CA_MT018_021
MT 18 STANDARD WATERS
INTRODUCTION (Note 1)
Instructions for the preparation of Standard Waters and of waters of any desired hardness are given in CIPAC Monograph 1. For the Standard Waters A to G, stock solutions of Ca++ and Mg++ are prepared; the working solutions are then made by dilution of these stock solutions.
All solutions should be stored in polyethylene containers.
Working solutions should be freshly prepared immediately before use.
A method for the determination of the hardness of water by EDTA titration is given in MT 73.
18.1 Preparation of Standard Waters A to G (MT 18.1.1 to 18.1.7) REAGENTS
Calcium carbonate (CaCO3) containing not less than 99% calcium carbonate; dry for 2 h at 105 °C before use
Magnesium oxide (MgO) containing not less than 99% magnesium oxide; dry for 2 h at 105 °C before use
Sodium hydrogen carbonate (NaHCO3) containing not less than 99% sodium hydrogen carbonate
Ammonia solution ( NH4OH) approximately 1 mol/l (1N)
Hydrochloric acid c (HCl) : 1 mol/l (1N) and 0.1 mol/l (0.1N) standardized solutions; RE 14.2 and 14.1
Sodium hydroxide c (NaOH) : 0.1 mol/l (0.1N) standardized solution; RE 25.1 Methyl red indicator 0.1% m/v aqueous solution; RE 18
STOCK SOLUTIONS
Solution I. 0.04M Ca++ solution
Weigh accurately calcium carbonate (4.000 g), and transfer to a 500 ml conical flask with a minimum of distilled water. Place a small filter funnel in the mouth of the flask and add slowly 1 mol/l hydrochloric acid (82.0 ml, measured from a burette), swirling the contents. When all the calcium carbonate has dissolved, dilute the solution to approximately 400 ml with distilled water, and boil gently to expel excess carbon dioxide. Cool the solution, add methyl red (2 drops) and neutralize to an intermediate orange colour with 1 mol/l ammonia solution, added drop wise.
Transfer the solution quantitatively to a 1000 ml volumetric flask and make up to volume with distilled water. The solution should be stored in a polyethylene container.
One ml of this solution when diluted to 1000 ml gives a water containing 4 ppm hardness expressed as calcium carbonate.
Solution II. 0.04M Mg++ solution
Weigh accurately magnesium oxide (1.613 g), and transfer to a 500 ml conical flask with a minimum of distilled water. Place a small filter funnel in the mouth of the flask and add slowly 1 mol/l hydrochloric acid (82.0 ml, measured from a burette), swirling the contents. When all the magnesium oxide has dissolved, dilute the solution to approximately 400 ml with distilled water. Add methyl red (2 drops) and neutralize to an intermediate orange colour with 1 mol/l ammonia solution, added drop wise. Transfer the solution quantitatively to a 1000 ml volumetric flask and make up to volume with distilled water. The solution should be stored in a polyethylene container.
One ml of this solution when diluted to 1000 ml gives a water containing 4 ppm hardness expressed as calcium carbonate.
Solution III. 1.0M sodium hydrogen carbonate solution
Weigh accurately sodium hydrogen carbonate (84.01 g), dissolve in 800 ml distilled water, transfer to a 1000 ml volumetric flask and make up to volume with distilled water.
One ml of this solution when diluted to 1000 ml gives a water containing the equivalent of 23 ppm of sodium.
Solution IV. 0.2M Ca++ solution.
Weigh accurately calcium carbonate (20.00 g), and transfer to a 1000 ml conical flask with a minimum of distilled water. Place a small filter funnel in the mouth of the flask and add slowly 1 mol/l hydrochloric acid (410 ml), swirling the contents. When all the calcium carbonate has dissolved, dilute the solution to approximately 800 ml with distilled water, and boil gently to expel excess carbon dioxide. Cool the solution, add methyl red (2 drops) and neutralize to an intermediate orange colour with 1 mol/l ammonia solution, added drop wise. Transfer quantitatively to a 1000 ml volumetric flask and make up to volume with distilled water. The solution should be stored in a polyethylene container.
