Page 316 - Multidimensional Chromatography

306 Multidimensional Chromatography

that the levels of migrated additives from polymeric materials are within the speci-
fied migration limits. The highest level of migration of these additives, on account of
their lipopphilic nature, is usually seen in edible oils or fats. Many references to the
analysis of oils by using HPLC–GC are given in the book by Grob (10). These food
products are usually very difficult to analyze due to the complex nature of the oils
and fats and usually many sample preparation steps are needed before chromato-
graphic separation is applied. Therefore, the use of multidimensional chromatogra-
phy has allowed for less sample handling, better quantitative results and efficient
analysis of such samples. Usually, normal phase HPLC is used for sample prepara-
tion, including the separation of the additive from the oil and fats. Then, the eluent
fraction containing the additive is transferred to either the GC system in the second
dimension or to another LC column, followed by GC analysis.
Baner and Guggenberger (11) have reported the analysis of a Tinuvin 1577 poly-
mer-additive-rectified olive oil, virgin olive oil, Miglyol 812 S, corn and sunflower
oils by using on-line coupled normal phase HPLC–GC. These authors have reported
the quantitative determination of Tinuvin 1577 from poly (ethylene terepthalate)
(PET) and polycarbonate (PC) polymers in these oil samples. The HPLC column
used for the analysis of virgin olive oil was a 125 mm 4.6 mm Spherisorb Si-5 m
column with a guard column, with the eluent being 30% dichloromethane in hexane.
A 50 L sample injection loop and a flow rate of 400 L min were used in this work.
The LC GC interface was a 300–500 L transfer loop and was dependent upon the
HPLC mobile phase flow rate and width of the Tinuvin 1577 HPLC peak. The GC
column was a DB–5HT (15 m 0.25 mm, 0.1 m coating thickness) high-tempera-
ture fused-silica capillary. The GC oven temperature program was 160 °C for 8 min
(the sample transfer and solvent evaporation temperature), a 10 °C min ramp to
260°C, a 5 °C/min ramp to 320 °C, and finally a 10 °C/min ramp to 360 °C for 15
min. The GC conditions included a He flow rate of 0.9 ml/min at 160°C, nitrogen
make-up gas and flame-ionization detection.
The Tinuvin 1577 (MW, 425.5) eluted on the silica column before the olive oil
triglycerides. Then, the HPLC eluent fraction containing the Tinuvin 1577 was trans-
ferred into the GC unit by using a loop-type interface. The detection limit was found
to be 0.19 0.07 mg L and the quantifiable limit was determined as being three
times the limit of detection (LOD). Figure 12.1 shows the HPLC and GC chro-
matograms of the blank oil versus the detection limit concentration of Tinuvin 1577
in virgin olive oil. This method has also been applied to separate other higher-
molecular-weight polymer additives such as Irganox 245 (MW, 586.8) and Irganox
1010 (MW, 1200), an antioxidant polymer additive.

12.5 SEC–GC APPLICATIONS

The premise of size exclusion chromatography (SEC) is that solute molecules are
separated according to their effective molecular size in solution. SEC allows the
separation of fractions according to their molecular weight and eliminates the