AS6 SODIUM & POTASSIUM IN CEMENT BY FLAME PHOTOMETRY Last Revised: May 2015
1. REAGENTS & EQUIPMENT 1.1 Cement 1.2 Mixed 100 mg/L Na/200 mg/L K standard 1.3 1000 mg/L Li 1.4 10 g/L Ca 1.5 Concentrated HCl 1.6 Flame photometer 2. PROCEDURE 2A. Prework 2.1 The typical level of CaO in cement is 60%. Calculate the concentration of Ca that should be incorporated in the standards to give an equal concentration of Ca to the sample. 2.2 Given that all solutions are made up to 100 mL, what volume of 10 g/L Ca should be added to the standards? 2B. Sample preparation 2.3 In triplicate, accurately weigh about 0.5 g of a ground, dried sample of cement. 2.4 Transfer to 150 mL beakers labelled S1, S2 & S3, add 20 mL of concentrated HCl to each. 2.5 Boil gently for 10 minutes – some solids may remain, but avoid boiling to dryness. 2.6 Cool to room temperature. 2.7 Carefully add 20 mL of water, and transfer to 100 mL volumetric flasks. Pipette 5 mL of 1000 mg/L Li into each flask, and make up to the mark with distilled water. 2.8 Filter about 50 mL of the solutions through #1 paper if necessary before analysis. 2C. Preparation of standards 2.9 Add (by measuring cylinder) the volume of 10 g/L Ca solution calculated in Prework 2 into five 100 mL volumetric flasks. Also add 5 mL of 1000 mg/L Li to each flask. 2.10 Add (by burette) 5, 10, 15 and 20 mL of the mixed 100 mg/L Na/200 mg/L K standard into different flasks. 2.11 Make up all flasks to the mark with 1 M HCl. 2.12 The other flask containing only Ca is the blank. 2D. Analysis 2.13 Set the setting to Na. Zero the instrument with the solution containing only Ca. 2.14 Set the instrument with the Gain controls using the highest concentration standard so that all elements read at least 100 but are on scale. 2.15 Read the intensity of each element for each solution – read all three elements for the solution before moving to the next solution. REPORT Calculations 1.
Determine the concentration of each standard. 2.
Calculate the analyte/lithium intensity ratio for each solution. 3.
Plot analyte/Li intensity ratio against concentration for each element, and if the plot is linear, determine the concentration of the samples 4.
If either of the graphs in (3) are not linear, then plot log10(intensity ratio) against log10(concentration) for each element, and use this to determine the concentration of the samples. 5.
Calculate the mass of Na and K in each sample. 6.
Convert these masses to the equivalent masses of Na2O and K2O. 7.
Calculate the %w/w of Na2O and K2O in the samples and then the averages. 8.
Plot a calibration graph of Na intensity (no internal standard) against concentration and determine the concentration for one of the samples. Discussion 
compare your answers with the expected values 
compare your two results (normal calibration and internal standard) 
give reasons why mixed standards are superior to separate standards 
explain the use of lithium 
explain why calcium is included in the standards Questions 1.
Why is a filter system suitable for this instrument when an AAS requires a monochromator? 2.
(a) What wavelengths are used to measure sodium, potassium and lithium emission? (b) What coloured filters would be used for these wavelengths? 3.
What is cement’s function in concrete? How does it work? AS6 p2 AS6. ANALYSIS OF NA & K IN CEMENT BY FLAME PHOTOMETRY
RESULTS SHEET
Masses (g) S1 S2 S3 Intensities Na K Li Blank STD1 STD2 STD3 S1 S2 S3