- 期刊
雷射誘導電漿光譜法之液態樣品定量分析
Laser-Induced Breakdown Spectroscopy for Liquid Sample Analysis
摘要
雷射誘導電漿光譜法(Laser-induced Breakdown Spectroscopy, LIBS)是一種快速的原子放光分析方法。它利用雷射光氣化並離子化部分樣品，產生局部氣態電漿包，經由觀測其原子放光光譜，可做快速之定性及定量化學分析。原則上LIBS可用於分析各種狀態之樣品且不需前處理，然而因雷射脈衝能量不穩及樣品本身的變動，LIBS的再現性及偵測極限通常受限。雖然雷射脈衝不穩可以利用對雷射能量之觀測來校正，但樣品本身的變動卻很難掌握，尤其是液態樣品。本文將介紹利用電灑法(Electrospray)與LIBS結合來做液態樣品分析之新方法。此法利用樣品被游離時產生之離子電流來校正LIBS取樣之不穩定性，大幅改善LIBS偵測水溶液樣品時的線性範圍(Dynamic Range)及偵測極限(Limit of Detection, LOD)。脈衝雷射波長、電漿溫度及鹽類基質(salt matrix)對分析結果之影響也將有深入之討論。最後利用電灑液態取樣方法，我們可將LIBS與線上注入分析(Flow-injectionAnalysis)系統結合，如此液態樣品可先進行分離及預濃縮，進而改善弱放射金屬如鋁離子之LIBS偵測極限。
並列摘要
Laser-induced breakdown spectroscopy (LIBS) is a rapid elemental analysis method based on atomic emission from laser induced plasma. LIBS can be applied to analyze the chemical composition of sample in solid, liquid or gas phase. Since LIBS is based on the hot plasma generated by intensive laser pulses, its precision and accuracy depend greatly on the stability of the plasma condition, which fluctuates with the laser pulse energy and the ever changing sample condition. While the former can be corrected by normalizing the signal with the laser pulse energy on a shotto- shot basis, the latter is usually hard to control and thus limits the sensitivity of LIBS as a quantitative chemical analysis method. Such signal fluctuation is particularly crucial for liquid phase sample analysis due to the fact that liquid samples have large inhomogeneity and a stable and fresh sample surface is hard to obtained. Here, we report on the development of correlation methods based on plasma-induced current normalization in analysis of the sample droplets, which is generated with an electrospray ionization needle. The intensities of time-resolved laser-induced breakdown emission were found to linearly correlate with the corresponding current intensities detected simultaneously on a single-shot basis. The limit of detection (LOD) obtained for the alkali-elements analysis may reach ＜ 1 mg/L even with the matrix salts added up to 2000 mg/L. The current normalization method may reduce the signal fluctuation and minimize interference by the matrix effect. The resultant LOD of Na sample is about 20 times better than that obtained by LIB/background normalization. The impinging laser energy dependence of both normalization methods is also investigated. The correlation linearity for the background normalization is restricted within a small range of laser energy. When the two-line ratio of plasma emission is considered to account for the plasma temperature, the linearity of the correlation plot is markedly improved. In combination with a flow-injection system for preconcentration and matrix separation, LIB spectroscopy is demonstrated to analyze liquid droplets of aluminum salt. The LOD is improved to 1.5 mg/L, which is about an order of magnitude lower than those achieved without preconcentration. The linear dy-namic range is also extended to more than two orders of magnitude.