碱溶分光光度法测定植硅体碳含量
杨杰 李永夫 黄张婷 姜培坤
1引言
近年来,植硅体碳作为一种了解全球气候变化潜力的稳定型有机碳已被科学工作者广泛研究\[1,2\]。为进一步对植硅体碳进行深入研究,开发出快速准确检验植硅体中有机碳含量的新方法变得尤为迫切。目前,植硅体碳的测定方法主要有Elementar Vario MAX CNS分析仪法和酸溶法\[3,\],前者需要高温条件及特定仪器,难于适应大批样品低损耗、快速经济检测的需求;后者存在环境污染的风险,同时也对操作人员具有一定的安全隐患,本实验建立了强碱快速溶解植硅体,重铬酸钾硫酸溶液氧化分光光度法定量测定植硅体碳的方法,扩大了检测限度,降低了分析成本。
2实验部分
2.1仪器与试剂722可见分光光度计(上海菁华科技仪器有限公司);万分之一电子天平(上海民桥精密科学仪器有限公司);微波消解仪(美国CEM公司); Elementar Vario MAX CN(德国)分析仪;低速离心机(中科中佳科学仪器有限公司)。
NO3, 2SO, Cl, 2O2, NaO, C22O·22O(优级纯,上海凌峰化学试剂有限公司);K2Cr2O7(分析纯,无锡海硕生物有限公司);eSO·(N)2SO·62O(分析纯,湖州湖试化学试剂有限公司);(N)6Mo7O2·2O(分析纯,合肥科华精细化工研究所);Si标准物质(国家有色金属及电子材料分析测试中心);土壤标准样(2013年5月以国家标准物质GBW0705校准);C612O6·2O(国药准字31021728;上海信谊金朱药业有限公司)。
2.2植硅体植硅体碳样本的制备植硅体的提取采用微波消解法\[5\],确保有机质完全除去后干燥确保足量。
2.3实验原理及方法在外加热(98 ℃)的条件下,用一定浓度的重铬酸钾硫酸溶液氧化有机碳\[6\],生成Cr3+,在590 nm下比色,根据K2Cr2O7的消耗量,计算有机碳含量。化学反应如下:
2K2Cr2O7 + 82SO + 3C=2K2SO + 2Cr2(SO)3 + 3CO2 + 82O(1)
分别称取0.0100 g植硅体样品于10 mL塑料离心管中,加入10 mol/L NaO 0.5 mL,摇匀,静置碱溶12 h。转移入30 mL玻璃离心管中,用超纯水清洗塑料离心管两次,每次0.7 mL,一并转入玻璃离心管。加入0.800 mol/L K2Cr2O7溶液1.0 mL,浓2SO.6 mL,轻轻摇匀。98 ℃沸水浴1 h,冷却,定容至25 mL,轻轻摇匀,2500 r/ min低速离心10 min,取上清液,于590 nm比色测定。
2.数据处理数据的处理在Microsoft Excel 2003中进行,数据的统计与检验在SPSS 18.0中进行。利用单因素方差分析,Duncan新复极差法检验不同处理方法的差异显著性(α=0.01, α=0.05)。Origin 8.5软件作图。
3结果与讨论
3.1称样量及碱溶时间的确定不同的植硅体样品中有机碳的含量不同\[7\]。根据植硅体种类的不同, 称取约0.0100 g植硅体样品待实验测定。为确保方法适用于更广泛的植硅体碳的测定,此步骤以纯净的SiO2代替植硅体,在不同的时间条件下进行碱溶,测定溶出的Si浓度。结果表明,碱浓度为10 mol/L、碱溶体积为0.5 mL的前提下,碱溶12 h是使植硅体外层SiO2溶解的最佳时间。
3.2氧化条件及水浴温度的选择本实验选择3种植硅体样品,在5个氧化梯度(浓硫酸与植硅体碱溶液比例分别为0.5∶1, 1∶1, 1.5∶1, 2∶1和2.5∶1)和5个水浴温度(30,60,90,95和98 ℃),设计正交试验,过程中加入土壤标准样品及有机碳标准溶液进行回收实验。结果表明,植硅体碳氧化的最佳条件是:浓硫酸与植硅体碱溶液体积比为1.5∶1,水浴温度98 ℃。此条件下,土壤标准样品及有机碳标准溶液中有机碳的回收率分别为100.1%~103.0%和10.8%~107.0%。
3.3标准曲线的绘制准确吸取有机碳标准溶液(0.90909 g/L)0, 0.5, 1.0, 1.5和2.0 mL于比色管中,以超纯水分别定容至2.0 mL,准确加入浓度为0.800 mol/L K2Cr2O7标准溶液1.0 mL,其余条件与样品处理条件相同,定容至25 mL,此时含有机碳浓度分别为0, 18.2, 36., 5.5和72.7 mg/L。用1 cm光程比色皿于590 nm下比色,记录吸光度。绘制标准曲线,建立回归方程。
3.实验样品的分析及方法可行性检验按照以上确定的步骤及方法对采自12个地方的20个土壤及植物样品所提取的植硅体样品进行分析,测定结果同目前常用的Elementar Vario MAX CNS分析仪的测定结果比较(图1)。结果表明,两种方法测定的植硅体样品的植硅体碳含量在数值上完全可以相互比对,不存在明显的系统差异。将两种方法的测定结果进行t检验而当自由度v=19时,在5%水平下t=2.09,|t| 1Wilding L P. Science, 1967, 156(3771): 66-67
2Parr J, Sullivan L, Chen B, Ye G , Zheng W P. Global Change Biology, 2010, 16(10): 2661-2667
3Parr J , Sullivan L A. Plant and Soil., 201, 37(12): 5-53
Song Z,Wang, , Strong, P.J, Li, Z. and Jiang, P. EarthScience Reviews., 2012, 115(): 319-331
5Parr J , Dolic V, Lancaster G, Boyd W E. Review of Palaeobotany and Palynology, 2001, 116(3): 203-212
6SoilDetermination of Organic CarbonPotassium Dichromate Oxidation Spectrophotometric Method. he people′s Republic of China national standard of environmental protection. J 615-2011
