University Duisburg – Essen

Campus Duisburg

Bachelor-Course Water: Chemistry,Analytics, Microbiology

Practical Course Instrumental Analytics

Flame atomic absorption spectrometry AAS

Instruction manual for AAS of the company Shimadzu and experimentinstruction for determination of calcium and magnesium in water sample

according to DIN EN ISO 7980

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Contents

1 MANUAL FOR THE FLAME ATOMIC ABSORPTION SPECTROMETER,VARIAN SPECTRAAA 3

1.1 Starting the atomic absorption spectrometer 3

1.2 Igniting the air-acetylene-flame 8

1.3 Measuring the blanc solution, the copper reference solution and the water sample 9

1.4 Saving and editing the data with EXCEL 10

2 PREPARATION OF THE SAMPLE 12

2.1 Copper stock solution, β(Cu) = 1000 mg/L Fehler! Textmarke nicht definiert.

2.2 Copper standard solution, β(Cu) = 100 mg/L Fehler! Textmarke nicht definiert.

2.3 Copper reference solution Fehler! Textmarke nicht definiert.

2.4 Blind sample Fehler! Textmarke nicht definiert.

2.5 Blanc solution Fehler! Textmarke nicht definiert.

3 EXECUTION OF THE MEASUREMENTSFEHLER! TEXTMARKE NICHTDEFINIERT.

3.1 Standard calibration method Fehler! Textmarke nicht definiert.

3.2 Addition method Fehler! Textmarke nicht definiert.

4 PROBLEM / TASK 14

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1 Manual for the flame atomic absorption spectrometer, AA 6200

1.1 Starting of the atomic absorption spectrometer The atomic absorption spectrometer of type AA 6200, Shimadzu, is equipped with a

laminar burner as heating source. To ignite the flame that burns with a mixture of

acetylene (fuel gas) and air (oxidant) you have to ensure the gas supply. You can

find the compressed gas cylinder for acetylene in the cupboard for compressed

inflammable gases. Firstly, you have to open the main valve at the compressed gas

cylinder and the pressure reducer (after being instructed by your supervisor). Then

you have to turn the red lever hold for the air supply located on the other side of the

table in direction of the flow. Secondly, the PC with the software installed for

controlling, measurement and evaluation can be switched on and then the atomic

absorption spectrometer (AAS), too. The switch is on the front side of the instrument.

Now start the program AA by clicking onto the icon on the desktop. Press the button

WIZARD in the dialog box that appears firstly in order to start the measurement and

sample assistant. By clicking CONNECT the connection between PC and AAS will be

established. Consider that the program window has to be maximized to get a better

overview over the measurement values.

Because the slit width has to be set manually and not automatically like described in

the program, you get an error message on the screen that you just have to confirm.

Set the slit width with the turning knob (on the left side of the AAS) to an appropriate

value needed for the measurement with the calcium- and magnesium-HCL (hollow

cathode lamp), respectively. If the slit width is already in the correct position change

and reset it with the turning knob. Then confirm with OK. The following window

appears:

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The control program automatically checks several device parameters while the

checked parameters are marked green, i.e. success, when they are OK. ASC is the

abbreviation for auto sampler but we will not use it with this experiment. Therefore

the software displays “not connected”. This procedure can take several minutes. If all

parameters are checked confirm with OK.

By pressing the button ... in the next dialog box you can select an element from

the periodic table that should be analysed. After this you are asked to select an

additional element that should be analysed after the calcium detection. Here you can

select an element for the “warm up mode”, in this case magnesium. Close this dialog

window by pressing Next. The following dialog box appears.

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In this dialog you can select the lamp current and the lamp socket (calcium: socket 2;

magnesium: socket 1 in warm up mode). The main resonance line for calcium is

given with 422,7 nm and for magnesium with 285,2 nm. Eventually you have to

equalise the manually set slit width with the predetermined slit width for calcium and

magnesium, respectively. The hollow cathode lamp has to be activated by clicking

the choice box Lamp ON. This also activates Warm up Lamp. To be sure that the

head of the burner is in the right position and the slit of the burner is in the optical

path, hold a piece of white paper into the optical path. By this you can control the

position of the head of the burner. If the position has changed inform your supervisor.

Pressing the icon Line search opens the following dialog window.

Do Line Search automatically starts searching the emission line of the hollow cathode

lamp with highest intensity (in most cases the main resonance line). After finding

close this window with Close. This will open the following window.

