Sahay Peeyush, Scherrer Susan T, Wang Chuji
Department of Physics and Astronomy, Mississippi State University, Starkville, Mississippi 39759, USA.
Rev Sci Instrum. 2012 Sep;83(9):095109. doi: 10.1063/1.4752223.
A portable optical emission spectroscopy-cavity ringdown spectroscopy (OES-CRDS) dual-mode plasma spectrometer is described. A compact, low-power, atmospheric argon microwave plasma torch (MPT) is utilized as the emission source when the spectrometer is operating in the OES mode. The same MPT serves as the atomization source for ringdown measurements in the CRDS mode. Initial demonstration of the instrument is carried out by observing OES of multiple elements including mercury (Hg) in the OES mode and by measuring absolute concentrations of Hg in the metastable state 6s6p (3)P(0) in the CRDS mode, in which a palm-size diode laser operating at a single wavelength 405 nm is incorporated in the spectrometer as the light source. In the OES mode, the detection limit for Hg is determined to be 44 parts per 10(9) (ppb). A strong radiation trapping effect on emission measurements of Hg at 254 nm is observed when the Hg solution concentration is higher than 50 parts per 10(6) (ppm). The radiation trapping effect suggests that two different transition lines of Hg at 253.65 nm and 365.01 nm be selected for emission measurements in lower (<50 ppm) and higher concentration ranges (>50 ppm), respectively. In the CRDS mode, the detection limit of Hg in the metastable state 6s6p (3)P(0) is achieved to be 2.24 parts per 10(12) (ppt) when the plasma is operating at 150 W with sample gas flow rate of 480 mL min(-1); the detection limit corresponds to 50 ppm in Hg sample solution. Advantage of this novel spectrometer has two-fold, it has a large measurement dynamic range, from a few ppt to hundreds ppm and the CRDS mode can serve as calibration for the OES mode as well as high sensitivity measurements. Measurements of seven other elements, As, Cd, Mn, Ni, P, Pb, and Sr, using the OES mode are also carried out with detection limits of 1100, 33, 30, 144, 576, 94, and 2 ppb, respectively. Matrix effect in the presence of other elements on Hg measurements has been found to increase the detection limit to 131 ppb. These elements in lower concentrations can also be measured in the CRDS mode when a compact laser source is available to be integrated into the spectrometer in the future. This exploratory study demonstrates a new instrument platform using an OES-CRDS dual-mode technique for potential field applications.
介绍了一种便携式光发射光谱 - 腔衰荡光谱（OES - CRDS）双模等离子体光谱仪。当光谱仪以OES模式运行时，使用紧凑、低功率的常压氩微波等离子体炬（MPT）作为发射源。在CRDS模式下，同一MPT用作衰荡测量的雾化源。通过在OES模式下观察包括汞（Hg）在内的多种元素的光发射光谱，并在CRDS模式下测量亚稳态6s6p (3)P(0)中Hg的绝对浓度来进行仪器的初步演示，其中光谱仪中内置了一个工作在单波长405 nm的手掌大小的二极管激光器作为光源。在OES模式下，Hg的检测限确定为每10(9)分之44（ppb）。当Hg溶液浓度高于每10(6)分之50（ppm）时，观察到在254 nm处Hg发射测量存在强烈的辐射俘获效应。这种辐射俘获效应表明，在较低（<50 ppm）和较高浓度范围（>50 ppm）的发射测量中，应分别选择Hg在253.65 nm和365.01 nm处的两条不同跃迁线。在CRDS模式下，当等离子体在150 W功率下运行且样品气体流速为480 mL min(-1)时，亚稳态6s6p (3)P(0)中Hg的检测限达到每10(12)分之2.24（ppt）；该检测限对应于Hg样品溶液中的50 ppm。这种新型光谱仪的优势有两方面，它具有大的测量动态范围，从几ppt到数百ppm，并且CRDS模式可作为OES模式的校准以及高灵敏度测量。还使用OES模式对其他七种元素砷（As）、镉（Cd）、锰（Mn）、镍（Ni）、磷（P）、铅（Pb）和锶（Sr）进行了测量，检测限分别为1100、33、30、144、576、94和2 ppb。已发现存在其他元素时对Hg测量的基体效应会使检测限提高到131 ppb。当未来有紧凑的激光源可集成到光谱仪中时，这些较低浓度的元素也可在CRDS模式下进行测量。这项探索性研究展示了一种使用OES - CRDS双模技术的新型仪器平台，用于潜在的现场应用。
