Domestic Microwave Research Articles

Determination of Cl and S in crude oil by ICP-OES after sample digestion by microwave-induced combustion in disposable vessels

A simple, fast and promising sample preparation method based on microwave-induced combustion in disposable vessels (MIC-DV) was developed for Cl and S determination in crude oil by inductively coupled plasma optical emission spectrometry (ICP-OES). The MIC-DV consists of a new approach of conventional microwave-induced combustion (MIC). For the combustion, crude oil was pipetted on a disk of filter paper and placed on a quartz holder, followed by the addition of igniter solution (40 μL of 10 mol L−1 NH4NO3). The quartz holder was inserted into a commercial 50 mL disposable polypropylene vessel containing the absorbing solution, which was then inserted in an aluminium rotor. The combustion occurs under atmospheric pressure in a domestic microwave oven not compromising the operator's safety. The following parameters of combustion were evaluated: type, concentration and volume of absorbing solution, sample mass and the possibility of performing consecutive combustion cycles. Using MIC-DV, up to 10 mg of crude oil were efficiently digested, using 2.5 mL of ultrapure H2O as absorbing solution. Moreover, up to 5 consecutive combustion cycles were possible without analyte losses, reaching a total sample mass of 50 mg. The MIC-DV method was validated according to Eurachem Guide recommendations. Results obtained for Cl and S by MIC-DV were in agreement with those obtained using conventional MIC, as well as those obtained for S in a certified reference material of crude oil (NIST 2721). Analyte spike recovery experiments were performed and recoveries at three concentration levels ranged from 99 to 101% for Cl and from 95 to 97% for S, indicating a good accuracy. The limit of quantification achieved by ICP-OES after MIC-DV were 73 and 50 μg g−1 for Cl and S respectively, applying 5 consecutive combustion cycles.

An innovative approach based on microwave radiation for synthesis of zeolite 4A and porosity enhancement

Advantages of microwave radiation in terms of reducing reaction time and enhancing product quality were exploited for template-free zeolite 4A synthesis, in which a domestic microwave oven was purposely utilized instead of a scientific microwave reactor. Experimental data proved that the microwave-assisted hydrothermal synthesized product crystallized at the same phase as the zeolite obtained from the conventional hydrothermal method. Moreover, compared to the hydrothermal synthesis, microwave radiation considerably improves zeolite's properties, including forming more uniform and finer zeolite crystals. However, both synthesis methods produced zeolites with relatively limited surface areas. To solve this problem, an attempt to utilize microwave radiation as a post-washing technique gained a significant improvement of the zeolite's exposed surfaces that revealed effectiveness of microwave on removing the obstacles to release the blocked pores in the zeolite's structure. On that basis, the adsorption characteristics of the 4A zeolites prepared from the two synthesis methods were studied in consideration of the influence of post-washing steps. A comparison on adsorption of these materials was carried out in treating a synthetic dye-containing wastewater of which methylene blue (MB) was used as a model compound. Experiments showed an increment of about quadruple MB uptake achieved from the microwave-assisted method in comparison to the conventional route.

Development of iron-based composite materials through electromagnetic radiations in a domestic microwave oven

Microwave hybrid heating, a novel technique, is used to develop iron-based alloy (SS316), SS316+10EWAC1004 (nickel-based), and SS316+10EWAC1004+5Cr7C3 composite castings. The domestic microwave having a frequency of 2.45 × 103 MHz and a power of 0.9 kW, is used with a variable exposure time of microwave radiations. The microwave interaction procedure with the metallic powder is discussed to optimize the exposure time and temperature. A microstructure study of developed castings revealed the uniform melting of matrix and EWAC1004 with an identical dispersion of Cr7C3. The X-ray diffraction results revealed various intermetallic (Ni3Fe, Ni2Si, Cr2Ni3, MoNi4, Fe3Si, Fe2Si, CrFeNi) and hard carbides (Fe3C, Cr3C2, Cr23C6) phases. The maximum average micro-hardness is for the SS316+10EWAC1004+5Cr7C3 composite, followed by SS316+10EWAC1004. The established composite casting had a hardness of around 2 times that of the commercial SS316. The maximum density of 97% was found for Iron-based SS316-based. The grain size of microwave-processed SS316, SS316+10EWAC, and SS316+10EWAC +5Cr7C3 specimens is found to be 21 ± 4 µm, 18 ± 3 µm, and 17 ± 2 µm, respectively. It has been observed that reinforced phases hinder grain growth, and hence grain size reduces significantly. In comparison, commercial SS316 had a grain size of 31 ± 6 µm. The ASTM B-276 standard is used to determine pores that are of the order of 1.98%.

