Cations

 

Rains, Theodore, C.1984.Atomic Absorption Spectrometry.Water Analysis, Vol II Edited by Roger A. Minear and Lawrence H. Keith.

 

1.Materials:

 

1.Reference standard solutions for atomic absorption + 1%:

Na+, (1000 ppm 100 ml poly bottle Fisher cat # SS 139-100)

K+, (1000 ppm 100 ml poly bottle Fisher cat # SP 351-100)

Mg+2, (1000 ppm 100 ml poly bottle Fisher cat # SM 51-100)

Ca+2(1000 ppm 100 ml poly bottle Fisher cat # SC 191-100)

2.20 100-ml volumetric flasks (5 per element)

3.5-ml volumetric pipette & pipette bulb

4.1000-ul pipette (calibrated), several tips for dilutionís

5.deionized water

6. HCl (trace metal grade)

7.10% Lanthanum Cloride (LaCL3 FW 371.38) (for calcium)

8.Absorption/Emission spectrophotometer

9.clean, dry scintillation vials (at least one per sample)

10.10 ml Re-pipette

 

2.Samples should be preserved by acidifying to ~ pH 2 (100 ul Ultrex HCL / 60 ml sample.

 

3.Sign up for use of the Absorption/Emission Spectrophotometer in the Instrument Room (Loeb 309 x7525).

 

4.The week that you plan to run your samples, make standards using stock solutions kept in the back room of the Aquatics Lab, second floor, Ecosystems. For each ion, make standards in concentrations of 1, 2, 3, 4, and 5 parts per million (ppm). Make the standards in 100-ml volumetric flasks (labeled) under the hood. *Use trace metal grade HCl, measured in the volumetric pipette.

 

1.1.00 ppm = 100 ul stock, 5 ml HCl, water to fill line.

2.2.00 ppm = 200 ul stock, 5 ml HCl, water to fill line.

3.3.00 ppm = 300 ul stock, 5 ml HCl, water to fill line.

4.4.00 ppm = 400 ul stock, 5 ml HCl, water to fill line.

5.5.00 ppm = 500 ul stock, 5 ml HCl, water to fill line.

 

5.IMPORTANT NOTE:

Chemical interference in flame AAS originates during dissociation of the analyte in the flame cell forming a compound that volatilizes at a different rate than the standard.One method of alleviating this type of interference is through the addition of a releasing agent or protective chelate.A releasing agent is a metal or salt that forms a more stable compound with the interferent than the analyte.For calcium analysis the addition of lanthanum, which acts a releasing agent and reduces interference with the calcium peak from Al, Si, PO43-, and SO42- is required.

Lanthanum Cloride (LaCL3 FW 371.38) should be added to a 1% final concentration to all samples and standards. 10% LaCL3 = 37.13 g / liter.

 

For each calcium standard, add 10 ml of 10% lanthanum solution

1.1.00 ppm = 100 ul stock, 5 ml HCl, 10 ml of 10% LaCL3 water to fill line.

2.2.00 ppm = 200 ul stock, 5 ml HCl, 10 ml of 10% LaCL3 water to fill line.

3.3.00 ppm = 300 ul stock, 5 ml HCl, 10 ml of 10% LaCL3 water to fill line.

4.4.00 ppm = 400 ul stock, 5 ml HCl, 10 ml of 10% LaCL3 water to fill line.

5.5.00 ppm = 500 ul stock, 5 ml HCl, 10 ml of 10% LaCL3 water to fill line.

 

For each 1 ml of sample add one of the following depending on concentration.

1 ml of (200 ml 10% LaCL3 in 1 liter DI) multiply reading by 2 for final conc.

9 ml of (Add 100 ml 10% LaCL3 to 900 ml DI) multiply reading by 10 for final conc.

 

6.Fill the large beaker (inverted on the front of the spec) with DI water (in the carboy on the shelf to the left of the gas cylinders). Turn on the exhaust fan (switch by the door).

 

 

7.When it is time to run the samples on the Absorption/Emission spec, fill out the log book in the Instrument Room (on the little table next to the AAS.Start up procedure varies depending on the elements being run.Emission methods are used for K+, Na+ analysis, while absorption methods are used for Mg+2 , Ca+2.For absorptionyou will need to fill out the log book for lamp and Continuous Operating current (Mg+2 , Ca+2. 15 ma).

