Method F-022G The Determination of Potassium in Glass
Equipment Required:
- Sherwood Flame photometer
- Platinum crucible
- Accurate balance weighing to +-0.0005g
Reagents:
- Sodium carbonate (analar)
- Sherwood 1000 ppm K flame photometer standard
- Sodium hydroxide
- Sodium chloride
- Glacial acetic acid
- Hydrochloric acid
Reagent Preparation:
Buffer Solution - Dissolve 2Og NaOH in 300 ml deionised water in a 600 ml
beaker. When completely dissolved add 30 ml glacial acetic acid. Add 29g NaCI and dissolve. Cool to ambient temperature and dilute to 1 litre in a volumetric flask with deionised water.
Blank Preparation:
To a 1 litre volumetric flask add 150 ml buffer solution and dilute to 1 litre using deionised water.
Standard Preparation:
To 10 mls of Sherwood 1000 ppm K standard in a 1 litre volumetric flask add 150 ml buffer solution. Adjust to pH 7.5 with HCI. Dilute to the mark with deionised water. This is 10 ppm potassium. From the 10 ppm K standard prepare 7.5, 5 and 2.5 ppm standards using the blank solution as diluent. Ensure all standards have a pH value of 7.5.
Sample Preparation:
Fuse an accurately weighed powdered sample with 2g potassium carbonate in a platinum crucible. When a clear fused melt is obtained continue heating for approximately 1 minute. Remove the crucible from the burner and pour the contents onto a cooling plate.
Place the crucible lid and cooled melt into a 400 ml beaker, add 75 ml buffer solution and dilute to 200 ml using boiling deionised water.
Place the beaker on a water bath for 30 minutes to loosen the melt from the crucible.
Remove crucible and lid from beaker. Filter the solution into a 1 litre volumetric flask ensuring that deionised water washings from the beaker are also filtered.
Dilute to 300 ml and adjust the pH to 7.5 with 1:3 HCI. Dilute to the mark with deionised water.
Method:
- Set the flame photometer up as in its instruction manual.
- Set the zero using the blank solution.
- Aspirate the standards into the instrument recording each displayed value.
- Construct a calibration plot of concentration vs. meter reading on linear graph paper.
- Aspirate the sample solution and record the stable display. (If the value is higher than that of the top standard, dilute sample with blank until the value falls in the range of the calibration curve.)
- Multiply the potassium concentration of the sample by the dilution factor.
