Hello, I’m Marcus Lake and welcome
to episode six in our GeoChem tutorial series.
In this episode we’ll be discussing
testing directly onto samples or choosing
choosing the correct sample containers for your XRF program.
As you can see I’m joined by my
esteemed colleague Todd Houlahan.
Todd how are you doing mate?
I’m OK mate, how are you?
I’m OK Todd.
So where do you want to start our discussion today?
I want to start our discussion with the nose of the analyzer.
Two things I want to point out.
The active area of measurement on our instruments
is about a circular oval shape
about nine millimeters wide.
So whatever you place in front of that area will be measured.
The second thing I want to point out
is that we have various Vanta models
and those models have different windows.
And those windows have different thicknesses.
And so that will have an impact
on the model that you choose to purchase.
But I thought today’s discussion was about sample containers.
It is, but the concept we need to get across
before we start talking about sample containers
is that whatever is between the detector
and the tube inside here and the sample
will affect the performance of the instrument
and attenuate x-rays.
So what your saying – the thickness and the density
of that window is very important to your XRF analysis.
It is. It directly affects
the performance and how low you can measure, generally.
So the top of the line analyzers that we use
have got better capabilities because of the size of that window.
Exactly, and the area of the detector
so we tend to align thinner windows
with larger area detectors
so we can maximize performance.
When we build our XRF’s here in Boston
we test and calibrate them under optimum conditions.
Optimum conditions means as a fine powder,
usually less than 150 or 250 microns,
in a sample cup with a thin prolene film.
That’s standard practice.
To achieve the best results possible
our samples are homogenous
and we put them under conditions to ensure
minimal distance between the material and the detector
It’s also very important for elements, titanium and lighter.
It’s these elements that are more easily absorbed
by anything between the sample and the detector.
So Todd should we check some samples?
Let’s do that.
Testing in sample cups can be great
however there are time and labor costs associated
with buying the cups, cleaning the cups, and making them.
So why would you test in cups?
Well, if you’re doing full sample prep.
If you want the best quality data possible.
And if light elements are very important.
Now let’s put it into a plastic bag.
OK. Lots of our customers test samples in a plastic bag.
So what’s the impact of the plastic on the results?
Let’s have a look and test the same sample
through one layer of plastic.
Now let’s put this into a pulp bag.
A lot of our customers,
when they get their samples back from the lab as pulps
they want to do a quick test.
Let’s have a look at the implication
of this paper on the quality of data.
So here’s paper.
Here’s in a plastic bag.
And here is straight into the sample cup.
Now shall we have a look at that in an Excel spreadsheet Todd?
Let’s do it.
So Todd tell me something about this data.
OK, when we plot up all the readings we took
the first thing I notice is we’re reading quite close
through cups to the true CRM value.
But maybe we could have tested for a little bit longer
because we only did quite short tests.
We only did a twenty second test time on each medium Todd.
The other thing I see quite quickly is
the impact of plastic bags particularly on the light elements.
Huge impact.
And that’s the big reason why I like to do this exercise
because I don’t think people appreciate
just how affected those light elements are by plastic.
And also see this aluminum,
it doesn’t drop off significantly from bags to paper.
Why is that Todd?
I think there’s some aluminum in the paper bag itself.
So I know some of our customers
are taking the chemistry of the bags
and subtracting it from their final data sets.
Yeah, and the way to do that
is to just put a blank underneath
whatever film, plastic or paper you’re using
to understand what chemistry is in the container.
That sounds like good practice Todd.
Good practice.
So Todd how would you summarize our findings here?
Sample containers are influencing your data
so it’s important that you understand
the extent of that influence.
And sample prep is very important as well.
Exactly, that’s why we’re going to cover that in the next video.
Thank you for joining us in this video.
We’ll see you in the next one.
Thank you Todd.
Thank you mate, safe travels.
For more detailed information on this topic
please take a look at this independently published paper
in the journal, Geochemistry – Exploration, Environment, Analysis.
Note that there is a fee payable to the Geological Society to download it.