Read PowerPoint Presentation text version

Welcome to our E-Seminar:

Ion Suppression Minimized in LC/MSD

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Outline

· What is ion/signal suppression and why · Approaches to minimize suppression · Different ionization process · ESI source design · Fruit and vegetable extract ESI results

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

What is Ion/Signal Suppression?

· LC/MS response obtained from a clean standard can differ significantly from matrix samples, usually lower in matrices · Different analytes in a run show large variations in response, in other words, suppression is not a fixed function in a run · Ion suppression presents a challenge in doing quantitative LC/MS applications

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Example of Signal Suppression

API-ESI (+) Orange, 50 ppb Methiocarb [M+Na]+ m/z 248 43% Recovery

8 Abundance, x103

6 4

2

0 22 24 26 28 Time, min

Courtesy of C. Stafford and A. Krynitsky, U.S. EPA.

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

29.247

ESI Source

HPLC inlet Nebulizer gas inlet Nebulizer Nebulizer tip aimed at 90° to inlet of MS

+ + + + +

Capillary

+

+ +

+ +

+ +

+

+

Waste

heated N2 Countercurrent gas for efficient evaporation and desolvation

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Orthogonal Spraying

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Rayleigh Limit Reached

Coulomb Explosions

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Dr. John Fenn Nobel Lecture

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

What Caused Ion Suppression?

+ ++ + + + + - + + + + + + + +

· Charges are on the surface · Salts, matrix, and many ions are inside

· Competition between matrix components and analytes to get charges in the droplet · Competition between matrix components and analytes to gain access to the droplet surface · Surface tension · Compound polarity (solvation) · ......

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Break Number 1

Please type your question into the Chat Box at any time during the presentation.

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Outline · What is ion/signal suppression and why · Approaches to minimize suppression

Different ionization process ESI source design

· Fruit and vegetable extract ESI results

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Approaches to Minimize Suppression

· More selective extraction procedure for matrix cleanup · More chromatographic retention of analytes · Changing buffer and its concentration · Flow-splitting or nano-spray · Different ionization process · Post-column addition · ESI source design · ......

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Signal Suppression Minimized in APCI Mode

APCI (+) Orange, 50 ppb Methiocarb [M+H]+ m/z 226 107% Recovery 21.864 16 18 20 22

20 Abundance, x103

15 10

5 0

10

12

14

24

Courtesy of C. Stafford and A. Krynitsky, U.S. EPA.

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Time, min

APCI Source

HPLC inlet Nebulizer gas inlet Heater Capillary

+ ++ + ++ ++ + + + + Corona needle heated N2

Waste

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

APCI Process

Analyte containing aerosol

Evaporation

DISCHARGE

+ ++ + + + ++ + + + + + + + + ++ + ++ ++

Charge transferred to analyte

Vapor

Charged reagent gas formed

+ +

+ + +

Analyte ions

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Agilent 1100 LC/MSD APCI Source

Corona Needle

Ionize the gas with a discharge

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Ion Suppression in APCI

Evaporation Analyte containing aerosol Vapor

· Competition between matrix components and analytes to get charges in the droplet -- ELIMINATED · Competition between matrix components and analytes to gain access to the droplet surface -- REDUCED · Surface tension -- REDUCED · Compound polarity (solvation) -- REDUCED

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

APCI-LC/MS

Advantages

· · · · ·

Complementary to API-Electrospray for less polar analytes Good sensitivity for compounds of intermediate MW and polarity Less sensitive to solution chemistry effects than API-ES

Disadvantages Less useful for thermally labile compounds Requires some compound volatility

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Nebulizing the Sample

Nebulizing nitrogen

Polymeric Damping Mechanism

Rigid stainless steel eluent delivery capillary

Micromachined tip

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

ESI Droplets Distribution

Agilent LC/MSD

Nebulizer design leads to smaller and more uniform droplets

Amount

Some competitive designs

Spray Droplet Size

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Break Number 2

Please type your question into the Chat Box at any time during the presentation.

