摘要:
The reliable quantification of perfluoroalkyl carboxylic acids (PFCAs) in environmental samples like surface water by using gas chromatography (GC) remains challenging because the polar PFCAs call for derivatization before injection and problems involving the integration of sample pretreatment and derivatization procedures. Here we proposed a cost-effective method for the GC based determination of C4-C12 PFCAs in surface water samples by integrating solid phase extraction and PFCAs anilide derivatization. First, we assessed the performance of different PFCAs derivatization methods, namely esterification and amidation. Esterification was unable to derivatize C4-C6 PFCAs. On the contrary, amidation procedures by using 2,4-difluoroaniline (DFA) and N,N '-dicyclohexylcarbodiimide (DCC) could successfully transform all the PFCA analogs to produce anilide derivatives, which could be easily detected by GC. Then the reaction conditions in the amidation approach were further optimized by using orthogonal design experiments. After optimizing the instrumental parameters of GC, the limits of detection (LOD) of this derivatization method were determined to be 1.14-6.32 mu g L-1. Finally, in order to establish an intact method for the quantification of PFCAs in surface water samples, solid phase extraction (SPE) was used for extraction and cleanup, which was further integrated with the subsequent amidation process. The SPE-amidation-GC method was validated for application, with good accuracy and precision reflected by the PFCAs recoveries and derivatization of triplicates. The method reported here could provide a promising and cost-effective alternative for the simultaneous determination of C4-C12 PFCAs in environmental water samples.
期刊:
International Journal of Science Education,2019年41(10):1408-1433 ISSN:0950-0693
通讯作者:
Deng, Yang
作者机构:
[Deng, Yang; Deng, Shili] Cent China Normal Univ, Coll Chem, Inst Chem Educ, 152 Luoyu Rd, Wuhan 430079, Hubei, Peoples R China;[Kelly, Gregory J.] Penn State Univ, Coll Educ, Dept Curriculum & Instruct, State Coll, PA USA
通讯机构:
[Deng, Yang] C;Cent China Normal Univ, Coll Chem, Inst Chem Educ, 152 Luoyu Rd, Wuhan 430079, Hubei, Peoples R China.
摘要:
Scientific writing is related to the practice of communicating scientific knowledge. This study treats scientific writing as a social practice, taking as its premise the notion that participating in related activities such as reading, peer evaluation, and discussion would positively affect the competence of students' scientific writing, by developing their epistemic cognition regarding scientific knowledge communication and legitimation. An empirical study was conducted with twenty-two Chinese undergraduate students to test this premise. These students were majoring in chemistry and undertook a researcher-designed intervention course (Advanced Organic Chemistry Experiment), which embodied the integrated strategy of reading, peer evaluation, and discussion on scientific writing. Based on data pertaining to those students' performance in terms of the normativity, objectivity, and logicality of scientific writing drawn from a previous study by the current author (Deng, Kelly, & Xiao, 2019. The development of Chinese undergraduate students' competence of scientific writing in the context of advanced organic chemistry experiment course. Chemistry Education Research and Practice, 20, 270-287), alongside data drawn from students' written texts in reading reflections and on-line discourse related to peer evaluation and discussion, this study claimed that the tasks of reading, peer evaluation, and discussion were seen gradually to lead to the development of Chinese undergraduate students' greater competence in scientific writing regarding the synthetic experiments of organic chemistry.
期刊:
Chemistry Education Research and Practice,2019年20(1):270-287 ISSN:1109-4028
通讯作者:
Deng, Yang
作者机构:
[Deng, Yang; Xiao, Lishi] Cent China Normal Univ, Coll Chem, Inst Chem Educ, Wuhan 430079, Hubei, Peoples R China.;[Kelly, Gregory J.] Penn State Univ, Coll Educ, Dept Curriculum & Instruct, State Coll, PA 16802 USA.
通讯机构:
[Deng, Yang] C;Cent China Normal Univ, Coll Chem, Inst Chem Educ, Wuhan 430079, Hubei, Peoples R China.
期刊:
Chemistry Education Research and Practice,2017年18(1):127-150 ISSN:1109-4028
通讯作者:
Deng, Yang;Wang, Houxiong
作者机构:
[Wang, Houxiong; Deng, Yang] Cent China Normal Univ, Dept Chem, Wuhan 430079, Hubei, Peoples R China.
通讯机构:
[Deng, Y; Wang, HX] C;Cent China Normal Univ, Dept Chem, Wuhan 430079, Hubei, Peoples R China.
摘要:
Attending to practice has become a significant topic in science education today. As scientific argumentation is a typical form of scientific practice as well as an important educational practice, more and more attention has been paid to it by science education researchers. Evaluating students' competence in scientific argumentation is one of the most important research topics, but in China, science researchers seldom concentrate on it because the diverse educational values of scientific argumentation need to be further understood. The present study sought to examine the performance of Chinese students participating in written scientific argumentation in the context of chemistry. After clarifying the conception of scientific argumentation in science education, and comparing the evaluation criteria in domestic and international science education research, written scientific argumentation tasks in the context of chemistry were designed and criteria for their evaluation were constructed and improved. In total five tasks were designed for evaluation. All of the five tasks were aimed at evaluating students' competence of selecting (or putting forward) claims, evidence and warrants, in addition, two tasks investigated the competence of refuting arguments. The general criteria for evaluation was constructed according to the four dimensions of scientific argumentation, they were the structure components, the content quality, the logic of justification and language. For each task, content criteria and performance criteria for evaluation were constructed. After analysis and improvement of the criteria based on two pilot tests and the Rasch model, it was obvious that the criteria met the standards, effectively and credibly, for this study on the assessment of students' competence in written scientific argumentation. The number of students who participated in the formal test was 578 (304 males and 274 females). Through this kind of evaluation, this study found that the students' competence in written scientific argumentation was generally weak, and was influenced by some factors. Specifically, firstly, the students could put forward claims and evidence more easily than warrants and rebuttals. Secondly, the specific tasks had an influence on the performance of the students in written scientific argumentation. In regard to other factors, gender did not influence the students' competence in written scientific argumentation, but the grade level and school level were key factors. The students' competence in written scientific argumentation at grade level four and three other school grade levels were significantly different. Finally, some changes to the Chinese chemistry curriculum were proposed based on the results of this study.