3.2: Sodium in Water Samples by Flame Atomic Emission
- Page ID
- 364567
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)A2: Sodium in Water Samples by Flame Atomic Emission
A natural gas/air flame is used: clearly the burner of the flame emission instrument in particular becomes very hot. Instruction must be obtained on the lighting of this flame. The chemicals used in this experiment pose little hazard provided that routine laboratory precautions are taken to avoid ingestion and skin contact.
Standard solutions
Stock standard solution contains 500 ppm of potassium (as KCl) and 250 ppm of sodium (as NaCl). Preparation of the combined 10, 8, 6, 4 and 2 ppm Na and 20, 16, 12, 8 and 4 ppm K standards
- Pipette 2.0, 1.6, 1.2, 0.8 and 0.4 ml of the joint standard solution into respective 50-ml volumetric flasks.
- Dilute to 50 ml with distilled water. These correspond to 10, 8, 6, 4 and 2- ppm standards of sodium, and twice these amounts of potassium.
NOTE: Sodium does not interfere in the flame photometric determination of potassium and potassium only interferes in sodium determination if the K: Na ratio is more than 10:1.
Test solutions
River water, tap water, swimming pool water, bath water, seawater.
Sample
Sample of solution from deceased’s lungs.
Procedure
- The flame should already be lit: if not, consult a demonstrator.
- Select the sodium filter and aspirate a sample of deionized water.
- Adjust the “blank” control until the LED reads zero.
- Transfer a little of the most concentrated standard solution to a clean plastic cup, swirl, discard and refill.
- Aspirate this solution and adjust the “fine” sensitivity control until the LED reads 100 (if necessary, adjust the “coarse” setting to bring the reading on-scale).
- Aspirate deionized water again and re-adjust the blank to zero if necessary.
- Aspirate the series of standards in turn (using plastic cups as before) and obtain a series of readings for the standard solutions.
- Without altering the sensitivity settings, obtain readings for the test solutions and lung water sample.
- If the readings are off-scale, dilute the samples accordingly.
- Use the standard results to plot a calibration curve, with sodium concentration on the x-axis and photometer reading on the y-axis.
- Use this graph to determine the sodium content of the test and sample solutions from the readings taken for these samples.
If time permits, repeat the procedure with the potassium filter selected.
Thinking about making valid measurements
To give evidence in court you have to show that the analytical method is producing valid results. Are you certain that any sample pre-treatment has not invalidated the analysis?
Improving your practical technique
- The instrument should be allowed to warm up before use.
- A wavelength check should be carried out to check the instrument is correctly set up.
- Instrument needs to be calibrated using a set of standards of differing concentration for quantitative analysis.
- Solid material must be removed from the sample before analysis.
- Check that liquid is being drawn up at reasonable speed.
- Consider doing duplicate samples.
- Analyze a blank sample (i.e. solvent blank).
- In many cases, samples may need to be diluted so that the measured emission is between the lowest and highest standard on the calibration curve.