Stripping voltammetric determination of trace cadmium and lead in Thai organic unpolished rice after ultrasound-assisted digestion

A Significant Fluorescent Aptamer Sensor Based on Carbon Dots and Graphene Oxide for Highly Selective Detection of Progesterone

In this paper, a fluorescent aptamer sensor was constructed based on the carbon dots (CDs) and graphene oxide (GO). This sensor combines the excellent fluorescence performance of CDs with the high specificity of aptamer, which can detect progesterone (P₄) with high sensitivity and selectivity. In the absence of P₄, the CDs-aptamer system and GO form a fluorescence resonance energy transfer process (FRET), which quenches the fluorescence of the CDs. When P₄ is added, the aptamer specifically binds to it, resulting the fluorescence of the CDs is recovered. At optimal conditions, the fluorescence intensity recovered by the CDs has a linear relationship with the concentration of P₄ in the range of 0.1-120 nM and the detection limit is 3.3 × 10^-11 M. Besides, the sensor has satisfactory detection results of P₄ in milk, indicating that constructed method has enormous potential for application in food safety.

A simple and cost-effective smartphone-based digital imaging device for the quantification of selected heavy metals in Thai rice

This paper describes smartphone-based digital imaging equipment for lead, cadmium, copper, and zinc determination in Thai rice that is both convenient and cost-effective. This smartphone-based digital imaging device has a built-in light control box made of poly(lactic acid) or PLA, a compostable and biodegradable plastic, with a light control circuit box underneath that uses a single white light-emitting diode (LED) lamp and takes photos at only 20 lux, which is very low but clearly captures the color of heavy metal complexes. In the present study, the dithizone ligand in different buffers is employed to produce a specific color solution for each heavy metal. According to the output from the free Color Name application, the concentration of heavy metals is proportional to the intensity of the resulting red color. A linear range of 0.1-1.0 mg L^-1 was obtained. The lower detection limit was determined to be between 0.01 and 0.05 mg L^-1, whereas the quantification limit was in the range from 0.04 to 0.15 mg L^-1. The intra-day precision (%RSD, n = 5) was 0.4-0.8 with high consistency, while the inter-day precision (%RSD, n = 5) was 0.5-0.8 with good efficacy. The recovery rate for heavy metals added to samples of Thai rice ranged from 99.4 to 105.5 percent. Heavy metals were detected in a variety of rice samples utilizing the smartphone-based digital imaging equipment, with acceptable accuracy when compared to atomic absorption spectrophotometric data using a paired t-test. This smartphone-based digital imaging is efficient, accessible, and cost-effective, and it provides a viable alternative to existing heavy metal detection methods in Thai rice.

Multi-elemental analysis of particulate matter PM2.5 and PM10 by ICP OES

The complexity of aerodynamic particulate matter's (PM) matrices poses a challenge for the extraction and quantification of metals, especially for analytes with low concentration. Aiming to solve this issue, a precise and accurate protocol with the ultrasound extraction combined with microwave radiation digestion (USMW), was applied to PM samples with excellent compensations in sample throughput, digestion efficiency, and energy consumption. After the digestion and extraction procedures, the inorganic analytes, including rare earth elements, were determined by ICP OES. Two types of particulate matter sampled from two stations, Gobernacion (GOB10 and GOB2.5) and Milan (MIL10), corresponding to PM_2.5 and PM₁₀, were digested with a combination between HF, HNO₃, and H₃BO₃. The absolute limits of detection ranged from 0.42 pg m^-³ for V, to 3459 pg m^-³ for As. The accuracy of the experimental study was assessed using two certified reference materials (CRMs), Coal Fly Ash (NIST1633b) and Fly Ash (BCR176). The method presented good accuracy, with recoveries ranging from 90 to 115%, except for Al (120%) and Fe (123%). Considering the replicates for the determination of analyte elements, the repeatability was below 10% for the relative standard deviation (RSD). A cloud point extraction (CPE) procedure, with parameters optimized for the determination of Pd and Pt, was successfully applied in digested PM samples with detection limits of 1.43 and 2.05 pg m^-³ for Pd and Pt in MIL10 sample, respectively, and 76.6 pg m^-³ for Pd and 110 pg m^-³ for Pt, in samples GOB10 and GOB2.5, respectively.

A rapid on-site analysis method for the simultaneous extraction and determination of Pb2+ and Cd2+ in cereals

In order to achieve rapid on-site screening and solve the problem of rapid pretreatment for the determination of lead (Pb²⁺) and cadmium (Cd²⁺) in cereals by a portable electrochemical analyzer with disposable screen-printed electrodes (SPEs), a new reliable and simple extraction method for Pb²⁺ and Cd²⁺ in cereals was developed. The Pb²⁺ and Cd²⁺ in cereals were purified by a mixed solution of 1 mol L⁻¹ potassium iodide (KI)/5% vitamin C (VC)/ethyl acetate after being extracted by 10% HNO₃, which transfers the Pb²⁺ and Cd²⁺ into ethyl acetate after a reaction with KI–VC. Then, the Pb²⁺ and Cd²⁺ were eluted from ethyl acetate with 5% HNO₃ and were determined by an electrochemical analyzer with screen printed electrodes. Under the optimized conditions, the matrix calibration curves of Pb²⁺ and Cd²⁺ in rice and wheat showed good linear relationships with R² > 0.996. The method shows a detection limit (LOD) for Cd²⁺ in rice and wheat of 6.7 μg kg⁻¹ and 11.5 μg kg⁻¹, and the corresponding values for Pb²⁺ were 34.9 and 31.1 μg kg⁻¹, respectively. The relative standard deviation (RSD) was less than 8.7% for Cd²⁺ and Pb²⁺. In addition, the recoveries of the tested reference materials using this method were between 80% and 120%. From sample pretreatment to testing results, the whole process took no more than 25 min, and the operation was simple for operators, green to the environment, cheap in terms of instruments, and above all suitable for on-site detection. The results implied that this portable electrochemical method with new pretreatment may be a good choice for screening Pb²⁺ and Cd²⁺ in cereal samples on-site.

To achieve rapid on-site screening rapid pretreatment for the determination of Pb²⁺ and Cd²⁺ in cereals by a portable electrochemical analyzer with disposable screen-printed electrodes, a new reliable and simple extraction method for Pb²⁺ and Cd²⁺ was developed.