Ion chromatography analysis methods and issues

1 Ion chromatography analysis methods and issues Jim Krol Sr Applications Chemist for Ion analysis Waters Corporation Feb/Mar 2000. Slide #. You Have a Choice for Ion analysis Ion analysis Options Ion Capillary Ion chromatography analysis Single Column Chemical IC Suppression IC. Slide #. Ion chromatography Hardware Configuration Options Data System chromatography Manager Anion Conductivity Isocratic Manual Exchange Pump Injector Detector Column Ion Suppressor Conductivity Gradient Autosampler Exchange CIA. Module Detector Pump Column Ion Exchange Photodiode Gradient Autosampler Suppressor Conductivity Column Array Pump Module Detector Detector Slide #. What Are Ions? Any chemical species that carries a electrical charge -Soluble in water -Exhibit conductivity in solution Example: NaCl + H20 Na+ + Cl- + H2O.

2 Na+ = Cation Cl- = Anion or NaH2PO4 + H2O Na+ + 2H+ + PO4-3. Slide #. Importance of pH and pKa Ions can exist in solution in a number of different forms Depending on pH of the solution and pKa of the ion pH = -log [H+]. pKa = the pH where the species is 50% ionized H3PO4 H+ + H2PO4-1 pKa = H2PO4-1 H+ + HPO4-2 pKa = HPO4-2 H+ + PO4-3 pKa = Slide #. Importance of pH and pKa Why is this important to IC? All ions in solution will convert to the form favored by the pH of the eluent. H3PO4. pH Anion Exchange H2PO4-1. pH HPO4-2. pH PO4-3. pH #. Importance of Ksp solubility Product Before an ion can be analyzed by IC, it must be in solution. Depending on the sample matrix, other ions influence solubility . Ksp = [A-][C+] pKsp = -log Ksp [AC]. Example: analysis of Cl in a sample matrix containing Ag, or analysis of SO4 in a sample with high Ca.

3 Ksp for AgCl is implying that Cl is not in solution Ksp for CaSO4 is implying that only a portion of the SO4 is in solution. Slide #. Important Questions to Ask About the Sample 1 What are the analyte ions of interest? 2 What is the expected concentration? 3 What else is in the sample matrix? Slide #. Detection of Ions Conductivity Direct: Net increase in conductivity;. low background eluent conductivity Indirect: Net decrease in conductivity high background conductivity UV/VIS. Direct: Generally between 200 and 220 nm Post Column Derivatization Electrochemical Slide #. Direct Conductivity Detection Conductivity of the analyte ion Conductance Observed conductivity response Analyte - Eluent Conductivity change due to displacement of eluent = Equivalent Ionic Conductance Slide #. Indirect Conductivity Detection Conductivity of the analyte ion Conductance Observed conductivity response Analyte - Eluent Conductivity change due to displacement of eluent Switch detector polarity for positive mV peaks Slide #.

4 What is Chemical Suppression Conductivity Detection A Suppressor is a device placed between the column and the detector, and acts to reduce the background conductivity of the eluent and enhance the conductivity of the analytes. For anion analysis , the suppressor is a high capacity cation exchange membrane or resin in the acid form. It removes cations from the eluent and replaces them with H+. The H+ neutralizes the highly conductive HCO3/CO3, or OH, to non-conductive H2CO3 and H2O. Puts the anions into their highly conductive acid form for conductivity detection. Lowers background conductivity and enhances anion conductivity. Slide #. Mechanism of Chemical Suppression Anion analysis Using Alltech ERIS. 1000HP. High C apacity C ation Exchange R esin in the H+ form O =S=O. O =S=O. O =S=O.

5 O =S=O. Na+ - - +. _ _. O. + H+ - _ _ -+. O. -H C C. O. _ _. O. _ _. HC O 3. _ _. _ _. From - H 2O To OH O =S=O O =S=O. Colum n H 2 CO 3. A- O -+ Suppression O +- Detector H Na + - C + H A. -E luent ions, Na, OH , and H CO 3 /C O 3 exhibit high conductivity -R esin in H + form acts to rem ove Na and Sam ple C ations, C+, from the eluent, and replaces them with H+. -H + interacts w ith OH and HC O 3 /C O 3 to yield H 2 O and H 2 CO 3 that have low conductivity and the conductivity of the eluent is significantly reduced - -S im ultaneously, the sam ple anions, A , are placed into their highly conductive acid form to enhance their conductivity response -O verall S/N and sensitivity is enhanced Slide #. Direct UV/VIS Detection Many anions and all organic acids are UV active in the general range of 200 to 220 nm Examples: Nitrite, Nitrate, Sulfite, ThioSulfate, ThioCyanate Chlorite, Bromide, Bromate, Iodide, Iodate Arsenite, Arsenate, Selenite, Selenate, All Organic Acids Slide #.

