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首页> 外文学位 >Experimental Measurements and Modeling to Understand Sensitivity and Plasma Sample Loading in Inductively Coupled Plasma Optical Emission Spectrometry.
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Experimental Measurements and Modeling to Understand Sensitivity and Plasma Sample Loading in Inductively Coupled Plasma Optical Emission Spectrometry.

机译：实验测量和建模，以了解电感耦合等离子体发射光谱法中的灵敏度和等离子体样品的负载量。

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摘要

This thesis presents a fast semi-quantitative analysis method for ICP-OES (inductively coupled plasma optical emission spectroscopy) using only one calibration standard with one element and a plasma model. The same plasma model was used to mathematically correct ICP-OES matrix effects which can degrade concentration accuracy. Also, efforts are described to improve: (1) detection limits by increasing the amount of sample delivered to the plasma per time (using a heated close coupled spray chamber (CCSC) and an electronic nebulizer (eNeb)) and (2) precision by evaporating droplets before they enter the plasma (CCSC) or introducing a consistent flow of small droplets with a narrow size distribution (eNeb). An ICP generated using flat plates was compared to an ICP generated by a helical load coil. The feasibility of two ICPs with separate RF generators was assessed for potential future use with a very high sample transport rate.;ICP-OES typically requires the measurement of calibration standards that contain all of the elements of interest over a range of concentrations. A fast, semi-quantitative analysis method is described based on one calibration standard containing only one element and a pLTE (partial local thermodynamic equilibrium) plasma model for determining the concentrations of 66 elements by ICP-OES. The concentration accuracy is within a factor of three for 85% of 227 emission lines from 66 elements studied. The pLTE model can also be used to improve the accuracy of ICP-OES analysis by correcting for analyte sensitivity changes that result from changes in plasma temperature due to differences in chemical composition (matrix) between the sample and standards. Sensitivity and detection limits could be improved by increasing the amount of sample delivered to the plasma per time (sample transport rate) if there is no change in plasma conditions or the ICP background. Two systems were evaluated for increasing the sample transport rate compared to a conventional sample introduction system: a heated close coupled spray chamber (CCSC) and a prototype vibrating mesh electronic nebulizer (eNeb).;The CCSC was used to increase the sample transport rate by a factor of four which resulted in improvements in sensitivities of four to nine times and detection limits of an average of a factor of five. Short term precision was improved by an average of a factor of two, perhaps due to the evaporation of large droplets before they enter the plasma. An increase in the velocity of the sample prior to entering the plasma was proposed to increase the sample transport rate able to enter the plasma without it being extinguished. At the highest sample transport rates the plasma was cooled and sensitivities decreased. A second plasma source is suggested to overcome this limitation. Initial results with a conventional sample introduction system showed a factor of three to seven times increase in end on sensitivity/background ratios but the same side on sensitivity to background ratios using the dual plasmas compared to a single plasma. It is hypothesized that it may be possible to increase the sample transport rate significantly compared to a conventional sample introduction system without cooling