The How’s And Why’s
1
All commercial goods must be tested, and before they are tested, they were probably sampled, and
before that, they were produced, and before that, the raw materials were processed, and before that,
they were supplied, and before that, they were extracted from the ground or harvested, and before
that there was the big bang, but that’s probably going back a bit far!
1.1 Why test?
Everything is a product at some stage of the chain. Figure 1.1 describes the basic chain of manufacture,
and consumers of a product at one stage become suppliers to the next stage.
RAW
MATERIALS
S
SEMIPROCESSED
GOODS
FINISHED
PRODUCT
C
C
S
S
C
FIGURE 1.1 The manufacturing chain (S = supplier; C = consumer)
There may be a number of processing steps under the category of Semi-Processed Goods, possibly
with different companies involved, and for all but the simplest of items, there will be multiple raw
materials and multiple semi-processed goods.
CLASS EXERCISE 1.1
As a supplier of product, why is it necessary to test?
As a consumer of product, why is it necessary to test?
Whose responsibility is it to test the product before it is further processed?
1. The How’s And Why’s
CLASS EXERCISE 1.2
Even for a relatively simple product – a bagged loaf of sliced white bread – there will have been
numerous processing steps along the way to providing the basic ingredients. As best as possible,
describe what level of processing would have been required for the ingredients listed below. Suggest
any other non-food ingredients that might be part of the final product.
wheat flour
water
yeast
salt
canola oil
sugar
soy flour
thiamin
The above exercise should give you an appreciation of why the supplier is the one responsible for
product quality. If the bread manufacturer needed to check the quality of all the ingredients, we would
be paying a lot more for our daily bread than we do!
CLASS EXERCISE 1.3
Would you expect that the bread manufacturer does no testing of the ingredients?
Industrial Products (Testing)
1.6
1. The How’s And Why’s
1.2 What to test for?
Before the loaf of bread leaves Tip-Top or Buttercup (or wherever), it will need to be tested before it
reaches the last consumer: the general public. As you are aware, end-of-line testing is only part of the
quality process: quality control will involve the checking of the partly finished product at different
stages along the line. Run or control charts document changes in the process and allow problems to
be detected, anticipated and corrected.
CLASS EXERCISE 1.4
What checks would be carried out on the bread during its manufacture? The basic bread making
process is as follows:
•
mixing of dry ingredients, followed by addition of water
•
formation of dough
•
division of the dough into loaf portions
•
controlled temperature/humidity conditions for the rising of the dough
•
baking
•
bagging
Certain tests will be carried out on every item (100% inspection), but for others, it must be done on
selected samples. For those which involve samples, a decision must be made on just how often
samples are taken and how much is taken.
But product testing is far more than just chemical or microbiological analysis: it is about product
performance. The general public are probably not all that interested in whether the bread has 9.5%
or 9.6% protein, but they will care about whether the bread tastes good etc.
CLASS EXERCISE 1.5
What do you think a loaf of bread should be tested for? For each measure, suggest how often this test
should be applied (e.g. every loaf, once an hour, once a shift etc).
Industrial Products (Testing)
1.6
1. The How’s And Why’s
All this testing is only valid if there is a comparison point to make a judgement against: a product
specification or standard. This describes the product in fine detail, and gives upper and lower limits
for its performance.
CLASS EXERCISE 1.6
Where would the detail for a product specification come from?
1.3 Who to do the testing?
With all this testing, you would think there should more jobs in the area! As with so many activities, it
is becoming increasingly the case that manufacturing facilities are outsourcing much of the testing
work. Often it is only the simple (ie cheap) work that is kept in-house.
Unfortunately, such a trend does reduce the amount of laboratory work available. One reason
is that the work for an outside laboratory does fluctuate, so casual staff are favoured, because they
are easy to get rid of, when there is a quiet period.
CLASS EXERCISE 1.7
Let’s return to the bread manufacturer. Who will actually carry the testing we have identified as being
necessary?
1.4 How to get the materials to test?
Otherwise known as sampling. In other subjects, you have covered some of the principles of obtaining
a representative sample. Methods such as stratified sampling are all very well and fine, particularly
for individual items – eg take the 4th, 10th and 23rd packet of Cornflakes from the production line.
But what if the population to be sampled is a 50 tonne railway carriage of coal? Or a 10, 000 L
vat of paint? What implements do we use to collect samples from large quantities of bulk material?
How much to take? Where to take it from?
Industrial Products (Testing)
1.6
1. The How’s And Why’s
Fortunately, many standard methods have been written to cover the sample collection from a range
of different bulk materials. These include the following Australian Standards listed in Table 1.1.