One ml of this solution when diluted to 1000 ml gives a water containing 20 ppm hardness expressed as calcium carbonate.
Solution V. 0.2M Mg++ solution
Weigh accurately magnesium oxide (8.065 g), and transfer to a 1000 ml conical flask with a minimum of distilled water. Place a small filter funnel in the mouth of the flask and add slowly 1 mol/l hydrochloric acid (410 ml), swirling the contents. When all the magnesium oxide has dissolved, dilute the solution to about 800 ml with distilled water. Add methyl red (2 drops) and neutralize to an intermediate orange colour with 1 mol/l ammonia solution, added drop wise. Transfer quantitatively to a 1000 ml volumetric flask and make up to volume with distilled water. The solution should be stored in a polyethylene container. One ml of this solution when diluted to 1000 ml gives a water containing 20 ppm hardness expressed as calcium carbonate.
APPARATUS
pH meter with suitable electrode assembly
PREPARATION OF WORKING SOLUTIONS (Notes 2 and 3)
18.1.1 Standard Water A
20 ppm hardness
pH 5.0 - 6.0
Ca++: Mg++ = 1:1
Pipette Solution I (2.5 ml) and Solution II (2.5 ml) into a 1000 ml beaker and dilute to about 800 ml with de-ionized water. Using a pH-meter, adjust to pH 5.0 to 6.0 (Note 4) by the drop wise addition of 0.1 mol/l sodium hydroxide or 0.1 mol/l (0.1N) hydrochloric acid as appropriate. Transfer the solution quantitatively to a 1000 ml volumetric flask and make up to volume with de-ionized water (Note 3).
18.1.2 Standard Water B
20 ppm hardness
pH 8.0 - 9.0
Ca++.: Mg++ = 4:1
Pipette Solution I (4.0 ml) and Solution II (1.0 ml) and Solution III (2.0 ml) into a 1000 ml beaker and dilute to about 800 ml with de-ionized water. Using a pH-meter, adjust to pH 8.0 to 9.0 (Note 4) by the drop wise addition of 0.1 mol/l sodium hydroxide. Transfer the solution quantitatively to a 1000 ml volumetric flask and make up to volume with de-ionized water (Note 3).
500 ppm hardness
pH 7.0 - 8.0
Ca++.: Mg++ = 4:1
Pipette Solution I (100 ml) and Solution II (25 ml) into a 1000 ml beaker and dilute to about 800 ml with de-ionized water. Using a pH-meter, adjust to pH 7.0 to 8.0 (Note 4) by the drop wise addition of 0.1 mol/l sodium hydroxide. Transfer the solution quantitatively to a 1000 ml volumetric flask and make up to volume with de-ionized water (Note 3).
18.1.4 Standard Water D
342 ppm hardness
pH 6.0 - 7.0
Ca++.: Mg++ = 4:1
Measure, from a burette, Solution I (68.5 ml) and Solution II (17.0 ml) into a 1000 ml beaker and dilute to about 800 ml with de-ionized water. Using a pH meter, adjust to pH 6.0 - 7.0 (Note 4) by the drop wise addition of 0.1 mol/l sodium hydroxide. Transfer the solution quantitatively to a 1000 ml volumetric flask and make up to volume with de-ionized water (Note 3).
18.1.5 Standard Water E
1500 ppm hardness
pH 7.0 - 8.0
Ca++.: Mg++ = 4:1
Measure, from a burette, Solution IV (60 ml) and Solution V (15.0 ml) into a 1000 ml beaker and dilute to about 800 ml with de-ionized water. Using a pH meter, adjust to pH 7.0 - 8.0 (Note 4) by the drop wise addition of 0.1 mol/l sodium hydroxide. Transfer the solution quantitatively to a 1000 ml volumetric flask and make up to volume with de-ionized water (Note 3).
18.1.6 Standard Water F
5000 ppm hardness
pH 6.0 - 7.0
Ca++ only
Transfer Solution IV (250 ml) to a 1000 ml beaker and dilute to about 800 ml with de-ionized water. Using a pH meter, adjust to pH 6.0 - 7.0 (Note 4) by the drop wise addition of 0.1 mol/l sodium hydroxide. Transfer the solution quantitatively to a 1000 ml volumetric flask and make up to volume with de-ionized water (Note 3).
