The following test method covers the iron contents of raw materials. Section A Iron determination by colourimetric method 5 to 50 ppm or determination of Iron Content and Determination of iron content in Water principle.
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A1 SCOPE
The limit test has been adapted from the EP 97 to give a maximum
of 50 p.p.m. It is a colour comparison with a standard. The test limit may be
varied by reducing or increasing the weight of the sample taken.
A2 REFERENCE
A2.1 EP 97 - European Pharmacopoeia 1997 - Sodium Bicarbonate Iron
content (Modified to give a limit of 5 ppm)
A2.2 Health & Safety Data Sheets for Chemicals & Reagents
used in this test method.
A2.3 Material Safety Data Sheets used for products being sampled.
A3 DEFINITIONS
A4 PRINCIPLE IRON CONTENT
A4.1 An acidic solution of the sample is prepared in a Nessler
tube with the addition of mercaptoacetic acid and made alkaline with ammonia. This
is compared against control with a known iron content treated in the same way
for colour. It passes the test if the colour is equal or less in colour than
the control.
A5 REFERENCE STANDARD
A5.1 Iron standard solution (Fe 20 ppm)
Prepare a 0.1726% w/v ammonium iron (III) sulphate in 0.05M
Sulphuric Acid. Pipette 10 ml of this solution into a 100 ml flask and dilute
to volume with water. This solution contains (Fe 20 ppm).
A5.2 Iron standard solution (Fe 1 ppm) Dilute 5 ml Iron standard
solution (20 ppm) to 100 ml with water.
A6 CHEMICALS & REAGENTS FOR IRON CONTENT
A6.1 Water - De-ionised or distilled
A6.2 0.05M Sulphuric Acid (4.9 g H2SO4 made up to 1 litre with water)
A6.3 Ammonium Iron (III) Sulphate - Analytical Reagent
A6.4 2M Hydrochloric Acid (73g HCl made up to one litre with
water).
A6.5 20% w/v Citric acid (20g in 100 ml water) Use Citric acid -
analytical reagent grade
A6.6 Mercaptoacetic acid (Thioglycollic acid) - Analytical Reagent
A6.7 10M Ammonia Solution - Analytical Reagent (170g NH3 made up to 1 litre with water) May
obtained by diluting 18 M (SG 0.880) to 10 M with water
A7 EQUIPMENT
A7.1 2 x 50 ml Nessler Cylinders (matched) in a rack with a bright
background.
A7.2 100 ml volumetric flask
A7.3 10 ml and 5 ml Pipette
A7.4 50 ml measuring cylinder
A7.5 10 ml measuring cylinder.
A8 INTERFERENCE
A8.1 This is a sensitive test for iron and will work well for most
simple salts that contain iron. It will not work with highly coloured compounds
which will mask the colour developed by thioglycolic acid.
A9 SAMPLING OF IRON CONTENT
Precautions: Read Material Safety Data Sheets for the materials
that you are going to sample. A liquid and sampling normally will not be a
problem. Powders may segregate and need special selection procedures to ensure
the sample represents the whole consignment. If sampling from a large
consignment then a sampling plan shall be prepared so that the samples taken
represent the whole consignment.
A10 IRON CONTENT TESTING PROCEDURE
Precautions: Read Health and Safety Sheets for all chemicals and
reagents used in this test method before starting the analysis.
A10.1  X, g of the sample to
the nearest mg in 10 ml 2M Hydrochloric acid and transfer to Nessler cylinder.
See table below.
Sample size    X,g ppm limit of iron
2g         =        5
1g         =             10
2.5 g dilute to 50 ml with 2 M hydrochloric acid pipette 10 ml
into Nessler tube = 20
1 g dilute to 50 ml with 2 M hydrochloric acid pipette 10 ml into
Nessler tube = 50
A10.2 Add 2 ml of 20% w/v citric acid and 0.1 ml of mercaptoacetic
acid, mix make alkaline with 10M ammonia solution and dilute to 20 ml then
allow to stand for 5 minutes.
A10.3 Repeat operation without the sample but replace it with 10
ml of iron standard solution (1 ppm Fe)
A10.4 The colour of the Sample solution shall be no greater than
the Control standard containing the standard iron solution that is not more
than 10 ppm iron.
A11 CALCULATION OF RESULTS- No calculations required.