TABLE 1.1 Australian Standards dealing with sampling of actual materials
AS
Material
1050.1
Iron and steel
1141.3.1
Aggregates
1166
Milk and milk products
1301.417s
Paper, pulp and board
1580.102.1
Paint and related materials
2347
Zinc and zinc alloys
2534
Lead and lead alloys
2612
Aluminium and aluminium alloys
2614
Copper and copper alloys
2806.1
Aluminium ores
4550
Essential oils
CLASS EXERCISE 1.8
What is the difference between the gross sample, laboratory sample and analytical sample? How do
you obtain one from the other?
1.5 How to test?
Any analysis requires a procedure. If it is a chemical analysis, then most of the procedure will involve
the preparation of the sample, particularly if it is a solid, since most analytical procedures require a
solution in the analytical step.
Standard methods exist for many analyses, and you have been introduced to various information
sources in the module Practical Project. For those of you who haven’t done this yet, some of the more
useful sources are listed in Table 1.2.
Industrial Products (Testing)
1.6
1. The How’s And Why’s
TABLE 1.2 Sources of standard methods
Source
Comment
Australian Standards
Comprehensive sets of procedures for analysis of steel and dairy
products; much less for other materials; somewhat outdated
Official Methods of Analysis
Extremely comprehensive for foods, pharmaceuticals and
agricultural products
Standard Methods of Analysis
Extremely comprehensive for metals, minerals, oils and similar
products
ASTM Methods of Analysis
Extremely comprehensive for metals, minerals, oils and similar
products
Laboratories will more often than not use a standard method, or a modification, because it saves
development work and it is easier to prove to NATA inspectors that it is a valid method.
Sample preparation
The major task of sample preparation is to produce a sample that can be conveniently and accurately
analysed. In most cases, this will mean removing some or all of the matrix from the analyte. The main
factors (in descending order of importance) in determining what type of sample preparation is required
are:
•
the physical state of the sample – if is already a liquid, that makes life much easier
•
the nature of the analyte – is it inorganic or organic/molecular?
•
the nature of the matrix – if it is relatively simple, then little preparation may be required
CLASS EXERCISE 1.9
(a) What types of sample preparation will be suitable for organic/molecular analytes?
(b)
What types of sample preparation will be suitable for inorganic analytes?
Industrial Products (Testing)
1.6
1. The How’s And Why’s
You have met each of these techniques before, but some comments about the different acids used in
wet ashing is appropriate at this point.
The main concentrated acids used to decompose organic or mineral samples are:
•
hydrochloric – not an oxidising acid; it is a better solvent for easily dissolved metals than the
oxidising acids
•
sulfuric – an oxidising acid, and also capable of decomposing organic matter “safely”
•
nitric – the most commonly used oxidising acid for dissolving metals; can be used with HCl (3
parts HCl:1 part HNO3) as aqua regia which is strong enough to dissolve the noble metals
•
perchloric – an explosion risk with organics, but will attack some steels which are otherwise
difficult
•
hydrofluoric – only used to dissolve silicate materials, such as rocks and glass; the silicon forms
a volatile compound and is lost
As you can see from Table 1.3, they are often used in mixtures or in series for dissolving metals. They
are also not always used in concentrated form. It is not always clear why certain mixtures are used,
but it is clear that different analytes require different acids. Iron itself dissolves readily in hydrochloric
acid, but the alloying elements are not so easy.
TABLE 1.3 Acids used in dissolving steels (from AS1050)
Element
Acids used
Al
1:1 nitric then conc. perchloric
B
conc. nitric + conc. HCl then conc. phosphoric and conc. sulfuric
Co
conc. HCl + 1:9 phosphoric, then conc. nitric then conc. perchloric
Co
1:7 mix of sulfuric and phosphoric
Cu
conc. HCl + conc. nitric then conc. perchloric
Cu
mix conc. HCl, nitric and perchloric
Mg
1:1 HCl then conc. nitric
Mn
1:4 sulfuric then conc. nitric
Mo
conc. HCl + 1:9 phosphoric then conc. nitric, HF and perchloric
Ni
4 M HCl + 3 M nitric + conc. perchloric
Ni
diluted nitric/perchloric mix
Sn
conc. HCl
Ti
conc. HCl then conc. nitric, then 10 M sulfuric then 5 M HCl
V
1:3 sulfuric
V
conc. HCl and nitric, then con c perchloric
What You Need To Be Able To Do
•
•
•
•
•
outline the reasons for testing products
discuss the responsibilities associated with product testing
identify the types of tests required for a given product
outline the role of the laboratory in product testing
compare different approaches to sample preparation
Industrial Products (Testing)
1.6