8000 ppm hardness
pH 6.0 - 7.0
Mg++ only
Transfer Solution V (400 ml) to a 1000 ml beaker and dilute to about 800 ml with de-ionized water. Using a pH meter, adjust to pH 6.0 - 7.0 (Note 4) by the drop wise addition of 0.1 mol/l sodium hydroxide. Transfer the solution quantitatively to
a 1000 ml volumetric flask and make up to volume with de-ionized water (Note 3).
18.2 Preparation of salted waters H and J.
Standard waters with properties which are intended to simulate waters occurring in Argentina and Brazil. The method of preparation was supplied by E V Pineda.
REAGENTS
Calcium chloride anhydrous (CaCl2) not less than 95%; dry for 2 h at 105 °C before use
Magnesium sulphate (MgSO4 ? 7 H2O) not less than 99.5% magnesium sulphate heptahydrate
Sodium sulphate (Na2SO4) not less than 99.5%; dry for 2 h at 105 °C before use Sodium chloride (NaCl) not less than 99.9%; dry for 2 h at 105 °C before use Hydrochloric acid c (HCl) : 0.1 mol/l (0.1N) standardized solution; RE 14.1 Sodium hydroxide c (NaOH) : 0.1 mol/l (0.1N) standardized solution; RE 21
STOCK SOLUTION
Weigh accurately into separate vessels 2.00 g calcium chloride; 1.80 g magnesium sulphate; 5.00 g sodium sulphate and 10.0 g sodium chloride. Dissolve each of the reagents in about 150 ml distilled water and transfer quantitatively to the same 1000 ml volumetric flask, mix the solution thoroughly, make up to volume with distilled water and mix again.
This solution should be stored in a polyethylene container and has a total hardness of 2535 ppm as calcium carbonate with Ca++.: Mg++ ratio about 2.5 : 1. Working solutions with total hardness 634 ppm and 63.4 ppm are prepared by dilution from this stock solution.
APPARATUS
pH meter with suitable electrode assembly
PREPARATION OF WORKING SOLUTIONS (Notes 2 and 3)
18.2.1 Standard Water H
634 ppm hardness
pH 6.0 - 7.0
Ca++.: Mg++ about 2.5 : 1
Transfer 250 ml of stock solution to a 1000 ml beaker and dilute to about 800 ml with de-ionized water. Using a pH meter, adjust to pH 6.0 - 7.0 (Note 4) by the drop wise addition of either 0.1 mol/l sodium hydroxide or 0.1 mol/l hydrochloric acid. Transfer the solution quantitatively to a 1000 ml volumetric flask and make up to volume with de-ionized water (Note 3).
18.2.2 Standard Water J
63.4 ppm hardness
pH 6.0 - 7.0
Ca++.: Mg++ about 2.5 : 1
Transfer 100 ml of Standard Water H to a 1000 ml beaker and dilute to about 800 ml with de-ionized water. Using a pH meter, adjust to pH 6.0 - 7.0 (Note 4) by the drop wise addition of either 0.1 mol/l sodium hydroxide or 0.1 mol/l hydrochloric acid. Transfer the solution quantitatively to a 1000 ml volumetric flask and make up to volume with de-ionized water (Note 3).
18.3 Non-CIPAC Standard Waters
18.3.1 WHO Standard Hard Water
342 ppm hardness (Note 5)
Ca++.: Mg++ 4 : 1 (Note 6)
Dissolve calcium chloride (0.304 g) and magnesium chloride (0.139 g of MgCl2.? 6 H2O) in distilled water and make up to 1000 ml.
18.3.2 GB Standard Water
400 ppm hardness
Ca++.: Mg++ about 1 : 1
Dissolve calcium carbonate (1.85 g) and magnesium oxide (0.74 g) in 2 mol/l hydrochloric acid. Evaporate to dryness and dissolve in distilled water, making up to 100 ml. Add 10 ml of this solution to sufficient distilled water to give a final volume of 1000 ml when the specified amount of sample is added.