Influence of tungsten carbide-cobalt reinforcement on flexural behavior of iron-based composite developed through microwave

The flexural behavior of iron-based composite castings has been analyzed under three-point loading conditions. The metal matrix composite casting of five varying compositions of powders by weight, that is, SS316, SS316+15EWAC, SS316+15EWAC+5WC−12Co, SS316+15EWAC+10WC−12Co, and SS316+15EWAC+15WC−12Co has been cast in a domestic microwave oven of maximum power and frequency of 0.9 kW and 2.45 × 103 MHz respectively. The casting of size 30 × 6 mm2 is prepared. The prepared sample’s mechanical properties, such as ultimate peak load, flexural strength, strain at peak load, strain at break and flexural modulus, are tested on Dak System UTM having load cell 10 kN as per ASTM 1161-18 standard. The flexural strength and peak load for SS316+15EWAC+10WC−12Co, strain at peak load for SS316+15EWAC+5WC−12Co, and flexural modulus and microhardness for SS316+15EWAC+15WC−12Co were found maximum value. The maximum microhardness value is obtained in the carbide phase. The microstructure of the cast samples shows equiaxed grain growth with identical melting of the matrix. The XRD pattern of the samples confirmed the presence of various intermetallic and carbide phases.

Inhibition effects of the applied dielectric on dimer-induced microwave plasma and focused hotspots

There are still challenges in the precise control of microwave energy for the industrial production, one of which is the effective inhibition of microwave hotspots or thermal runaway during microwave radiation, which has become a long-standing problem for improving heating uniformity and further expanding applications. Nevertheless, the evolution process and the underlying mechanism of microwave hotspots in high-dielectric dimers within different applied dielectrics are not fully understood due to the difficulty of internal temperature measurement. In this Letter, an optical indirect observation method has been proposed to characterize the hotspots distribution inside the applied dielectric. The grapes with high relative permittivity have been selected, which are easy to cut and absorb microwave, to conduct an in situ investigation of microwave hotspots evolution for dimers in a domestic microwave oven using the thermal and optical imaging. The results show that with the increase in the relative permittivity of applied dielectric, the starting of microwave plasma is prevented, and the focused hotspots disappear. Most significantly, the heating uniformity of dimers in water is improved by about ten times compared to that in air. The reduction of the calculated focused energy density near the contact point verifies the weakening effect of applied dielectric on the microwave cooperative resonance of dimers and explains the experimental phenomenon. These findings can be directly applied to inhibit the formation of focused hotspots for dimers or even multi-particle systems during the microwave processing and also provide a better understanding for cooperative interaction of Mie resonances.

Green synthesized nitrogen-doped carbon quantum dots for the sensitive determination of larotrectinib in biological fluids and dosage forms: Evaluation of method greenness and selectivity

