Title;
Coupled LC-GC for the Analysis of Pesticide in Food
Ryoichi Sasano, Yutaka Nakanishi
Saika Technological Institute Foundation,
75-2, Kuroda, Wakayama-city, Japan
E-mail: sasano@saika.or.jp
Abstract;
The purpose of this study is to couple reversed-phase high performance liquid chromatography (LC)with gas chromatography (GC) for automated analysis of pesticide in food samples.
The interface employed for coupling LC with GC consists of two channels equipped with a solid
phase extraction (SPE) cartridge. One is a channel where water is added to the eluate containing thetarget compound separated by LC and continuously it is loaded on the SPE cartridge. The target
compound is adsorbed in the SPE cartridge. The other is channel where the adsorbed target
compound is eluted from the SPE cartridge and the eluate is injected directly into the GC injector.
By using SPE for coupling LC with GC, it becomes possible to change to the solvent which can beinjected into the GC (e.g., acetone and hexane) from the solvent which cannot be injected (e.g.,water and acetonitrile). The GC injector is a PTV injector equipped with a stomach type of insert inorder to inject all of eluate from the SPE cartridge. This LC-(SPE)-GC system has been evaluated byanalyzing chlorpyriphos in spinach. The recovery and repeatability were satisfactory.

Coupled LCLC--GC for the Analysis of Pesticide in Food
Ryoichi Sasano, Yutaka Nakanishi
Introduction
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 20
mL of hexane and the eluate is directly injected into a GC injector viaa 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 from the SPE cartridge.
Finally, the performance of this LC-(SPE)-GC system has been
evaluated by inspecting the data with analyzing chlorpyriphos inspinach.

Saika Technological Institute Foundation75
75--2, Kuroda, Wakayama
Wakayama--city, Japan
Application

LCLC-(SPE)(SPE)--GC system
HPLC
HPLC Column

Pump

Sample preparation
Valve 1

Interface SPE

UV
Pump
Water

Waste
Valve 2

SPECartridge
NeedleWaste Bottle

mAU

HPLC (MIDAS;Spark, Agilent 1100)
Injection:
100 mL, Sample loop
Column:
2.1 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 SPESPE:
2 mm i.d.×10 mm C18Diluting:water 0.4 mL/min
Purge:
N2 gas, 1 min
Elution:Hexane, 20 mL
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 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

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

40
35
N2 GasAutosampler

Syringe Pump
Hexane30GC/MS

25
2010SPE Interface

Chlorpyriphos
elutearound
8.2min. The fraction eluting from
7.8 to 8.6 min was transferred tothe SPE interface.

(a)155Dilution & Concentration
HPLC0Elution &Injection-5(b)0246810121416min

Retention time(min)1.E+0797S

1000e38.E+06ClNOP(OCH2CH3)2750e3

SPECl

199

6.E+06

Pump
WaterExperimental

20 g portions of homogenized spinach were extracted with 70 mL of acetonitrile.
The
extract
solutionwasadjusted to 100
mL
withwater.
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.

Cl500e365250e34.E+06

0e32.E+06

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

Hexane
The analyte is eluted from the SPE withhexane and the eluate is directly
injected into a GC injector via a needle.

PTV Interface

0.E+0010314

1255081134 146
100258

201

109
60

150

169

215

182
200m/z

244
250

288
278
300

Fig. 3 MS spectrum of peak
10.5

1111.51212.5

13Retention time
Fig. 2 GC/MS-SCAN(min)chromatogram of theLC-(SPE)-GC/MS analysis of a spinach spikedwith 1 mg/g of chlorpyriphos
The excellent chromatography obtained can be observed in Fig. 2. The cleaningachievedwiththeLCprocess
ishighlysatisfactory.
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 mg/g of chlorpyriphos. The
recovery was found to be higher than 98%. Reproducibility parameters ( RSD ) for thepeak 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 theboiling point ofsample solvent.

While theevaporated sample
solvent is exhausted,
the sample isconcentrated.

Target compounds
are transferred tothe column at anelevatedtemperature.

Matrix compounds
are eliminated fromthe insert at further
elevated
temperature.

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