ProtocollAnalytical Chemistry WS 09/10

V2/1: Determination of chlorideand nitrate in a watersample with

ion chromatography

Execution: 19.02.2010Protocol hand-over: 22.02.2010

executed by: Sven Otto

1 Theory

Ion chromatography (IC) is a technique to seperate and detect ions with using ion-exchangechromatography, which based on coulombic interactions.An eluent is �owing under high preasure (≈ 100 bar) through a seperatingcolumn �lled withsmall pellets (3 − 10µm diameter). The high preasure is necessary to gain an adaquate�owspeed through the very compact column.On the surface of the pellets are functional groups on which the ions of the sample can beadsorped. When there is no analyt in the column these functional groups are occupied by theions of the eluent. Depending on which sort of ions should be seperated there were di�erentsorts of functional groups used. For seperating chloride and nitrate like in the experimentthis are quartary ammoniumgroups. When anions came through the column they interactwith this groups and displace anions of the eluent (which is phtalic acid in this case):

pellet-N+R3E− + A− � pellet-N+R3A

− + E− (1)

Depending on the ion radius and the charge of it the ion will stay longer adsorped on thesurface. This is why bigger an higher charged ions took longer till they pass the column andthis is how the IC works.After the ions pass the collumn the have to be detcted. This happens with an conductivitydetctor, which sends the data to a computer or a chart recorder.

The �rst peak that came after injecting a sample in the IC is called the dead time t0 - it isnegative, because it is just water without any conduktivity. The gross retention time is thetime an ion needs to pass the column. The clear retention time is as the di�erence betweengross retention time and the dead time:

tclear = tgross − t0 (2)

The kapacityfactor k′ describes the quality of the seperation between di�erent ions. Thebigger the di�erence between them is the better they will be seperated.

k′ =tcleart0

(3)

2 Chemicals

• 1000mg/L chloride solution

• 1000mg/L nitrate solution

• 8mmol/L phtalic acid

2

3 Execution

First the 3 standards of chloride an nitrate solution were prepared out of the 1000mg/L root-solutions and weighted.After that they were used for creating the calibration line.Befor each measering the syringe was �ushed with water and the sample. Than the samplewas injected in the IC with the lever in "`load"'-position and the sample loop was �ushedtoo.At least the loop was �lled again and the lever put in the "`inject"' position. This procedrewas rerunned for everey new sample.After creating the calibration line our unknown samples were �lled up to 100mL and mea-sured twice.

4 Analysis

4.1 Data

Table 1: Chloride standard solutions: wanted and real massconcentration

standard β(Cl−)mg·L−1

V0(Cl−)µL

m(Cl−)g

V ′0(Cl−)

µLβ′(Cl−)mg·L−1

0 0 0 0 0 01 6 600 0,58 580 5,82 12 1200 1,18 1180 11,83 25 2500 2,46 2460 24,6

Table 2: Nitrate standard solutions: wanted and real massconcentration

standardβ(NO−3 )

mg·L−1

V0(NO−3 )

µL

m(NO−3 )

g

V ′0(NO−3 )

µL

β′(NO−3 )

mg·L−1

0 0 0 0 0 01 12 1200 1,15 1150 11,52 25 2500 2,47 2470 24,73 50 5000 4,98 4980 49,8

3

With these standard solutions, the following peaks were measured:

Table 3: Peak heights of the standard solutions

Anion β′/mgL−1 Peak 1 / cm Peak 2 / cm Arithmetic mean STD

Cl−5,8 1,40 1,60 1,50 0,1411,8 3,10 3,40 3,25 0,2124,6 5,85 5,80 5,83 0,04

NO−3

11,5 0,90 1,00 0,95 0,0724,7 2,10 2,20 2,15 0,0749,8 3,95 3,90 3,93 0,04

Table 4: Dead and retention times of standard solutions and their arithmetic means

standard t0min

tgross(Cl−)

mintclear(Cl−)

min

tgross(NO−3 )

min

tclear(NO−3 )

min

1 3,0 6,6 3,6 11,4 8,41 3,0 6,6 3,6 11,4 8,42 3,0 6,6 3,6 11,4 8,42 3,0 6,6 3,6 11,4 8,43 3,0 6,6 3,6 11,4 8,43 3,0 6,7 3,7 11,4 8,4

t 3,0 6,6 3,6 11,4 8,4σ(t) 0,0 0,1 0,1 0,0 0,0

k′ - 1,2 2,8

The di�erence in the kapacityfactors give evidence that both, chloride and nitrate could bedetermined in the same sample.