Recently, the kinase receptor inhibitor drug larotrectinib has been approved as a monotherapy for the treatment of patients with solid tumors containing the neurotrophic receptor tyrosine kinase gene fusion. In this paper, a novel sensitive spectrofluorimetric method was proposed for the determination of larotrectinib based on nitrogen-doped carbon quantum dots (N-CQDs) fluorescent probes. The proposed method is the first spectroscopic method for analysis of the cited drug, which is simple to implement and involves no pre-treatment steps or complicated techniques. The N-CQDs synthesis was performed by adopting a straightforward, fast, and environmentally friendly approach. It was achieved by means of a standard domestic microwave with inexpensive and readily available starting materials: orange juice (carbon source) and urea (nitrogen source). The synthesized N-CQDs were subjected to microscopic and spectroscopic characterization procedures. They were found to be stable with a sufficiently high fluorescence quantum yield (25.3%) and a small particle size distribution (2–5 nm). The motivation for the use of N-CQDs in this study arose from their excellent fluorescence intensities at 417 nm when excited at 325 nm. Larotrectinib was found to have a quantitative and selective quenching effect on the QDs fluorescence allowing for its sensitive determination. The drug’s quenching mechanism was investigated and found to be of the static type. Under optimal conditions, the proposed approach permitted the determination of larotrectinib over the concentration interval of 5.0–28.0 µg/mL. The method showed sufficient sensitivity with a detection limit of 0.19 µg/mL and a quantitation limit of 0.57 µg/mL, enabling the determination of LARO in spiked human plasma samples. The approach’s recovery percentage was found to be in the range of 99.09–100.73% for pure samples and 97.35–102.59% for plasma samples. The study also successfully applied the proposed approach to the commercial oral solution form of larotrectinib (Vitrakvi®) with high selectivity. Method greenness was further evaluated by adopting two metric tools, including the complementary green analytical procedure index (ComplexGAPI) and Analytical GREENNESS metric approach (AGREE), and it was confirmed to be excellent green. The proposed method was validated in accordance with the ICHQ2 (R1) recommendations and is considered an excellent candidate for potential application in the therapeutic monitoring of larotrectinib.

Performance evaluation of ANFIS, ANN and RSM in biodiesel synthesis from Karanja oil with Domestic Microwave set up

Performance evaluation of ANFIS, ANN and RSM in biodiesel synthesis from Karanja oil with Domestic Microwave set up

Effects of mode of heat transfer on puffing quality of rice grain: A modeling and simulation analysis

AbstractCereal grains can be puffed by heating in hot sand bed or domestic microwave oven. The purpose of this study was to explore and compare the reasons of transformational changes in preconditioned rice during its sand bed heating and microwave heating in domestic microwave oven. Mathematical modeling and simulation techniques were used to estimate the changes in microwave power absorption density and temperature of rice with the heating methods. Sand puffing, initiated from the tips of rice, progressed toward the central region of the rice following the change in temperature profile of rice and outcomes were completely puffed rice. The rice grains, placed in the different radial zones on the turntable of oven cavity, experienced nonuniform and inconsistent rate of microwave power absorption within the rice due to its placement and rotation, the oven factors, grain's shape, size, and dielectric properties. Microwave puffing, initiated from the central region of rice, progressed toward the tips of the rice. The slow rate of heating resulted in evaporative cooling of rice and most of the rice were unable to puff completely. However, the rate of microwave heating of rice was comparable with that of sand heating and about 92.0 ± 2.3% puffed was observed when rice was place in radial zone of 5.0 cm. Hence, the exact placement of rice in the oven cavity was required for achieving good puffing quality of rice.Practical applicationsThe present study helps to understand the reasons for uneven puffing of rice in domestic microwave oven. This understanding of puffing process in domestic microwave oven provides an opportunity to develop strategy for microwave puffing of rice or design a specific microwave puffing equipment suitable for achieving quantitative and qualitative puffing of rice.

Use of green fluorescent nano-sensors for the determination of furosemide in biological samples and pharmaceutical preparations