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The bar diagrams and the three display areas show the temporary, the maximum and

the minimum radiation intensity of the hollow cathode lamp at the previously selected

emission line. These values should be stable (± 0,010 units max) and range between

0,580 und 0,650 units. Because the hollow cathode lamp needs a certain “burn-in

time”, the monitoring of long time stability for 1 hour (max) is provided. If no stable

value arises after one hour “burn-in time” inform your supervisor. Maybe you have to

readjust the position of the hollow cathode lamp, what should be done by the

supervisor.

Close the window with Next and automatically the previous window appears. Now

select the lamp mode. For the first series of measurements select NON-BGC (no

background compensation). The following measurements should be performed with

an background compensation by a deuterium lamp (BGC-D2). Start searching the

line again by pressing Do Line Search. Close that window with Close. You enter the

previous dialog box that you can also close with Next. Do the same in the window

that appears afterwards.

That window is usually used to connect an auto sampler or a PC.

In the next dialog box select the calibration method.

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The following calibration methods is relevant for you:

1. Standard calibration method (calibration curve)

The addition calibration method should be use in the case of interferences by the

sample matrix. For the determination of calcium and magnesium it is not necessary

to use addition calibration method. The simple addition method (SMSA) can also be

selected but will not be used in this practical. In the field (No. of STD) on the upper

right side you can enter the number of reference solutions that shall be measured. In

the table below you can enter the concentrations of the reference solutions that are

called “standards” here. In the field Conc. Unit you should select mg/L as unit like

prescribed in DIN. Exit the window with Next.

In the next dialog window set in what periodic time distances blind samples should be

measured and corrections of the sensitivity should be done. In the menu Options the

nebulising time can be set (here we set 0s because no auto sampler is used and the

capillary must not be cleaned). Additionally, you can set the integration time. 10

seconds are recommended.

Activate now Repeat Conditions. In this dialog box you can enter the number of

repeated measurements of blank solutions, reference solutions and analysed sample

solutions. Usually you can accept the proposed values. In this experiment of the

practical 5 repetitions of measurement for each solution are demanded. Exit the

window with Next. Overstep the appearing window with Next because it is a standard

setting.

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In the last dialog window select the particular mixture of oxidant gas and burning gas.

As mentioned at the beginning we use air as oxidant gas and acetylene (C2H2) as

burning gas. The given flow rates are guide lines. The real flow rate can be adjusted

with the flow control unit at the front side of the AAS after igniting the burner flame.

The setting of the operation parameters can be finished by pressing the button

Finish.

1.2 Igniting the air-acetylene-flame To ignite the flame press the buttons IGNITE and PURGE under the flow control

device simultaneously for several seconds. By this the air supply will be reduced

automatically and the burning process will be initiated by an integrated fuse. The

resulting flame should be almost transparent and constant. If this is not the case you

have to optimize the flame by varying the gas mixture. Ask your supervisor if you are

not sure. The door of the AAS must be kept close for security reason when the flame

is ignited. You can open the door only to check the transparency of the flame.

Now the AAS is ready for measurement!

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1.3 Measuring blank solution, calcium and magnesium reference solution,and water sample

According to the operation parameters the measurement window is displayed in

report-style.

The recorded measurement series can be saved with the menu option File Save

as in the main menu bar. In the menu Parameters you can start the Sample Wizard

or the Measurement Wizard that help you to change the operational parameters later.

With the menu option Measure clear Result you can delete all measurement

results in the window and return to the basic settings.

With the help of the blank solution (ultra pure water) you do the initialisation by

activating Auto Zero. Then press the START button and run the solutions one after

the other according to the prepared measurement program. Principally the blank is

measured first. For this fill a part of the blank solution into a beaker so that the

absorption sample tube is covered with fluid.

By pressing START the measurement begins. Afterwards measure the calcium

reference solutions 5 times each one after the other in rising order of concentration.

Please consider that you first have to flush with ultra pure water after changing the

sample and that you have to wait for at least 1 minute after dipping the sample tube

into the reference solution. Before measuring the water sample flush with ultra pure

water.

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For the determination of magnesium in the water sample activate the magnesium

hollow cathode lamp (warm up mode) by changing the socket (right side of the AAS)

and changing of the operating parameters according to the procedure described for

calcium (e.g. line search, control of emission intensity). The magnesium reference

solutions have to be measured in the same way as described for measuring of the

calcium reference solutions.

1.4 Saving and editing the data with EXCELWith the menu option File Save as in the main menu bar you can save the

measurement series. You should name the file “Ca-Mg1.txt” or similar and save it on

a disk so that you can edit the data in a spread sheet program like EXCEL. If you

want to open the file with EXCEL select “alle Dateien” (all data) in field “Dateityp”

(data type).

