ADV06-15_1-412

Fast, Simple Sample Cleanup

Using QuEChERS SPE Tubes

• Achieve a fou r-fold increase in sample throughput.

Significant ly reduce mat erial costs.

Convenient, ready to use cent rifuge tubes with ult ra pure, pre-weighed adsorbent mixture s.

Qu ick, Easy, Cheap, Effective, Rugged, and Safe, the QuEChERS ("catchers") method for extrac ting pesticides from food is based on research

by the US Department of Agriculture.I In addition to using less solvent and materials versus conventional SPE meth ods, Qu EChERS emy loys

a novel and mu ch qu icker dispersive solid pha se extraction cleanup (dSPE). QuEChERSmethods, includ ing an AOACOfficial Method and

modifications to the methods, have been posted on the Internet.3 These methods have several basic steps in common:

Step 1:

Sample preparation and extraction

Commodities are uniformly comminuted.

Acetonitrile solvent is added for a shake

extract ion. Salts, acids and buffers may be

added to enhance extraction efficiency and

protect sensitive analytes. Surroga te standards

can be added to monitor extraction efficiencies.

Step 2:

Extract cleanup - A subsample of sol

vent extract is cleaned up using dSPE, a key

improvement incorporated in the QuEChERS

technique. Small polypropylene centrifuge

tubes are prefilled with precise weights of

MgSO4 and SPE adsorbents to remove excess

water and unwanted contaminants from the

extracted samples. After agitation and cen

trifugation, the cleaned extracts are ready for

analysis.

Step 3:

Sample analysis - Samples may be pH

adjusted to protect sensitive pesticides and/or

solvent-exchanged to improve analysis by

either GC/MS or LC/MS. Intern al standards

can be added.

Table I

Mod ified mini-mult iresidue QuEChERS for pesticides from

strawberries.

Sam~pre

aration and extraction

sample:

109 of strawberrieswere homogenized and placed in a SOmLPTFEcentrifuge tube

Solvent:

10mL of acetonitrile wereaddedto homogenate

Shakefor 1 minute, until uniform

Salts:

4.0g MgS04 (powder or granular)

1.1.0g NaCi

L Og trisod ium citrate dihydrate

O.5gdisodiumhydrogencitrate sesquihydrate

Salts wereadded and vigorously shaken for 1 minute. Sample was centrifuged and

the supernatant removed for cleanup.Pesticides standards (200ng/mL) were spiked

inat this point.

~.!!Ip

extr.a~

cleanup

QuEChERS tubes: I mL of supernatant fromthe previousstep wasplaced intoseveral 2mL

polypropylenecentrifuge tubes, each containing one of the following adsorbent mixes:

A.SOmg PSA

l S0mg MgS04 (cat.# 26124)

B. SOmgPSA

l S0mg MgS04

SOmg 08 (cat.# 26125)

50mg PSA

l S0mgMgS04

50mg GCB (cat.# 26123)

Cleanup:

Sampleswereshakenwith theadsorbents for 30seconds (carbon for 2 minutes),

then centrifu edto roducea clear su ernatant for

GC/MS

anal sis.

Internal standard: Pentachloronitrobenzene ina fOm ""e.;solu",ti",,,-lP"H"-".:

",r",i""c",-acid """" on S.

PSA- primary andsecondary amine exchange material.

GCB- graphitized carbon black

Table

II Instrument conditions.

Column:

Rtx®'CLPesticides2 20m, 0.18mmID,

0.14J..1m

(cat.# 42302)

Sample:

custompesticidemix 200J..lg/mLeach pesticide,

internal standards:

8140-8141 ISTD,

1000J..lg/ mL

(cat.# 32279),

Qu EChERSmethods are convenient, rugged meth508.1ISTD 100J..lg/mL (cat.# 32091),

triphenylphosphate

1000J..lg/ml

(cat.# 32281)

ods that simplify extract cleanup, reduce mat erial

Inj.:

1.0J..lLsplitless (hold 1 min.)

costs, and improve sample throughput. Here we

Inj. temp.:

250°C

demo nstrate the effectiveness of QuEChERS samCarrier gas:

helium

ple cleanup using a multiresidue analysis of pestiFlow rate:

constant linear velocity

40cm/sec

cides on strawberr ies.

Oventemp.:

40°C(hold1 min.) to 320°C

12°Clmin.

Del:

Shimadzu GCMS·QP2010Plus

Experimental

Transfer linetemp.: 300°C

Ionization:

Electron ionization

Strawberr y extra cts were prepared, spiked, and

Mode:

Selected ionmonitoring

dSPE treated according to Table I. Analytical condi

tion s are presented in Table II.

One microliter splitless injections of the extracts

were performed by a Shimadzu AOC-20i autosarn

Rtx@-CLPesticides2Columns (fused silica)

pier using "mid" injection speed into a Shimadzu

QP-2010 Plus GC-MS system operated und er the

df lIlml

temp. limits

lengt....h

-'c!!l #

0.18mm

0.14

-60 to

310/330°C

20M"'""r

4230=..

'-'·o,-,ete

....:"'"'2

condi tions in Table II.

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