Coupled LC-GC for the Analysis of Pesticide in Food
Ryoichi Sasano, Yutaka Nakanishi
Saika Technological Institute Foundation
75-2 Kuroda, Wakayama-city, JapanKey Words: LC-GC, SPE, large volume injection, pesticide, food
1. Introduction
Analysis of pesticide residues in food is not so easy to do because various foods contain complex matrix.
Recently several reports have been described that on-line LC-GC system is useful for the analysis ofcomplex samples such as pesticide residues in food. The high sample capacity and wide range of separation
performance of LC can be utilized in selective cleanup of sample and GC has high separation efficiency.
However, coupling of LC to GC is not a trivial matter because the introduction of a large amount of LC
fraction into a GC column requires the use of special techniques to separate the solvent from the sample.
One of the subject for coupling LC with GC is a technique of eliminating water which is contained in LC
fraction. Another subject is a technique of transferring analytes to GC.
The purpose of this study is coupling reversed-phase HPLC with GC for attaining automated analysis ofpesticide residues in food. An interface equipped with a SPE cartridge is developed for coupling LC withGC. Finally, the performance of this LC-(SPE)-GC system has been evaluated by inspecting the data withanalyzing chlorpyriphos in ginger.
2. Experiment
The system is shown in the following. With adding water to the LC fraction, the diluted fraction is loadedon the SPE cartridge. The analyte is adsorbed on the SPE. The cartridge was dried with nitrogen gas. The
analyte is eluted from the the SPE cartridge with 20 µL of hexane by syringe pump and the eluate is
directly injected into a GC injector via a needle. The GC injector consists of a PTV injector equipped with astomach shaped insert. The stomach shaped insert makes it possible to accept all of the injected eluate fromthe SPE cartridge.

Valve 1
Pump

HPLC Column

Valve 2Syringe
Pump

SPE
Cartridge
Needle

UV

Waste
Waste

SampleAutosample r

PTVInjector
Pump(Wate r)N2 Gas

GC/MSHPLC
Fig. Schematic flow diagram of LC-GC system.

LC-GC System Conditions
HPLC (MIDAS;Spark, Agilent 1100)
Injection:
100 µL, Sample loop
Column:3.0 mm i.d. ×100 mm
Inertsil ODS-3Solvents:
A: Acetonitrile/Water (50/50)
B: Acetonitrile
Flow rate 0.5 mL/min
Detector:
UV 210 nm
Interface SPE（LGI-S100）
SPE:
2 mm i.d.×10 mm C18Diluting:Water 0.4 mL/min
Purge:
N2 gas, 0.5 min
Elution:Hexane, 20 µL

Interface Injector (LaviStoma; EMINET)
Insert:Stomach Type Insert
Solvent Vent: 10 sec, Purge flow 150 mL/min
Splitless:
3 min
Inj. Temp.:
70ºC(3min)-120ºC/min-220ºC/min(3min) -50ºC/min-260ºC(10min)
GC/MS (QP-5050A; Shimadzu)
Column:0.25 mm i.d.×30 m, 0.25 µm
Inert Cap 5MS/Sil
Oven:
70ºC(3min)-20ºC/min-280ºC(4min)
Carr. gas:He, 1 mL/minMS:
SCAN;50-550 mz

Sample preparation
20 g portions of homogenized ginger were extracted with 70 mL of acetonitrile. The extract solution wasadjusted to 100 mL with water.
Then 1 mL of the extract was cleaned up through an C18 cartridge (50 mg) for avoiding HPLC column
from deteriorating, and adjusted to 2 mL with 70% acetonitrile-water for LC-(SPE)-GC/MS analysis.
3. Result and Discussion
The performance of the system was investigated with respect to the LC-(SPE)-GC process by a ginger
spiked with 0.1 µg/g of chlorpyriphos. Chlorpyriphos elute around 8.2min. The fraction eluting from 7.8 to
8.6 min was transferred to the SPE interface. The excellent chromatography obtained can be observed inFig. 2. The cleaning achieved with the LC process is highly satisfactory.
20.0e6mAU

17.5e6

175

Intensity

(a)

150
125
100

15.0e612.5e610.0e67500e3

75

13.9

14.0

14.1

14.2

14.3

14.4

14.5

14.6

5000e350
252500e3(b)02468

10121416min

Time (min)Fig.2 HPLC chromatogram of a ginger
spiked with 0.1 µg/g of chlorpyriphos (a)and a standard solution of it (b).
Marked fraction transferred to the SPEcartridge.

111213141516171819Time (min)Fig.3 GC/MS-SCAN chromatogram of theLC-(SPE)-GC/MS analysis of a ginger
spiked with 0.1 µg/g of chlorpyriphos.

4. Conclusion
Coupling of LC with GC has been accomplished by a new SPE interface and a PTV injector equipped witha stomach shaped insert. The LC-(SPE)-GC system provides very high efficiency and selectivity
performance, and then allows automated analysis of pesticide residues in food.

