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