Mass Bias Effects Research Articles

Reduction of Mass Bias and Matrix Effects in Inductively Coupled Plasma Mass Spectrometry with a Supplemental Electron Source in a Negative Extraction Lens

Electrons from a heated tungsten filament are created inside the extraction lens and driven out toward the skimmer. These electrons move through the ion path and reduce space charge effects between positive ions in the beam. The ion transmission efficiency is improved by factors of two (for Pb+) to 27 (for Li+). The greater sensitivity improvement for low-mass ions leads to a substantial reduction in mass bias. With the additional electrons, MO+/M+ and M2+/M+ abundance ratios increase but can be minimized with a small reduction in aerosol gas flow rate. No new background ions are observed with this technique. Matrix effects can be significantly diminished when the electron source is operated under the high electron current mode. The mass dependence of matrix-induced suppression of analyte signals is essentially eliminated. Using flow injection analysis to minimize solid deposition, the technique can tolerate Na matrix up to 10000 ppm (1%) with only approximately 15% loss of analyte sensitivity.

External ion accumulation of low molecular weight poly(ethylene glycol) by electrospray ionization fourier transform mass spectrometry

The combination of electrospray ionization (ESI) with Fourier transform mass spectrometry (FTMS) is a powerful tool in characterizing synthetic polymers. ESI permits the generation of intact, multiply charged high mass ions, whereas FTMS provides high mass resolution and correspondingly improved mass accuracy. However, under “nonideal” empirically determined operating conditions, a mass discrimination effect occurs as a function of accumulation time that can result in significant differences for calculated average mass values ( M n , M w ) and polydispersities. A multidimensional tuning process to eliminate the deleterious effects of mass bias is demonstrated for several sodiated poly(ethylene glycol) samples containing oligomers with masses covering a 600–3350 Da mass regime. In addition, experiments are performed in order to elucidate the possible mechanism(s) that cause the mass discrimination effect. It is proposed that extended collisions (reactive and nonreactive) occur in the hexapole to alter the energy (and velocity) distributions of the ions before injection into the trap. By choosing higher skimmer potentials, ions over a narrower energy “window” are preselected in the hexapole and exhibit lower overall mass bias effects.

Ultra-trace determination of Se in sediments by electrothermal vaporizer-inductively coupled plasma-mass spectroscopy: use of the ETV as a thermochemical reactor

The performance of electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) was evaluated for the ultra-trace determination of total selenium in sediment reference materials. Citric acid, when combined with an appropriate thermal program, promoted the early release of Se in a molecular form from the graphite surface, effecting a separation of the analyte from the concomitant matrix, thereby demonstrating the use of the ETV as a thermochemical reactor. No special sample pretreatment is needed and an absolute detection limit of 10 pg was achieved. Concentrations of Se in different sediment CRMs were determined and results obtained by both isotope dilution (ID) and standard addition (SA) methodologies were compared and evaluated. Mass bias effects prevented accurate application of ID techniques.

Determination of cadmium in environmental and biological reference materials using isotope dilution analysis with a double focusing ICP-MS: a comparison with quadrupole ICP-MS

J. Pablo Valles Mota, J. Ruiz Encinar, M. Rosario Fernández de la Campa, J. Ignacio García Alonso and A. Sanz-Medel, J. Anal. At. Spectrom., 1999, 14, 1467 DOI: 10.1039/A901753D

Determination of lithium as a chemical tracer and its application to flow rate measurements

An isotope dilution equation is derived whereby the spike concentration is calibrated through so-called reverse isotope dilution with the primary standard solution. It is also demonstrated that potential systematic errors due to false spike enrichment values and the mass bias effect are minimized provided that spike additions are judiciously controlled so that the isotope ratio of the spiked primary standard solution does not differ from those of the spiked samples by more than 20%. Lithium was used as a chemical tracer to measure flow rates in an experimental test facility. Thirty-two samples were collected downstream of the injection point and analysed by isotope dilution ICP-MS. Six experiments were carried out on September 28 and November 8, 1995, to measure flow rates by the chemical tracer method. By optimizing the experimental conditions, the chemical tracer method gave flow rates that differed by < 0.4% from the reference value.

Detection mass bias in atmospheric pressure ionization mass spectrometry

A previously uncharacterized source of detection mass bias is shown to be associated with atmospheric pressure ionization mass spectrometry (APIMS), and is attributed to a mass dependence in the sampling of ions from the supersonic free jet expansion of gas emerging from the ion source. The halide ions Cl −, Br −, and I − are shown to be transported from the ion source aperture to a quadrupole mass filter with efficiencies that increase linearly with increasing mass of the ion. While the polyatomic anions SF − 6 and C 7F − 14 are detected with even greater efficiencies than would be expected for monatomic anions of the same mass, this additional sensitivity to the polyatomic anions is thought to be related to ion loss processes occurring within the ion source. The experimental conditions under which these mass bias effects can be minimized or enhanced in APIMS are described.

Matrix interferences from methacrylic acid solutions in inductively coupled plasma mass spectrometry

It was found that substantial interference effects were present, which dramatically reduced sensitivity in the determination, by inductively coupled plasma mass spectrometry, of trace elements in methacrylic acid solution. Mass bias effects were observed, which led to either enhancement or suppression of analyte signals, depending on the conditions used and the concentration of methacrylic acid present in solution (1–10% m/v). An instrumental procedure based on optimizing plasma conditions and spectrometer ion optics settings was found to reduce significantly the magnitude of the interference effect. However, the use of aqueous calibration standards still gave rise to errors (changes in slope of 1–18% in the presence of 5% m/v methacrylic acid), which could not be corrected for by the use of internal standards when using compromise multi-element analysis conditions. The use of the standard additions method, under conditions optimized for the matrix, is proposed to avoid such calibration problems.