Quantitative composite testing model based on measurement uncertainty and its application for the detection of phthalate esters.

To improve the quantitative detection efficiency of chemical analysis and reduce the detection cost, the sample pass rate was estimated and mathematical statistics were used to calculate the optimal group size (K opt) of the composite testing to save on the maximum workload. A quantitative composite testing model was developed based on chemical analysis measurement uncertainty. Using this model, the maximum allowable number of composited samples (K max) is first calculated using parameters of regulated limits (L), limit of quantification (LOQ), and method measured uncertainty (U rel) to ensure that the sensitivity of the composite testing can meet the limit requirements. Finally, the appropriate composite group size (K a) can be obtained by creating a balance between K opt, K max, and the practical information used for that particular test. Furthermore, based on a constructed model, a practical quantitative composite testing method of 3-10 samples was established for the routine detection of toy phthalates (PAEs). The experimental results showed that the quantitative limits of 7 PAEs were 9.1-41.8 mg/kg, the relative expansion uncertainties were 16.6%-23.2%, and the recovery rates were 91.0%-112.3%, with a relative deviation of less than 10%. All these meet international PAEs standards. Compared with the traditional individual and qualitative composite testing, this model will not decrease the detection sensitivity, but can save up to 17.9%-80.4% of the workload when it is employed in toy PAEs testing with the pass rate of 80%-99%. This quantitative composite testing method will be implemented in the coming revision of ISO 8124-6 toy PAEs standards.

Chemometrics-based Discrimination of Virgin and Recycled Acrylonitrile-Butadiene-Styrene Plastics Toys via Non-targeted Screening of Volatile Substances.

Owing to the growing emphasis on child safety, it is greatly urgent to identify and assess the unknown compounds and discriminate the recycled materials for plastic toys. In this study, gas chromatography mass spectrometry coupled with static headspace has been optimized by response surface methodology for non-targeted screening of unknown volatiles in acrylonitrile-butadiene-styrene (ABS) plastic toys. Optimum conditions for static headspace were 120 °C for extraction temperature and 48 min for extraction time. A total of 83 volatiles in 11 categories were qualitatively identified by matching the NIST database library, retention index and standard materials. Considering high positive rate and potential toxicity, high-risk volatiles in ABS plastic toys were listed and traced for safety pre-warning. Moreover, the differential volatiles between virgin and recycled ABS plastics were screened out by orthogonal partial least-squares discrimination analysis. Principal component analysis, hierarchical cluster analysis and linear discrimination analysis were employed to successfully discriminate recycled ABS plastic toys based on the differential volatiles. The proposed strategy represents an effective and promising analytical method for non-targeted screening and risk assessment of unknown volatiles and discrimination of recycled materials combining with various chemometric techniques for children's plastic products to safeguard children's health.

Experimental and Theoretical Study on the False Positive of Monomethyltin Determination in Toys Based on Gastric Juice Migration.

BACKGROUND: Organic tin compounds (OTCs), a group of high-risk hazardous substances, are highly concerned in safety regulation of consumer products especially for toys because they can cause serious damage to organs after prolonged or repeated exposure. Gastric juice migration is nowadays widely implemented to assess organic tin intake from toys or food-contact materials; however, the followed up detection method using sodium tetraethylborate [NaB(Et4)] as a derivatization agent may directly lead to false positive of monomethyltins (MMT). OBJECTIVE: In order to avoid the phenomena of false positive of MMT in the course of laboratory testing of toys, it is necessary and important to perform relative experimental and theoretical studies to reveal the cause of false positive of MMT. METHOD: With metal tin powder as a representative of inorganic tin which existed in real samples, it was treated with artificial gastric juice (0.07 mol/L·HCl), followed by ethyl derivatization using sodium tetraethylborate [NaB(Et)4] and then analyzed by gas chromatography-mass spectrometry (GC-MS) according to the procedure specified in the standard of EN 71-3:2013+A3:2018 issued by the European Committee for Standardization (CEN). RESULTS: Without any OTCs in the starting materials, MMT false positive can be reproduced by detecting 0.56 mg/L of triethylmethyltin (TEMT) together with approximately 1000 mg/L of tetraethyltin (TeET), which is similar to real samples. Further, it is demonstrated that the detected amount of TEMT is linearly related with the added amount of NaB(Et)4, and that the formation of TEMT (methyl derivative) is easier than TeET (ethyl derivative) even though the ethyl group is present in a larger amount than the methyl group. CONCLUSIONS: The phenomena of MMT false positive which occurred in the laboratory testing of toys is mainly because that TEMT is highly likely to be obtained from the reaction of inorganic tin and trace level of methylation agent impurities contained in the derivatization reagent-NaB(Et)4. To avoid MMT false positive, it is concluded that the maximum acceptable mole ratio of methylation agent impurities contained in NaB(Et)4 is approximately 0.028%. This research is helpful to be aware of methylation impurities and is favorable to avoid false judgment caused by MMT false positive in routine analysis of toys.

