The riffle splitter is a static and fractional sub-sampling device that can be used for dividing a lot of dry particulate material into two half-lots. The device is usually constructed with
steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
sheet and should be designed to have an even number of opposing inclined chutes (the riffles), with each chute having the same width. The recommended chute width should be at least 2.5× the size of the maximum particle diameter that can be found in the lot to be split. Riffle splitters are typically used in
assay
An assay is an investigative (analytic) procedure in laboratory medicine, mining, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity of a ...
and analytical
laboratories
A laboratory (; ; colloquially lab) is a facility that provides controlled conditions in which scientific or technological research, experiments, and measurement may be performed. Laboratory services are provided in a variety of settings: physicia ...
to reduce the size of samples provided from other sources (crushed rock,
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
s, powders and so on) to a lot size that is appropriate for the next stage of analytical sample preparation.
Design
There are many different versions of the riffle splitter. However, not all can be considered correct sub-sampling devices, in that the two sub-sample halves are deemed to be representative of the original lot. The issue of correctness of a riffles split sub-sample are function of both the design and the use of the splitter.
The design key items are:
* The splitter should have an even number of riffles so the two sub sample have the same
mass
Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...
* The
chute widths should be 2.5× the maximum
particle
In the Outline of physical science, physical sciences, a particle (or corpuscule in older texts) is a small wikt:local, localized physical body, object which can be described by several physical property, physical or chemical property, chemical ...
size so as to preclude blocking of the chutes by groups larger fragments in the lot. Typically this maximum particle size is in the order of 15 mm for most commercially available riffle splitters
* The chutes should have relatively sharp edges so a fragment falling onto a chute edge is directed into an adjacent chute and does not bounce away into a non-edge-adjacent chute
* The feeder to the chute (either a pan or dump-box) should have the same width as the set of riffles
* The design of tiered riffle splitters (splitters stacked in tiers above one another) is often incorrect as the outflow from an upper tier does not usually fall vertically in the centre of the next tier (see correct use below)
Use
Incorrect use of a riffle splitter will lead to sample biases, with the subs lot potentially having unacceptably higher or lower concentrations of the lot
analyte
An analyte, component (in clinical chemistry), or chemical species is a substance or chemical constituent that is of interest in an analytical procedure. The purest substances are referred to as analytes, such as 24 karat gold, NaCl, water, etc. ...
s or attributes being measured. The main operational factors are as follows:
* The splitter should be operated in an environment where any dust generated is captured in an appropriate manner that does not endanger the health and safety of the operator, with operators using appropriate
dust mask
A dust mask is a flexible paper pad held over the nose and mouth by elastic or rubber straps for personal comfort against non-toxic nuisance dusts. They are not intended to provide protection from toxic airborne hazards. The European FFP1 mask ...
s when splitting potential hazardous materials, such a rock silica dust.
* The primary lot being split must by dry and free-flowing.
* The splitter should be fed by a
pan,
bucket
A bucket is typically a watertight, vertical Cylinder (geometry), cylinder or Truncation (geometry), truncated Cone (geometry), cone or square, with an open top and a flat bottom, attached to a semicircular carrying handle (grip), handle called ...
or
hopper
Hopper or hoppers may refer to:
Places
*Hopper, Illinois
* Hopper, West Virginia
* Hopper, a mountain and valley in the Hunza–Nagar District of Pakistan
* Hopper (crater), a crater on Mercury
People with the name
* Hopper (surname)
* Grace H ...
that is the same width as the set of riffles in the device.
* Before splitting the material in the feed, the device should be leveled such that approximately the same volume of material will pass through each riffle. Dumping material from bags, buckets or shovels is incorrect and may lead to unacceptable sub sampling biases.
* The material from the primary lot should be fed slowly to the centre of the device so as to fall vertically under
gravity
In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
through the splitter. Feeding the material to one side of the device usually results in flooding of the riffles with the excess material flowing (often the fine fraction) into an adjacent riffle (see Gy, 1982 p. 295).
* A good practice is to alternate between the two sub lots from
sample
Sample or samples may refer to:
Base meaning
* Sample (statistics), a subset of a population – complete data set
* Sample (signal), a digital discrete sample of a continuous analog signal
* Sample (material), a specimen or small quantity of s ...
to sample when selecting the sub lot that is to be subject to analysis or further splitting or other sample preparation, so as to mitigate any potential bias that may occur by always selecting the sub lot from the same side of the splitter.
* Importantly, the splitter needs to be cleaned after each use using a brush and or compressed air streams to blow away any retained dust.
Use in mineral exploration
In many real-world situations outside the laboratory obeying the correct use advice above is not always possible. In particular tiered riffle splitters are widely used in the
mineral industry
Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic via ...
for sub sampling drill hole cuttings at the drilling site. These devices are problematic in that they are usually fed rapidly, the dump-devices are not well designed to allow the material to flow evenly and freely, and the volume of material and sometimes moist state, often results, in choking of the splitter, overflows and sample losses. The best approach is usually to slow the rate of drilling, split the primary lot after drilling as a separate exercise (not part of the drilling routine) and only split samples that are dry and free flowing (all other need be dried and crushed). Importantly replicates samples from the splitter rejects need to be collected regularly to monitor the potential splitter bias that may occur when the analytical sub sample is always collected from the same side of the splitting device.
See also
*
Sampling (statistics)
In statistics, quality assurance, and survey methodology, sampling is the selection of a subset (a statistical sample) of individuals from within a statistical population to estimate characteristics of the whole population. Statisticians attempt ...
*
Gy's sampling theory Gy's sampling theory is a theory about the sampling of materials, developed by Pierre Gy from the 1950s to beginning 2000sGy, P (2004), Chemometrics and Intelligent Laboratory Systems, 74, 61-70. in articles and books including:
*(1960) Sampling no ...
References
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Sampling (music)