Icp ms 7700

All single quadrupole-based data were collected on an Agilent 7700 ICP-MS equipped with a helium collision cell, torch shield, and bonnet. The autosampler used was an Agilent ASX-500. Oxides were minimized by using low sample uptake (0.1 rps) in combination with a sampling depth of 8 mm and a double-pass spray chamber held at 2 °C. These tuning conditions typically produced a CeO⁺/Ce⁺ ratio of <0.6% with the He flow optimized. The energy discrimination (ED, is the difference in potential between the octopole and the quadrupole) was set at 5 V in order to capitalize on the kinetic energy difference between analyte ions and polyatomic ions and to minimize the potential impact of any polyatomic ion formation in the cell.²⁰ The ED of 5 V was used in combination with an octopole bias of −12 V unless otherwise noted. The collision cell He was an ultra high-purity grade (99.999%, Indiana Oxygen, Indianapolis, IN) and was passed through a triple filter (Agilent, part number 5182–9705) prior to entering the cell. This triple filter cartridge is a single carrier filter that removes hydrocarbon, moisture and oxygen. Data were collected in normal resolution mode (0.8 amu at 10% peak height) and narrow resolution mode (0.4 amu at 10% peak height) to evaluate the abundance-sensitivity implication of utilizing half-mass integration to estimate M²⁺ correction factors. The resolution mode is often a variable; for this reason, this information was included in the footnotes associated with each figure to ensure clarity. The deflect lens located downstream of the collision cell and before the plate bias voltage was optimized to reduce the M²⁺. In general, the deflect lens voltage works in combination with the cell exit voltage and the plate bias voltage to determine ion trajectory post collision cell. In this work, several experiments are performed in which the deflect lens potential was varied while maintaining a consistent exit cell and plate bias voltage to monitor the effect of deflect lens voltage changes on M²⁺ and analyte sensitivity. All half-mass data were exported and integrated using a 0.15 amu integration window in Excel. This external integration was necessary to estimate some of the M²⁺ correction factors prior to use in the instrument’s interference-correction software. All concentrations were determined using indium as an internal standard after adding the necessary M²⁺ correction factors in the interference-correction software. Fig. 1 highlights the experimental factors (e.g., mass selection, acquisition mode) that impact the formulation of the appropriate M²⁺ correction factor applied to the Agilent 7700 data. Fig. 1 includes an example of the associated M²⁺ calculation for an Nd correction on arsenic using a narrow resolution mode and an external rare earth standard solution to estimate the response at m/z 71.5 (Nd²⁺) and 143 (Nd¹⁺). In Fig. 1, these experimental factors are denoted using subscripts and superscripts to ensure clarity. A complete set of example calculations is included in the ESI‡ section entitled: M²⁺ correction equations for figures and data tables.
All ICP-QQQ data were collected using an Agilent 8800 ICP-MS. Both As and Se were analyzed in a mass-shift mode using oxygen (0.5 mL min⁻¹) as a reaction gas at m/z 91 and 94, respectively. Yttrium (YO⁺, 89 → 105) was used as an internal standard for the mass-shifted analytes because of the increased sensitivity of the oxygen reaction product ions compared to other commonly used internal standards. The short term reproducibly of the 89 → 105 mass-shift was determined by analyzing multiple yttrium fortified calibration standards over the course of one hour. Based on the plasma conditions used in this work less than a 3% change in cps (counts per second) for the 89 → 105 mass-shift was measured. All data were collected using selective ion monitoring with a 0.99 s per amu integration time with yttrium (YO⁺, 89 → 105) as an internal standard.
High-resolution data were collected using a Thermo Finnigan Element2 double-focusing magnetic sector ICP-MS equipped with a 100 μL min⁻¹ PFA micronebulizer and a cyclonic quartz spray chamber (Elemental Scientific, Omaha, NE). Both ⁷⁵As and ⁷⁸Se were analyzed in the high-resolution mode to provide resolution between the analyte and the associated M²⁺ ions. The sensitivity for ⁷⁵As and ⁷⁷Se are 1166 and 127 cps μg⁻¹ L⁻¹, respectively in high resolution mode. All data were collected using 40 samples per peak over a 0.200 s sampling time, 30% search and 60% integration windows, and indium as the internal standard over 3 runs and 2 passes (n = 6). The Auto Lock Mass feature was active during analysis.