Liquid Sampling-Atmospheric Pressure Glow Discharge (LS-APGD) Ionization Source for Elemental Mass Spectrometry: Preliminary Parametric Evaluation and Figures of Merit

Journal Article · Sun Jan 01 00:00:00 EST 2012 · Analytical and Bioanalytical Chemistry

DOI:https://doi.org/10.1007/s00216-011-5359-7· OSTI ID:1033048

Quarles, C. Derrick; Carado, Anthony J.; Barinaga, Charles J.; Koppenaal, David W.; Marcus, R. Kenneth

A new, low power ionization source for the elemental analysis of aqueous solutions has recently been described. The liquid sampling-atmospheric pressure glow discharge (LS-APGD) source operates at relatively low currents (<20 mA) and solution flow rates (<50 μL min-1), yielding a relatively simple alternative for atomic mass spectrometry applications. The LS-APGD has been interfaced to what is otherwise an organic, LC-MS mass analyzer, the Thermo Scientific Exactive Orbitrap without any modifications; other than removing the electrospray ionization (ESI) source supplied with that instrument. A glow discharge is initiated between the surface of the test solution exiting a glass capillary and a metallic counter electrode mounted at a 90° angle and separated by a distance of ~5 mm. As with any plasma-based ionization source, there are key discharge operation and ion sampling parameters that affect the intensity and composition of the derived mass spectra; including signal-to-background ratios. We describe here a preliminary parametric evaluation of the roles of discharge current, solution flow rate, argon sheath gas flow rate, and ion sampling distance as they apply on this mass analyzer system. A cursive evaluation of potential matrix effects due to the presence of easily ionized elements (EIEs) indicate that sodium concentrations of up to 500 μg mL-1 generally cause suppressions of less than 50%, dependant upon the analyte species. Based on the results of this series of studies, preliminary limits of detection (LOD) have been established through the generation of calibration functions. Whilst solution-based concentrations LOD levels of 0.02 – 2 μg mL-1 3 are not impressive on the surface, the fact that they are determined via discrete 5 μL injections leads to mass-based detection limits at picogram to singlenanogram levels. The overhead costs associated with source operation (10 W d.c. power, solution flow rates of <50 μL min-1, and gas flow rates <10 mL min-1) are very attractive. While further optimization in the source design is suggested here, it is believed that the LS-APGD ion source may present a practical alternative to inductively-coupled plasma (ICP) sources typically employed in elemental mass spectrometry.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1033048
• Report Number(s): PNNL-SA-82307; 44090; NN2001000; TRN: US201202%%550
• Journal Information: Analytical and Bioanalytical Chemistry, Vol. 402, Issue 1; ISSN 1618-2642
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
AQUEOUS SOLUTIONS
ARGON
CALIBRATION
DETECTION
ELECTRODES
EVALUATION
FLOW RATE
GAS FLOW
GLASS
GLOW DISCHARGES
ION SOURCES
IONIZATION
MASS SPECTRA
MASS SPECTROSCOPY
MODIFICATIONS
OPTIMIZATION
PLASMA
SAMPLING
SENSITIVITY
SODIUM
liquid sampling-atmospheric pressure glow discharge
ionization source
microplasma
mass spectrometry.
Environmental Molecular Sciences Laboratory