Time and Cost Effective Methods for Reducing Background Noise and Signal Suppression in Problem Matrices for Residue Analysis by LC-MS/MS

Presented at NACRW 2016
Joseph Kolb1, Ariana Ramdin1, Ryan Undeen1
1Merieux NutriSciences Corporation, Gainsville, FL 32607

Introduction

Several clean-up methods are compared for background reduction, analyte recovery, and cost effectiveness in order to successfully analyze a wide variety of multiclass multiresidues in difficult matrices including Chili Powder and Tobacco. The most critical aspects of reliable multiresidue analysis are the reduction of interferences from the sample matrix and analyte recovery. eXtreme|FV®, were compared to an existing ISO accredited QuEChERS method, as well as a dilute and shoot approach are analyzed in conjunction with different filtration techniques for residue analysis by LC-MS/MS for minimal number of steps, speed, reduced reagent use and reduced cost.

Experimental

In order to successfully analyze multi-residue methods on difficult matrices such as habanero flakes and tobacco, several different clean-up procedures may need to be employed. This method investigates the use of different clean-up procedures and a dilute and filter approach to successfully analyze 20 pesticide compounds facing problems from matrix effects. The cost-effectiveness of different filtering techniques was also considered.

The following difficult to analyze compounds were tested:

5-OH ThiabendazoleClofentezineCoumaphosEtoxazole
MetolachlorPhosalonePirimiphos-methylPrallethrin
ProchlorazPymetrozinePyraclostrobinQuinoxyfen
SimazineSpinetoram-majorSpinetoram-minorThiobencarb
Thiophanate-methylTolyfluanidTriazophosTrifloxystrobin

Equipment

  • Sciex API 4000 Qtrap Mass Spectrometer
  • Shimadzu LC-20AD Pumps
  • Flow Rate: 0.25 mL/min
  • Run Time: 20 minutes
  • Injection Volume: 15µL
  • Mobile Phases:
    • A: 0.1% Formic Acid and 10mM Ammonium Acetate in HPLC Water
    • B: 0.5% Formic Acid in Methanol
    • Gradient:
      • Time (min.)%A%B
        9010
        0.59010
        15298
        19298
        209010
  • Column Temperature: 40˚C
  • Column: Waters Zorbax C18 3.5µm 3mm x 150mm
  • Centrifuge
  • Thomson eXtreme|FV® 0.2µm PTFE (p/n 85530)*
  • Thomson 48 position Vial Filter Press (p/n 35015-476)

*Special Note: For some autosamplers it is important to adjust the needle depth of your autosampler when using Thomson filter vials to improve the reproducibility of injections

Method

28 QuEChERS extracts were prepared and the filtration step was performed using two different approaches. Samples were evaluated for % recovery and timed. In both cases the samples need to be diluted with mobile phase prior to filtration in order to filter out precipates that are formed with the addition of aqueous solvent.

Sample Preparation

eXtreme|FV:

  1. Weigh 1g sample and add internal standards and standards as appropriate.
  2. Dispense 10mL water and then 15mL ACN.
  3. Cap and shake for 30 seconds.
  4. Centrifuge for 10 minutes at 3600 rpm.
  5. Transfer 400uL and filter using Thomson eXtreme 0.2 µm PTFE Filter Vial.

Traditional Method:

  1. Weigh 5g sample and add internal standards and standards as appropriate
  2. Dispense 10mL water and then 15mL 1% Acetic Acid in ACN.
  3. Cap and shake
  4. Add Magnesium Sulfate and Sodium Acetate QuEChERS salts to tube, vortex and then shake on Genogrinder for 1 minute.
  5. Centrifuge for 10 minutes at 3600 rpm
  6. Decant top layer into dispersive clean-up tubes, shake and vortex for 1 min (EMR salt clean-up requires a second dispersive SPE step)
  7. Centrifuge for 5 minutes at 3600 rpm
  8. Dilute 1:1 with Aqueous Mobile Phase and Filter

Results

Data Comparison Table of 20 Analyte Recoveries from different extracts/matrices spiked at 30ppb. Habanero Flakes and Tobacco showed less matrix effects and increased reproducibility using the dilute and filter method and compared to the QuEChers and filter method.

AnalyteHabanero Flakes QuEChERS +PSA
% Recovery
Habanero Flakes QuEChERS + EMR
% Recovery
Habanero Flakes Dilute and Filter
% Recovery
Tobacco QuEChERS +PSA
% Recovery
Tobacco Dilute and Filter
% Recovery
5-OH Thiabendazole30.941.875.635.559.3
Clofentezine11.920615123282.2
Coumaphos15.310787.9129135
Etoxazole6580.892.4447189
Metolachlor32.8110150117174
Phosalone54.712186.3135111
Pirimiphos-methyl192409262267264
Prallethrin12835132123228.0
Prochloraz75.8186130146140
Pymetrozine136129328449319
Pyraclostrobin28.135.677.698.7103
Quinoxyfen51.613283.139.191.0
Simazine73.611718611297.9
Spinetoram-major49.6160104120124
Spinetoram-minor46.911492.7119146
Thiobencarb28.569.678.171.583.5
Thiophanate-methyl18.510594.7314128
Tolyfluanid14.471.354.9101115
Triazophos15.38.9434.827.429.4
Trifloxystrobin40.813710875.7106

*Note: Several high recoveries (>200%) caused by matrix suppression of internal standard or matrix enhancement of analyte.

Data

reduce background noise results

For the pesticides we compared the traditional QuEChERS method and cleaned up with PSA and syringe & filter to simply dilute and shoot with the eXtreme PTFE Thomson Vial for Chili Powder and Tobacco. Diluting the samples gives better or comparable sensitivity with several difficult analytes in which we have been experiencing matrix suppression. Here are some of the analytes where the dilute and shoot method counteracted matrix suppression: 5-Hydroxythiabendazole, Clofentezine, Coumaphos, Etoxazole, Metolachlor, Phosalone, Pirimiphos-methyl, Prallethrin, Prochloraz, Pymetrozine, Pyraclostrobin, Quinoxyfen, Simazine, Spinetoram, Thiobencarb, Thiophanate-methyl, Tolyfluanid, Triazophos, and Trifloxystrobin. The dilution extraction helped us to include these analytes in our screen despite the heavy matrix effect we saw in QuEChers extraction.

Conclusion

The first approach was a traditional QuEChers method including filtration using a syringe, 0.2µm PTFE filter, and needle. The time taken to assemble the syringes and filter, as well as the time to mix the extract and mobile phase prior to placing in the syringe was included in the timing. The entire process took 64 minutes and 52 seconds.

reduce background noise time graph

With the second approach, the extract and mobile phase were placed into the bottom of a Thomson eXtreme Filter Vial together, the 0.2µm PTFE filter and cap was placed on top of the vials, and all the samples were pressed simultaneously using the Thomson Multi-Use Press. The entire process took 12 minutes and 51 seconds. Giving a time savings of 52 minutes!

Title

Time and Cost Effective Methods for Reducing Background Noise and Signal Suppression in Problem Matrices for Residue Analysis by LC-MS/MS

Description

Several clean-up methods are compared for background reduction, analyte recovery, and cost effectiveness in order to successfully analyze a wide variety of multiclass multiresidues in difficult matrices including Chili Powder and Tobacco. The most critical aspects of reliable multiresidue analysis are the reduction of interferences from the sample...

PDF Application

Product Used in Application

eXtreme|FV® - PTFE 0.2µm

Pre-Split Septum, Green Cap

pn#85530-200

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