18.3.3 AOAC Standard Water
Theoretical hardness varies according to dilution
Ca++.: Mg++ about 7 : 3
(a) Dissolve calcium chloride (73.99 g) in 400 ml boiled, distilled water. Dissolve magnesium chloride (67.76 of MgCl2? 6 H2O) in 400 ml boiled, distilled water. Mix the solutions in a 1000 ml volumetric flask and make up to volume.
(b) Dissolve sodium hydrogencarbonate (56.03 g) in boiled distilled water and make up to 1000 ml. Waters of differing hardness may be made by combining x ml of (a) with 4 ml of (b) and making up to 1000 ml.
One ml of (a) diluted to 1000 ml gives a water containing 100 ppm of hardness expressed as calcium carbonate.
18.3.4 US Navy Hard Water
500 ppm hardness
Ca++.: Mg++ about 6 : 4
Dissolve calcium chloride dihydrate (CaCl2? 2 H2O; 0.235 g) and magnesium chloride hexahydrate (MgCl2? 6 H2O; 0.268 g) in water and make up to 1000 ml. 18.3.5 Synthetic Nile Water
170 ppm hardness
Ca++.: Mg++ 4 : 1
Dissolve magnesium chloride hexahydrate (0.1024 g) and sodium hydrogen-carbonate (0.1600 g) in 400 ml distilled water. Dissolve calcium oxide hydrate [Ca(OH)2; 0.0910 g] in 150 ml distilled water. Mix the two solutions in a 1000 ml flask and make up to the mark. Adjust the pH of the solution to 8.4 by the addition of small pieces of solid carbon dioxide.
18.3.6 ASTM Hard Water
300 ppm hardness
Ca++.: Mg++ about 3 : 2
Dissolve calcium chloride dihydrate (CaCl2? 2H2O; 1.764 g) and magnesium sulphate (1.968 g) in distilled water and make up to 1000 ml. Dilute 150 ml of this solution to 1000 ml for the working solution.
18.4 Preparation of Standard Waters of required hardness
By use of stock solutions I, II, IV and V waters of any hardness up to 20000 ppm can be prepared with any Ca ++.: Mg ++ ratio.
18.4.1 Dilution of stock solutions
Waters of the following hardness are obtained when 1 ml of the individual stock solution is diluted to 1000 ml.
Stock solution
Hardness (as ppm CaCO 3) Cation
I 4 Ca ++ only II 4 Mg ++ only IV 20 Ca ++ only V 20 Mg ++ only
18.4.2 Preparation of waters with a hardness of up to 600 ppm . Use stock solutions I and/or II only.
To prepare 1000 ml of a Standard Water of hardness H ppm calcium carbonate, the total volume of stock solution(s) required is H /4 ml.
Thus, to prepare 1000 ml of a standard water of hardness H ppm containing Ca ++ or Mg ++ only, the volumes of stock solution required are H /4 ml of stock solution I or II respectively. To prepare 1000 ml of a Standard Water of hardness H ppm containing both Ca ++ and Mg ++ and where a ratio of Ca : Mg = C : 1 is required, the volumes of stock solutions required are respectively:
1
4+×C C H ml of stock solution I and
1
4+×C C H ml of stock solution II
For example:
Prepare 1000 ml of Standard Water with a hardness of 575 ppm and where Ca ++.: Mg ++ = 4 : 1
Total volume of stock solutions required =
4575
= 143.75 ml Volume of stock solution I required = 144
4575+× = 115 ml
Volume of stock solution II required = 1
41
4575+× = 28.75 ml
18.4.3 Preparation of waters with a hardness greater than 600 ppm . Use stock solutions IV and/or V only.
To prepare 1000 ml of a Standard Water of hardness H ppm calcium carbonate, the total volume of stock solution(s) required is H/20 ml.
