Study on the rapid determination of lead content in liquid coatings

0 Introduction:
lead is a non-essential harmful element of the human body, and there is a rich effect in the human body. Long-term exposure to lead-containing substances tends to damage bones, hema production systems, nervous systems, and brain cells in the human body, especially in children. In recent years, with the increasing awareness of human health and fierce competition in international trade, lead content in coatings (including coatings) has become a hot issue, and many countries have set strict limit
s on lead content in
coatings. Due to the need of source management, the detection method of lead content in liquid coatings has become a hot research topic.
At present, for the detection of lead content in liquid coatings, the detection method of lead content in liquid coatings is widely used at home and abroad, that is, liquid coatings are coated into solid-state coatings, the scraping coating is crushed for acid extraction or digestion, and finally the use of flame atom absorption spectroscopy or inductively coupled plasma spectroscopy to determine . Although these methods can accurately determine the lead content in the coating, but they are time-and-effort, and in the sample pre-processing process is prone to errors. X-ray fluorescence spectroscopy (XRF) is a fast, accurate and non-destructive method of rapid non-destructive non-destructive analysis developed in recent years, which has been recognized as an effective method of rapid semi-quantitative testing in the relevant detection of the EU RoH S Directive. In order to shorten the test time and reduce the test cost, this paper draws on the advantages of X-ray fluorescence spectroscopy in the rapid semi-quantitative analysis, and for the first time establishes a fast semi-quantitative method for lead content in liquid coatings.
1 Materials and Methods
1 1 Instruments, Reagents and Materials
X-ray Fluorescence Spectrometer: Izuzu EDX - 720 Energy Dispersion X-ray Fluorescence Spectrometer, Rh Target X-ray Tube, Tube Voltage 50 kV, Tube Current 100 uA, Ag Filter.
other equipment: German B rand 0.01 to 1.0 mL liquid transfer gun; Swiss M ettler AG 2.85 millionths of a ng of high-precision electronic balance; French M illipore ultra-pure water.
lead standard solution: accurately named a certain amount of pure lead nitrate (accurate to 0.000 1 g), configured with ultra-pure water into 5,000 mg /kg of lead master liquid, and then configured with liquid paint as a base of 10 mg /kg, 20 m /kg, 40 m g /kg, 80 mg / kg series of lead standard solution.
1 2 Work Curve Production
In accordance with the EDX-720 production steps on the working curve, set the instrument analysis conditions, test the above series of standard samples on the instrument, each standard sample test time of about 150 s.
select the characteristics of lead elements X-ray spectrum Pb Lb1 (12.42 to 12.82 keV), based on the fit peak area to establish a paint-based lead working curve.
2 Results and Discussion
2 1 Standard Curve
In X-ray fluorescence spectroscopic analysis, the absorption of X-rays by the sample substate affects the determination of the target element, and the working curve of the commercial EDX instrument with other materials as the substation may not be accurately applied to the determination of lead content in liquid coatings. Therefore, this paper first selected A, B, C 3 different coatings as a substation to configure the series of lead-containing standard samples, in order to investigate the feasibility of self-built lead standard curve. Table 1 shows the results of standard samples from the lead-containing series of 3 coatings. Lead concentration of X i in the working curve; Ii is the corresponding characteristic X-ray intensity.
Table 1 shows that in different coating substates, the X-ray signature line strength of lead elements at the same concentration level is basically the same, the characteristic spectral strength of lead elements in blank substates is close to 0, and the minimum correlation coefficient of 3 standard curves is 0.998 6 squared. This shows that the coating substit span is not significantly absorbed for lead feature X-rays, different paint substitums have little effect on the accuracy of lead element analysis results, and the working curve of certain types of coatings can be applied to the determination of lead content in other types of coatings.
2 2 Analog Sample Verification
To verify the effectiveness of the working curve, four simulated samples with different lead concentrations were re-provisioned with Class D coatings (1, 2, 3, 4), and then quantitatively tested separately using the Class C paint working curve, the results of which are in Table 2.
table 3 showed that the six reproducible measurements of lead elements in three different coating substitums were basically the same, with a maximum standard deviation of 2 20 m g /kg. This indicates that the method is more reproducible.
2 4 method detection limit
using the class C paint working curve for 12 repeated measurements of unleaded blank coatings, with 3 times the standard deviation calculation method detection limit, the result is 3.1 m g / kg. It shows that the method detection limit is lower than the existing standard limit, and the method has a large application space.
comparison of the 2 5 method
Due to the lack of previous research on lead content detection of EDX applied to liquid coatings, commercial EDX equipment has not yet been seen to come with a working curve based on liquid coatings. In this case, the user is generally recommended to use the plastic working curve that come with the EDX device. In order to compare the accuracy of these two working curves, 4 different types of coatings were selected as substitins, and the theoretical value of 25 m g/kg was configured with analog samples of 11, 22, 33, 44, using the C paint working curve and the instrument's own plastic working curve for quantitative determination, the test results can be seen in Table 4.
Table 4 shows that the maximum error of the plastic working curve test results is 115.6%, the average error is 71.6%, and the maximum error of the self-built C-type coating working curve test results is 30.8%, and the average error is 15.1%. This shows that, relative to the plastic working curve, the self-built working curve can significantly improve the accuracy of lead content test results in liquid coatings due to the use of coatings as a substitin.
3 Conclusion
On the energy dispersion X-ray fluorescence spectrometer (EDX), a liquid coating-based lead element working curve is built, and in the lead content range of 0 to 100 m g /kg, the lead element working curve of different types of coatings is basically the same, and the semi-quantitative determination of different paint samples can be performed with a single working curve. The results of simulation sample verification and method reproducible test show that the method has good accuracy and reproducity, and the method detection limit is 3.1 m g /kg, which can meet the requirements of rapid semi-quantitative screening of lead content of liquid paint. Compared with the plastic working curves commonly used in commercial EDX, self-built working curves have obvious advantages in accuracy and accuracy. In short, the method does not require any chemical pre-treatment of samples, with fast, simple, more accurate data and so on, can greatly reduce the testing workload, promote the use of the regulatory authorities to improve testing efficiency, but also help manufacturers to strengthen internal control.