Ion Enhancement Effect of Laser-Enhanced Ionization Induced by One-Step Excitation and Two-Step Excitation

1999

Anal. Chem.

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The flame laser-enhanced ionization (LEI) technique is coupled with the flow injection analysis system to measure the trace lead amounts in aqueous solution and in seawater. The flow injection (FI) manifold is incorporated with a microcolumn packed with a C18 bonded silica. The chelating agent DDPA is used to form the Pb-DDPA complex, which may be sorbed in the microcolumn and then eluted with methanol. The preconcentrated Pb is then detected by the LEI technique with either single-step or two-step excitation. At 5- and 15-mL volume-fixed sample loading, the detection limits of 0.011 and 0.0033 ng/mL (11 and 3.3 ppt) and enrichment factors of 16 and 48 are achieved, respectively, using a two-step FI-LEI. The sensitivity of the current system proves to be better by at least 1 order of magnitude than that of conventional LEI method. The FI-LEI also increases the tolerance of matrix interference. The LEI signal is slightly reduced to 80% intensity as 10,000 micrograms/mL (ppm) Na and K matrixes are mixed in the lead solution. The resistance to the alkali matrixes is enhanced approximately 4 times that reported previously using a similar water-immersed probe as a LEI collector. Finally, the FI-LEI is for the first time applied to detect the Pb content in seawater, achieving a result of 0.0112 +/- 0.0006 ng/mL (ppb) consistent with the certified value of 0.013 +/- 0.005 ng/mL (ppb).

Section: Resultsmentioning

confidence: 99%

“…Flame System . As described elsewhere, , a commercial burner assembly (Perkin-Elmer) with a 100 mm × 0.5 mm slot burner head coupled with an interlocked gas control system was employed. The fuel C 2 H 2 and air were regulated at flow rates of 0.5 and 12.5 L/min, respectively, and were premixed prior to reaching the burner head.…”

Section: Methodsmentioning

confidence: 99%

Laser-Enhanced Ionization Detection of Pb in Seawater by Flow Injection Analysis with On-Line Preconcentration and Separation

1999

Anal. Chem.

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“…Flame Burner. The experimental apparatus of a twostep LEI has been illustrated previously, 11,15,16,26 so only a brief description is given below. We performed the LEI experiment, as shown in Fig.…”

Section: Methodsmentioning

confidence: 99%

“…The ion enhancement induced by a two-step LEI scheme is strongly affected by the secondstep excitation. The explicit formula is expressed as 15 2 l A I k uh hu uh hi S (TLEI) 5 S (SLEI). ( 6)…”

Section: Theoretical Modelingmentioning

confidence: 99%

“…Equation 6, ignoring the possibility of atom depletion during the laser pulse, is equivalent to equation 36 given by Axner et al 29 The atom depletion effect may become negligible by an appropriate selection of the upper state h, so that the inverse of collisional ionization rate from this state is larger than the laser pulse duration. 15 Provided that the laser energy and wavelength for the second-step excitation are ® xed, the enhanced factor becomes constant. Analogously to Eq.…”

Section: Theoretical Modelingmentioning

confidence: 99%

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Spatially Resolved Temperature Determination of an Air/Acetylene Flame Using the Two-Step Laser-Enhanced Ionization Technique

1998

Appl Spectrosc

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We have demonstrated a two-step laser-enhanced ionization (LEI) technique to be potentially useful in measuring a spatially resolved temperature in an atmospheric air/acetylene flame. As a complement to the existing optical methods, LEI detection shares the advantages of extremely high sensitivity and the capability of achieving a high spatial resolution, confined to the dual-beam intersection area of 1 mm × 1 mm. A theoretical model was developed to precisely extract the temperature information from the obtained two-step LEI signal. The physical parameters required in the experiment include simply the relative values of the LEI signals, associated with the fine-structure doublets of a selected thermometric species, and their corresponding laser energies. The subsequent treatment is also convenient without the need to know the absolute energy of the incident laser beam and to accurately calibrate the detection system. Al and Ga were selected as the thermometric species. The resultant radial and axial temperature mappings are consistent with each other and are also comparable with those reported by other optical methods.

Applications of Laser‐Enhanced Ionization In Analytical Chemistry

1994

J Chinese Chemical Soc

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Various applications of laser‐enhanced ionization (LEI) in analytical chemistry are reviewed. This technique was applied to determine some physical quantities associated with a flame through development of an appropriate model. Determinations of flame temperature and atomization efficiency of an element in the flame are examples. As trace analysis is an important application of this technique, we compare the ion yield induced in a two‐step LEI with that in a one‐step LEI. The factors governing the ion enhancement via two‐step excitation are examined in order to make efficient use of the two‐step LEI apparatus. A novel technique was designed to couple flow‐injection analysis to a conventional LEI device; in this manner, electrical interference, a severe problem inherent in LEI, was successfully removed.