soohyuna Is there a way to specify concentration for each isotope when making reference standard?
At the moment, no there isn't. There is an assumption in the concentration equations that the isotopic composition of the standard and the sample are the same (or very similar). The only exception to this is Pb, where for materials with radiogenic-Pb, the ratios might be very different between standard and sample, which is why you might see a TotalPb channel. But unless you have significant isotopic differences, you don't need to specify the concentrations on a per isotope basis.
soohyuna Under QA/QC Element check, you have the "Accepted" value, which we obtain from QQQ, and then we have the "Measured". I want to understand how the "Measured" is calculated....
The 'Measured' value is the average of the group (i.e. the average of the selection averages). The Accepted value, in contrast, is just the value in your reference material file and normally comes from the literature, GeoREM etc.
soohyuna what is Totalbeam measuring?
TotalBeam is the sum of all channels. iolite calculates this because it is very useful to have a channel that always has signal, so to speak. For example, if you have silicates and Fe-oxides in one experiment, and you try to use Si to determine your baselines, you may inadvertently select the Fe-oxide intervals because they have no Si in them. If you use the Fe channel, you may select some silicates that don't have Fe in them, and so on. In this example, TotalBeam will show some signal everywhere there is a sample.
I hope that helps? If you have any questions, please let me know.