BackgroundCarbon quantum dots (CQDs) are new class of carbon nanoparticles. Recently, they have been widely used as fluorescent probes due to their easy accessibility, optical properties and chemical inertness. Many available precursors are used in the synthesis of carbon quantum dots. The electrical and optical properties of CQDs could be enhanced by doping hetero atoms such as nitrogen or sulfur into their structure.ObjectiveThe current work presents the synthesis and characterization of water-soluble nitrogen doped carbon quantum dots (N-CQDs) and their use as fluorescent nano-sensors for the spectrofluorimetric determination of furosemide in its pharmaceutical preparations and spiked human plasma.MethodsA domestic microwave was used to prepare the N-CQDs by heating a solution of sucrose and urea till complete charring (about ten minutes). The produced N-CQDs exhibit a strong emission band at 376 nm after excitation at 216 nm. Furosemide caused a quantitative quenching in the fluorescence intensity of the produced N-CQDs.ResultsThe proposed method was validated according to ICH Guidelines. The method was found to be linear over the range of 0.1–1.0 µg/mL with LOQ of 0.087 µg/ml.ConclusionEcofriendly nano fluorescent sensors (N-CQDs) were successfully synthesized. The size of N-CQDs was distributed in the range of 6.63 nm to 10.23 nm with an average of 8.2 nm. The produced N-CQDs were used as fluorescent probes for the estimation of furosemide in its pharmaceutical preparations as well as spiked human plasma samples.

Effect of addition of surfactant on physicochemical properties of cobalt oxide nanoparticles synthesised using a domestic microwave: Applications as photocatalyst and supercapacitor

The present work highlights the comparison of the physicochemical properties of the metal oxide nanoparticles of cobalt synthesised using a domestic microwave in the presence and absence of surfactant. XRD analysis revealed that the addition of the surfactant was responsible for the reduction in the crystallite size of the metal oxide nanoparticles. SEM images showed more agglomeration in the case of surfactant-capped nanoparticles than the bare ones. The elemental composition obtained using EDAX of both nanoparticles showed a higher percentage of oxygen in the bare nanoparticles and better elemental stoichiometry in the surfactant-capped nanomaterials. The energy band gap calculated from the optical studies was higher in the case of surfactant-loaded nanoparticles than the bare ones. The photocatalytic studies of nanoparticles without and with surfactant showed 48 % and 40 % degradation of Methylene blue, respectively, in the presence of UV light with 1 g L−1 catalyst dose and 50 mg L−1 dye concentration at 300 min of irradiation time. Langmuir-Hinshelwood kinetic plots showed a marginally higher apparent rate constant value (2.22 × 10−3 min−1) for nanoparticles without surfactant than for nanoparticles with surfactant (2.11 × 10−3 min−1). The cyclic voltammograms of both the nanoparticles at a scan rate of 5 mV s−1 were faradic in nature and showed pseudo capacitance. The capacitance of nanoparticles with surfactant (166 F g−1) was found to be higher than that obtained for bare nanoparticles (111 F g−1). A comparison of the properties indicated that the addition of surfactant plays a vital role in tuning the properties of cobalt oxide nanoparticles for their specific application.

Evaluating the dynamic characteristics of microwave-casted metal matrix composite material by using experimental modal analysis

This paper proposes an experimental modal analysis technique to measure the dynamic characteristics of microwave-casted metal matrix composite (MMC). To fabricate MMC, silicon carbide (SiC) is reinforced into the SS202 matrix. The damping capacities of MMC at different reinforcements of SiC powder such as 0.05%, 0.1% and 0.2% are measured through experimental modal analysis. The main objective is to study the effect of reinforcement on the damping capacity of SS202. The domestic microwave oven with the specification of 2.45 GHz and 900 W power is used to cast the MMC material. The graphite split mold is used for in-situ microwave casting. The mechanical characterization in terms of micro-hardness and scanning electron microscopy (SEM) of MMC is also examined. From SEM imagining, complete diffusion of the SiC in SS matrix is observed for 0.05% of SiC reinforcement; however, incomplete diffusion is observed for 0.1% and 0.2% of SiC reinforcement. It is observed that the hardness of the SS202 is increasing with the decrease in the percentage of SiC powder. The experimental modal analysis is carried out by using SO Analyzer. The response model in terms of the frequency response function (FRF) curve is measured when the specimen is excited at impact excitations. The half power bandwidth method is used to calculate the damping factor of the material from the measured FRFs. It is observed that the damping capacity increases with the increase in percentage of SiC in SS202. SS202 with 0.05%, 0.1% and 0.2% SiC have the hardness value of 155.33 HV, 107.33 HV and 58.33 HV, respectively.