 

8.Turn on the air (the knob is on the wall above the gas cylinders). Then, turn on the acetylene.The low stage should stay above 15 (in red), and the high stage should not fall below 70 psi. If a new tank is needed, call Martha@ 7272).

 

9.Initial set up for all elements.

1.Push [Power on].

2.Make the following control settings:

SIGNAL - LAMP

GAIN - Fully counterclockwise

BG Corrector - AA

LAMP current control - fully counterclockwise

 

3.Set the SIGNAL control to set up.Set the SLIT control to the setting appropriate for the element of interest.Adjust with the course adjust wavelength control to obtain the wavelength of interest.

K+, wavelength = 766.5 and slit width = 0.7.

Na+, wavelength = 589.0 and slit width = 0.2.

Mg+2 wavelength 285.2 and slit width .7

Ca+2 wavelength is 422.2 and slit width is .7)

 

4.Push [Flame on].If an error message appears (E 50) it is due to air in the lines, push [Flame on] again.

5.Put the sipper tube into the DI in the big beaker.

6.Adjust the ratio of air/fuel so that it is about 18:40.

 

10.Emission methods (use for K+, Na+ analysis)

 

1.If a lamp is installed be sure to unplug it at this point.

2.Turn the [Signal] knob to EM (emission)

3.While aspirating a blank solution press [AZ] to auto-zero the spec.

4.Aspirate the most concentrated standard solution, optimize the wavelength by adjusting the [Fine adjust] dial slowly back and forth to provide maximum energy.Adjust the gain control as necessary to keep the LAMP /ENERGY display on scale.

5.Pick two standards between which samples fall (range of 1 ppm).While sipping the higher of the two standards adjust GAIN to provide a reading of about 75 on the LAMP/ENERGY display.Note that every time standards are changed the gain must also be changed.

NOTE:Calibration curves for flame emission measurements may not be accurate over extended concentration ranges

 

6.Change the integration time to 3 seconds by hitting 3 [t],††

7.Set values for the standards: hit 1.00 and [s1] and 2.00 [s2] for 1ppm and 2 ppm if two decimal places are desired use two.

7.Hit [az] to auto zero while sipping DI.Sip low standard and wait for absorbance to stabilize and hit [s1] repeat for standard 2

8.Sip s1 again to check reading if not similar redo calibration

9.Run all standards in a given range while periodically checking high standard to be sure gain has not dropped if it has either edge it back or reset gain to 75.

 

11.Absorption (Mg+2 , Ca+2)

 

1.Place correct hollow cathode lamp in lamp holder and plug in.

2.Turn the lamp current control until the LAMP/ENERGY display shows the proper lamp current, as given on the lamp label for continuous operation (continuous operating currentfor Ca+2 & Mg+2 ††lamp is 15).

3.Turn signal knob to set up.Turn the FINE ADJUST wavelength control slowly to obtain a maximum reading on the LAMP/ENERGY display.Use the gain control to adjust the maximum reading to 75.If the gain should become too high, an over range reading of EE will be obtained.

4.Align lamp by turning the two alignment knobs on the lamp holder to maximize the LAMP /ENERGY display reading.Again use the gain control to make the maximum reading 75.

NOTE:As the lamp warms up, the display value may increase slightly drop gain back down to final setting of 75

5.Close the lamp compartment door.

6.Wait ten minutes

 

7.Set the SIGNAL control to concentration.

8.Hit [az] to auto zero while sipping DI.Sip low standard and wait for absorbance to stabilize and hit [s1] repeat for standard 2

9.Sip s1 again to check reading if not similar redo calibration

10.Run all standards in a given range while periodically checking gain and readjust to 75 as lamp warms

 

12.Shut down

1.       after last sample let run for 10 minutes

2.       turn signal, gain, lamp counter clockwise

3.       fill out log book

4.       turn flame off

5.       pull sipper out of DI and dump DI

6.       shut off air and acetylene

7.       empty lines of air and acetylene by hitting [check 0-2 ] [check fuel]

8.       turn off machine

9.       turn off fan

10.    unplug lamp