To prepare 1000 ml of a Standard Water of hardness H ppm containing Ca ++ or Mg ++ only, the volumes of stock solutions required are H/20 ml of stock solution IV or V respectively. To prepare
1000 ml of a standard water of hardness H ppm and where a ratio of Ca ++ : Mg ++ = C : 1 is required, the volumes of stock solutions required are respectively:
1
20+×C C H ml of stock solution IV
1
20+×C C H ml of stock solution V
For example:
Prepare 1000 ml of Standard Water with a hardness of 2300 ppm and where Ca ++ : Mg ++ = 4 : 1
Total volume of stock solutions required = 202300
= 115 ml Volume of stock solution IV required = 144
202300+× = 92 ml
Volume of stock solution V required = 141
202300+× = 23 ml
18.5 Units of measurement for the hardness of water and their conversion
The unit used in this method is ppm calcium carbonate.
Other units which may be encountered are: The milliequivalent per 1000 ml (me/l) 1 me/l Ca hardness = 20.04 mg Ca ++ / l 1 me/ l Mg hardness = 12.16 mg Mg ++/l
The English degree of hardness (°gb), corresponding to 1 grain calcium carbonate in an Imperial gallon.
The German degree of hardness (°d), corresponding to 10 mg calcium oxide in 1 litre.
The French degree of hardness (°f), corresponding to 100 g calcium carbonate in 10 m 3.
The American degree of hardness (°usa), corresponding to 1 grain calcium carbonate in an American gallon.
1 grain = 0.064798918 g 1 gallon (Imp) = 4.54596 l 1 gallon (US) = 3.7853 l
TABLE I Comparison of Units of Measurement of Hardness of Water
ppm CaCO 3me/l Ca
++
°gb
°d
°f
°usa
1 ppm calcium carbonate
1.00
0.020 0.07020.0560 0.100 0.0585
1 mol/l Ca ++
50.0 1.00 3.51 2.80 5.00 2.925 1 English degree 14.3 0.285 1.00 0.798 1.43 0.829 1 German degree 17.8 0.357 1.25 1.00 1.78 1.044 1 French degree 10.0 0.200 0.702 0.560 1.00 0.583 1 American degree
17.1
0.342
1.20
0.958
1.71
1.00
Note 1 For further information see CIPAC Monograph 1, Standard Waters;
Recommendations for the preparation of standard waters used for testing pesticidal and other formulations and an FAO survey of naturally occurring waters, R de B Ashworth & B Crozier, edited G R Raw, 1972. W Heffer & Sons Ltd, Printers, King's Hedges Road Cambridge, England.
Note 2 All working solutions should be stored in polyethylene containers and must be freshly made up before use, as Ca++ and Mg++ will be lost from
solution on standing.
Note 3 It is recommended that de-ionized water be used for the preparation of all working solutions, since distilled water may have a pH 5.0,
requiring excessive addition of sodium hydroxide for pH adjustment. Note 4 The pH after adjustment should be near the middle of the stated range, to allow for any slight pH change on standing.
Note 5 The total hardness of water is calculated by the following formula: Total hardness as ppm calcium carbonate = 2.495 × ppm Ca++ + 4.115 × ppm
Mg++.
Note 6 Ca++ and Mg++ are expressed as their contribution to the total hardness in terms of calcium carbonate and not as their individual ionic contributions.
MT 19 PHOSPHATE BUFFER SOLUTIONS
REAGENTS
Sodium dihydrogen orthophosphate (NaH2PO4? 2 H2O) (Note 1)
diSodium hydrogen orthophosphate (Na2HPO4? 12 H2O) (Note 1) Hydrochloric acid c (HCl) : 0.25 mol/l (0.25N) standardized solution; RE 14.5 Bromocresol green 0.4% indicator solution; RE 55.1
Sodium hydroxide c (NaOH) : 0.25 mol/l (0.25N) standardized solution; RE 25.8 Thymol blue 0.04% indicator solution; RE 30.2
Sodium chloride (NaCl) 0.25 mol/l solution
APPARATUS
Two weighing bottles
Four volumetric flasks 250 ml
Class A burette 100 ml
Burette 50 ml
Four conical flasks 250 ml
Two polyethylene bottles 250 ml
METHOD
(a) Preparation of standard phosphate solutions
Weigh accurately 23.0 g of di sodium hydrogen orthophosphate and 10.0 g of sodium dihydrogen orthophosphate. Dissolve each salt separately in distilled water, recently boiled and cooled, and make both solutions up to 250 ml in volumetric flasks (Note 2). Titrate 25 ml di sodium hydrogen orthophosphate solution with hydrochloric acid using three drops of bromocresol green solution as indicator. Match the colour at the end point with that of a mixture of sodium dihydrogen orthophosphate solution (25 ml), bromocresol green solution (3 drops), and sodium chloride solution (25 ml). Calculate the exact amount of di sodium hydrogen orthophosphate needed to give a 0.25 mol/l solution in 250 ml of water. Dissolve this exact amount in 250 ml water and check the concentration of the solution by titration with hydrochloric acid as before.
