Agilent 7500a ICP-MS Tuning Guidelines Using Hot Plasma Conditions
Plasma Conditions
RF Power: 1300-1500 W.
High RF power ensures decomposition and ionization of sample. In cool plasma applications the RF is usually run at 700-900W (with a shield torch in place). Normally, as you increase RF power you decrease the amount of doubly charged and oxide species. Increasing the RF may also bring about a reduction in sensitivity as well as an increase in RSDs.
RF Matching: 1.6-1.9.
Used to minimize reflected power. Select “Meter Æ Meter Control Panel” menu item and check the boxes for forward and reflected power. Adjust RF matching so that reflected power value is at 0 or 1. This rarely needs adjustment.
Sample Depth: 7-10mm.
Usually a trade off between sensitivity and interference. As Sample Depth decreases (plasma is moved closer to sample cone) the sensitivity increases but so do the oxide and doubly charged interferences.
Torch-H (horizontal): -1.5 - +1.5mm.
Adjust for maximum sensitivity. Align central channel of plasma with orifice of the sample cone.
Torch-V (vertical): Same as Torch-H
Carrier Gas (Nebulizer gas) L/min: Babington: 1.05-1.25 L/min, Mira mist: 0.9-1.1 L/min, PFA-100: 0.7-0.9 L/min.
Carrier gas works in a manner similar to sample depth. Generally as you increase carrier gas you tend to get more sensitivity by virtue of “punching through” the plasma. However, this increase is usually accompanied by an elevation in oxide and doubly charged species. If the carrier gas is taken even higher the Li-7 signal will continue to increase while Y-89 and Tl-205 start decreasing. Also, signal can get noisier when flows become excessive.
Makeup Gas L/min: Babington: usually 0 L/min, Mira mist 0.1-0.25 L/min, PFA-100: 0.2-0.4 L/min.
A total flow (carrier + makeup) of about 1.2 L/min is usually required to get adequate punch through of the plasma. Some nebulizers produce aerosols optimally at flows less than this. The makeup gas flows coaxially to the nebulizer and assists in the delivery of material through the plasma and to the sample cone. Behavior is similar to carrier gas.
Peripump: 0.08-0.12 rps (revolutions per second).
On most systems this value is set to 0.1. If the standard 1mm tygon tubing is installed in the pump a setting of 0.1 corresponds to a flow of about 400 uL/min.
S/C Temp (Spray Chamber Temp): 2 deg C.
This is always set right above the freezing point of water. Since the S/C temp has an accuracy of ±1 deg C it is kept at 2 deg C so that no freezing can occur. A cooled spray chamber helps remove water vapor from the plasma and thus reduces oxides as well enhancing signal.
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