PDF《氢化物发生-》

氢化物发生- 冷蒸气原子吸收 光谱法测定水中的 砷、 硒和汞 简介 工业和生活用水中砷、 硒和汞的污染来源于天然矿床, 工业排放, 水源流经采矿区, 垃圾填埋和农业活动.

食 用被污染的水会引起皮肤损害 (砷) , 肾脏和神经系统 损伤 (汞) 以及手指和脚趾的麻木 (硒) [1] . 美国环境保 护署(EPA)和加拿大环境部长理事会(CCME) 为保护海 洋和淡水水生生物, 保护农业已经对砷, 硒和汞的浓度 制定了限值[1] [2] . 由于砷, 硒和汞的限值水平很低, 所以 在低噪音水平下对这些元素进行精密而准确的测定是 非常重要的. 氢化物(HG)是一种非常有效的分析技术, 它可以通过改变酸度把待测元素 从一定范围的基质中氢化分离出来, 进行测定. 加热石英管原子化器在测定砷和硒时特 别有用, 因为这些元素的吸收波长在200nm以下, 这一区域主要受到来自火焰自由基的 强烈干扰, 这些干扰极大的影响检出限. 汞很容易从溶液中挥发出来, 产生元素汞, 也就 是被称为冷蒸气 (CV) 汞. 这种技术能有效的将汞从一定范围的基质中分离出来. 这一分 析技术可将检出限提高约3000倍, 即是火焰原子吸收检出限的3000倍, 并且与通常的石 墨炉原子吸收技术相比有较少的干扰. 把分析物从基质中分离出来的目的是可以提高原 原子吸收 应用说明作者 Aaron Hineman PerkinElmer公司 加拿大 安大略省 子吸收技术的灵敏度, 避免来自物理的, 基体的和光谱的干 扰. 从基体中将分析物氢化分离从而导入到原子吸收分光光 度计(AAS)中可以进行高效分析. 这项技术的浓度影响和灵 敏度的增加, 最终可使实验室获得较低的检出限, 从而可达 到环保法规的要求. 实验条件 仪器 测量使用PerkinElmer? PinAAcle? 900T原子吸收光谱仪 ( 谢尔顿, CT, 美国) 配以用于原子吸收的直观的WinLab?32 软件. 该软件具有用于样品分析, 报告和数据完成以及确保 符合规范的所有工具. PinAAcle光谱仪添加了一个FIAS400 流动注射分析系统, 这一系统具有2个蠕动泵, 一个5端口流 量喷射阀和一个可调节气体供应站. 所有的分析元素: 砷, 硒和汞, 均使用软件中的默认参数. 使用的FIAS-AAS系统, 其循环流动进样注射阀门充满了酸化的样品, 空白, 或标 准. 该阀门可以自动切换注射位置, 使样品与泵入的还原剂 混合, 使用硼氢化钠作为还原剂来氢化, 或使用氯化亚锡还 原汞, 产生气体蒸气. 在使用还原剂发生还原反应的时候, 砷或硒的氢化物或者元素汞的蒸气随即产生, 它们和硼氢化 钠产生的氢气一起, 产生了一个两相混合物: 其中有分析物 蒸气和使用的还原剂. 氩气流也被添加到该混合物蒸气中, 它们同时进入到气/液分离器中. 在这里, 包含分析物蒸气的 气相进入到石英管中用于原子吸收光谱法分析, 而其余的液 体泵到一个废液容器中. FIAS的参数参见表1, 图1是FIAS系 统的示意图. 生成的氢化物在一个加热的石英管 (货号 B0507486) 中 分解和原子化, 石英管被放置在一个加热罩中 (图2) , 适 配器(货号 N3160162 用于PinAAcle 900T, 900H, 900F 模式;

N3160161 用于PinAAcle 900Z 模式)放置在燃烧 器组件中. 氢化物在石英管中被加热到900?C, 汞蒸气被 加热到100?C, 从而避免分析物在管中冷凝. 石英管用于 氢化物分析前要先用30%氢氟酸清洗. 所有元素均使用高能无极放电灯(EDLs)( 货号: As: N3050605;