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Outline · What is ion/signal suppression and why · Approaches to minimize suppression

Different ionization process ESI source design

· Fruit and vegetable extract ESI results

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Samples Preparation

MATRIX EXTRACTS: Beans, Carrots, Corn, Endive, Escarole, Grapes, Lettuce, Oranges, Potatoes, Squash, Tomato, Zucchini

(courtesy of Walter Hammack and Donna Kilpatrick at Florida Dept of Agriculture & Consumer Services)

· Pipette 80 µL matrix solution into a 1.5-mL highrecovery vial · Air dry in hood · Add 80 µL of the 40 ppb standard solution in MeOH · Shake and inject 2 µL Standards: Thiabendazole, Methomyl, Imazalil

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Ion Suppression?

(2 µL of 40 ppb injected) All traces in the SAME Scale (SIM)

Imazalil 297, 299

Thiabendazole 202, 203 Methomyl 163, 164

Area %RSD = 20%

Area %RSD = 19%

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Area %RSD = 20%

Ion Suppression?

Each trace in FULL Scale (SIM)

Imazalil 297, 299

Thiabendazole 202, 203 Methomyl 163, 164

Using ISTD, the area %RSD is below 10% for each of the three peaks.

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

BEANS-GR, LETTUCE, SQUASH-Y, TOMATO, ZUCCHINI, 40PPB(MeOH) (80 pg on column)

Each trace in Full Scale

Fenuron 165, 166

50000 40000 30000 20000 10000 0 1.5 2 2.5 3 3.5 4 4.5 min

Aminocarb 209, 210

Mexacarbate 223, 224 Neburon 275, 277

Methomyl 163, 164

2 µL of 1 ppm 5-std mix in MeOH was added to 48 µL of matrix solution. (1 ppm / 25 = 40 ppb)

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Summary

· Signal suppression is sometimes due to the ionization process of Electrospray Ionization · Different ionization process (e.g., APCI) could minimize the suppression · The electrospray nebulizer design could play an important role in minimizing the suppression Polymeric damping mechanism Small and uniform droplets

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

References

· · More selective extraction procedure Matuszewski BK, Constanzer ML, Chavez-Eng CM, ANAL CHEM 70 (5): 882-889 MAR 1 1998 More chromatographic retention of analytes Muller C, Schafer P, Stortzel M, et al., J CHROMATOGR B 773 (1): 47-52 JUN 15 2002 Matuszewski BK, Constanzer ML, Chavez-Eng CM, ANAL CHEM 70 (5): 882-889 MAR 1 1998 · Changing buffer and its concentration Choi BK, Hercules DM, Gusev AI, FRESEN J ANAL CHEM 369 (3-4): 370-377 FEB 2001 Kuhlmann FE, Apffel A, Fischer SM, et al., J AM SOC MASS SPECTR 6 (12): 1221-1225 DEC 1995 · · · Flow-splitting Gangl ET, Annan M, Spooner N, et al., ANAL CHEM 73 (23): 5635-5644 DEC 1 2001 Nano-spray Bahr U, Pfenninger A, Karas M, Stahl B, ANAL CHEM 69(22): 4530-4535 NOV 15 1997 Post-column addition Choi BK, Gusev AI, Hercules DM, ANAL CHEM 71 (18): 4107-4110 SEP 15 1999 Kuhlmann FE, Apffel A, Fischer SM, et al., J AM SOC MASS SPECTR 6 (12): 1221-1225 DEC 1995 · 2-dimensional chromatography Pascoe R, Foley JP, Gusev AI, ANAL CHEM 73 (24): 6014-6023 DEC 15 2001

Dial +44 (0) 207 162 0125, Chairperson John Vis for e-Seminar Audio

Information

PowerPoint Presentation

28 pages

Report File (DMCA)

Our content is added by our users. We aim to remove reported files within 1 working day. Please use this link to notify us:

Report this file as copyright or inappropriate

634353