Synthesis of polyamids from some of the medical drugs after the Insertion of 1,3,4-thiadiazole ring in their composition

This search include preparation of polyamids Containing some of the medical drugs, by the polycondensathion method for amino-1,3,4-thiadiazole compounds with dicarboxylic acids (terephthalic acid and phthalic acid) in presence of triphenyl phosphite and by using domestic microwave oven. Electrical conductivity were determined by using electrical conductivity cell unit.
 The prepared compounds were characterized by UV/Vis (Ultraviolet/visible), IR (Infra-red) and 1H-NMR (Proton nuclear magnetic resonance) spectra in (d6-DMSO) Solvent ,in addition to using elemental analyses apparatus (C.H.N) for some prepared compounds.

Highly luminescent Gd2O2S:Er3+,Yb3+ upconversion microcrystals obtained by a time- and energy-saving microwave-assisted solid-state synthesis

Er3+-doped and Er3+,Yb3+-co-doped Gd2O2S are one of the most efficient upconversion (UC) materials available to date. However, preparing lanthanide oxysulfides can be challenging as it requires several hours of heating at>1000 °C in high power furnaces. Nonetheless, in designing a new synthesis technology for UC materials, one should consider that these systems suffer from defect quenching, responsible for significant optical energy losses. In this work, the microwave-assisted solid-state (MASS) synthesis was explored as an alternative to synthesize this class of materials, using two different starting compounds – lanthanide oxides (Ln2O3) and hydroxycarbonates (Ln(OH)CO3), where Ln3+: Gd, Er, Yb. Different Er3+,Yb3+ concentrations were investigated, and the Er3+(5%),Yb3+(5%) and Er3+(1%),Yb3+(10%) were shown to give the most intense UC output comparable to commercially available materials. Using Ln(OH)CO3 instead of the more common Ln2O3 for the MASS synthesis contributed to higher UC efficiencies and a more homogeneous Er3+ and especially Yb3+ distribution through the Gd2O2S lattice as verified by luminescence lifetime measurements. These high-quality materials were prepared in a simple two-step synthesis of 50 min and using a domestic microwave oven, leading to a remarkable decrease of 79% in processing time and 93% in energy consumption, making the MASS method suitable to be explored as an alternative synthesis methodology for high performance UC materials.

The Effect of Rapid Tissue Processing on Fixation Time Using Microwave Techniques

The quest for a faster means of tissue processing has been on the increase to accomplish the needs of medical scientists, especially for treating patients with critical health conditions. Specimens were processed using different schedules at different temperatures to ascertain the effect of rapid tissue processing on fixation time. A domestic microwave model of MW007GA-MG823 (W)/MW- MB0823MP, rated voltage: 230V5 0HZ was used for the study. A total of four (4) organs were used, each divided into two, one part processed with the microwave and the other processed with the conventional method. The rapid technique started without prior routine fixation, except a schedule that was fixed for nine (9) hours before the rapid process started at a temperature of 42°C following dehydration, clearing of tissues was carried out with isopropanol. Fixation times for the rapid schedules are 30 and 20 minutes. An independent t-test conducted between the rapid and conventional techniques showed Mean±SD = 30±2.00 mins, Mean±SD = 20±2.00 mins, and Mean±SD = 2880±2.00 mins respectively at p = 0.00 depicting statistical significance. The rapid technique produced sections of good quality without compromising the tissue architecture. Isopropanol could be used as a clearing agent instead of xylene as it is inflammable in the microwave.

Amine Functionalized Gadolinium Oxide Nanoparticles-Based Electrochemical Immunosensor for Cholera.

