Protocoll Analytical Chemistry WS 09/10. V2/1: Determination of chloride and nitrate in a watersample with ion chromatography

Transcription

1 Protocoll Analytical Chemistry WS 09/10 V2/1: Deteration of chloride and nitrate in a watersample with ion chromatography Execution: Protocol hand-over: executed by: Sven Otto

2 1 Theory Ion chromatography (IC) is a technique to seperate and detect ions with using ion-exchange chromatography, which based on coulombic interactions. An eluent is owing under high preasure ( 100 bar) through a seperatingcolumn lled with small pellets (3 10 µm 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 be adsorped. When there is no analyt in the column these functional groups are occupied by the ions of the eluent. Depending on which sort of ions should be seperated there were dierent sorts of functional groups used. For seperating chloride and nitrate like in the experiment this are quartary ammoniumgroups. When anions came through the column they interact with this groups and displace anions of the eluent (which is phtalic acid in this case): pellet-n + R 3 E + A pellet-n + R 3 A + E (1) Depending on the ion radius and the charge of it the ion will stay longer adsorped on the surface. This is why bigger an higher charged ions took longer till they pass the column and this is how the IC works. After the ions pass the collumn the have to be detcted. This happens with an conductivity detctor, 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 t 0 - it is negative, because it is just water without any conduktivity. The gross retention time is the time an ion needs to pass the column. The clear retention time is as the dierence between gross retention time and the dead time: t clear = t gross t 0 (2) The kapacityfactor k describes the quality of the seperation between dierent ions. bigger the dierence between them is the better they will be seperated. The k = t clear t 0 (3) 2 Chemicals 1000 mg /L chloride solution 1000 mg /L nitrate solution 8 mmol /L phtalic acid 2

3 3 Execution First the 3 standards of chloride an nitrate solution were prepared out of the 1000 mg /L rootsolutions 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 sample was injected in the IC with the lever in "`load"'-position and the sample loop was ushed too. At least the loop was lled again and the lever put in the "`inject"' position. This procedre was rerunned for everey new sample. After creating the calibration line our unknown samples were lled up to 100 ml and measured twice. 4 Analysis 4.1 Data Table 1: Chloride standard solutions: wanted and real massconcentration standard β(cl ) mg L 1 V 0 (Cl ) µl m(cl ) g V 0 (Cl ) µl β (Cl ) mg L , , , , , ,6 Table 2: Nitrate standard solutions: wanted and real massconcentration standard β(no 3 ) mg L 1 V 0 (NO 3 ) µl m(no 3 ) g V 0 (NO 3 ) µl β (NO 3 ) mg L , , , , , ,8 3

4 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 11,8 3,10 3,40 3,25 0,21 5,8 1,40 1,60 1,50 0,14 24,6 5,85 5,80 5,83 0,04 11,5 0,90 1,00 0,95 0,07 24,7 2,10 2,20 2,15 0,07 49,8 3,95 3,90 3,93 0,04 NO 3 Table 4: Dead and retention times of standard solutions and their arithmetic means standard t 0 t gross(cl ) t clear (Cl ) t gross(no 3 ) t clear (NO 3 ) 1 3,0 6,6 3,6 11,4 8,4 1 3,0 6,6 3,6 11,4 8,4 2 3,0 6,6 3,6 11,4 8,4 2 3,0 6,6 3,6 11,4 8,4 3 3,0 6,6 3,6 11,4 8,4 3 3,0 6,7 3,7 11,4 8,4 t 3,0 6,6 3,6 11,4 8,4 σ(t) 0,0 0,1 0,1 0,0 0,0 k - 1,2 2,8 The dierence in the kapacityfactors give evidence that both, chloride and nitrate could be detered in the same sample. The used equations are: t = σ(t) = N i=1 t i (4) N 1 N (t i t) N 1 2 (5) i=1 k = t clear t 0 (6) 4

5 Table 5: Peak heights and retention times for sample B1 Substance Peak 1/cm Peak 2/cm t gross,1 t gross,2 t clear,1 t clear,2 H 2 O - - 3,0 3,0 - - Cl 3,1 3,1 6,7 6,7 3,7 3,7 NO3 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

6 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 cm 4 µg 1 (9) β(no 3 ) = h(no 3 ) 0, 079 cm 4 µg 1 (10) 6

7 So the results are: Table 6: Mass concentration of chloride and nitrate in sample B1 substance β 1 mg L 1 β 2 mg L 1 β mg L 1 σ(β) mg L 1 Cl 12,5 12,5 12,5 0,0 NO3 30,4 32,9 31,7 1,7 The sample B1 contained 12, 5 mg /L chloride and 31, 7 mg /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. So chloride is the smallest and will elute rst. Then comes nitrate and at lat the higher charged sulfate. 2. Which values in a chromatogramm contain qualitave and which quantitative information? The retention times give qualitative infomation, which are intressting for comparing dierent ions. Quantitative information are given by the height of the peaks, they are proportional to the ions concentration. 3. Which kind of other chromatographytypes are there? Give three examples with an short explaination of the separationprinziple. There are several types of chromatograpy like the gas chromatography (GC), the thin layer 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 stream of inert gas. The inside of the column is coverd with the static phase, which interact with the analyte an seperate the dierent components. For this type of chromatography the 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 specic speed. The HPLC uses high pressure. The analyte is dissolved in a liquid eluent and pumped through closed packege of ion exchanger. Depending to the properties of the compnents of the analyte they stay dierent times in the column. 7

8 6 Appendix References [1] Grundpraktikum Analyitsche Chemie, Skriptum für das Wintersemester 2009/ Prof. Dr. Thorsten Homann, Prof. Dr. Nicolas Bings; ; 20AC%20II%20Analytik%20WS0910.pdf List of Figures 1 Calibration line for chloride Calibration line for nitrate Chromatorgramm: standard Chromatorgramm: standard Chromatorgramm: standard Chromatorgramm: sample B

9 6.1 Original data Figure 3: Chromatorgramm: standard 1 Figure 4: Chromatorgramm: standard 2 9

10 Figure 5: Chromatorgramm: standard 3 Figure 6: Chromatorgramm: sample B1 10