturing process, which decreases the organic fraction of the coating substantially. As a result, a better environmental stability and higher transmission in the ultraviolet range was achieved.

Highly Sensitive AdSV Method for Fe(III) Determination in Presence of Solochrome Violet RS on Renewable Amalgam Film Electrode

AbstractThe new DP AdSV method for high sensitive Fe(III) determination in the presence of Solochrome Violet RS was developed. The use of an innovative renewable amalgam film electrode Hg(Ag)FE allowed to obtain high sensitivity and significantly minimize the mercury consumption. The best results were obtained for surface area of Hg(Ag)FE equal to 11.8 mm2. Instrumental parameters were optimized. The optimal results were obtained using differential pulse technique for the following values: sampling and waiting time ts=tw=10 ms, step potential Es=5 mV, pulse amplitude ΔE=50 mV. Measurements were conducted in 0.05 M acetate buffer (pH 5.6), the concentration of SVRS was equal to 5 μM. Deposition step was carried out at the potential −400 mV for 20 s. Calculated detection limit for 40 s preconcentration time was equal to 1.4 nM (78 ng L−1). The influence of the common in environment, organic and inorganic interferences was studied. The developed method for Fe(III) determination was successfully applied and validated by investigation of certified reference material SPS‐SW2 Batch 118 and recovery of Fe(III) from various spiked samples as snow, tap water and bottom sediments. The repeatability (for 50 nM of Fe(III)) of the developed method expressed as CV was equal 3.1 % (n=5).

Solid-phase microextraction of heavy metals in natural water with a polypyrrole/carbon nanotube/1, 10–phenanthroline composite sorbent material

A simple and sensitive method for simultaneous microextraction and determination of heavy metals using a new direct immersion solid-phase microextraction (DI–SPME) sorbent material combined with inductively coupled plasma mass spectrometry (ICP–MS) was investigated. In this method, sorbent coating composites were prepared by simultaneous electropolymerization of pyrrole on pencil lead in the presence of carbon nanotubes (CNTs) and different metal chelating ligands. Among the coatings evaluated, a polypyrrole coating with entrapped CNTs and the chelator 1, 10 phenanthroline allowed the determination of silver, cadmium, cobalt, iron, nickel, lead, and zinc. Parameters influencing microextraction efficiency including pH, extraction time, and desorption time were optimized. The linear dynamic ranges were 1–1000 μg L−1 for Ag, 1–750 μg L−1 for Cd, Pb, and Zn, and 1–500 μg L−1 for Co, Fe, and Ni with limits of detection of 0.012–0.163 μg L−1 and limits of quantification of 0.039–0.542 μg L−1. The relative standard deviations (RSDs, n = 5) ranged from 1.85% to 5.01%. The effect of inorganic interferences on the determination of the heavy metals also was examined and finally, the method was successfully applied for the determination of heavy metals in real water samples.

Electrochemical determination of naproxen in the presence of acetaminophen using a carbon paste electrode modified with activated carbon nanoparticles

In this study, cyclic voltammetry and differential pulse voltammetry were used to determine the electrochemical properties and concentration of naproxen in pharmaceutical formulation and human serum samples by using a carbon paste electrode modified with activated carbon nanoparticles. Optimum conditions were obtained at an electrode with 0.005 g activated carbon nanoparticles in a phosphate buffer solution of pH 6 as a supporting electrolyte. Linear calibration curves were obtained in the range of 0.1–120 μM, and the detection limit of naproxen determined was 0.0234 μM. The modified electrode shows good selectivity for naproxen in the presence of some organic and inorganic interferences and very good precision in real samples. Finally, naproxen was measured in the presence of acetaminophen.

Complementary online aerosol mass spectrometry and offline FT-IR spectroscopy measurements: Prospects and challenges for the analysis of anthropogenic aerosol particle emissions

The aerosol mass spectrometer (AMS) is well established in investigating highly time-resolved dynamics of submicron aerosol chemical composition including organic aerosol (OA). However, interpretation of mass spectra on molecular level is limited due to strong fragmentation of organic substances and potential reactions inside the AMS ion chamber. Results from complementary filter-based FT-IR absorption measurements were used to explain features in high-resolution AMS mass spectra of different types of OA (e.g. cooking OA, cigarette smoking OA, wood burning OA). Using this approach some AMS fragment ions were validated in this study as appropriate and rather specific markers for a certain class of organic compounds for all particle types under investigation. These markers can therefore be used to get deeper insights in the chemical composition of OA based on AMS mass spectra in upcoming studies. However, the specificity of other fragment ions such as C2H4O2+ (m/z 60.02114) remains ambiguous. In such cases, complementary FT-IR measurements allow the interpretation of highly time-resolved AMS mass spectra at the level of molecular functional groups. Furthermore, this study discusses the challenges in reducing inorganic interferences (e.g. from water and ammonium salts) in FT-IR spectra of atmospheric aerosols to decrease spectral uncertainties for better comparisons and, thus, to get more robust results.