The used equations are:

t =

∑Ni=1 tiN

(4)

σ(t) =

√√√√ 1

N − 1

N∑i=1

(ti − t)2 (5)

k′ =tcleart0

(6)

4

Table 5: Peak heights and retention times for sample B1

Substance Peak 1/cm Peak 2/cm tgross,1

min

tgross,2

min

tclear,1

min

tclear,2

min

H2O - - 3,0 3,0 - -Cl− 3,1 3,1 6,7 6,7 3,7 3,7NO−3 2,4 2,6 11,4 11,1 8,4 8,1

4.2 Calibration lines

For creating the calibration lines the peak height of the standard solutions were plot in origin.The linear equation was created via linear regression.

Figure 1: Calibration line for chloride

Linear equation for the chloride peaks:

h(Cl−) = 0, 225 cm4/µg · β(Cl−) + 0, 286 cm (7)

5

Figure 2: Calibration line for nitrate

Linear equation for the nitrate peaks:

h(NO−3 ) = 0, 079 cm4/µg · β(NO−3 ) (8)

4.3 Calculation of the Cl−- and NO−3 -concentration

For the calculation of the concentrations the equations 7 and 8 needed to be transponsed:

β(Cl−) =h(Cl−)− 0, 286 cm

0, 237 cm4 · µg−1(9)

β(NO−3 ) =h(NO−3 )

0, 079 cm4 · µg−1(10)

6

So the results are:

Table 6: Mass concentration of chloride and nitrate in sample B1

substance β1

mg·L−1β2

mg·L−1β

mg·L−1

σ(β)mg·L−1

Cl− 12,5 12,5 12,5 0,0NO−3 30,4 32,9 31,7 1,7

The sample B1 contained 12, 5mg/L chloride and 31, 7mg/L nitrate.

5 Questions

1. Explain the eluationorder of the anions chloride, nitrate and sulfate!

The separation depends on the ionradius and the charge, as said in the theory. Sochloride is the smallest and will elute �rst. Then comes nitrate and at lat the highercharged sulfate.

2. Which values in a chromatogramm contain qualitave and which quantitative informa-tion?

The retention times give qualitative infomation, which are intressting for comparingdi�erent ions.Quantitative information are given by the height of the peaks, they are proportional tothe ions concentration.

3. Which kind of other chromatographytypes are there? Give three examples with anshort explaination of the separationprinziple.

There are several types of chromatograpy like the gas chromatography (GC), the thinlayer chromatography (TLC) and the high pressure liquid chromatography(HPLC).

For the GC the analyte will be vaporized and send through a capillar column on a streamof inert gas. The inside of the column is coverd with the static phase, which interactwith the analyte an seperate the di�erent components. For this type of chromatographythe sample has to be able of varporization without disintigration.

Using a TLC the analyte is brnged up on a thin plate, which is dipped in an solution.The components of the analyte will move up the plate with speci�c speed.

The HPLC uses high pressure. The analyte is dissolved in a liquid eluent and pumpedthrough closed packege of ion exchanger. Depending to the properties of the compnentsof the analyte they stay di�erent times in the column.

7

6 Appendix

References

[1] Grundpraktikum Analyitsche Chemie, Skriptum für das Wintersemester2009/2010 - Prof. Dr. Thorsten Ho�mann, Prof. Dr. Nicolas Bings; 10.02.2010;http://www.chemie.uni-mainz.de/Praktikum/AC/AC2a/pdf/Scriptum%20-%

20AC%20II%20Analytik%20WS0910.pdf

List of Figures

1 Calibration line for chloride . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Calibration line for nitrate . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Chromatorgramm: standard 1 . . . . . . . . . . . . . . . . . . . . . . . . . 94 Chromatorgramm: standard 2 . . . . . . . . . . . . . . . . . . . . . . . . . 95 Chromatorgramm: standard 3 . . . . . . . . . . . . . . . . . . . . . . . . . 106 Chromatorgramm: sample B1 . . . . . . . . . . . . . . . . . . . . . . . . . 10

8

6.1 Original data

Figure 3: Chromatorgramm: standard 1

Figure 4: Chromatorgramm: standard 2

9

Figure 5: Chromatorgramm: standard 3

Figure 6: Chromatorgramm: sample B1

10