DIBK ALIQUAT 336 SOLVENT EXTRACTION METHOD FOR GOLD Atomic Absorption Spectroscopy
Digest sample in a 500 – 600 ml beaker containing around 250ml of 1 part nitric acid to 4 parts hydrochloric acid.
The aqua regia must be freshly made, do not bottle for later use.
The beaker is heated to a simmer on a hot plate in a fume cupboard, orange brown fumes will evolve.
Continue the heating until the fumes change colour to white, give it a few more minutes and remove from hot plate to cool.
When cool the solution is filtered, usually in a Whatman No1 paper and the paper is rinsed with water from a wash bottle to get all traces of gold into the filtrate.
After filtering has finished the filtrate is made up to usually 250ml with water and poured into a clean beaker to evenly distribute the gold values in the solution.
In a clean 50ml glass extraction tube add 50ml of the final filtrate and then add 5 ml of DIBK Aliquat 336 (1%) ( straight hypochlorite solution is ok, but Aqua Regia must have Nitrates expelled as above). This is a 10:1 concentration ratio.
Shake thoroughly 100 times. Allow to settle. If there are drops of solvent adhering to the walls of the extrtaction tube the tube is sharply but gently finger flicked to dislodge those drops and have them join the organic phase.
If any haze is seen in the solvent section, or there is concern of excessive iron in the sample, add drop by drop some concentrated hydrochloric acid in a very slow and controlled manner dropwise with a 2 ml or similar dispenser. The now clear DIBK solution at the top of the extraction tube is ready to scan directly on AA.
Special note: The standards used on DIBK extraction must be made of DIBK Aliquat 1%, eg. The 0 ppm reference is straight DIBK Aliquat 1%, and the 1ppm and 5ppm need to be made up from straight DIBK Aliquat 1% solution and addition of Gold chloride standard.
Flame adjustment is only needed if maximum sensitivity is required , the flame can be of lesser intensity for DIBK than the flame used for direct aspiration of aqueous liquors.
Usually the small improvement in sensitivity when using DIBK is not worth the fuss of flame adjustment and the flame is set so that aqueous samples may be direct aspirated with out flame out and this setting is used for all liquids.
NOTE THAT THE DIBK STANDARD READING WILL DIFFER FROM A GOLD CHLORIDE OR CYANIDE READING DUE TO THE DIFFERENCE IN UPTAKE RATES FOR THE SAME STANDARDS.
**This method removes all Iron and interfering impurities from the leach to negligent levels even in saturated Iron solutions. DIBK solvent cannot be used on it’s own but needs an addition of 1% of Aliquat 336 (quartenary ammonium salts) to make it effective and have a relatively high viscosity to enable it’s use, this is called DIBK Aliquat 336 (1%) solution. It is made by having 10ml of Aliquat 336 placed in a 1lt volumetric flask and bringing the volume to exactly 1000ml with DIBK solvent. This is then the stock solution to make standards and direct use.
Oxidizing or non oxidizing solutions to be tested can be used with this method without any prior treatment but strong oxidisers eg. Straight Aqua Regia or any other nitrate containing oxidiser must have the nitrates expelled. Strong oxidizing solutions are more harsh on components in the nebuliser of the Atomic Absorbtion Spectrometer as well as being promotors of side reactions in the extractant components which can lead to false metal readings.
If the 10:1 concentration ratio gives an absorbance value which is higher than the value for a 5 ppm gold standard then a lower ratio is used.
A 1:1 ratio will just clean out interferents without enhancing the reading range.
If the solution you are testing has such a high precious metal level that a 1:1 ratio will still land you outside the 5 ppm limit, you can reverse the ratios such that the DIBK : liquor ratio is, say, 10:1 rather than the standard ratio of 1:10.
The reason you try to keep the metal readings in the DIBK below the 5ppm standard reading is that from 0 to 5 ppm the readings are straight line. This means that the absorbance reading for a 5 ppm standard will be 5 times as high as the absorbance reading for a 1ppm standard.
However, if you plot the readings above 5 ppm you will get what is called a calibration curve.
Most AAS machines have calculation circuitry in the electronics which will give you the actual value of the true absorbance reading for these higher values.
All of the above works brilliantly in a lab where clean synthetic solutions are being used, it tends to be more variable when real world gunged up solutions are being run.
The above represents the difference between an operator's idea of a bare bones AAS unit and the developer's idea. The developer's idea is that a simple unit only has relatively small amount of circuitry dedicated to the above type of calculations, the operator wants this type of circuitry kept to an absolute minimum to avoid processing errors.
The real difference is in the interpretation of the word "relatively", to the developer it seems to mean that he has restrained himself from installing as much software as he could possibly fit into the unit.
You can avoid most of the analytical problems just by keeping the DIBK/liquor ratios such that the absorbance values are maxed out around the 5 ppm standard values.
DIBK usually comes in 20 litre drums, Aliquat 336 comes in various 50 to 1000 ml containers.
The mixed DIBK/Aliquat solution is usually dispensed in 5 ml pump volumes from a dispenser mounted on a Winchester bottle.