硒: N3050672;

汞: N3050634) . 高能无极放电灯通常比空心阴极灯能够提供更高的能 量, 并能提高灵敏度和检出限, 特别是砷和硒. 所有组分 样品环的大小都是500μL, 还可根据检出限的需要分别 增减通量. 载气流量对灵敏度的影响很大. 一个足够快 的载气流能获得一个尖锐的峰值, 从而可具有更高的灵 敏度. 如果载气流量过高, 原子或氢化气体分散得太快,

22 The generated hydrides were decomposed and atomized in a heated quartz cell (Part No. B0507486) placed in a heating mantle (Figure 2) with adaptor (Part No. N3160162 for PinAAcle 900T, 900H, 900F models and N3160161 for the PinAAcle 900Z model) in the place of the burner assembly. The quartz cell was heated to

900 ?C for the hydrides and

100 ?C for mercury vapor analysis to avoid any condensation in the cell. The quartz cell used for hydride analysis was cleaned prior to use with 30% hydrofluoric acid. High-energy electrodeless discharge lamps (EDLs) were used for all the elements (Part Nos. As: N3050605;

Se: N3050672;

Hg: N3050634). EDLs typically provide higher energy than the corresponding HCLs and improve sensitivity and detection limits, especially for arsenic and selenium. The sample loop size was

500 ?L for all analytes and could have been increased or decreased to improve detection limits or throughput, respectively. The carrier gas stream has a large influence on sensitivity. The objective is to have a fast enough carrier flow to obtain a sharp peak, therefore greater sensitivity. If the flow is too high, the atom or hydride cloud is dispersed too rapidly and Separating the analyte from the matrix can improve the sensitivity of the atomic absorption technique and avoids physical, matrix and spectral interferences. The separation of the hydride from the matrix allows for high efficiency of analyte introduction into the atomic absorption spectro- photometer (AAS). The concentration effect and added sensitivity of these techniques ultimately enables laboratories to meet the lower detection limits required for environmental regulations. Experimental Conditions Instrumentation The measurements were performed using a PerkinElmer? PinAAcle? 900T atomic absorption spectrophotometer (Shelton, CT, USA) equipped with the intuitive WinLab32? for AA software, which features all the tools to analyze samples, report and archive data and ensure regulatory compliance. The PinAAcle spectrometer was coupled to a FIAS

400 flow injection analysis system that incorporates two peristaltic pumps, a 5-port flow injection valve and a regulated gas supply. Default parameters found in the software were used for all three elements: As, Se, and Hg. Using a FIAS-AAS system, a sample loop on the flow injection valve is filled with the acidified sample, blank, or standard. The valve is automatically switched to the inject position and the sample is mixed with a pumped stream of reductant, sodium borohydride for hydrides or stannous chloride for mercury to produce the gaseous vapors. At the point of reaction with the reductant, arsenic or selenium hydrides or elemental mercury vapor are produced, along with hydrogen from the sodium borohydride, resulting in a two-phase mixture: vapor with the analyte in it and the used-up reductant. A flow of argon is added to this mixture and the vapors are carried through a gas/liquid separator. This allows the gaseous phase which contains the analyte vapor to enter the quartz cell on the AAS for analysis while the remaining liquids are pumped to a waste container. Refer to Table

1 for the FIAS parameters and Figure

1 for a schematic of the FIAS system. Table 1. FIAS pump and valve timing. Pump

1 Pump

2 Valve Read Step # Time (rpm) (rpm) Position Trigger Fill Inject Prefill

15 100

120 X

1 10

100 120 X

2 15

0 120 X X

3 1

100 120 X Figure 2. PerkinElmer heating mantle for the PinAAcle 900T spectrometer. Figure 1. Schematic diagram of FIAS