20

Coupled LC-GC for the Analysis of Pesticide in Food
Ryoichi Sasano, Yutaka Nakanishi
Analysis of pesticide residues in food is not so easy to do because
various foods contain complex matrix. Recently several reports havebeen described that on-line LC-GC system is useful for the analysis ofcomplex samples such as pesticide residues in food. The high sample
capacity and wide range of separation performance of LC can beutilized in selective cleanup of sample and GC has high separation
efficiency. However, coupling of LC to GC is not a trivial matterbecause the introduction of a large amount of LC fraction into a GC
column requires the use of special techniques to separate the solvent
from the sample. One of the subject for coupling LC with GC is atechnique of eliminating water which is contained in LC fraction.
Another subject is a technique of transferring analytes to GC.
The purpose of this study is coupling reversed-phase HPLC with GC
for attaining automated analysis of pesticide residues in food. Aninterface equipped with a SPE cartridge is developed for coupling LCwith GC. The system is shown in the following. With adding water tothe LC fraction, the diluted fraction is loaded on the SPE cartridge.
The analyte is adsorbed on the SPE. The cartridge was dried withnitrogen gas. The analyte is eluted from the the SPE cartridge with 20µL of hexane and the eluate is directly injected into a GC injector via
a needle. The GC injector consists of a PTV injector equipped with aspiral insert. The spiral insert makes it possible to accept all of theinjected eluate from the SPE cartridge.
Finally, the performance of this LC-(SPE)-GC system has beenevaluated by inspecting the data with analyzing chlorpyriphos inspinach.

75-2, Kuroda, Wakayama-city, Japan
Application

LC-(SPE)-GC system
Valve 1Pump

Sample preparation
SyringePump

Valve 2HPLC (MIDAS;Spark, Agilent 1100)
Injection: 100 µL, Sample loop
Column:
2.1 mm i.d. ×100 mm
Inertsil ODS-3
Solvents:
A: Acetonitrile/water (50/50)
B: Acetonitrile
flow rate 0.5 mL/min
Detector:
UV 210 nm
Interface SPESPE:
2 mm i.d.×10 mm C18
Diluting:
water 0.4 mL/min
Purge:
N2 gas, 1 min
Elution:Hexane, 20 µL
Interface Injector (LVI-S200; EMINET)
Insert:Spiral Insert
Solvent Vent: 10 sec, Purge flow 150 mL/min
Splitless:
3 min
Inj. Temp.: 70ºC(3min)-120ºC/min-220ºC/min(3min)-50ºC/min-260ºC(10min)
GC/MS (QP-5050A; Shimadzu)
Column:0.25 mm i.d.×30 m Inert Cap 5MS/Sil
Oven:
70ºC(3min)-20ºC/min-280ºC(4min)
Carr. gas: He, 1 mL/minMS:
SCAN;50-550 mz, SIM;199, 314 mz

Cartridge
NeedleHPLC Column UV

Waste
Waste

PTV
Injector

20 g portions of homogenized spinach were extracted with 70 mL of acetonitrile.
The extract solution was adjusted to 100 mL with water.
Then 1 mL of the extract was cleaned up through an C18 cartridge (50 mg) for
avoiding HPLC column from deteriorating, and adjusted to 2 mL with 70%
acetonitrile-water for LC-(SPE)-GC/MS analysis.
mAU

Fig. 1 HPLC chromatogramof a spinach spiked with 1µg/g of chlorpyriphos (a) anda standard solution of it (b).
Marked fraction transferredto the SPE interface.

40SamplePump(Water)

Autosampler

35

N2 Gas30

GC/MSHPLC

25
20
15SPE Interface

Chlorpyriphos
elutearound8.2min. The fraction eluting from
7.8 to 8.6 min was transferred tothe SPE interface.

(a)105Dilution & Concentration

0Elution & Injection-5(b)0246810121416min

Retention time (min)SPE

1.E+0797S

1000e3

HPLC
Column8.E+06

SPEUV
Syringe
Pump(Hexane)

Pump
Water

Experimental

SPECl
199

6.E+06

GC injector

The analyte is eluted from the SPEwith hexane and the eluate is directly
injected into a GC injector via a needle.

PTV Interface

OP(OCH2CH3)2ClCl

500e3
65314

125

250e3
605081134 146
100258201

109

4.E+060e3

With adding water to the LC fraction,
the diluted fraction is loaded on theSPE cartridge. The analyte is adsorbedon the SPE.

N750e3

Intensity

Introduction

Saika Technological Institute Foundation

150169215

182
200244250288
278
300m/z2.E+06

Fig. 3 MS spectrum of peak
0.E+001010.51111.51212.5

13Retention time (min)Fig. 2 GC/MS-SCAN chromatogram of theLC-(SPE)-GC/MS analysis of a spinach spiked
with 1 µg/g of chlorpyriphos
The excellent chromatography obtained can be observed in Fig. 2. The cleaningachieved
withtheLCprocessishighlysatisfactory.
The performance of the system was investigated with respect to the LC-(SPE)-GC
process by a standard solution or a spinach spiked with 1 µg/g of chlorpyriphos. The
recovery was found to be higher than 98%. Reproducibility parameters ( RSD ) forthe peak area was below 2%.

Split Mode

Splitless

Split Mode

1st Stage

2nd Stage

3rd Stage

4th Stage

Injection

Concentration

Transfer

Elimination

The injector is kept at
a temperature lower
than the boiling pointof sample solvent.

While the evaporated
sample solvent isexhausted, the sample
is concentrated.

Target compounds
are transferred to thecolumn at an elevatedtemperature.

Matrix compounds
are eliminated fromthe insert at further
elevated temperature.

Conclusion
Coupling of LC with GC has been accomplished by a new SPE interface anda PTV injector equipped with a spiral insert. The LC-(SPE)-GC systemprovides very high efficiency and selectivity performance, and then allows
automated analysis of pesticide residues in food.