Herein, we report the synthesis and functionalization of gadolinium oxide nanoparticles (Gd2O3 NPs) to fabricate a highly efficient immunosensor for the detection of Vibrio cholera toxin (CT). Gd2O3 NPs were produced in a straightforward manner utilizing the microwave irradiation technique using a domestic microwave oven. X-ray diffraction, transmission electron microscopy, and spectroscopic techniques were used to characterize the structural and physical aspects of Gd2O3 NPs. The Gd2O3 NPs were then functionalized with 3-(Aminopropyl) triethoxysilane (APTES) and electrophoretically deposited onto an ITO-coated glass substrate. The anti-CT monoclonal antibodies were covalently attached to the APTES-Gd2O3/ITO electrode via EDC-NHS chemistry, followed by bovine serum albumin (BSA). For CT detection, electrochemical response experiments using BSA/anti-CT/APTES-Gd2O3/ITO immunoelectrodes were carried out (5-700 ng mL-1). The immunoelectrode demonstrated an outstanding electrochemical reaction against CT, with a sensitivity of 8.37 mA ng-1 mL cm-2 and a detection limit of 1.48 ng mL-1.

Revisiting “Non-Thermal” Batch Microwave Oven Inactivation of Microorganisms

Over the last few decades there has been active discussion concerning the mechanisms involved in “non-thermal” microwave-assisted inactivation of microorganisms. This work presents a novel non-invasive acoustic measurement of a domestic microwave oven cavity-magnetron operating at fo = 2.45 ± 0.05 GHz (λo ~ 12.2 cm) that is modulated in the time-domain (0 to 2 minutes). The measurements reveal the cavity-magnetron cathode filament cold-start warm-up period and the pulse width modulation periods (time-on time-off and base-time period, where time-on minus base-time = duty cycle). The waveform information is used to reconstruct historical microwave “non-thermal” homogeneous microorganism inactivation experiments: where tap-water is used to mimic the microorganism suspension; and ice, crushed ice, and ice slurry mixture are used as the cooling media. The experiments are described using text, diagrams, and photographs. Four key experimental parameters are indentified that influence the suspension time-dependent temperature profile. First, where the selected process time > the time-base, the cavity-magnetron continuous wave rated power should be used for each second of microwave illumination. Second, external crushed ice and ice slurry baths induce different cooling profiles due to difference in their heat absorption rates. In addition external baths may shield the suspension resulting in a retarding of the time-dependent heating profile. Third, internal cooling systems dictate that the suspension is directly exposed to microwave illumination due to the absence of surrounding ice volume. Fourth, four separated water dummy-loads isolate and control thermal heat transfer (conduction) to and from the suspension, thereby diverting a portion of the microwave power away from the suspension. Energy phase-space projections were used to compare the “non-thermal” energy densities of 0.03 to 0.1 kJ·m-1 at 800 W with reported thermal microwave-assisted microorganism inactivation energy densities of 0.5 to 5 kJ·m-1 at 1050 ± 50 W. Estimations of the “non-thermal” microwave-assisted root mean square of the electric field strength are found to be in the range of 22 to 41.2 V·m-1 for 800 W.

Microwave-assisted synthesis of octahedral Rh nanocrystals and their performance for electrocatalytic oxidation of formic acid.

Uniform and well-defined octahedral Rh nanocrystals were rapidly synthesized in a domestic microwave oven for only 140 s of irradiation by reducing Rh(acac)3 with tetraethylene glycol (TEG) as both a solvent and a reducing agent in the presence of an appropriate amount of KI, didecyl dimethyl ammonium chloride (DDAC), ethylene diamine (EDA) and polyvinylpyrrolidone (PVP). KI, DDAC and EDA were essential for the creation of octahedral Rh nanocrystals. Electrochemical measurements showed a significantly enhanced electrocatalytic activity and stability for the as-prepared octahedral Rh nanocrystals compared with commercial Rh black.

