AA procedures for water analyses

Environmental Analysis 2001

Sodium and Potassium.

Maximum amount with curve correction: Na 6 g/mL; K 12 g/mL.

Must add 1000 g/mL Cs to samples and standards to prevent ionization interference.

Stock solutions. 1000 g/mL Na from NaCl and 1000 g/mL K from KCl. Dry salts and cool in desiccator before massing. (These currently prepared.)

Working solutions. Make a high, medium and low by serial dilution using class A volumetric ware and no pipette smaller than 5 mL. Handier to make a mixed Na plus K solution. Use no volumetric flack small than 100 mL unless really necessary.

Example for 100 mL of mixed Na plus K standards from a 1000 g/mL stock solution.

Equipment; 500 mL volumetric flask, 25, 10 and 5 mL pipettes.

Remember to describe the process completely in your laboratory notebook.

Cesium blank solution.

Blank solution of Cs. Add about 50 mL DI water to a 100 mL flask. Add 10 ml of the 10000 g/mL Cs solution to the flask with the repipette device. Dilute to volume with DI water and mix thoroughly. Store in a plastic bottle.

Low Na + K standard.

Low standard (1 g/mL Na and 2 g/mL K). Add about 100 mL DI water to a clean 500 mL flask. Pipette 5 mL Na stock to the flask. Pipette 10 mL K stock to the flask. Dilute to volume with DI water and mix thoroughly. Concentration Na = 5 mL x 1000 g/mL Na / 500 mL = 10 g/mL Na. Concentration K = 10 mL x 1000 g/mL K / 500 mL = 20 g/mL K.

Add about 50 mL DI water to a 100 mL flask. Pipette 10 mL of the 10 g/mL Na; 20 g/mL K solution to the 100 mL flask. Add 10 ml of the 10000 g/mL Cs solution to the flask with the repipette device. Dilute to volume with DI water and mix thoroughly. Store in a plastic bottle.

Concentration Na = 10 mL x 10 g/mL Na / 500 mL = 1 g/mL Na.

Concentration K = 10 mL x 20 g/mL K / 500 mL = 2 g/mL K.

Medium Na + K standard.

Medium standard (3 g/mL Na and 6 g/mL K). Add about 100 mL DI water to a clean 500 mL flask. Pipette 10 mL Na stock to the flask, pipette 5 mL additional Na stock to the flask (total = 15 mL). Pipette 25 mL K stock to the flask, pipette 5 mL additional K stock to the flask (total = 30 mL). Dilute to volume with DI water and mix thoroughly. Concentration Na = 15 mL x 1000 g/mL Na / 500 mL = 30 g/mL Na. Concentration K = 30 mL x 1000 g/mL K / 500 mL = 60 g/mL K.

Add about 50 mL DI water to a 100 mL flask. Pipette 10 mL of the 30 g/mL Na; 60 g/mL K solution to the 100 mL flask. Add 10 ml of the 10000 g/mL Cs solution to the flask with the repipette device. Dilute to volume with DI water and mix thoroughly. Store in a plastic bottle.

Concentration Na = 10 mL x 30 g/mL Na / 500 mL = 3 g/mL Na.

Concentration K = 10 mL x 60 g/mL K / 500 mL = 6 g/mL K.

High Na standard (no K).

High standard (6 g/mL Na only). Add about 100 mL DI water to the 500 mL flask. Pipette 25 mL Na stock to the flask, pipette 5 mL additional Na stock to the flask (total = 30 mL). Dilute to volume with DI water and mix thoroughly. Concentration = 30 mL x 1000 g/mL Na / 500 mL = 60 g/mL Na.

Add about 50 mL DI water to a 100 mL flask. Pipette 10 mL of the 60 g/mL Na solution to the 100 mL flask. Add 10 ml of the 10000 g/mL Cs solution to the flask with the repipette device. Dilute to volume with DI water and mix thoroughly. Store in a plastic bottle. Na = 10 mL x 60 g/mL Na / 500 mL = 6 g/mL Na.

Calcium and Magnesium standards.

In a very similar way make Ca and Mg working standards, with high, medium and low for Mg as the total range is only 3 g/mL, but only medium and low for Ca (15 and 5 g/mL). High Mg = 3 g/mL, medium Mg = 1.5 g/mL, and low Mg = 0.5 g/mL; medium Ca = 15 g/mL, and low Ca = 5 g/mL.

Add 5 mL of 40000 g/mL lanthanum (La) to samples and standards for a total final concentration of 2000 g/mL La. The La keeps Si, Al and other elements from interfering with the Ca and Mg determination. Make a blank containing La but no Ca or Mg.

EA 2002 Atomic Absorption

Preparation of water samples.

Note, most natural waters have much higher Na than K.

Lake and Bog Water.

Filtered samples only. For sodium dilute with DI water only until the highest expected concentration is between 10 and 40 g/mL (40 mg/L or ppm). You will have to estimate the Na concentration from previous analyses (handout for Soap Lake, Lenore Lake), conductivity, or by the lake type (fresh or saline). Pipette 10 mL of diluted sample to a 100 mL volumetric flask. Add 10 mL of the 10000 g/mL Cs. Dilute to volume and mix. Store in a plastic bottle. These samples will keep for a few days, maybe longer. Try to run potassium on the same sample. Take care to record dilutions carefully. You will need them to calculate Na and K concentrations in the original, undiluted, sample.

Thurston County lakes and western WA bogs will probably require a 2 to dilution or a 10 to 1 dilution to get sodium in the working curve range (max 6 ppm). This is 50 ml filtered lake or bog sample + 10 ml Cs then diluted to 100 ml in a 100 ml volumetric flask, or 10 ml filtered lake or bog sample + 10 ml Cs then diluted to 100 ml in a 100 ml volumetric flask.

Other waters (FYI).

Rain water. Filter sample, add 50 mL to a 100 mL volumetric flask. Add 10 mL of the 10000 g/mL Cs and 5 mL of the 40000 g/mL La solutions to the flask. Dilute to volume and mix. Store in a plastic bottle.

Stream waters. Most of these will have a ground water component and might be much higher in Na, K, Ca, and Mg than rain water. Try a dilution factor to 10 by adding 10 mL stream water to a 100 mL volumetric flask. Add 10 mL of the 10000 g/mL Cs and 5 mL of the 40000 g/mL La solutions to the flask. Dilute to volume and mix. Store in a plastic bottle. If necessary dilute less or more so the samples are all in the working curve concentration range.

Ground waters. Most of these will have substantial Na, K, Ca, and Mg. Too much dilution and K get diluted out, too little and Mg remains above the working range. Try a dilution factor of 20 by adding 5 mL ground water to a 100 mL volumetric flask. Add 10 mL of the 10000 g/mL Cs and 5 mL of the 40000 g/mL La solutions to the flask. Dilute to volume and mix. Store in a plastic bottle. If necessary make two dilutions one with a dilution factor of 10 or 20 for Ca and K, and one of 40 or even more for Na and Mg. Also consider making a dilution for just Na and K with Cs; and an entirely different dilution for Ca and Mg with just the La. Try to conserve the Cs and La reagents, but not at the expense of good analyses.

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AA for Na K Ca Mg water analysis.doc