土壤有机碳的测定重铬酸钾氧化分光光度法. 中华人民共和国国家环境保护标准. J 615-2011
7Parr J , Dolic V, Lancaster G, Boyd W E. Review of Palaeobotany and Palynology, 2001, 116(3): 203-212
AbstractA method to determine phytolithoccluded carbon (PhytOC) was explored. Sodium hydroxide solution was used to dissolve the silicon compound(SiO2·n2O) which occluding on the carbon, and then potassium dichromatesulphuric acid solution was used to oxidize the released organic carbon. he concentration of Gr3+produced from the reaction was measured by spectrophotometry with its absorbance at 590 nm wavelength. he organic carbon concentration was calculated based on the amounts of potassium dichromate consumed. his analytical method was verified well accuracy and repeatability by running standard addition and recovery experiments. It has the advantages of low carbon loss, easy to operate, low cost; and hardly any influence to body health, as compared with acid dissolutionElementar Vario MAX CN method. he results obtained from this method have a good correlation with these determined by Elementar Vario MAX CN (Germany).
KeywordsPhytolith; Phytolithoccluded carbon; Alkali dissolution; Spectrophotometry
Song Z,Wang, , Strong, P.J, Li, Z. and Jiang, P. EarthScience Reviews., 2012, 115(): 319-331
5Parr J , Dolic V, Lancaster G, Boyd W E. Review of Palaeobotany and Palynology, 2001, 116(3): 203-212
6SoilDetermination of Organic CarbonPotassium Dichromate Oxidation Spectrophotometric Method. he people′s Republic of China national standard of environmental protection. J 615-2011
土壤有机碳的测定重铬酸钾氧化分光光度法. 中华人民共和国国家环境保护标准. J 615-2011
7Parr J , Dolic V, Lancaster G, Boyd W E. Review of Palaeobotany and Palynology, 2001, 116(3): 203-212
AbstractA method to determine phytolithoccluded carbon (PhytOC) was explored. Sodium hydroxide solution was used to dissolve the silicon compound(SiO2·n2O) which occluding on the carbon, and then potassium dichromatesulphuric acid solution was used to oxidize the released organic carbon. he concentration of Gr3+produced from the reaction was measured by spectrophotometry with its absorbance at 590 nm wavelength. he organic carbon concentration was calculated based on the amounts of potassium dichromate consumed. his analytical method was verified well accuracy and repeatability by running standard addition and recovery experiments. It has the advantages of low carbon loss, easy to operate, low cost; and hardly any influence to body health, as compared with acid dissolutionElementar Vario MAX CN method. he results obtained from this method have a good correlation with these determined by Elementar Vario MAX CN (Germany).