6 Direct UV Detection in Series with Conductivity Detection 1 2. 3 C o n d u c tiv ity w ith C h e m ic a l S u p p re s s io n 4. 1 .8 u S. 5 C o lu m n : W a te rs IC -P a k A / H C. 7. 6. E lu e n t: 1 .2 m M N a 2 C O 3 /. 1 .2 m M N a H C O 3. F lo w ra te : 2 .0 m L /m in In je c tio n V o l:5 0 L. 0 .0 0 4 .0 0 8 .0 0 1 2 .0 0 1 6 .0 0 2 0 .0 0 2 4 .0 0. M in u te s 3. U V (P D A ) a t 2 1 4 n m 1. F lu o rid e 1 ppm 5 2. C h lo rid e 2 ppm 3. N itrite 4 ppm 50 m AU. 4. B ro m id e 4 ppm 5. N itra te 4 ppm 6. P h o s p h a te 6 ppm 7. S u lfa te 4 ppm 4. 0 .0 0 4 .0 0 8 .0 0 1 2 .0 0 1 6 .0 0 2 0 .0 0 2 4 .0 0. M in u te s Slide #. UV/VIS Detection with Post Column Derivatization Column Mixing UV/VIS. Rx Coil Detector Tee Reagent Pump Additional hardware is necessary to the basic IC.

7 To do this type of application Used for bromate with EPA , and for transition metal analysis Slide #. Ion chromatography Applications and methods Common Anion analysis : EPA 300, Std Mtds 4110, & ASTM D4327;. and Std Mtds 4140 & ASTM Dxxx using Capillary Ion analysis Fluoride, Chloride, Bromide, Nitrite, Nitrate, o-Phosphate, and Sulfate Oxyhalide analysis : EPA & , ASTM pending Chlorite, Bromide, and Bromate Perchlorate analysis : EPA 314 (?), no ASTM or Std Mtds Chromate (Cr+6): EPA , or Std Mtds 3500, no ASTM. Alkali/Alkaline Earth Cations: No EPA, Std Mtds, or ASTM. Slide #. IC Anion Exchange Selectivity All EPA methods use an anion exchange column; Dionex or Equivalent Waters columns and Alltech ERIS 1000HP Auto Suppressor are considered equivalent Not all anion exchange columns are alike; selectivity and capacity C AT IO N S Will require changes in eluent composition D e te c to r R e s p o n s e depending on the column capacity O R G A N IC A C ID S.

8 CO3. IN O R G A N IC. A N IO N S. R e te n tio n 3 0 m in u te s Slide #. Vo Ion chromatography for Anion analysis The Validation issues Hardware: The Ion Chromatograph Software: Data Processing Method: The Chemistry Sensitivity and Detection Limits Linearity and Accuracy System Suitability: QA / QC. Slide #. Method Validation was Performed Using Waters Alliance System for IC. W a te rs 2 6 9 0 S e p a ra tio n s M o d u le -3 1 6 S ta in le s s S te e l, lo w d is p e rs io n -E n h a n c e d F lo w P re c is io n , 0 .0 7 5 % R S D. -C o n tin u o u s E lu e n t V a c u u m D e g a s s in g -In te g ra te d S a m p le M a n a g e m e n t, 0 .5 % a t 1 0 0 L. W a te rs IC -P a k A n io n H R ( Equivalent Column). -6 m ; 4 .6 m m x 7 5 m m ; P o ly M e th a c ry la te B a s e d W a te rs 4 3 2 C o n d u c tiv ity D e te c to r -5 E le c tro d e D e s ig n P ro v id in g H ig h S e n s itiv ity a t H ig h B a c k g ro u n d C o n d u c tiv ity -D ire c t T e m p e ra tu re C o n tro l A llte c h E R IS 1 0 0 0 H P A u to S u p p re s o r ( Equivalent Suppressor Device).

9 -T w o H ig h C a p a c ity C a tio n E x c h a n g e S o lid P h a s e C e lls in P a ra lle l -E le c tro c h e m ic a l S e lf-R e g e n e ra tio n w ith E lu e n t W a te rs M ille n n iu m D a ta P ro c e s s in g Slide #. Alliance System for Ion chromatography 2690 996. IC-Pak A HR. PhotoDiode Separations Array Detector (Optional). Module with Integrated Alltech 432. Sample Column ERIS 1000HP Conductivity Heater AutoSuppressor Detector Management @ 30oC @ 35oC. Typical Eluents Millennium Borate Gluconate Data Processing Carbonate Bicarbonate Waste Nitric Acid Anion DI Water analysis Slide #. Anion analysis Method Validation Design Individual Youden Pair Standards, in ppm 1 2 3 4 5 6 7 8. Cl Analyte Anion Br NO2 SO4 NO3 F PO4 The collaborative design is intended to demonstrate performance between and 50 ppm anion, except for Fluoride between and 25 ppm.

10 Standard 9 is 100 ppb of each anion for detection limit calculations. All Standards prepared from Certified 1000 ppm Stock Standards Slide #. Single Column Ion chromatography Direct Conductivity Detection Column: Waters IC Pak A/HR. Eluent: Borate / Gluconate 1 Fluoride = 1 ppm 4. Back Cond: 240 S 2 Bicarbonate 3 Flow Rate: 1 mL/min 3 Chloride =2. Inj Volume: 100 L 4 Nitrite =4. 5 Bromide =4. 6 Nitrate =4. 5 6 7 o-Phosphate = 6. S. 8 Sulfate =4. 1. 8. 7. 2. 0 .0 0 5 .0 0 1 0 .0 0 1 5 .0 0. M in u t e s Slide #. Single Column Ion chromatography Peak Area Response Linearity 3E+6. Chloride r2 = 3E+6 Chloride Fluoride r2 = 2E+6. Peak Area Bromide r2 = 2E+6 Fluoride 1E+6 Bromide 5E+5. 7 Data Points per Concentration 0E+0. 0 10 20 30 40 50. ppm Anion Slide #. Single Column Ion chromatography Peak Area Response Linearity 3E+6.