of the center of the plasma and decreasing sensitivities using dual plasmas.;The eNeb generates droplets by ejecting sample through a vibrating mesh of regularly spaced holes. Detection limits were up to four times improved compared to a conventional sample introduction system by electronically increasing the sample transport rate with the eNeb. Perhaps due to the consistent production of small droplets with a narrow size distribution the short term RSDs of analyte emission intensity averaged 0.21% (a factor of four to five improvement over a conventional sample introduction system).;Water droplets (generated using the eNeb) and water vapor with dried analyte particles (generated using the CCSC) were separately introduced into the plasma to compare the effect of each as the sample transport rate is increased. The maximum sample transport rate able to enter the plasma without it being extinguished was 75 mg/min of water vapor and 57 mg/min of water droplets. The smaller tolerated transport rate of water droplets tolerated may be due to increased cooling and movement downstream of the bottom of the plasma. Water droplets were also found to result in more cooling of the plasma center than the same transport rate of water vapor. However, sample introduced as water droplets resulted in a higher plasma temperature, sensitivity, and background intensity in the normal analytical zone.;Flat plates were investigated as an alternative to the helical load coil used to generate the plasma. The plasma generated using the flat plates can be operated at approximately 2/3 the argon gas flow and was found to tolerate more solvent. While the sensitivities for the plasma generated using the flat plates are the same to 9 times lower (likely due to the lower plasma temperature) the standard deviation in blank emission intensity is smaller for the flat plates generated plasma. This leads to detection limits that range from 6 times improved to three times worse.
机译：本文提出了一种ICP-OES的快速半定量分析方法（电感耦合等离子体光发射光谱法），该方法仅使用一种元素和一个等离子体模型的校准标样。使用相同的血浆模型来数学校正ICP-OES基质效应，这会降低浓度精度。此外，还描述了以下方面的努力：（1）通过增加每次送至血浆的样品量（使用加热的紧密耦合喷雾室（CCSC）和电子雾化器（eNeb））来提高检测限，以及（2）通过在液滴进入等离子体（CCSC）之前先将其蒸发，或者引入具有窄尺寸分布（eNeb）的小液滴持续流动。将使用平板产生的ICP与由螺旋负载线圈产生的ICP进行比较。评估了两个带有独立RF发生器的ICP的可行性，以备将来以非常高的样品传输速率使用。ICP-OES通常需要测量校准标准液，其中包含浓度范围内所有感兴趣的元素。描述了一种快速，半定量的分析方法，该方法基于仅包含一种元素的校准标准和用于通过ICP-OES测定66种元素的浓度的pLTE（局部局部热力学平衡）等离子体模型。对于来自研究的66种元素的227条发射线的85％，浓度精度在三分之二以内。通过校正由于样品和标准品之间化学成分（基质）不同而引起的血浆温度变化而导致的分析物灵敏度变化，pLTE模型还可用于提高ICP-OES分析的准确性。如果血浆条件或ICP背景没有变化，则可以通过增加每时间向血浆中输送的样品量（样品传输速率）来提高灵敏度和检测限。与传统的样品引入系统相比，对两个系统进行了评估以提高样品传输速率：加热的密闭喷雾室（CCSC）和原型振动筛网电子雾化器（eNeb）.CCSC用于通过以下方式提高样品传输速率：灵敏度是四分之一，因此灵敏度提高了四到九倍，检测极限平均提高了五倍。短期精度平均提高了两倍，这可能是由于大液滴在进入等离子体之前已经蒸发了。建议增加进入等离子体之前样品的速度，以增加能够在不熄灭的情况下进入等离子体的样品传输速率。在最高的样品传输速率下，血浆被冷却，灵敏度降低。建议使用第二等离子体源以克服该限制。常规样品引入系统的初步结果显示，与单血浆相比，使用双血浆时，灵敏度/背景比率的终点增加了三到七倍，但灵敏度与背景比率的差异却相同。假设与传统的样品引入系统相比，可以在不冷却等离子体中心且不使用双等离子体的情况下降低灵敏度的情况下显着提高样品传输速率; eNeb通过将样品通过振动筛网喷射而产生液滴。规则间隔的孔。通过电子提高eNeb的样品传输速率，与传统的样品导入系统相比，检测限提高了四倍。也许是由于始终如一地产生了窄尺寸分布的小液滴，所以分析物发射强度的短期RSD平均为0.21％（比常规样品引入系统提高了四到五倍）。水滴（使用eNeb生成）将水和带有干燥分析物颗粒（使用CCSC生成）的水蒸气分别引入血浆中，以比较随着样品传输速率的提高而产生的影响。能够在不熄灭的情况下进入血浆的最大样品传输速率为75 mg / min的水蒸气和57 mg / min的水滴。容许的水滴的较小的容许传输速率可能是由于增加的冷却和等离子体底部下游的移动所致。还发现，与水蒸气的相同传输速率相比，水滴导致等离子体中心的冷却更多。但是，以水滴形式引入的样品导致较高的血浆温度，灵敏度；以及正常分析区域中的背景强度。；研究了平板，以替代用于产生等离子体的螺旋负载线圈。使用平板产生的等离子体可以在氩气流量的约2/3下运行，并且被发现可以承受更多的溶剂。尽管使用平板产生的等离子体的灵敏度降低了9倍（可能是由于较低的等离子体温度），但平板产生的等离子体的空白发射强度的标准偏差却较小。这导致检测极限从改进的6倍到恶化的3倍不等。

著录项

  • 作者

    Dettman, Joshua R.;

  • 作者单位

    The Ohio State University.;

  • 授予单位 The Ohio State University.;
  • 学科 Chemistry Analytical.
  • 学位 Ph.D.
  • 年度 2011
  • 页码 382 p.
  • 总页数 382
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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