Total reflection X ray fluorescence spectrometry
This report describes the analysis process of rice samples using total reflection X ray fluorescence analysis, which is especially suitable for the inspection of rice samples in small or remote areas.
Arsenic (As) is a kind of metal element, which is between metal and nonmetal. Arsenic, nitrogen and hydrogen are the same elements in the periodic table of elements. Therefore, its chemical properties are similar in many respects to the two dietary elements. This may be the reason for the high levels of arsenic in marine organisms, algae and marine plants.
Generally speaking, the soil and water in the world contain arsenic. The content of arsenic in groundwater is usually less than 10ug/l (1/1000000000), while groundwater is an important source of drinking water, but in some areas the content can reach 5000ug/l. Arsenic is very common in rocks in the Himalaya mountains, where Ganges RIver and other rivers are brought to the densely populated plains of India, Bangladesh and other Asian countries.
About 80% of the world's rice comes from paddy fields (see Table 1 of the top five rice producing countries), so compared with grains, rice arsenic intake is more than ten times. In addition, the water flooded soil conditions with anaerobic characteristics, thus leading to arsenic from adhesion or stable form of conversion to a mobile form.
The rice contains large amounts of arsenic in dry conditions, between its concentration per kilogram, usually between 0.1 - 0.4mg or higher. Although the amount of arsenic in fish and other seafood is usually high, most of the arsenic is converted into low toxic or non-toxic organic compounds.
Health effects of exposure to high concentrations of arsenic
Studies have shown that long-term arsenic exposure is associated with bladder cancer, lung cancer, skin cancer, prostate cancer and heart disease. In the short term, prolonged exposure to arsenic can cause gastrointestinal problems, muscle cramps, and hand and foot problems.
Therefore, the highest level of the total content of arsenic in drinking water in most countries is limited to 10ppb, but only a few countries have formulated the relevant provisions of the highest level of arsenic in foods, such as cereals, rice or seafood (Table 2).
Rapid analysis and cost analysis of arsenic in Rice
Although there are a large number of analytical methods for total arsenic in rice, there is a strong demand for analytical methods that are suitable for routine operation. Nowadays, it is important to analyze the total amount of arsenic in rice as an important task in developing countries and remote areas.
In the past few years, a total reflection X fluorescence analysis (TXRF) technique has been developed for the determination of trace elements in environmental and biological samples . This report uses TXRF technology for direct analysis of rice samples.
In this report, 12 rice samples were analyzed by using TXRF technique and the data from two references in Southeast Asia and Australia (1568a and NIST NIST).
All the samples are used to test bench top opening type milling machine (Retsch MM400), and the configuration of the zirconium material container with the ball, with a three minute at a frequency of 30Hz.
Subsequently, 100+/-5mg rice flour was added into the centrifuge tube and suspended in 5ml Triton X-100 aqueous solution (1 vol.-%).
The 30ul was added into Y solution (1g/l) by internal standard method. In completely after homogenization, the sample is placed in ultrasonic cleaner, time is three minutes.
After that, the sample is fixed in the sample automatic shaking device, and the 800r/min is moved slowly to avoid precipitation.
The suspension of 10ul is transferred to the silica glass container and dried. Prepare ten times the reference sample and use other rice samples as samples.
The use of S2 PICOFOX spectrometer measured 1000 seconds. The spectrometer is equipped with 50 W X ray tube, molybdenum target and the detection range for XFlash silicon drift detector effective area - 60 mm.
Figure 2 shows the amplified spectra of arsenic in rice samples detected by TXRF technique. At the same time, some of the major components (phosphorus, sulfur, chlorine, potassium, calcium) and other trace elements (Cr, Mn, Ni, Fe, Cu, Zn, Se, Rb, Sr, Ba, and so on) were detected.
Figure 3 presents the results of TXRF measurements and ICP-MS data for 12 rice samples with two reference standards. Taking into account the standard deviation of the value, the TXRF results of rice samples were consistent with the certified reference materials.
There is no standard deviation of ICP-MS data for rice samples. The TXRF value is consistent with the ICP-MS data, and its content is lower than 0.2ppm.
Figure 3 shows the highest level of arsenic recognized by the EU and china. Because the detection limit of TXRF is about 4 to 5 factors, it is possible to control the legal limit. When the measurement time is extended, the detection limit can even be lower than 0.03ppm.
Because of its high sensitivity, TXRF is suitable for the detection of arsenic content in rice products. The technique provides a quick and cost-effective solution to the arsenic content in the legal limit.
In short, compared with AAS, ICP-OES and ICP-MS, TXRF spectrometer S2 PICOFOX has the following advantages:
The sample preparation method in TXRF is simple and time-saving, such as acid digestion.
S2 PICOFOX spectrometer is portable, can be used in the field and used in remote areas.
No need to install advanced intake and exhaust laboratory infrastructure.
No need for frequent maintenance of spectrometers.
After a simple training, the basic analytical skills of the laboratory personnel can operate S2 PICOFOX.
Bruker TXRF total reflection X ray fluorescence spectrometer
Bruker total reflection X ray fluorescence spectrometer S2 PICOFOX is the world's first portable desktop spectrometer for application of total reflection X ray fluorescence analysis (TXRF) principle, the quantitative and semi quantitative analysis of trace elements in liquid, suspension, and solid pollutants.
Application: water, wastewater and pollution elements in soil; toxic elements in the blood, urine and tissues; food, medicine, environmental protection, criminal investigation, ceramics, cement, building materials, geology and other fields.
The solid, liquid, powder, suspension, filter, air particulates, thin film samples of qualitative and quantitative analysis, a range of elements 13Al-92U, in the range of PPB to 100%, the detection limit to 2pg.
Small sample quantity to the liquid and suspended matter samples of 1-50 increased slightly, 10 micrograms of powder samples.
The unique portable total reflection fluorescence instrument, the equipment is compact, the integral structure design, does not need any auxiliary equipment and the gas, the liquid nitrogen and so on, may obtain the scene to carry on the analysis.
1 and 25 fully automatic sample injector design of the two, respectively, for a small number of samples and a large number of samples every day automatic analysis.
The fourth generation XFlash SDD silicon drift detector, using the Parr post cooling technology, does not require liquid nitrogen, no consumption. The resolution is better than 160eV at MnKa 100Kcps.
Because of the total reflection, the fluorescence intensity is directly proportional to the element content. The standard curve factory has been calibrated, and the user can do quantitative analysis without standard samples.
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