Estimation of Bacteriophage MS2 Inactivation Parameters During Microwave Heating of Frozen Strawberries

Frozen berries have been repeatedly linked to acute gastroenteritis caused by norovirus, the most common cause of foodborne illness in the United States. Many guidelines recommend that frozen berries be microwaved for at least 2 min, but it is unclear if this thermal treatment is effective at inactivating norovirus. The objective of this study was to model the effect of microwave heating at varying power levels on the survival of bacteriophage MS2, a norovirus surrogate, when inoculated onto frozen strawberries. Bacteriophage MS2 was inoculated onto the surface of frozen strawberries with a starting concentration of approximately 10 log PFU/g. Samples (either 3 or 5 whole strawberries) were heated in a 1300-Watt domestic research microwave oven (frequency of 2450 MHz) at power levels of 30, 50, 70, and 100% (full power), for times ranging from 15 to 300 s to determine inactivation. Temperatures at berry surfaces were monitored during heating using fiberoptic thermometry. All experiments were conducted in triplicate. The primary model for thermal inactivation was a log-linear model of logN vs. time. The secondary model was for a D-value decreasing linearly with temperature and an added term that was path-dependent on the thermal history. Parameters in the model were estimated using dynamic temperature history at the surface of the berry, via nonlinear regression using all data simultaneously. The root mean square error was ∼0.5 PFU/g out of a total 6-log reduction. Log reductions of 1.1 ± 0.4, 1.5 ± 0.5, 3.1 ± 0.1, and 3.8 ± 0.2 log PFU/g were observed for 30, 50, 70, and 100% microwave power levels when three berries were heated for 60 s. D-values were 21.4 ± 1.95 s and 10.6 ± 1.1 s at 10 and 60°C, respectively. This work demonstrates an approach to estimate inactivation parameters for viruses from dynamic temperature data during microwave heating. These findings will be useful in predicting the safety effect of microwave heating of berries in the home or food service.

A Ratiometric Probe Based on Carbon Dots and Calcein & Eu3+ for the Fluorescent Detection of Sodium Tripolyphosphate.

Sodium tripolyphosphate, a food additive, is applied broadly in food industry. However, excessive accumulation of sodium tripolyphosphate can result in electrolyte abnormality of the body. Therefore, it is of great importance to investigate an effective method for the detection of sodium tripolyphosphate. In this work, nitrogen-doped carbon dots (NCDs) with constant fluorescence were fabricated using a domestic microwave oven. A ratiometric fluorescent probe was constructed in which NCDs were as internal standard, calcein & Eu3+ were as the detection signal. The fluorescence of calcein at 515nm was quenched by Eu3+, whereas the emission peak of NCDs at 446nm was almost unchanged. Additionally, the fluorescence of calcein was recovered because of the strong interaction of sodium tripolyphosphate and Eu3+. The linear range for sodium tripolyphosphate was 0.5-6 µmol/L with detection limit of 0.12 µmol/L. Furthermore, the ratiometric fluorescent probe was applied for sodium tripolyphosphate detection in real milk samples.

Simple and cheap preparation of fluorescence paper sensor based in carbon dot for visual detection of chloramphenicol.

Carbon dots (CDs) are nanometer-scale particles produced from carbon sources that exhibit fluorescence emission. The present work presents the synthesis and characterization of CDs, as well as the sensing studies for the determination of chloramphenicol (CAP). CAP is an antibiotic used in human medicine and agriculture, and its indiscriminate use and inappropriate disposal have caused damage to human health and the environment. The carbonaceous precursor used in the synthesis of CDs was 3,4-diaminobenzoic acid (3,4-DABA) through the hydrothermal method via domestic microwave irradiation. The first synthesis procedure was carried out in the presence of water/ethanol (a-CDs) and the second in the presence of 1 mol/L sodium hydroxide/ethanol (b-CDs). The CDs were initially characterized in terms of spectroscopic properties in the ultraviolet and visible region (UV-visible), Fourier-transform infrared (FTIR) spectra, Raman spectroscopy, and fluorescence emission spectroscopy. Sensing studies for the antibiotic C were performed by fluorescence suppression in the presence of a- and b-CDs, as well as the precursor 3,4-DABA. The a- and b-CDs presented similar values of linear range 0.00080-0.0050 mg/ml and limit of detection (LOD) = 0.00030 mg/ml (0.30 ppm) for CAP. Then, a- and b-CDs were embedded in Whatman and Mellita® filter paper, and CAP sensing was evaluated through UV light excitation.