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| Tribasic
Copper Chloride Assay Data |
A
Statistical Review
The
Chemical Structure of TBCC
TBCC
is a manufactured form of a natural mineral substance with
the empirical formula -Cu2(OH)3Cl - and a theoretical copper
concentration of 59.5%. Strict chemical nomenclature for this
compound is dicopper chloride trihydroxide, but a somewhat
less cumbersome common name is tribasic copper chloride. In
nature, under differing geologic conditions, various crystal
structures of this chemical compound were formed. They have
the same elemental make-up and general behavior in chemical
reactions, but differ slightly in the geometric structure
of the crystal lattice (angles and lengths of bonds between
elements). Three such forms occur frequently enough in nature
to have been thoroughly defined by crystallographers and assigned
standard x-ray diffraction patterns – atacamite, paratacamite
and botallackite. Botallackite has one extra water molecule
incorporated into the crystal structure - Cu2(OH)3Cl× H2O
- and therefore has a lower theoretical assay of 54.5%. As
shown in the product specification sheet, TBCC is very low
in impurities. The primary factor affecting the copper assay
of the product is the amount of water bound in the structure.
In manufacturing TBCC, the conditions in the crystallizer
produce a product with the predominant structure of atacamite,
but the assay is influenced by the presence of minor amounts
of botallackite. The guaranteed minimum copper concentration
is 57%, but mean of the statistical distribution of actual
results is 58%, which is the level that should be used for
calculating dietary formulations. The following discussion
explains the assay variation that may be observed in the product.
The
Data Base
Statistical
evaluations were performed on two sets of data – one covering
over four years of analyses performed from March, 1996 through
June, 2000 and the other covering a twelve month period from
July, 1999 through July, 2000. The tighter distribution of
the more recent results reflects Micronutrients’ continuous
improvement efforts. Included in each set are three different
ways of analyzing the available data. The first (labeled ALL)
includes data from all sources. The second (called MICRO)
is the analyses done internally at the Micronutrients lab.
The third is a separate view of the data from the various
external labs that have been used as a quality check on the
internal lab work.
While both databases include all material produced by the
manufacturing process, Micronutrients rigorously adheres to
a policy of not shipping material to customers which has an
assay below the guarantee level of 57%. Removing the data
on rejected lots from the databases would slightly shift the
statistical results. However, as indicated by the histograms,
the impact would be small.
Comments
- In
addition to inherent variation in a particular product,
there is also an uncertainty (or confidence interval)
associated with every laboratory analytical result. The
scatter in a set of data is a combination of the two.
- The
inherent precision in the lab result is often evaluated
by analyzing "splits" or replicates of a given product
sample. We have done this on various occasions with both
our internal and external labs. By submitting blind splits,
this approach tests both the precision of the final analytical
technique as well as the entire system including sample
prep. Typically we find our internal capability to be
in the range of ± 0.5%, while the same sample sent to
multiple labs will give results varying ± 3-5%. This phenomenon
explains the unusual statistical distributions (see histograms)
for the external lab results.
- The
same issues affect analysis of any copper source. An analytical
result for copper sulfate of 25%, with a confidence interval
of ± 1% means that it is somewhere between 24.75% and
25.25%. The same uncertainty on a TBCC sample at 58% puts
it between 57.4 and 58.6%. Superficially, the range on
TBCC seems to be 2.4 times as large, but the impact for
feed formulation purposes is identical.
- As
shown below, the hygroscopicity of copper sulfate is much
higher than TBCC. Thus, the true copper concentration
of a given sample of copper sulfate can change by as much
as 5% depending on whether it was taken on a humid August
day or a relatively dry day. Aside from the impact on
lab analyses, this issue also affects how much copper
gets added in a mill depending on the day’s humidity.
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| Method:
All samples dried in silica gel desiccator for
24 hours, weighed, then placed in 90% relative
humidity chamber for 24 hours and reweighed. |
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| Copper
Assay Data Analysis on Micronutrients TBCC® |
| March,
1996 through June, 2000 |
| DESCRIPTIVE
STATISTICS |
| N
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967 |
895 |
72 |
| MEAN
|
58.006 |
57.931 |
58.937 |
| SD
|
1.3417 |
1.2561 |
1.9175 |
| SE
MEAN |
0.0431 |
0.0420 |
0.2260 |
| C.V.
|
2.3130 |
2.1682 |
3.2535 |
| MINIMUM
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55.500 |
55.500 |
55.610 |
| MAXIMUM
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65.100 |
65.100 |
63.960 |
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| Copper
Assay Data Analysis on Micronutrients TBCC® |
| July,
1999 through June, 2000 |
| DESCRIPTIVE
STATISTICS |
| ALL
DATA MICRO EXTERNAL |
| N
|
190 |
166 |
24 |
| MEAN
|
57.817 |
57.716 |
58.516 |
| SD
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0.6914 |
0.4989 |
1.2491 |
| SE
MEAN |
0.0502 |
0.0387 |
0.2550 |
| C.V.
|
1.1959 |
0.8644 |
2.1347 |
| MINIMUM
|
55.800 |
56.700 |
55.800 |
| MAXIMUM
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60.760 |
58.990 |
60.760 |
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