[Determination of monomethyltin migration from toys by gas chromatography-mass spectrometry and confirmation of its false positive].

Based on migration procedures using simulated gastric juice specified in the EU toy Safety Standard EN 71-3:2013/A2:2017, a method was developed for the determination of monomethyltin (MMT) migration from toys by gas chromatography-mass spectrometry (GC-MS). Further, a reliable confirmation method for judgement of a false positive for MMT obtained by GC-MS, was established. After optimizing the migration conditions, derivatization steps and chromatographic parameters, the method yielded a linear range from 0.02 to 1.0 mg/L with a correlation coefficient (R2) of 0.9992. The limits of detection and quantification of the method were 0.11 and 0.32 mg/kg, respectively. The recoveries were 86.2%-104.2% under different spiked levels (0.5, 1.0 and 1.5 µg), and the relative standard deviations were 3.1%-8.2% (n=6). MMT migration ranging from 0.44 to 0.67 mg/kg was detected in the surface coating of tin-plating (Sn-Fe alloy) toy materials, which was subsequently confirmed to be false positive. Therefore, a novel confirmative approach using methanol or acetone as the migration solvent was proposed, aiming at verifying the false positive of MMT. The results showed that the previously positive MMT detected by GC-MS could no longer be detected when treated by these migration solvents.Hence, this approach can be used to confirm false positive detected for MMT after GC-MS detection.

Aluminum Foil Lattice Method for Characterizing Performance of Bath-Type Ultrasonic-Assisted Extraction Equipment.

Background: Bath-type ultrasonic-assisted extraction (UAE) has been developed as one of the most important sample pretreatment methods, especially for batch-sample pretreatment. So far, however, requirements for the performance of bath-type UAE equipment have not been standardized, nor has a suitable evaluation method that can be used to judge the feasibility of ultrasonic equipment for extraction been presented in the available regulations or standards. Objective: A simple and efficient method that can be used to evaluate the performance of bath-type UAE equipment is necessary to be proposed and established. Methods: First, distribution of a sound field in ultrasonic equipment was measured by acoustimeter and the dyeing method, through which influencing factors including frequency, preheating time, and output power of the equipment, as well as the horizontal and vertical position for locating the sample in the equipment, were investigated, and optimized parameters for extraction were achieved. Then, through the aluminum foil lattice method, by calculating the perforated rate of the aluminum foil, cavitation intensity of the ultrasonic equipment can be quantitatively determined. Results: With the optimized working conditions and by selecting appropriate parameters for the aluminum foil, perforated holes formed on the foil displayed a good pattern. Further validation experiments indicated conformity between the established method and the actual extraction effect of the ultrasonic equipment, proposing a suitable requirement for the cavitation effect of the bath-type UAE equipment. Conclusions: The aluminum foil lattice method has been proved to be simple, convenient, inexpensive, and reliable for quickly evaluating the extraction performance of bath-type UAE equipment.

[Simultaneous determination of the total content of As, Ba, Cd, Cr, Hg, Pb, Se, Sb in paint coating on toys by ICP-AES].

ICP-AES was used for the simultaneous determination of the total content of As, Ba, Cd, Cr, Hg, Pb, Se, Sb in paint coating on toys. Digestion procedures of these materials with different acid mixtures have been developed. The sample was dissvolved in the acid mixture of nitric acid, tartaric acid, and a little phosphoric acid. The matrix elements effect was studied and the preferable experimental conditions were investigated. The recovery rates of this procedure were between 99% and 109%. The RSD was within 1.5%. The proposed method was simple, rapid and can be used in daily inspection of toys.