400 system for automated hydride generation. 表1. FIAS泵和阀门 步骤 # 时间 泵1(rpm) 泵2(rpm) 阀位置 读触发器 填充 注射 充液

15 100

120 X

1 10

100 120 X

2 15

0 120 X X

3 1

100 120 X

2 The generated hydrides were decomposed and atomized in a heated quartz cell (Part No. B0507486) placed in a heating mantle (Figure 2) with adaptor (Part No. N3160162 for PinAAcle 900T, 900H, 900F models and N3160161 for the PinAAcle 900Z model) in the place of the burner assembly. The quartz cell was heated to

900 ?C for the hydrides and

100 ?C for mercury vapor analysis to avoid any condensation in the cell. The quartz cell used for hydride analysis was cleaned prior to use with 30% hydrofluoric acid. High-energy electrodeless discharge lamps (EDLs) were used for all the elements (Part Nos. As: N3050605;

Se: N3050672;

Hg: N3050634). EDLs typically provide higher energy than the corresponding HCLs and improve sensitivity and detection limits, especially for arsenic and selenium. The sample loop size was

500 ?L for all analytes and could have been increased or decreased to improve detection limits or throughput, respectively. The carrier gas stream has a large influence on sensitivity. The objective is to have a fast enough carrier flow to obtain a sharp peak, therefore greater sensitivity. If the flow is too high, the atom or hydride cloud is dispersed too rapidly and Separating the analyte from the matrix can improve the sensitivity of the atomic absorption technique and avoids physical, matrix and spectral interferences. The separation of the hydride from the matrix allows for high efficiency of analyte introduction into the atomic absorption spectro- photometer (AAS). The concentration effect and added sensitivity of these techniques ultimately enables laboratories to meet the lower detection limits required for environmental regulations. Experimental Conditions Instrumentation The measurements were performed using a PerkinElmer? PinAAcle? 900T atomic absorption spectrophotometer (Shelton, CT, USA) equipped with the intuitive WinLab32? for AA software, which features all the tools to analyze samples, report and archive data and ensure regulatory compliance. The PinAAcle spectrometer was coupled to a FIAS

400 flow injection analysis system that incorporates two peristaltic pumps, a 5-port flow injection valve and a regulated gas supply. Default parameters found in the software were used for all three elements: As, Se, and Hg. Using a FIAS-AAS system, a sample loop on the flow injection valve is filled with the acidified sample, blank, or standard. The valve is automatically switched to the inject position and the sample is mixed with a pumped stream of reductant, sodium borohydride for hydrides or stannous chloride for mercury to produce the gaseous vapors. At the point of reaction with the reductant, arsenic or selenium hydrides or elemental mercury vapor are produced, along with hydrogen from the sodium borohydride, resulting in a two-phase mixture: vapor with the analyte in it and the used-up reductant. A flow of argon is added to this mixture and the vapors are carried through a gas/liquid separator. This allows the gaseous phase which contains the analyte vapor to enter the quartz cell on the AAS for analysis while the remaining liquids are pumped to a waste container. Refer to Table

1 for the FIAS parameters and Figure

1 for a schematic of the FIAS system. Table 1. FIAS pump and valve timing. Pump

1 Pump

2 Valve Read Step # Time (rpm) (rpm) Position Trigger Fill Inject Prefill

15 100

120 X

1 10

100 120 X

2 15

0 120 X X

3 1

100 120 X Figure 2. PerkinElmer heating mantle for the PinAAcle 900T spectrometer. Figure 1. Schematic diagram of FIAS

400 system for automated hydride generation. 图1. FIAS 400系统自动氢化物发生示意图. 图2. PerkinElmer 用于PinAAcle 900T分光光度计的加热套 硒: 样品与标准在分析之前都要进行预还原反应 (将Se6+ 还原到Se4+ ) , 使用浓度为1:1的盐酸在90?C加热30 分钟来完成预还原反应. 使用PerkinElmer SPB 50-24 块状消解系统 (货号 N9308019) 和SBP触摸控制器 ( 货........