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Streamlining Sample Analysis Using Automated
Injection of Internal Standards
Labor intensive sample preparation work can be reduced, thus resulting in higher lab efficiency.
Optimized method for sandwich-injection comes pre-configured on the autoinjector, allowing anyone to perform the analysis
with confidence.
Automatic injection using the autoinjector enables error-free addition of internal standards.
H. Tsujihata, Y. Higashi
GC Nexis™ GC-2030, AOC-30i
Introduction
The internal standard method is a quantitative analysis method
in gas chromatography (GC), and is widely used because it can
correct for instrument sensitivity and injection volume errors.
On the other hand, accurate addition of the internal standard
(IS) to all samples is necessary, and more sample preparation
work is required in comparison with the absolute calibration
curve method (external standard method).
In this article, commonly-used alcohols, ketones, esters, ethers,
and aromatics were analyzed using sandwich-injection mode of
the Sampler Navigator function of the AOC™-30 autoinjector,
and satisfactory linearity of the calibration curves and
repeatability of the peak area ratios were verified.
Sampler Navigator Function
In sandwich-injection with the AOC-30 autoinjector, the syringe
draws up the IS first, followed by the sample, and then
simultaneously injects the two compounds into the injection
port (Fig. 1). When the sandwich-injection of Sampler Navigator
function is selected, the recommended conditions for
automated injection of the IS can be set with one click.
Fig. 1 Flow of Suction and Injection of IS and Sample
Rinse solvent vials
Sample L1
Waste liquid vials
IS vial L3
Fig. 2 Turret of AOC-30
Preparation of Mixed Samples
Table 1 shows the composition of the mixed samples and the IS
used in this experiment. Concentrations of 20 ppm, 200 ppm,
1000 ppm, and 2000 ppm for the mixed samples were prepared
by dilution with the solvents indicated in the table 1.
1000 ppm solutions of the internal standards for mixtures 1 and
2 were prepared via dilution using the respective solvents. A
1000 ppm was used for mixture 3.
Table 1 Compositions of Mixed Samples and IS and Solvents Used
Mixture 1
(Alcohol)
Mixture 2
(Ketone, ester,
ether)
Mixture 3
(Aroma)
Sample
Methanol THF Benzene
2-Propanol Ethyl acetate Toluene
Ethanol MiBK o-Xylene
n-Propanol MBK Ethyl benzene
i-Butanol - Tetralin
IS 2-Butanol MEK p-BFB
Solvent Acetone Acetone Methanol
p-BFB: p-Bromofluorobenzene-Fluorobenzene Mixture Standard Solution
(each 1 mg/ml Methanol Solution)
Conditions of Sandwich-Injection Analysis
The analysis of the mixed samples was conducted under the
conditions in Table 2 using a Nexis GC-2030 + AOC-30i. The
mixed samples were set at L1 in Fig. 2, and the internal standard
at L3.
Model : Nexis GC-2030 / AOC-30i
Injection Mode : Sampler Navigator – sandwich-injection
(IS 5 %, sample 0.5 μL)
*1
Syringe : 10 μL syringe for AOC (P/N 221-34618)
Injection Volume : 0.5 μL (IS) + 0.5 μL (Mixture)
Injection Temp. : 200 ˚C
Injection Mode : Split
Split Ratio : 1: 30 (Mixture 1, 3) 1: 50 (Mixture 2)
Carrier Gas : He
Carrier Gas Control : Linear velocity (35 cm/s)
Column : SH-PolarWax (60 m × 0.32 mm I.D., 1.0 µm)
*2
Column Temp.
Mixture1 : 70 ˚C (5 min) - 5 ˚C/min - 80 ˚C
- 15 ˚C/min - 140 ˚C (5 min)
Mixture2 : 60 ˚C (5 min) - 10 ˚C/min - 80 ˚C
- 40 ˚C/min - 140 ˚C (5 min)
Mixture3 : 90 ˚C - 20 ˚C/min - 200 ˚C(5 min)
Detector : Flame ionization detector (FID)
Detector Temp. : 250 ˚C
Detector Gas : H
2
32 mL/min, Air 200 mL/min
Makeup Gas : N
2
24 mL/min
Table 2 Analysis Conditions
Internal standard
(IS)
1.0
0.5
10 μL syringe
Sample
1.0
0.5
Injection port
1.0
0.5
Sample
injection
*1 The IS injection volume can be selected for 5 % or 10 % of the syringe
volume.
*2 P/N: 227-36252-02
