1. Ion-chromatographic determination of small concentrations of nitrate in solutions of high salinity Michael Raessler and Ines Hilke Max-Planck-Institut fuer Biogeochemie, Hans-Knoell-Strasse 10, D-07745 Jena, Germany

2. Common methods for the determination of small amounts of nitrate Capillary electrophoresis Chemilumnescence Electrochemical detection Fluorescence Disadvantage: not appropriate to solutions of high sanility

3. Ion Chromatography with UV Detection Instrumental Set-up Instrument:Dionex 500 Pump module:Dionex GP 40 Detection:Dionex AD 20 (UV/VIS detector) Sample loop:100 µl Column: Hamilton PRP X-100, 250 x 4,1 mm Eluent: 0,1 M KCl based on KCl 99,999% „suprapur“ (Merck) Flowrate:2 mL/min Wavelength:λ = 210 nm

4. Application: Determination of NO 3 - in soil extracts of 1 M KCl Problem: KCl of „p.A.“ grade may contain up to 0,005 % Br -  Solution of 1 M CKl contains up to 1725 µg/L Br -  Br - interferes with NO 3 - determination at trace level

5. 1500 µg/L NO 3 - in 1 M KCl of „p.A.“ grade

6. 150 µg/L NO 3 - in 1 M KCl of „p.A.“ grade

7. NO 3 - [µg/L] Peak square in KCl „suprapur“ SD RSD [%] Peak square in KCl „p.A.“ SD RSD [%] Relation [%] 150334236021,85568537876,860 250518949341,87375243525,970 3507480711971,68878729303,384 4509301913961,59791523512,495 80015859319031,216434521361,396 100019951619981,020798118720,998 15002918079550,73006689020,398

8. Reliable determination of NO 3 -, if concentration ≥ 450µg/L Solution: Spiking 50µL of spike containing 50mg/L NO 3 - are added to 5 mL of extract Correction factor necessary:  Volume of extract is changed by 1%!

9. Model Extract [µg/L] Mean Concen- tration [µg/L] Expected Concen- tration [µg/L] Standard Deviation [µg/L]RSD[%]Recovery[%] 0+500 0+500 503,8 503,8 495,0 495,0 5,6 5,6 1,1 1,1 101 101 25+500 25+500 528,4 528,4 519,7 519,7 3,9 3,9 0,7 0,7 101 101 50+500 50+500 553,4 553,4 544,5 544,5 6,3 6,3 1,1 1,1 101 101 75+500 75+500 574,5 574,5 569,2 569,2 6,2 6,2 1,1 1,1 100 100 100+500 100+500 601,0 601,0 594,0 594,0 5,0 5,0 0,8 0,8 100 100 150+500 150+500 650,6 650,6 643,5 643,5 3,8 3,8 0,6 0,6 100 100 200+500 200+500 694,2 694,2 693,0 693,0 4,2 4,2 0,6 0,6 99 99 500+500 500+500 981,6 981,6 990,0 990,0 5,9 5,9 0,6 0,6 98 98 1000+5001462,71485,0 15,7 15,7 1,1 1,1 98 98

10. QCP 042-1 True Value Certified Value Acceptance Limits NO 3 - [µg/L] Dilution 1:50 NO 3 - [µg/L] 6643133 6555 6555 131,1 131,15270-7884105,4-157,7 Concentration after addition of spike [µg/L]: 631,1 Mean (N=10) [µg/L]:629,4±7,8 Recovery [%] :99,7% RSD [%]:1,24

11. Extract Extract SFA SFA Dilution DilutionConcentration + Spike Spike IC-UV IC-UV A-1 A-1 2529 2529 1:50 1:50 551 551 493 493 A-2 A-2 2594 2594 1:50 1:50 552 552 513 513 B-1 B-1 928 928 1:25 1:25 537 537 523 523 B-2 B-2 1360 1360 1:25 1:25 554 554 550 550 C-1 C-1 3599 3599 1:100 1:100 860 860 840 840 C-2 C-2 3752 3752 1:100 1:100 875 875 849 849 D-1 D-1 1619 1619 1:25 1:25 565 565 534 534 D-2 D-2 1764 1764 1:25 1:25 571 571 535 535 E-1 E-1 1539 1539 1:25 1:25 562 562 499 499 E-2 E-2 1555 1555 1:25 1:25 562 562 530 530

12. Chromatogram of soil extract „B-1“ (523 µg/L NO 3 - )