![]() ![]() 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. Though the mechanism of fragmentation is currently unclear, observations indicate it could result from the interaction of peptides with gas-phase radicals or ultraviolet radiation generated within the = ,Ī new, low power ionization source for the elemental analysis of aqueous solutions has recently been described. #Elcad plasma spectra series#At lower currents (35 mA), many peptides exhibit extensive fragmentation, with a-, b-, c-, x-, and y-type ion series present as well as complex fragments, such as d-type ions, not previously observed with atmospheric-pressure dissociation. At high discharge currents (e.g., 70 mA), electrospray-like spectra are observed, dominated by singly and doubly protonated molecular ions. As the liquid stream contacts the electrical discharge, peptides from the solution are volatilized, ionized, and fragmented. In the new source, a direct-current plasma is sustained between a tapered metal rod and a flowing sample-containing solution. Here in this paper, a novel approach is described that enables ionization and controlled, tunable fragmentation of peptides at atmospheric pressure. Unfortunately, these methods are limited to specialized mass spectrometry instrumentation. Samples with high salt content (e.g., well water) caused positive matrix effects (i.e., 2.0- to 3.6-fold signal enhancements), but also ~ 1.5 times higher RSDs.Modern “-omics” (e.g., proteomics, glycomics, metabolomics, etc.) analyses rely heavily on electrospray ionization and tandem mass spectrometry to determine the structural identity of target species. The precision for In, Rh and Te in aqueous standards, expressed as relative standard deviation (RSD), was not higher than 4.6%, 6.4% and 7.4%, respectively. Calibration curves were linear up to 100–150 mg L − 1. The detection limits for In, Rh and Te were 0.01, 0.5 and 2.4 mg L − 1, respectively. Conversely, the use of acidity lower than pH 1 caused lower plasma volume, due to its contraction into the sample introduction capillary, and discharge instability in terms of its frequent self-extinction. The emission intensities were highly sample pH dependent, i.e., analytical signals could only be detected at pH levels lower than 2. Te and Rh showed lower emission intensities than In (determined at In I 451.1 nm), even using the most sensitive, interference-free transitions (i.e., Te I 214.3 nm, Te I 238.6 nm and Rh I 437.5 nm). In several cases, the background spectrum of the ELCAD hindered the use of conventional, resonant analytical lines in the UV due to overlaps with bands of molecular species (e.g., OH, NO, N 2). #Elcad plasma spectra free#The UV–Vis spectrum was scanned for analytical lines, free from spectral overlap interferences, and sensitive enough for quantifying the analytes at mg L − 1 or lower levels. ![]() Acid/additive type, sample pH and flow rate were optimized. An electrolyte cathode atmospheric glow discharge optical emission spectrometry (ELCAD-OES) method was developed for the detection of the industrially relevant In, Rh and Te in water samples. ![]()
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