Combined atomic and molecular (CAM) ionization with the liquid sampling-atmospheric pressure glow discharge microplasma.

In a world where information-rich methods of analysis are often sought over those with superior figures of merit, there is a constant search for ionization methods which can be applied across diverse analytical systems. The liquid sampling-atmospheric pressure glow discharge (LS-APGD) is a microplasma device which has the inherent capabilities to operate as a combined atomic and molecular (CAM) ionization source. The plasma is sustained by placement of a high voltage (~500 V, dc) onto an electrolytic solution through which the analyte is generally delivered to the discharge. Judicious choice of the solvent provides a means of obtaining atomic/elemental and/or molecular mass spectra. Presented here are the diverse modes of sample introduction and mass spectrometer platforms to which the LS-APGD has been interfaced. Likewise, representative spectra and figures of merit are presented towards elemental and isotope ratio measurements, as well as application to small organic molecules, organometallic complexes, and intact proteins. It is believed that the diversity of analytical applications and ready implementation across the entirety of mass spectrometry platforms portends a level of versatility not realized with other ionization sources.

Rapid Determination of Uranium Isotopic Abundance from Cotton Swipes: Direct Extraction via a Planar Surface Reader and Coupling to a Microplasma Ionization Source.

The collection of solid particulates and liquids from surfaces by the use of cloth swipes is fairly ubiquitous. In such methods, there is a continuous concern regarding the ability to locate and quantitatively sample the analyte species from the material. In this effort, we demonstrate the initial coupling of an Advion Plate Express plate reader to a liquid sampling-atmospheric pressure glow discharge (LS-APGD) microplasma ionization source with an Orbitrap mass spectrometer to perform uranium isotopic analyses of solution residues on cotton swipes. The Plate Express employs a sampling probe head to engage and seal against the swipe surface. Subsequentially, the analyte residues are desorbed and transported within a 2% HNO3 electrolyte flow to the ionization source. Quantitative recoveries were observed following a single 30 s extraction step, with the absolute mass sampled per extraction being ∼100 ng. While the intrasample variability in the analytical responses for triplicate sampling of the same swipe yield ∼30% RSD, this lack of precision is offset by the ability to determine isotope ratios for enriched uranium specimens with a precision of better than 10% RSD. Pooled, intersample precision (n = 9) was found to be <5%RSD across the various sample compositions. Finally, 235U/238U determinations (ranging from 0.053 to 1.806) were accurate with errors of <10%, absolute. The 234U- and 236U-inclusive ratios were determined with similar accuracy in enriched samples. While the driving force for the effort is in the realm of nuclear nonproliferation efforts, the ubiquitous use of cloth swipes across many application areas could benefit from this convenient approach, including the use of versatile, reduced-format mass spectrometer systems.

Rapid metal speciation of cell culture media using reversed-phase separations and inductively coupled plasma optical emission spectrometry.

Cell culture media metal content is critical in mammalian cell growth and monoclonal antibody productivity. The variability in metal concentrations has multiple sources of origin. As such, there is a need to analyze media before, during, and after production. Furthermore, it is not the simple presence of a given metal that can impact processes, but also their chemical form that is, speciation. To a first approximation, it is instructive to simply and quickly ascertain if the metals exist as inorganic (free metal) ions or are part of an organometallic complex (ligated). Here we present a simple workflow involving the capture of ligated metals on a fiber stationary phase with passage of the free ions to an inductively coupled plasma optical emission spectrometry for quantification; the captured species are subsequently eluted for quantification. This first level of speciation (free vs. ligated) can be informative towards sources of contaminant metal species and means to assess bioreactor processes.

Quantitative trace metal determinations in cell culture media using LS-APGD-MS and ICP-OES with free/bound species differentiation following polymer fiber separations.

Liquid sampling-atmospheric pressure glow discharge-mass spectrometry (LS-APGD-MS) and inductively coupled plasma-optical emission spectroscopy (ICP-OES) were employed for the quantification of trace metals in cell culture media and their capabilities compared. The LS-APGD is interfaced here to a compact mass spectrometer (Advion CMS) towards the development of an at-bioreactor process monitoring strategy. Both techniques have been previously employed for the quantification of trace metals in samples of various complexities, making them a natural choice for this application. They have also demonstrated comparable analytical figures of merit including limits of detection (LOD), matrix tolerance, etc. While cell culture media is a complex sample, the ICP-OES technique was unaffected by the matrix. However, the LS-APGD-MS suffered from increases in spectral background. Despite this, both techniques achieved appropriate LODs for all metals analyzed in this work (Cu, Fe, Zn, Co, Mn, Ni; LOD < 100 ng mL-1), except for Mn and Ni via LS-APGD-MS. To overcome the increased background seen on the LS-APGD-MS, a capillary channeled polymer (C-CP) polypropylene (PPY) fiber stationary phase was employed as an on-line separation for the removal of organic components prior to sample introduction into the plasma. It was further determined that Ni was retained on the column, preventing the detection of this element via LS-APGD-MS, and insights into metal speciation were discussed. Following implementation of this on-line separation strategy, the agreement between the techniques was acceptable for all analytes, and was excellent for Cu, Fe, and Zn.