I agree with Randy.
0.2 mg/mL MgO is 0.020 g/100 mL in samples, which is within maximum total dissolved solids limits for ICP-MS, but you have also added 0.1% thiourea along with 2% sulfuric acid, you are pushing total ions passing through the plasma higher. Consider the sulfur from both H2SO4 and thiourea. The sulfur along with the high MgO will suppress signal due to space-charge effect. If your internal standards efficiently correct for the suppression, then you can correctly quantitate, but I would ask myself the question whether I really need 2% sulfuric acid going into the plasma, for one, or could I dilute further as Randy suggested? Could thiourea be reduced to 0.05% as well?
R. Steven Pappas, Ph.D.
Team Lead, Tobacco Inorganics Group
Centers for Disease Control & Prevention
4770 Buford Highway, NE
M.S. F44, Building 110
Atlanta, GA 30341-3717, USA
From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). <[log in to unmask]> On Behalf Of Randy Mercurio
Sent: Tuesday, August 7, 2018 4:05 PM
To: [log in to unmask]
Subject: Re: Intensities of all elements suppresing in presence of magnesium oxide
It sounds like you are seeing the EIE effect. That's 200 mg/L of Mg that is stealing your plasma energy causing a suppression of your internal standard signal. Try lowering your Mg concentration by dilutions and/or make sure you have the same amounts of Mg in your calibration standards.
Trace Metals Task Lead
Eastern Research Group, Inc.
601 Keystone Park Drive
Morrisville, N.C. 27560
Office (919) 468 – 7922
From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). <[log in to unmask]> On Behalf Of Prasad Lavisetty
Sent: Tuesday, August 7, 2018 3:56 PM
To: [log in to unmask]
Subject: Intensities of all elements suppresing in presence of magnesium oxide
Currently I am working on a project that has 10% of magnesium oxide. It is pharmaceutical product. It dissolves freely in water. I am not digesting the sample. The acid matrix currently I am working is 2.5% nitric acid +0.5% hydrochloride acid+ 2% sulfuric acid. I am adding thiourea solution in dilution to get 0.1% concentration.
Calibration curve is good for all elements (cd, pb, as, hg, co, no, v), internal standards also the recovery is around 100%.
When it comes to samples and spiked samples the intensities are down to 75% (both analyte and internal standards). The intensities are same throughout the Samples.
I am thinking my sample containing magnesium oxide is causing suppression of intensities. The final concentration of magnesium oxide is going to ICPMS is 0.2mg/ mL. Anybody faced same issue ever before.
Thanks in advance