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 Jena, Germany

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

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

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

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

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

NO 3 - [µg/L] Peak square in KCl „suprapur“ SD RSD [%] Peak square in KCl „p.A.“ SD RSD [%] Relation [%] , , , , , , , , , , , , , ,398

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%!

Model Extract [µg/L] Mean Concen- tration [µg/L] Expected Concen- tration [µg/L] Standard Deviation [µg/L]RSD[%]Recovery[%] ,8 503,8 495,0 495,0 5,6 5,6 1,1 1, ,4 528,4 519,7 519,7 3,9 3,9 0,7 0, ,4 553,4 544,5 544,5 6,3 6,3 1,1 1, ,5 574,5 569,2 569,2 6,2 6,2 1,1 1, ,0 601,0 594,0 594,0 5,0 5,0 0,8 0, ,6 650,6 643,5 643,5 3,8 3,8 0,6 0, ,2 694,2 693,0 693,0 4,2 4,2 0,6 0, ,6 981,6 990,0 990,0 5,9 5,9 0,6 0, ,71485,0 15,7 15,7 1,1 1,

QCP True Value Certified Value Acceptance Limits NO 3 - [µg/L] Dilution 1:50 NO 3 - [µg/L] ,1 131, ,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

Extract Extract SFA SFA Dilution DilutionConcentration + Spike Spike IC-UV IC-UV A-1 A :50 1: A-2 A :50 1: B-1 B :25 1: B-2 B :25 1: C-1 C :100 1: C-2 C :100 1: D-1 D :25 1: D-2 D :25 1: E-1 E :25 1: E-2 E :25 1:

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