Optimization of the operating conditions of solid sampling electrothermal vaporization coupled to inductively coupled plasma optical emission spectrometry for the sensitive direct analysis of powdered rice

High sensitive detection of Cd, Hg, Pb and Cr in rice based on LA-MPT-OES with optimized excitation regions by two-dimensional characterization of plasma plume

Direct, rapid and highly sensitive detection of heavy metals in rice is essential to ensure food safety. In this research, a combination of laser ablation and microwave plasma torch optical emission spectrometry (LA-MPT-OES) was proposed. Based on the optimal observation positions, a high sensitivity and direct determination of Cd, Hg, Pb and Cr in rice were realized. The limits of detection (LOD) were 0.97, 0.12, 0.61 and 0.15 μg/kg, respectively, which were reduced by one order of magnitude compared to the optimal observation height. In addition, the LOD was reduced by one to two orders of magnitude compared with the techniques that require sample pre-treatment. Moreover, the results of the Certified Reference Materials and real samples were in agreement with the reference values with a relative error in the range of 0.28% ∼ 14.16%. The results demonstrated that LA-MPT-OES could be a promising tool to detect heavy metals in rice.

Rapid and sensitive determination of Se and heavy metals in foods using electrothermal vaporization inductively coupled plasma mass spectrometry with a novel transportation system

Rapid, sensitive and simultaneous determination of trace multi-elements in various plant food samples such as grain, oilseed, vegetable and tea is always a challenge thus far. In this work, a rapid determination method for Se, Cd, As and Pb in food samples by inductively coupled plasma mass spectrometry (ICP-MS) using slurry sampling electrothermal vaporization (SS-ETV) was developed. To improve the analytical sensitivity and precision as well as eliminate the memory effect, a gas turbulator line and signal delay device (SDD) were for the first time designed for the graphite furnace (GF) ETV coupled with ICP-MS. The signal acquisition parameters of ICP-MS, ashing and vaporization conditions, and the flow rates of carrier gas and gas turbulator were investigated for Se, Cd, As and Pb in food samples. Under the optimized conditions, the limits of determination (LODs) for Se, Cd, As and Pb were 0.5 ng g^-1, 0.3 ng g^-1, 0.3 ng g^-1 and 0.6 ng g^-1, respectively; the limits of quantification (LOQs) for Se, Cd, As and Pb were 1.7 ng g^-1, 1.0 ng g^-1, 1.0 ng g^-1 and 1.9 ng g^-1, respectively; linearity (R²) in the range of 1 to 4,000 ng g^-1 was >0.999 using the standard addition method. This method was used to analyze 5 CRMs including rice, tea and soybeans, and the concentrations detected by this method were within the range of the certified values. The recoveries of Se, Cd, As and Pb in plant food matrices including grain, oilseed, celery, spinach, carrot and tea samples were 86-118% compared to the microwave digestion ICP-MS method; and the relative standard deviations (RSDs) were 1.2-8.9% for real food sample analysis, proving a good precision and accuracy for the simultaneous determination of multi-elements. The analysis time was less than 3 min, slurry preparation time < 5 min without sample digestion process. The proposed direct slurry sampling ICP-MS method is thus suitable for rapid and sensitive determination of Se, Cd, As and Pb in food samples with advantages such as simplicity, green and safety, as well as with a promising application potential in detecting more elements to protect food safety and human health.

Fast and Sensitive Determination of Cadmium and Selenium in Rice by Direct Sampling Electrothermal Vaporization Inductively Coupled Plasma Mass Spectrometry

In this work, a direct solid sampling device based on modified graphite furnace electrothermal vaporization (GF-ETV) with inductively coupled plasma mass spectrometry (ICP-MS) was established for the simultaneous detection of trace selenium and cadmium in rice samples. A bypass gas was first designed in GF-ETV to improve the device’s analytical sensitivity and precision. The ashing and vaporization conditions, the flow rates of the Ar carrier and the bypass gases of ICP-MS were all investigated. Under the optimized conditions, the limits of detection (LODs) for Se and Cd were 0.5 μg kg−1 and 0.16 μg kg−1, respectively; the relative standard deviations (RSDs) of repeated measurements were within 8% (n = 6). The recoveries of Cd and Se in rice samples were in the range of 89−112% compared with the microwave digestion ICP-MS method, indicating good accuracy and precision for the simultaneous detection of Se and Cd in rice matrix. The whole analysis time is <3 min without the sample digestion process, fulfilling the fast detection of Se and Cd in rice samples to protect food safety.

Multi-elemental risk assessment of various baby rice cereals: some cause for concern?

This study used batch and online methods to accurately determine how much arsenic (As), chromium (Cr), selenium (Se), cadmium (Cd), lead (Pb), copper (Cu), iron (Fe), and zinc (Zn) can be leached from baby rice cereals into a baby’s body. Speciation analysis of the saliva and gastric juice leachates was conducted to further assess the risk associated with the continued consumption of baby rice cereal for infants. A simple 15 min chromatographic analysis successfully separated eight species consisting of As(III), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), As(V), Se(IV), Se(VI), Cr(III), and Cr(VI). Given that 95%–100% As, 29%–100% Cr, 62%–100% Pb, 70%–100% Se, 63%–100% Cd, 36%–100% Cu, 67%–100% Fe, and 70%–100% Zn were bio-accessible and the speciation analysis results showed all bio-accessible As and Se to be in the forms of As(V) and Se(VI) and 70%–100% of Cr to be in the Cr(III) form, a variety of foods should be fed to infants rather than just baby rice cereal to ensure a well-balanced diet and less exposure to As at such a young age.

