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Hello, I’m Marcus Lake and welcome

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to episode six in our
GeoChem tutorial series.

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In this episode we’ll be discussing

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testing directly onto samples
or choosing

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choosing the correct sample containers
for your XRF program.

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As you can see I’m joined by my

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esteemed colleague Todd Houlahan.

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Todd how are you doing mate?

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I’m OK mate, how are you?

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I’m OK Todd.

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So where do you want to
start our discussion today?

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I want to start our discussion
with the nose of the analyzer.

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Two things I want to point out.

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The active area of measurement
on our instruments

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is about a circular oval shape

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about nine millimeters wide.

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So whatever you place in front of
that area will be measured.

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The second thing I want to point out

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is that we have various Vanta models

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and those models
have different windows.

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And those windows have
different thicknesses.

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And so that will have an impact

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on the model that you
choose to purchase.

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But I thought today’s discussion was
about sample containers.

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It is, but the concept
we need to get across

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before we start talking
about sample containers

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is that whatever is
between the detector

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and the tube inside here
and the sample

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will affect the performance
of the instrument

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and attenuate x-rays.

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So what your saying –
the thickness and the density

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of that window is very important
to your XRF analysis.

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It is. It directly affects

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the performance and how low
you can measure, generally.

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So the top of the line analyzers
that we use

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have got better capabilities because
of the size of that window.

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Exactly, and the area of the detector

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so we tend to align thinner windows

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with larger area detectors

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so we can maximize performance.

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When we build our XRF’s here in Boston

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we test and calibrate them
under optimum conditions.

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Optimum conditions means
as a fine powder,

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usually less than 150 or 250 microns,

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in a sample cup
with a thin prolene film.

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That’s standard practice.

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To achieve the best results possible

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our samples are homogenous

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and we put them under
conditions to ensure

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minimal distance between the
material and the detector

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It’s also very important for elements,
titanium and lighter.

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It’s these elements that are
more easily absorbed

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by anything between the
sample and the detector.

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So Todd should we
check some samples?

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Let’s do that.

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Testing in sample cups can be great

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however there are time
and labor costs associated

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with buying the cups, cleaning
the cups, and making them.

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So why would you test in cups?

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Well, if you’re doing
full sample prep.

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If you want the best
quality data possible.

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And if light elements
are very important.

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Now let’s put it into a plastic bag.

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OK. Lots of our customers
test samples in a plastic bag.

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So what’s the impact of
the plastic on the results?

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Let’s have a look and
test the same sample

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through one layer of plastic.

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Now let’s put this into a pulp bag.

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A lot of our customers,

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when they get their samples
back from the lab as pulps

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they want to do a quick test.

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Let’s have a look at the implication

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of this paper on the quality of data.

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So here’s paper.

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Here’s in a plastic bag.

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And here is straight
into the sample cup.

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Now shall we have a look at that
in an Excel spreadsheet Todd?

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Let’s do it.

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So Todd tell me something
about this data.

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OK, when we plot up
all the readings we took

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the first thing I notice is
we’re reading quite close

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through cups
to the true CRM value.

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But maybe we could have tested
for a little bit longer

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because we only did quite short tests.

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We only did a twenty second test
time on each medium Todd.

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The other thing I see quite quickly is

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the impact of plastic bags
particularly on the light elements.

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Huge impact.

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And that’s the big reason why
I like to do this exercise

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because I don’t think
people appreciate

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just how affected those light
elements are by plastic.

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And also see this aluminum,

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it doesn’t drop off significantly
from bags to paper.

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Why is that Todd?

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I think there’s some aluminum
in the paper bag itself.

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So I know some of our customers

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are taking the chemistry of the bags

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and subtracting it from
their final data sets.

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Yeah, and the way to do that

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is to just put a blank underneath

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whatever film, plastic
or paper you’re using

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to understand what chemistry
is in the container.

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That sounds like good practice Todd.

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Good practice.

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So Todd how would you
summarize our findings here?

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Sample containers are
influencing your data

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so it’s important that you understand

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the extent of that influence.

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And sample prep is
very important as well.

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Exactly, that’s why we’re going to
cover that in the next video.

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Thank you for joining
us in this video.

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We’ll see you in the next one.

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Thank you Todd.

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Thank you mate, safe travels.

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For more detailed information
on this topic

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please take a look at this
independently published paper

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in the journal, Geochemistry
– Exploration, Environment, Analysis.

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Note that there is a fee payable to
the Geological Society to download it.