Similarly, titrate 25 ml sodium dihydrogen orthophosphate solution with the sodium hydroxide solution, using three drops of thymol blue solution as indicator. Match the colour at the end point with that of a mixture of the di sodium hydrogen-orthophosphate solution (25 ml), thymol blue solution (3 drops), and water (25 ml). Hence, calculate the exact amount of sodium dihydrogen ortho-phosphate required to give 250 ml of exactly 0.25 mol/l solution. Dissolve exactly this amount in 250 ml water and check the concentration of the solution by titration with hydrochloric acid as before.
(b) Preparation of buffer solutions
(i) MCPA analysis
Prepare the buffer solution by mixing 112 ml of exactly 0.25 mol/l disodium hydrogen orthophosphate and 83 ml of exactly 0.25 mol/l sodium dihydrogen-orthophosphate solutions, using a Class A burette to measure the volumes, and mix well (Note 2).
(ii) Dinoseb analysis
Mix 100 ml of 0.25 mol/l di sodium hydrogen orthophosphate
solution and 10 ml of 0.25 mol/l sodium dihydrogen orthophosphate solution. Note 1 As the percentage of water of crystallization in these salts is variable, approximately 0.25M solutions are made up and standardized.
Note 2 Store all phosphate solutions in polyethylene bottles at 0 °C to prevent mould growth and chemical contamination. Always shake the bottle
and bring to room temperature before use.
MT 20 STABILITY OF DILUTE EMULSION
REAGENT
Standard Water MT 18, (Note 1)
APPARATUS
Beakers 250 ml, 6 cm internal diameter
Two burettes 50 ml graduated in 0.1 ml
Measuring cylinders 100 ml graduated in 1.0 ml
PROCEDURE
To Standard Water (70 ml) at the specified temperature (Note 2) in a beaker, add the formulation under test at the rate of about 5 ml per 12 seconds, from a burette. During the addition, stir with a glass rod at the rate of about 3 turns per second, and direct, continuously, the flow of the concentrate towards the centre and not against the wall of the beaker. Sufficient formulation is added so that when subsequently the solution is diluted to 100 ml, it will be as recommended for use by the supplier. Make up the volume to 100 ml by adding distilled water from the other burette, as above. Transfer the emulsion immediately to a clean, dry measuring cylinder and keep at the specified temperature ± 1 °C (Note 2) for 1 h without disturbing in any way the cylinder or its contents. At the end of 1 h Note any changes in the emulsion and the volume of any separated material. Repeat the whole operation using distilled water instead of Standard Water. Note 1 Use CIPAC Standard Water D (MT 18.1.4) unless otherwise specified. Note 2 If no temperature is specified, the temperature used should be 30 ± 1 °C.
MT 21 SILICA FOR CHROMATOGRAPHY
21.1 Silica
REAGENTS
Sodium silicate solution; d20 about 1.70
Methyl orange indicator solution; RE 17.1
Hydrochloric acid (HCl) concentrated, d20 1.18
- 0.2 mol/l (0.2N) solution
Ethanol (CH3CH2OH) or Industrial Methylated Spirit 95%
APPARATUS
Beaker 10000 ml
Burette 100 ml
Buchner flask and funnel large
Oven at 110 °C
Oven at 400 °C
Sieve 75 μm
Sieve 53 μm
PREPARATION
Dilute the sodium silicate solution (1500 ml) with two volumes of water containing a little methyl orange solution and cool to 8 °C. Stir the solution and add concentrated hydrochloric acid from a burette until the solution is just acid.