Fast and High Sensitive Analysis of Lead in Human Blood by Direct Sampling Hydride Generation Coupled with in situ Dielectric Barrier Discharge Trap

A direct sampling hydride generation (HG) system based on modified gas liquid separator (GLS) coupled with in situ dielectric barrier discharge (DBD) is first rendered to detect lead in blood samples. Herein, a triple-layer coaxial quartz tube was employed as DBD trap (DBDT) to replace the original atomizer of atomic fluorescence spectrometry (AFS) to satisfy the in situ preconcentration. After 40-fold dilution, foams generated from protein in a blood sample can be eliminated via the double-GLS set; and lead in a blood sample were generated as plumbane under 3.5% HNO₃ (v:v) and 30 g/L NaOH with 8 g/L KBH₄, 10 g/L H₃BO₃, and 5 g/L K₃[Fe(CN)₆]. Then, lead analyte was trapped on the DBD quartz surface by 9 kV discharging at 50 mL/min air; and subsequently released by 12 kV discharging at 110 mL/min H₂. The absolute detection limit (LOD) for Pb was 8 pg (injection volume = 2 mL), and the linearity (R² > 0.997) range was 0.05 - 50 μg/L. The results were in good agreement with that of blood certified reference materials (CRM), and spiked recoveries for real blood samples were 95 - 104% within a relative standard deviation of 5% (RSD). Via gas phase enrichment, the established method improved analytical sensitivity (peak height) by 8 times. The entire analysis time including blood sample preparation can be kept to within 10 min. The combination of modified GLS and DBDT can facilitate the quickness, accuracy, and sensitivity, revealing a promising future for monitoring lead in blood to protect humans, especially children's health.

Determination of metal uptake in single organisms, Corophium volutator, via complementary electrothermal vaporization/inductively coupled plasma mass spectrometry and laser ablation/inductively coupled plasma mass spectrometry

RATIONALE

(Eco-)toxicological effects are mostly derived empirically and are not correlated with metal uptake. Furthermore, if the metal content is determined, mostly bulk analysis of the whole organism population is conducted; thus, biological variability is completely disregarded, and this may lead to misleading results. To overcome this issue, we compared two different solid sampling techniques for the analysis of single organisms.

METHODS

In this study, complementary electrothermal vaporization/inductively coupled plasma mass spectrometry (ETV/ICP-MS) ⇔ laser ablation/inductively coupled plasma mass spectrometry (LA/ICP-MS)-based methods for the analysis of individual organisms were developed and the results obtained were compared with the concentrations obtained after digestion and measured using ICP-MS. For this purpose, a common (eco-)toxicological test organism, the mud shrimp Corophium volutator, was selected. As proof-of-concept application, these organisms were incubated with environmentally relevant metals from galvanic anodes, which are often used for protection against metal corrosion in, for example, offshore wind farms.

RESULTS

The bulk analysis revealed that large quantities of the incubated elements were detectable. Using the ETV/ICP-MS method, we could identify a high biovariability within the population of organisms tested. Using the LA/ICP-MS method, it could be determined that the large quantities of the elements detected were due to adsorption of the metals and not due to uptake, which correlates well with the absence of (eco-)toxicological effects.

CONCLUSIONS

The results obtained imply the efficiency of complementary methods to explain the absence or presence of (eco-)toxicological effects. In particular, methods that allow for single-organism analysis or provide even a spatial resolution support the interpretation of ecotoxicological findings.

Tuning of the Amount of Se in Rice (Oryza sativa) Grain by Varying the Nature of the Irrigation Method: Development of an ICP-MS Analytical Protocol, Validation and Application to 26 Different Rice Genotypes

The amount of specific trace elements like selenium (Se) may be of health concern for humans if contained in too high (or low) quantities in staple foods like rice. Among the attempts aimed to optimize the Se concentration in rice, only few studies have been focused on the use of irrigation methods other than continuous flooding. Since intermittent irriguous methods, like sprinkler and saturation, have found to be effective in modifying the bioaccumulation of arsenic and cadmium in rice kernels, the main goal of this study is to measure the amount of the total Se contained in grains of 26 rice genotypes cultivated for two consecutive agrarian vintages in the same open field and with the same water, but differently irrigated with continuous flooding, sprinkler or saturation. To do this, an original and validated ICP-MS method has been developed. The validation parameters accounted for a high sensitivity and accuracy. Sprinkler irrigation is able to reduce in the average of 90% the amount of total Se in kernels in comparison to values measured in rice irrigated with continuous flooding. In conclusion, different irrigation techniques and rice genotypes seem to be valuable tools in order to allow in the future the customized modulation of the Se concentration in rice grain according to the needs of the various populations.

Simultaneous trapping of Zn and Cd by a tungsten coil and its application to grain analysis using electrothermal inductively coupled plasma mass spectrometry

For the first time, a tungsten coil (TC) was employed to trap Zn and Cd at room temperature and release them by heating simultaneously.