A12 ACCURACY
The analysis will give an accuracy of ±10% for this limit test.
A13 REPORTS OF IRON CONTENT
Report results as equal to (as selected in table A10.1 ppm) or
less than standard if the test is satisfactory. If not report as greater than
10 ppm and exceeds the limit in the specification and give recommendations. Quote the
number of the test method 24567A, date of analysis, analyst, identification of
sample and any deviations from the test method.
Section B - Iron Content (Iodometric method) used for Nerva aid Fe DP10
SCOPE
The method is designed for iron contents of 11 -12% and the range
may be extended by taking a different sample size. It is based on liberating
iodine from potassium iodide and therefore is only suitable for ferric iron
when other oxidizing or reducing agents are absent.
REFERENCE
2.1 Material Safety Data Sheet for materials being sampled for
this analysis.
2.2 Health & Safety Data Sheets for chemicals & reagents
used in this analysis.
2.3 Instruction Manual for the Potentiometric titrator used for
this analysis.
DEFINITIONS OF IRON CONTENT
The method is based on the reaction between Ferric ions and Iodide
ions, liberating Iodine. This is titrated with 0.1M Sodium Thiosulphate
potentiometrically. The liberated iodine is directly proportional to the Iron
present.
REFERENCE STANDARD
5.1 0.1 M Sodium Thiosulphate - Volumetric solution with a certificate of analysis showing strength. This solution may be standardized
against a primary standard such as dried Potassium Iodate.
5.2 The method may be validated using pure iron wire, dissolving
it in hydrochloric acid and ensuring that it is oxidized to the ferric form.
CHEMICALS & REAGENTS - Use Analytical Reagent grades
throughout
6.1 Water - Distilled or de-ionized.
6.2 0.1 M Sodium Thiosulphate - Volumetric Solution
6.3 Potassium Iodide
6.4 36% w/w Hydrochloric Acid
6.5 5% w/v Sodium Hydrogen Carbonate
EQUIPMENT
7.1 Potentiometric titrating equipment fitted with a combination
of Platinum & Calomel electrodes.
7.2 Balance weighing to 0.1 mg (Calibrated)
7.3 5 ml measuring cylinder
7.4 25 ml measuring cylinder.
7.5 50 ml Burette - calibrated
INTERFERENCE
Oxidising agents & reducing will interfere with the analysis.
SAMPLING
Precautions: Read material Safety Data Sheet before sampling. Powders
are often difficult to sample as they are prone to segregation and pick up
moisture. It may be necessary to use a Quartering device to obtain a sample
representative of the whole.
Determination of iron in water by phenanthroline method
Precautions: Read the health & Safety Data Sheet on chemicals &
Reagents before carrying out the analysis. Also, read instructions on the
potentiometric titrator before commencing the analysis.
10.1 Weigh 0.7 to 0.8 g to nearest 0.1 mg into auto titrator
beaker. Dissolve in approximately 100 ml of water and 20 ml 36% w/w
hydrochloric acid. Add 1.8 - 2.2g Potassium Iodide then 5 ml of 5% sodium
hydrogen carbonate solution (must be added last).
10.2 Stir then leave to stand for 8 - 10 minutes. Titrate with 0.1
M sodium thiosulphate solution using a combination of Platinum and Calomel
electrodes. The endpoint is taken at a maximum change in potential per unit
volume addition and normally occurs in the range of 50 - 150 mv.
10.3 Prepare a blank by dissolving 2 g of potassium iodide in 100 ml of water and 20 ml of 36% w/w hydrochloric Acid. The blank is normally 0.25 ml.
Calculate iron content
% Iron = (Titre - Blank) x Molarity X 5.585/Weight of Sample
ACCURACY
To determine the repeatability carry out the analysis 15 times and
discard analytes that were not strictly done according to the method.
Calculate the standard deviation and multiply by 2. This is equal to the
variance at a 95% confidence level. The variance shall be less than half the
specification range (0.8%). To validate the method a primary standard (pure
Iron wire) shall be used and the mean result must be within the 95% variance
range for the true result.
REPORTS
Report as % w/w Iron giving the result to 1 decimal place. Record the following: the test method No 24567B, the date of the analysis, the name of the analyst, whether the result is within specification, recommendations, the identification of the samples and any deviation from the test method.
>Residues on Ignition USP and includes Ash EP, Sulphated Ash EP