Comparison of sample preparation methods for the GC⿿MS analysis of monoethanolamine (MEA) degradation products generated during post-combustion capture of CO2

As the development of chemical absorption technology for post-combustion capture (PCC) of CO2 from coal-fired power station flue gases proceeds towards commercial deployment, the focus on establishing a thorough understanding of the degradation of the aqueous amine absorbents is increasing. However, there is a need to develop and demonstrate robust analytical methods that are capable of measuring the concentrations of amine degradation products in aqueous monoethanolamine (MEA) matrix during pilot-scale PCC. In this study, sample cleanup and derivatisation methods that enable reliable and robust analysis of MEA degradation products by GC⿿MS are described. Two sample cleanup methods were evaluated: dehydration (by rotary evaporation and molecular sieves) and cation exchange. The cation exchange sample preparation method was preferred for the analysis of organic degradation products in these samples because it achieved higher recovery and repeatability of GC⿿MS measurements than those obtained with the dehydration method. Furthermore, the cation exchange method resulted in less continued amine degradation during subsequent analysis steps because of its ability to separate acidic analytes from basic analytes, as well as to remove some inorganic interferences. Further improvement of the sensitivity, repeatability and accuracy of this GC⿿MS analytical method can be accomplished by: (a) increasing the scale of the cation exchange and/or derivatisation procedures; (b) optimizing the derivatisation reaction conditions; and (c) using a narrower bore (e.g. 0.25mm ID) GC⿿MS column. The proposed cation exchange and derivatisation procedures can be readily adopted for the quantification of organic degradation products in other aqueous amine absorbents to provide important insights into the degradation of amine absorbents during PCC of CO2.

Low-Range Detection of the Phosphate Group by a Molecularly Imprinted Polymer-Modified Carbon Paste Electrode

A series of size-selective polymeric sensors for the phosphate group was designed and synthesized using the molecularly imprinted polymer (MIP) technique based on the noncovalent interaction of the template dipentyl phosphate with the functional monomer methacrylic acid. Very low-range specific electrochemical detection of phosphate molecules was performed by square wave voltammetry with a modified carbon paste electrode (CPE). Calibration curves were obtained within the linear range of 20-300 nmol L <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> for all modified CPEs, with the lowest detection limit determined as 8.82 nmol L <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . Potential inorganic interferents, such as carbonate, nitrate and sulfate ions, were investigated and no signal disturbance was observed for relative concentrations 100 times higher than the phosphate concentration. Furthermore, the modified electrodes also showed good selectivity for phosphate molecules containing alkyl chains up to five carbon atoms. The selectivity study confirmed that imprinted sites were successfully synthesized and only structures that are the same size or smaller than those of the template molecule are selected by maximizing intermolecular interactions at the MIP binding site. Moreover, the sensors presented good stability, maintaining the same degree of selectivity for several months. These sensors were also applied in the determination of phosphate in a cola soft drink.

Polypyrrole-based bilayer nitrate amperometric biosensor with an integrated permselective poly- ortho-phenylenediamine layer for exclusion of inorganic interferences

A bilayer amperometric nitrate biosensor with an integrated permselective layer has been developed for exclusion of inorganic anion and cation interferences. The inner PPy(polypyrrole)–NaR–NADH layer of the biosensor is formed by galvanostatic polymerization of pyrrole (Py) in presence of nitrate reductase (NaR) and nicotinamide adenine dinucleotide (NADH), followed by formation of the outer permselective poly- ortho-phenylenediamine (P- o-PDA) layer by potentiodynamic polymerization of ortho-phenylenediamine ( o-PDA). The exclusion efficiency ( E eff) of the outer layer in rejecting inorganic cation and anion interferences is evaluated by a new proposed relationship. 73–87% and 47–84% of anion and cation interferences, respectively, were efficiently rejected with the permselective layer. Further improvement in the exclusion efficiency for cations was accomplished by combining the use of the outer layer with the addition of 1 mM EDTA into the measurement solution. The addition of EDTA improved the E eff achieved for cation rejection by 10–40% to give net E eff of 89–94%. The inclusion of the outer layer also aided the retention of NaR and NADH in the inner PPy–NaR–NADH layer and, hence, enabled improved amperometric detection of nitrate, achieving a detection limit of 0.20 μM and a linear concentration range of 10–500 μM with a 3.4% rsd ( n = 10).

Pyrolysis-molecular beam mass spectrometry to characterize soil organic matter composition in chemically isolated fractions from differing land uses

Today’s questions concerning the role of soil organic matter (SOM) in soil fertility, ecosystem functioning and global change can only be addressed through knowledge of the controls on SOM stabilization and their interactions. Pyrolysis molecular beam mass spectrometry (py-MBMS) provides a powerful and rapid means of assessing the biochemical composition of SOM. However, characterization of SOM composition alone is insufficient to predict its dynamic behavior. Chemical fractionation is frequently used to isolate more homogeneous SOM components, but the composition of fractions is frequently unknown. We characterized biochemical SOM composition in two previously studied soils from the USA, under contrasting land uses: cultivated agriculture and native vegetation. Bulk soils, as well as chemically isolated SOM fractions (humic acid, humin and non-acid hydrolysable), were analyzed using py-MBMS. Principal components analysis (PCA) showed distinct differences in the SOM composition of isolated fractions. Py-MBMS spectra and PCA loadings were dominated by low molecular weight fragments associated with peptides and other N-containing compounds. The py-MBMS spectra were similar for native whole-soil samples under different vegetation, while cultivation increased heterogeneity. An approach based on previously published data on marker signals also suggests the importance of peptides in distinguishing samples. While the approach described here represents significant progress in the characterization of changing SOM composition, a truly quantitative analysis will only be achieved using multiple internal standards and by correcting for inorganic interference during py-MBMS analysis. Overall, we have provided proof of principle that py-MBMS can be a powerful tool to understand the controls on SOM dynamics, and further method development is underway.