KeywordsPhytolith; Phytolithoccluded carbon; Alkali dissolution; Spectrophotometry
Song Z,Wang, , Strong, P.J, Li, Z. and Jiang, P. EarthScience Reviews., 2012, 115(): 319-331
5Parr J , Dolic V, Lancaster G, Boyd W E. Review of Palaeobotany and Palynology, 2001, 116(3): 203-212
6SoilDetermination of Organic CarbonPotassium Dichromate Oxidation Spectrophotometric Method. he people′s Republic of China national standard of environmental protection. J 615-2011
土壤有机碳的测定重铬酸钾氧化分光光度法. 中华人民共和国国家环境保护标准. J 615-2011
7Parr J , Dolic V, Lancaster G, Boyd W E. Review of Palaeobotany and Palynology, 2001, 116(3): 203-212
AbstractA method to determine phytolithoccluded carbon (PhytOC) was explored. Sodium hydroxide solution was used to dissolve the silicon compound(SiO2·n2O) which occluding on the carbon, and then potassium dichromatesulphuric acid solution was used to oxidize the released organic carbon. he concentration of Gr3+produced from the reaction was measured by spectrophotometry with its absorbance at 590 nm wavelength. he organic carbon concentration was calculated based on the amounts of potassium dichromate consumed. his analytical method was verified well accuracy and repeatability by running standard addition and recovery experiments. It has the advantages of low carbon loss, easy to operate, low cost; and hardly any influence to body health, as compared with acid dissolutionElementar Vario MAX CN method. he results obtained from this method have a good correlation with these determined by Elementar Vario MAX CN (Germany).
KeywordsPhytolith; Phytolithoccluded carbon; Alkali dissolution; Spectrophotometry
1引言
近年来,植硅体碳作为一种了解全球气候变化潜力的稳定型有机碳已被科学工作者广泛研究\[1,2\]。为进一步对植硅体碳进行深入研究,开发出快速准确检验植硅体中有机碳含量的新方法变得尤为迫切。目前,植硅体碳的测定方法主要有Elementar Vario MAX CNS分析仪法和酸溶法\[3,\],前者需要高温条件及特定仪器,难于适应大批样品低损耗、快速经济检测的需求;后者存在环境污染的风险,同时也对操作人员具有一定的安全隐患,本实验建立了强碱快速溶解植硅体,重铬酸钾硫酸溶液氧化分光光度法定量测定植硅体碳的方法,扩大了检测限度,降低了分析成本。
2实验部分
2.1仪器与试剂722可见分光光度计(上海菁华科技仪器有限公司);万分之一电子天平(上海民桥精密科学仪器有限公司);微波消解仪(美国CEM公司); Elementar Vario MAX CN(德国)分析仪;低速离心机(中科中佳科学仪器有限公司)。
NO3, 2SO, Cl, 2O2, NaO, C22O·22O(优级纯,上海凌峰化学试剂有限公司);K2Cr2O7(分析纯,无锡海硕生物有限公司);eSO·(N)2SO·62O(分析纯,湖州湖试化学试剂有限公司);(N)6Mo7O2·2O(分析纯,合肥科华精细化工研究所);Si标准物质(国家有色金属及电子材料分析测试中心);土壤标准样(2013年5月以国家标准物质GBW0705校准);C612O6·2O(国药准字31021728;上海信谊金朱药业有限公司)。
2.2植硅体植硅体碳样本的制备植硅体的提取采用微波消解法\[5\],确保有机质完全除去后干燥确保足量。
2.3实验原理及方法在外加热(98 ℃)的条件下,用一定浓度的重铬酸钾硫酸溶液氧化有机碳\[6\],生成Cr3+,在590 nm下比色,根据K2Cr2O7的消耗量,计算有机碳含量。化学反应如下:
2K2Cr2O7 + 82SO + 3C=2K2SO + 2Cr2(SO)3 + 3CO2 + 82O(1)
分别称取0.0100 g植硅体样品于10 mL塑料离心管中,加入10 mol/L NaO 0.5 mL,摇匀,静置碱溶12 h。转移入30 mL玻璃离心管中,用超纯水清洗塑料离心管两次,每次0.7 mL,一并转入玻璃离心管。加入0.800 mol/L K2Cr2O7溶液1.0 mL,浓2SO.6 mL,轻轻摇匀。98 ℃沸水浴1 h,冷却,定容至25 mL,轻轻摇匀,2500 r/ min低速离心10 min,取上清液,于590 nm比色测定。