Allow the precipitated silica gel to settle for 3 h. Filter through a large Buchner funnel and wash the gel with water, using approximately 10 l. Suspend the gel in sufficient 0.2 mol/l hydrochloric acid to form a thin slurry and allow to stand for two days. Again filter through a Buchner funnel.
Transfer the silica to the original container, add water (2500 ml), stir mechanically for 30 min and filter through a Buchner funnel. Repeat this washing operation 15 times to remove all the sodium chloride then repeat twice with ethanol (2500 ml) instead of water, filtering through the Buchner funnel after each washing. Drain the material thoroughly in the filter and remove most of the ethanol by vacuum drying in a desiccator. Transfer the silica in open trays to an oven at 100 °C and dry for 2 days. Break down any lumps with a glass rod and ignite in open trays at 400 °C for 4 days.
Pulverize the silica until most of the material passes through a 75 μm sieve. Store in sealed bottles, rejecting any material not passing the sieve.
The material thus prepared is adequate for most purposes, but slightly better performance is obtained with silica which passes a 75 μm sieve and is retained by a 53 μm sieve. The separation of this fraction is, however, very time consuming.
21.2 Sorbisil? M 60
Sorbisil? M 60 is a selective adsorption grade of silica gel which has been specially developed for use in separating aromatics from aliphatic and cycloparaffins.
PHYSICAL DATA
Particle size 90% passing a 200μm sieve and retained
on a 75μm sieve
Loss on ignition at 1000 °C Maximum: 7.0%
Alcohol/ether solubles Maximum 0.01%
Surface area (BET N2 ads) 575 ± 75 m2/g
Pore volume 0.4 - 0.5 cm3
Bulk density 0.6 g/cm3
pH (extraction to 5 to 6
equilibrium)
CHEMICAL DATA (ANHYDROUS MATERIAL)
Silica as SiO299.8%
0.1%
Sulphate as SO42-
Sodium as Na+0.04%
Iron as Fe3+0.04%
PERFORMANCE
For hydrocarbon separation Sorbisil? M 60 complies with the ACS toluene adsorption test (D H Mair method). Typical runs with a 50/50% v/v mixture of toluene and n-heptane gave the following results:
Recovery
Column Depth Toluene n-Heptane
25 cm 49.8 % 50.2 %
30 cm 50.2 % 49.8 %
?′Sorbisil′ is a registered trade mark of Crosfield Chemicals Ltd, Warrington, England.
21.3 Florisil (Note 1)
INTRODUCTION
Florisil is a synthetic magnesium oxide-silica gel adsorbent widely used in chromatography. In pesticide chemistry, it is often of value in instances where the compound under examination breaks down on silica gel, for example, endrin.
The material consists of hard, porous, white granules, stable in water and organic solvents and having the following average composition:
± 0.5% m/m
MgO 15.5
± 0.5% m/m
SiO2 84.0
Na2SO40.5% m/m (1.0% m/m maximum)
PHYSICAL DATA
Particle size 150 - 250 μm
pH (aqueous slurry, 20%) 8.4
Bulk density 0.47 g/cm3
Surface area (BET nitrogen 300 m2/g
adsorption)
PERFORMANCE
The following references give some idea of the capabilities of Florisil as a chromatographic adsorbent.
(a) 'Official Methods of Analysis of the Association of Official Analytical
Chemists' 14th edition (1984), page 533. Method of calibrating Florisil columns for mixed pesticide residue analysis based on the separation of fenchlorphos, ethion, heptachlor epoxide, dieldrin, endrin and malathion into groups.
(b) Residue Reviews (published by Springer Verlag), 1971, 34, p. 37. 'Separation of
chlorinated pesticides from polychlorobiphenyls'.
Note 1 Florisil is a registrated trade mark of the Floridin Company, Pittsburgh, USA.