Three assistant dialogs appear one after the other. Select the options as described in

the following three figures. In the last dialog window mark all columns and select

“Text” as format for the columns. Close the window with the button Ende. Now your

file (e.g. Ca-Mg1.txt) can be edited with Excel.

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Before you can do the regression analysis you have to replace all points with

commas as shown in the following figure. Use the function search and replace

(Suchen und Ersetzen) of Excel. Now you can save the file in Excel format with e.g.

Ca-Mg.xls as file name.

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2 Preparation of the sampleIn principal for the following samples only use water from the ultra pure water system

of company Millipore. It has a quality equal to bi-distilled water. The operating of the

pure water system may only be done by authorised personnel.

All solutions, which have to be measured, have to be prepared according to DIN EN

ISO 7980.

Tip: Practice the usage of the Varipette when preparing the samples. Use water for it.

Attend to follow exactly all steps described in the manual of the Varipette. Otherwise

it is possible that the concentration error when preparing the sample is very high.

Water from the pure water system is used as blank sample. Principally you can use

the zero-value solution as blank solution if the copper concentration in the zero value

solution is negligibly low.

The execution of the measurements will be done according to DIN EN ISO 7980. The

initialisation of the instrument will be done with the blank solution (see manual). The

blank solution is injected at first. For the determination of the reference curve

(calibration curve) you have to measure the reference solutions in rising order. After

each concentration step you should rinse with water and by this control the zero

point. Finally the sample has to be measured. For this you have to open the cold

water tap at the sink and after a flow of 4 minutes you take a water sample (sampling

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device: a glass beaker cleaned with diluted nitric acid in advance). For degasification

of the water sample treat it in an ultrasonic bath for 5-10 minutes.

After the experiment clean all glass equipment with diluted nitric acid several times

and then with pure water. The burner flame of the AAS has to be switched off with

the button Extinguish and the AAS itself on the main switch. Also the main valve of

the acetylene compressed gas cylinder has to be closed and the lever of the air

supply has to be turned over.

IMPORTANT: Put the waste into the provided container for elimination of heavy

metal containing aqueous solutions !!!

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3 Problem / Task

1) Determine the calcium and the magnesium concentration in a laboratory water

sample at two different currents of the calcium and magnesium hollow cathode lamp

using the standard calibration method. Make a regression analysis with the

measurement values achieved for both measurement programs and state the results

in an analysis report. Discuss the differences in the results.

2) Determine the pump rate of the nebuliser. By which operational parameters is the

pumping rate defined?

3) Determine the calcium and magnesium concentration in a water sample at

optimized lamp current once with background compensation and once without

background compensation. Please explain the difference.

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List of chemicals for the experiment: Atomic absorptionspectrometry

Symbols1Name Formula Poisonouscategory1 T+ T Xn Xi C O F N

Ca stocksolution

Ca

Mg stocksolution

Mg

Aqu. hydrogenchloride

HCl

Lanthanumchloride

LaCl3

Caesiumchloride

CsCl

Symbols: T+: very toxic, T: toxic, Xn: harmfull to health, Xi: reizend, C: caustic, O:oxidising, F: flammable, N: environmentally hazardousPoisonous categories (Swiss): 1* very strong poison (cancerogen, mutagen,

teratogen); 1-2 very strong poison; 3 strong poison; 4 not harmless substances and

products; 5 substances and products with lowest harm

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List of materials for the experiment: Atomic absorptionspectrometry

Nr. Item disp.. notdisp.

Comment

1 Varipette 47201 Varitips for Varipette 4720 1 PE-water bottle 1 Beaker 600 mL3 Beaker 100 mL7 Flask 100 mL3 Flask 1000 mL 1 Flask 10 mL1 Pipette ball1 Pipette with fixed volume 50 mL1 Pipette with fixed volume 20 mL1 Pipette with fixed volume 25 mL1 Measuring pipette 10 mL1 Instruction manual Eppendorf

Varipette 47201 Instruction manual Shimadzu AA

62001 Calcium hollow cathode lamp1 Magnesium hollow cathode lamp1 1L bottle filled with ultra pure

water

The equipment of the workplace is equivalent to the list above

Signature of supervisor:…………………………………………………

Signature of student:……………………………………………………

Duisburg, …………………………………

When handing over the workplace the following items were missing or damaged:

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Signature of supervisor:…………………………………………………

Signature of student:……………………………………………………

Duisburg, …………………………………