2.数据处理数据的处理在Microsoft Excel 2003中进行,数据的统计与检验在SPSS 18.0中进行。利用单因素方差分析,Duncan新复极差法检验不同处理方法的差异显著性(α=0.01, α=0.05)。Origin 8.5软件作图。
3结果与讨论
3.1称样量及碱溶时间的确定不同的植硅体样品中有机碳的含量不同\[7\]。根据植硅体种类的不同, 称取约0.0100 g植硅体样品待实验测定。为确保方法适用于更广泛的植硅体碳的测定,此步骤以纯净的SiO2代替植硅体,在不同的时间条件下进行碱溶,测定溶出的Si浓度。结果表明,碱浓度为10 mol/L、碱溶体积为0.5 mL的前提下,碱溶12 h是使植硅体外层SiO2溶解的最佳时间。
3.2氧化条件及水浴温度的选择本实验选择3种植硅体样品,在5个氧化梯度(浓硫酸与植硅体碱溶液比例分别为0.5∶1, 1∶1, 1.5∶1, 2∶1和2.5∶1)和5个水浴温度(30,60,90,95和98 ℃),设计正交试验,过程中加入土壤标准样品及有机碳标准溶液进行回收实验。结果表明,植硅体碳氧化的最佳条件是:浓硫酸与植硅体碱溶液体积比为1.5∶1,水浴温度98 ℃。此条件下,土壤标准样品及有机碳标准溶液中有机碳的回收率分别为100.1%~103.0%和10.8%~107.0%。
3.3标准曲线的绘制准确吸取有机碳标准溶液(0.90909 g/L)0, 0.5, 1.0, 1.5和2.0 mL于比色管中,以超纯水分别定容至2.0 mL,准确加入浓度为0.800 mol/L K2Cr2O7标准溶液1.0 mL,其余条件与样品处理条件相同,定容至25 mL,此时含有机碳浓度分别为0, 18.2, 36., 5.5和72.7 mg/L。用1 cm光程比色皿于590 nm下比色,记录吸光度。绘制标准曲线,建立回归方程。
3.实验样品的分析及方法可行性检验按照以上确定的步骤及方法对采自12个地方的20个土壤及植物样品所提取的植硅体样品进行分析,测定结果同目前常用的Elementar Vario MAX CNS分析仪的测定结果比较(图1)。结果表明,两种方法测定的植硅体样品的植硅体碳含量在数值上完全可以相互比对,不存在明显的系统差异。将两种方法的测定结果进行t检验而当自由度v=19时,在5%水平下t=2.09,|t|
2Parr J, Sullivan L, Chen B, Ye G , Zheng W P. Global Change Biology, 2010, 16(10): 2661-2667
3Parr J , Sullivan L A. Plant and Soil., 201, 37(12): 5-53
Song Z,Wang, , Strong, P.J, Li, Z. and Jiang, P. EarthScience Reviews., 2012, 115(): 319-331
5Parr J , Dolic V, Lancaster G, Boyd W E. Review of Palaeobotany and Palynology, 2001, 116(3): 203-212
6SoilDetermination of Organic CarbonPotassium Dichromate Oxidation Spectrophotometric Method. he people′s Republic of China national standard of environmental protection. J 615-2011
土壤有机碳的测定重铬酸钾氧化分光光度法. 中华人民共和国国家环境保护标准. J 615-2011
7Parr J , Dolic V, Lancaster G, Boyd W E. Review of Palaeobotany and Palynology, 2001, 116(3): 203-212
AbstractA method to determine phytolithoccluded carbon (PhytOC) was explored. Sodium hydroxide solution was used to dissolve the silicon compound(SiO2·n2O) which occluding on the carbon, and then potassium dichromatesulphuric acid solution was used to oxidize the released organic carbon. he concentration of Gr3+produced from the reaction was measured by spectrophotometry with its absorbance at 590 nm wavelength. he organic carbon concentration was calculated based on the amounts of potassium dichromate consumed. his analytical method was verified well accuracy and repeatability by running standard addition and recovery experiments. It has the advantages of low carbon loss, easy to operate, low cost; and hardly any influence to body health, as compared with acid dissolutionElementar Vario MAX CN method. he results obtained from this method have a good correlation with these determined by Elementar Vario MAX CN (Germany).
