Date of Award
Master of Science
The groundwork for coupling gradient liquid chromatography (LC) with inductively coupled plasma mass spectrometry (ICP-MS) is developed. An alternative method of quantification to isotope dilution is evaluated. Using a micronebulizer (100 [Mu]L/min) and the Apex-Q desolvation system from Elemental Scientific, Inc., samples containing up to 40% methanol are introduced to the plasma with lower destabilization effects than attributed to straight sample introduction. Samples are introduced by flow injection (FI) to evaluate peak broadening. The desolvation system broadens the FI peak from 2 to 25 s. Ion signal ratios are measured in the presence of increasing methanol concentration to simulate gradient elution. Analyte-internal standard (AIS) pairs are found whose signal ratios remain consistent (deviations < ±10%) over a methanol concentration range of 5 - 35%. Such deviations are similar to those found for natural isotopic pairs (63Cu/65Cu, 69Ga/71Ga, 203Tl /205T1) over the same concentration range. AIS pairs that remain consistent in simulated methanol gradients are tested in actual gradients. Those that show the best stability in simulated gradients (59Co/60Ni, 208Pb/205Tl) display equal signal ratio consistency in an 8% to 32% methanol gradient. High resolution trials are performed in order to remove polyatomic interferences for the AIS pairs whose ratios are inconsistent in low resolution (deviations above 10%). The addition of N2[subscript (g)] is shown to increase the tolerable amount of methanol that can be introduced to the desolvator. As a result, 75As+/125Te+ signal ratio values remain consistent throughout the entire methanol range studied. Quantification experiments are performed in low resolution using 60Ni as an internal standard, added post-column, to quantify Co in a store-bought sample of cyanocobalamin (vitamin B-12). The calculated concentration is determined to be 20% off the expected value.
Patrick Allen Sullivan
Sullivan, Patrick Allen, "Reduction of solvent effect in reverse phase gradient elution LC-ICP-MS" (2006). Retrospective Theses and Dissertations. 20940.