Ion-chromatographic Ion-chromatographic determination of small determination of small
concentrations of nitrate in concentrations of nitrate in solutions of high salinitysolutions of high salinity
Michael RaesslerMichael Raessler and Ines Hilke and Ines Hilke
Max-Planck-Institut fuer Biogeochemie, Hans-Knoell-Strasse 10, Max-Planck-Institut fuer Biogeochemie, Hans-Knoell-Strasse 10, D-07745 Jena, GermanyD-07745 Jena, Germany
Common methods for the Common methods for the determination of small amounts of determination of small amounts of
nitratenitrate
Capillary electrophoresisCapillary electrophoresis
ChemilumnescenceChemilumnescence
Electrochemical detectionElectrochemical detection
FluorescenceFluorescence
Disadvantage:Disadvantage: not appropriate to solutions not appropriate to solutions of high sanilityof high sanility
Ion Chromatography with UV Ion Chromatography with UV Detection Instrumental Set-upDetection Instrumental Set-up
Instrument:Instrument: Dionex 500Dionex 500
Pump module:Pump module: Dionex GP 40Dionex GP 40
Detection:Detection: Dionex AD 20 Dionex AD 20 (UV/VIS detector)(UV/VIS detector)
Sample loop:Sample loop: 100 µl100 µl
Column: Column: Hamilton PRP X-100, Hamilton PRP X-100, 250 x 4,1 mm250 x 4,1 mm
Eluent: Eluent: 0,1 M KCl based on KCl 0,1 M KCl based on KCl 99,999% „suprapur“ (Merck)99,999% „suprapur“ (Merck)
Flowrate:Flowrate: 2 mL/min2 mL/min
Wavelength:Wavelength: λλ = 210 nm = 210 nm
Application:Application: Determination of NODetermination of NO33-- in soil in soil
extracts of 1 M KClextracts of 1 M KCl
Problem:Problem: KCl of „p.A.“ grade KCl of „p.A.“ grade
may contain up to 0,005 % Brmay contain up to 0,005 % Br--
Solution of 1 M CKl Solution of 1 M CKl
contains up to 1725 µg/L Brcontains up to 1725 µg/L Br--
BrBr- - interferes with NOinterferes with NO33--
determination at trace leveldetermination at trace level
1500 µg/L NO1500 µg/L NO33-- in 1 M KCl of „p.A.“ in 1 M KCl of „p.A.“
gradegrade
0 1,00 2,00 3,00 4,00 5,00 6,00 7,00
min
-2,5
0
2,5
5,0
7,5
10,0
12,5
15,0
17,5
20,0
mAU
NO3 / 4,73
150 µg/L NO150 µg/L NO33-- in 1 M KCl of „p.A.“ in 1 M KCl of „p.A.“
gradegrade
0 1,00 2,00 3,00 4,00 5,00 6,00 7,00
min
-2,0
0
2,0
4,0
6,0
8,0
10,0
mA
U NO3 / 4,75
NONO33--
[µg/L][µg/L]
Peak Peak square in square in KCl KCl „suprapur“„suprapur“
SDSD RSD RSD [%][%]
Peak Peak square square in KCl in KCl „p.A.“„p.A.“
SDSD RSD RSD [%][%]
Relation Relation [%][%]
150150 3342333423 602602 1,81,8 5568555685 37873787 6,86,8 6060
250250 5189451894 934934 1,81,8 7375273752 43524352 5,95,9 7070
350350 7480774807 11971197 1,61,6 8878788787 29302930 3,33,3 8484
450450 9301993019 13961396 1,51,5 9791597915 23512351 2,42,4 9595
800800 158593158593 19031903 1,21,2 164345164345 21362136 1,31,3 9696
10001000 199516199516 19981998 1,01,0 207981207981 18721872 0,90,9 9898
15001500 291807291807 955955 0,70,7 300668300668 902902 0,30,3 9898
Reliable determination of NOReliable determination of NO33--,,
if concentration if concentration ≥ 450µg/L≥ 450µg/LSolution:Solution: SpikingSpiking
50µL of spike 50µL of spike containing 50mg/L NOcontaining 50mg/L NO33
--
are added to 5 mL of are added to 5 mL of extractextract
Correction factor necessary: Correction factor necessary: Volume of extract is Volume of extract is changed by 1%!changed by 1%!
Model Model ExtractExtract
[µg/L][µg/L]
Mean Mean Concen-Concen-trationtration
[µg/L][µg/L]
Expected Expected Concen-Concen-trationtration
[µg/L][µg/L]
Standard Standard DeviationDeviation
[µg/L][µg/L]
RSDRSD
[%][%]
RecoveryRecovery
[%][%]
0+5000+500 503,8503,8 495,0495,0 5,65,6 1,11,1 101101
25+50025+500 528,4528,4 519,7519,7 3,93,9 0,70,7 101101
50+50050+500 553,4553,4 544,5544,5 6,36,3 1,11,1 101101
75+50075+500 574,5574,5 569,2569,2 6,26,2 1,11,1 100100
100+500100+500 601,0601,0 594,0594,0 5,05,0 0,80,8 100100
150+500150+500 650,6650,6 643,5643,5 3,83,8 0,60,6 100100
200+500200+500 694,2694,2 693,0693,0 4,24,2 0,60,6 9999
500+500500+500 981,6981,6 990,0990,0 5,95,9 0,60,6 9898
1000+5001000+500 1462,71462,7 1485,01485,0 15,715,7 1,11,1 9898
QCP 042-1QCP 042-1 True ValueTrue Value Certified Certified ValueValue
Acceptance Acceptance LimitsLimits
NONO33-- [µg/L] [µg/L]
Dilution 1:50Dilution 1:50
NONO33-- [µg/L] [µg/L]
66436643
133133
65556555
131,1131,1
5270-78845270-7884
105,4-157,7105,4-157,7
Concentration after additionConcentration after addition ofof spike [µg/L]:spike [µg/L]: 631,1631,1
Mean (N=10) [µg/L]:Mean (N=10) [µg/L]: 629,4629,4±7,8±7,8
Recovery [%] :Recovery [%] : 99,7%99,7%
RSD [%]:RSD [%]: 1,241,24
ExtractExtract SFASFA DilutionDilution Concentration Concentration
+ +
SpikeSpike
IC-UVIC-UV
A-1A-1 25292529 1:501:50 551551 493493
A-2A-2 25942594 1:501:50 552 552 513513
B-1B-1 928928 1:251:25 537537 523523
B-2B-2 13601360 1:251:25 554554 550550
C-1C-1 35993599 1:1001:100 860860 840840
C-2C-2 37523752 1:1001:100 875875 849849
D-1D-1 16191619 1:251:25 565565 534534
D-2D-2 17641764 1:251:25 571571 535535
E-1E-1 15391539 1:251:25 562562 499499
E-2E-2 15551555 1:251:25 562562 530530
Chromatogram of soil extract „B-1“ Chromatogram of soil extract „B-1“ (523 µg/L NO(523 µg/L NO33
--))
0 1,00 2,00 3,00 4,00 5,00 6,00 7,00
min
0
2,5
5,0
7,5
10,0
12,5
15,0
17,5
20,0
mAU
NO3 / 4,93