KeywordsPhytolith; Phytolithoccluded carbon; Alkali dissolution; Spectrophotometry
Song Z,Wang, , Strong, P.J, Li, Z. and Jiang, P. EarthScience Reviews., 2012, 115(): 319-331
5Parr J , Dolic V, Lancaster G, Boyd W E. Review of Palaeobotany and Palynology, 2001, 116(3): 203-212
6SoilDetermination of Organic CarbonPotassium Dichromate Oxidation Spectrophotometric Method. he people′s Republic of China national standard of environmental protection. J 615-2011
土壤有机碳的测定重铬酸钾氧化分光光度法. 中华人民共和国国家环境保护标准. J 615-2011
7Parr J , Dolic V, Lancaster G, Boyd W E. Review of Palaeobotany and Palynology, 2001, 116(3): 203-212
AbstractA method to determine phytolithoccluded carbon (PhytOC) was explored. Sodium hydroxide solution was used to dissolve the silicon compound(SiO2·n2O) which occluding on the carbon, and then potassium dichromatesulphuric acid solution was used to oxidize the released organic carbon. he concentration of Gr3+produced from the reaction was measured by spectrophotometry with its absorbance at 590 nm wavelength. he organic carbon concentration was calculated based on the amounts of potassium dichromate consumed. his analytical method was verified well accuracy and repeatability by running standard addition and recovery experiments. It has the advantages of low carbon loss, easy to operate, low cost; and hardly any influence to body health, as compared with acid dissolutionElementar Vario MAX CN method. he results obtained from this method have a good correlation with these determined by Elementar Vario MAX CN (Germany).
KeywordsPhytolith; Phytolithoccluded carbon; Alkali dissolution; Spectrophotometry
Song Z,Wang, , Strong, P.J, Li, Z. and Jiang, P. EarthScience Reviews., 2012, 115(): 319-331
5Parr J , Dolic V, Lancaster G, Boyd W E. Review of Palaeobotany and Palynology, 2001, 116(3): 203-212
6SoilDetermination of Organic CarbonPotassium Dichromate Oxidation Spectrophotometric Method. he people′s Republic of China national standard of environmental protection. J 615-2011
土壤有机碳的测定重铬酸钾氧化分光光度法. 中华人民共和国国家环境保护标准. J 615-2011
7Parr J , Dolic V, Lancaster G, Boyd W E. Review of Palaeobotany and Palynology, 2001, 116(3): 203-212
AbstractA method to determine phytolithoccluded carbon (PhytOC) was explored. Sodium hydroxide solution was used to dissolve the silicon compound(SiO2·n2O) which occluding on the carbon, and then potassium dichromatesulphuric acid solution was used to oxidize the released organic carbon. he concentration of Gr3+produced from the reaction was measured by spectrophotometry with its absorbance at 590 nm wavelength. he organic carbon concentration was calculated based on the amounts of potassium dichromate consumed. his analytical method was verified well accuracy and repeatability by running standard addition and recovery experiments. It has the advantages of low carbon loss, easy to operate, low cost; and hardly any influence to body health, as compared with acid dissolutionElementar Vario MAX CN method. he results obtained from this method have a good correlation with these determined by Elementar Vario MAX CN (Germany).
KeywordsPhytolith; Phytolithoccluded carbon; Alkali dissolution; Spectrophotometry