Deano
Digest sample in a 500 – 600 ml beaker containing around 250ml of 1 part nitric acid to 4 parts hydrochloric acid.
The aqua regia must be freshly made, do not bottle for later use.
The beaker is heated to a simmer on a hot plate in a fume cupboard, orange brown fumes will evolve.
Continue the heating until the fumes change colour to white, give it a few more minutes and remove from hot plate to cool.
When cool the solution is filtered, usually in a Whatman No1 paper and the paper is rinsed with water from a wash bottle to get all traces of gold into the filtrate.
After filtering has finished the filtrate is made up to usually 250ml with water and poured into a clean beaker to evenly distribute the gold values in the solution.
In a clean 50ml glass extraction tube add 50ml of the final filtrate and then add 5 ml of DIBK Aliquat 336 (1%) ( straight hypochlorite solution is ok, but Aqua Regia must have Nitrates expelled as above). This is a 10:1 concentration ratio.
Shake thoroughly 100 times. Allow to settle. If there are drops of solvent adhering to the walls of the extrtaction tube the tube is sharply but gently finger flicked to dislodge those drops and have them join the organic phase.
If any haze is seen in the solvent section, or there is concern of excessive iron in the sample, add drop by drop some concentrated hydrochloric acid in a very slow and controlled manner dropwise with a 2 ml or similar dispenser. The now clear DIBK solution at the top of the extraction tube is ready to scan directly on AA.
Special note: The standards used on DIBK extraction must be made of DIBK Aliquat 1%, eg. The 0 ppm reference is straight DIBK Aliquat 1%, and the 1ppm and 5ppm need to be made up from straight DIBK Aliquat 1% solution and addition of Gold chloride standard.
Flame adjustment is only needed if maximum sensitivity is required , the flame can be of lesser intensity for DIBK than the flame used for direct aspiration of aqueous liquors.
Usually the small improvement in sensitivity when using DIBK is not worth the fuss of flame adjustment and the flame is set so that aqueous samples may be direct aspirated with out flame out and this setting is used for all liquids.
NOTE THAT THE DIBK STANDARD READING WILL DIFFER FROM A GOLD CHLORIDE OR CYANIDE READING DUE TO THE DIFFERENCE IN UPTAKE RATES FOR THE SAME STANDARDS.
**This method removes all Iron and interfering impurities from the leach to negligent levels even in saturated Iron solutions. DIBK solvent cannot be used on it’s own but needs an addition of 1% of Aliquat 336 (quartenary ammonium salts) to make it effective and have a relatively high viscosity to enable it’s use, this is called DIBK Aliquat 336 (1%) solution. It is made by having 10ml of Aliquat 336 placed in a 1lt volumetric flask and bringing the volume to exactly 1000ml with DIBK solvent. This is then the stock solution to make standards and direct use.
Oxidizing or non oxidizing solutions to be tested can be used with this method without any prior treatment but strong oxidisers eg. Straight Aqua Regia or any other nitrate containing oxidiser must have the nitrates expelled. Strong oxidizing solutions are more harsh on components in the nebuliser of the Atomic Absorbtion Spectrometer as well as being promotors of side reactions in the extractant components which can lead to false metal readings.
If the 10:1 concentration ratio gives an absorbance value which is higher than the value for a 5 ppm gold standard then a lower ratio is used.
A 1:1 ratio will just clean out interferents without enhancing the reading range.
If the solution you are testing has such a high precious metal level that a 1:1 ratio will still land you outside the 5 ppm limit, you can reverse the ratios such that the DIBK : liquor ratio is, say, 10:1 rather than the standard ratio of 1:10.
The reason you try to keep the metal readings in the DIBK below the 5ppm standard reading is that from 0 to 5 ppm the readings are straight line. This means that the absorbance reading for a 5 ppm standard will be 5 times as high as the absorbance reading for a 1ppm standard.
However, if you plot the readings above 5 ppm you will get what is called a calibration curve.
Most AAS machines have calculation circuitry in the electronics which will give you the actual value of the true absorbance reading for these higher values.
All of the above works brilliantly in a lab where clean synthetic solutions are being used, it tends to be more variable when real world gunged up solutions are being run.
The above represents the difference between an operator's idea of a bare bones AAS unit and the developer's idea. The developer's idea is that a simple unit only has relatively small amount of circuitry dedicated to the above type of calculations, the operator wants this type of circuitry kept to an absolute minimum to avoid processing errors.
The real difference is in the interpretation of the word "relatively", to the developer it seems to mean that he has restrained himself from installing as much software as he could possibly fit into the unit.
You can avoid most of the analytical problems just by keeping the DIBK/liquor ratios such that the absorbance values are maxed out around the 5 ppm standard values.
DIBK usually comes in 20 litre drums, Aliquat 336 comes in various 50 to 1000 ml containers.
The mixed DIBK/Aliquat solution is usually dispensed in 5 ml pump volumes from a dispenser mounted on a Winchester bottle.
Deano