Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/5176
標題: 農地土壤重金屬之測定-密閉微波法與熱板迴流法之比較
Determination of Heavy Metals in Agricultural Soils by Flame Atomic Absorption Spectrometry: Microwave Acid Digestion versus Aqua Regia Extraction
作者: 范育湘
Fan, Yu-Hsiang
關鍵字: soil;土壤;heavy metal;closed microwave digestion;heavy metal analytic method;重金屬;密閉微波消化;重金屬分析方法
出版社: 環境工程學系所
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摘要: 
本研究利用密閉微波法消化土壤,並以火焰式原子吸收光譜法分析鎘、銅、鉛、鋅四種金屬元素,目的在探討以密閉微波法取代傳統王水熱板迴流消化法,測定土中重金屬之可行性。
研究步驟依序為:1、以彰化和美重金屬污染農地土樣做為供試樣品,探討密閉微波法之最適條件;2、分析土壤標準參考樣品CRM 2003、CRM141R及CRM026-050,以評估方法的準確性;3、分析取自桃園、彰化、高雄、台東等地區之14個真實土樣,以瞭解所建立微波方法的適用性;4、嘗試利用逐步萃取法的測定結果,探討密閉微波法溫度不同(180℃及112℃)所造成分析值差異的原因。
所建立之密閉微波法操作條件為土樣0.5 g、加入試劑後靜置時間1 hr、採標準控制模式、消化瓶數16瓶、功率600 W、微波消化時間10分鐘,微波消化溫度以112℃為主,另外為進行不同方法的比較,微波溫度亦採用180℃。以建立之密閉微波法於112℃及180℃的微波溫度下分別消化三種土壤參考樣品,結果顯示以微波溫度112℃進行消化分析時,鎘的回收率在104%-106%之間,精密度為0.05%-2.42%;銅的回收率在102%-103%之間,精密度為0.05%-0.17%;鉛的回收率在100%-143%之間,精密度為0.47%-2.14%;鋅的回收率在104%-108%之間,精密度為1.44%-2.81%;微波溫度採用180℃時,各金屬的回收率則有偏高的情形,而分析值的變異也較大。以上結果顯示欲以密閉微波消化法取代傳統熱板迴流法時,微波溫度應選用112℃。
以所建立的密閉微波消化法分析14個真實土樣,將其結果與熱板迴流法之測值相比較得知,鎘、鉛、鋅的分析結果均很接近,銅之分析值在使用密閉微波法時測值稍高於熱板迴流法的測值。整體而言,微波法與熱板法的差異百分比(以熱板法為基準)皆在±20%以內,在環境樣品的分析上,此為可接受的範圍。因此,以本研究所建立的微波消化分析方法具有其實用性。
另外,利用逐步萃取法的分析結果與微波法(112℃與180℃)的分析結果相比較,大部分土樣以兩種溫度的微波法萃出之濃度值均約略可達到逐步萃取法的第五態(殘餘態),而此結果亦無法提供解釋來說明,微波溫度不同時為何測值會有差異。
整體而言利用本密閉微波法消化土壤重金屬,除了在樣品量、酸的使用量較熱板迴流法少之外;加入試劑後的靜置時間及消化時間亦顯著縮短;且具有良好的精密度以及可接受的準確度,所以具有實用的價值。另外,因是密閉消化方式,所以人員及設備暴露於強酸環境的機會可大幅降低。

Closed-microwave method is employed in this study for digesting soil samples, and four heavy metals (Cd, Cu, Pb, and Zn) are analyzed by flame atomic absorption spectrophotometry (FAAS). The purpose of the study is to investingate the feasibility of closed-microwave method instead of traditional aqua regia hotplate reflux method for heavy metal determination in soil.
In this paper, Firstly, a contaminated farm soil taken Hemei, Zanhua was used to optimize the conditions of closed-microwave method. Secondly, three standard reference materials(CRM 2003、 CRM 141 and CRM 026-050)were analyzed to evaluate the accuracy of the method. Thirdly, fourteen real soil samples were used to test the applicability of this microwave method. Finally, results obtained by sequential extraction wre used to explain why different results occurred at different digestion temperature.
The optimized conditions of closed-microwave digestion method are as follows: 0.5 g soil sample, settling for 1 hour after adding oxidizing reagent(4.6 mL aqua regia),a batch of sixteen digestion bottles, power of 600 W, microwave digestion at 112℃ for 10 min. Three standard reference soil samples were analyzed by microwave digestion combined with FAAS. The results show that for Cd the recovery is 104%-106%, the precision is 0.05%-2.42%; for Cu the recovery is 102%-103%, the precision is 0.05%-0.17%; for Pb the recovery is 100%-143%, the precision is 0.47%-2.14%; for Zn the recovery is 104%-108%, the precision is 1.44%-2.81%. Three standard reference materials were also digested at 180℃. The results illustrated higher recoveries and lower variation. According to the above outcomes, temperature of 112℃ is a better choice when the microwave-digestion is applied for soil digestion instead of traditional hotplate reflux method.
Fourteen real soil samples were analyzed by microwave and traditional methods. The results had good agreement and the relative difference were within ±20%. Therefore, the microwave-assisted digestion method has proved to be a viable alternative to the traditional aqua regia reflux method for rapidly determining heavy metals in farmland soil samples.
In addition, the results obtained by sequential l extractions were not able to explain why the results obtained with 112℃ digestion were different from that obtained with 180℃ digestion.
In sum, using closed-microwave digestion method for heavy metal determination method in soil samples has the advantages including fewer amounts of sample used , less acid required and less time consumed. Thus, the method is of great applicability. In addition, the strong-acid exposure risk of facilities and workers can be decreased significantly because of closed-microwave system.
URI: http://hdl.handle.net/11455/5176
其他識別: U0005-1808200614595200
Appears in Collections:環境工程學系所

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