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A Novel Technique to Identify Mineral Oil Contaminants in Vegetable Oil

A Novel Technique to Identify Mineral Oil Contaminants in Vegetable Oil

Keywords: Hydrocarbon, Solid Phase Extraction, Paraffin, Gas Chromatography.


A simple, fast gas chromatographic-flame ionization detection (GC/FID) method combined with a solid phase extraction (SPE) has been established to determine the mineral oil-saturated hydrocarbons (MOSH) in vegetable oils.

Mineral oils are certain fractions from petroleum refining and maybe traded under various designations such as Paraffinum Liquidum, Paraffin, Petrolatum (soft paraffin), Paraffin wax, Paraffin oil, Ozokerite, White (mineral) oil, depending on type liquid or solid or field of application. Vegetable oils, like many other foodstuffs, are often contaminated by mineral oil products during harvesting, processing, transportation and storage. Source of mineral oil also includes food packaging, food additives, processing aids, and lubricants. Presently, there is no established method available for quantitative assay of mineral oil even FSSAI only indicates about presence or absence of mineral oil.

The mineral oil contaminants found in food can be primarily divided into two types, the saturated hydrocarbons (MOSH), which include straight, branched and cyclic alkenes, and the mineral oil aromatic hydrocarbons (MOAH), which are mostly alkyl-substituted. Since the MOSH are the predominant part of the mineral oil and more easily analysed than the MOAH, they are usually treated as markers for the presence of mineral oils.

Literature review revealed, analysis of MOSH in vegetable oils and other food is on-line high performance liquid chromatography coupled with GC-FID (HPLC-GC-FID), in which HPLC as separation column plays purification role to isolate MOSH from lipid in food. But the corresponding coupled instrumentation is available only in few laboratories because of its high price.

It is utmost important to ensure the absence of mineral oil as contaminants in food. Hence, the present study aimed to provide a simple GC/FID method which includes offline glass SPE cartridge that was packed with silver impregnated activated silica gel to remove the fat and other interferences (primarily olefins) in vegetable oils to identify/estimate the presence of mineral oil contaminants in vegetable oil. The method was also validated for Precision, Accuracy & Linearity. Thus, the GLC method can be used as a rapid tool in industry to ensure the absence of mineral oil

Additionally, the advantages of the method include quantification of mineral oil hydrocarbons with simplicity, low cost and high sensitivity.


  • Apparatus

Glass SPE cartridges used for extraction and sample preparation. Thermo Scientific TRACE™ 1310 Gas Chromatograph equipped with FID used for GC analysis.

  • Chemicals, reagents and standards

n-Hexane (99% purity). The standard mixture of hydrocarbon (n-alkanes ranging C10–C40) (Sigma-Aldrich ). Silica gel (mesh size 80-120), Silver nitrate (Merck)

  • SPE Cartridge preparation

As no commercial glass SPE with Ag-silica gel was available, a 20-mL glass column was used for the lab-made SPE cartridge. The silica gel was activated at 500°C for 4 h in a muffle furnace and then coated with 1% silver nitrate solution then the mixture was homogenized on the rotary evaporator and dried in an oven at 125 °C.

For making the SPE column, 10 g Ag-activated silica gel was loaded into the cartridge.

Before analysis, 25 mL of n-hexane was loaded through SPE to rinse the entire column until the upper level of solvent was 0.5 cm higher than the silica gel bed.

  • Sample preparation

0.5g of oil weighed, spiked with appropriate amount of standard (dissolved in 1-mL n-hexane) and finally loaded onto the prepared SPE column and the first elute was discarded until close to dryness. Then, 25 mL of n-hexane was added & initial 10 mL of elute was collected, concentrated to 1 mL in a gentle nitrogen stream, and used for GC-FID analysis.

GC-FID Analysis

A 2-μL aliquot of test solution was injected (without split) into DB-5HT (25 m × 0.25 mm i.d. × 0.10 μm, separation column coated with a 0.10-μm film of 5% phenyl/95%methylpolysiloxane).

The MOSH area was determined by integrating the area of peak corresponding to hydrocarbons ranging from C10 to C30.Recovery was tested by spiking the oil with three concentrations (10, 50, and 100 mg/kg) and the repeatability was determined by analyzing an oil sample 3 times spiked with 10 mg/kg.

Results & Discussion


The calibration curve was prepared for each hydrocarbon using reference standards at five calibration levels. The calibration curve of alkane mixture was prepared from standard concentrations of 5.0 to 40.0 mg/L. All correlation coefficients square (R2) were higher or equal to 0.98.


The recovery was found between 70-120% for each individual hydrocarbon compounds spiking at three different level before extraction. The results are incorporated in Table No.1.


Precision was calculated from the 3 replicate determinations at lower spiking level. The results of repeatability as obtained were presented in terms of the relative standard deviation (%RSD) in Table No.2. Over all the Relative standard deviation values were found to be within 20%.


In the present study, mineral oil saturated hydrocarbons (MOSH) which is marker of mineral oil contaminants was estimated by employing the SPE followed by GC-FID analysis. The method succeeds over the other method in terms of Limit of detection as the method can be applied for quantification of mineral oil contaminants in ppm level.

Table and Figures

Table: 1 Result for %Recovery at different spiking level

Hydrocarbon % Recovery


 at 10mg/kg

% Recovery at 50 mg/kg   % Recovery


at 100 mg/kg

n-Decane 75.204 70.96 105.09
n-Undecane 81.212 70.05 103.50
N-Dodecane 70.561 71.19 104.28
n-Tridecane 79.708 70.84 104.12
N-Tetradecane 73.913 71.99 103.19
n-Pentadecane 73.291 70.91 104.33
n_Hexadecane 71.821 70.94 108.25
n_Heptadecane 72.411 70.29 104.06
n-Octadecane 70.98 73.08 105.25
n_Nonadecane 71.138 72.18 105.48
n-Eicosane 71.804 71.78 106.11
n-Heneicosane 70.767 70.27 103.93
n-Docosane 82.32 73.59 102.24
n-Tricosane 70.244 71.33 104.26
n-tetracosane 72.038 72.31 104.71
n-Pentacosane 77.322 71.01 104.64
n-Hexacosane 76.766 74.27 104.83
n-Heptacosane 77.482 71.19 103.80
n-Octacosane 76.179 72.61 107.46
Nonacosane 74.982 75.59 108.08
n-Triacontane 73.242 75.77 108.29
n-hentriacosane 70.364 71.58 101.55
n-Dotriacosane 71.862 74.17 101.96
n-Tritriacontane 76.659 75.95 102.02
n-Tetratriacontane 71.204 71.40 98.10
n-Pentatriacontane 77.554 72.63 109.27
n-Hexatriacontane 75.59 78.35 94.89
Heptatriacontane 70.79 71.85 104.01
Octatriacontane 81.734 78.54 93.22

Table: 2 Result for % RSD of recoveries

Hydrocarbon % Recovery SET 1 % Recovery SET 2 % Recovery SET 3 % RSD of recovery
n-Decane 75.20 77.42 73.21 2.79
n-Undecane 81.21 71.61 77.72 6.33
N-Dodecane 70.56 71.14 74.71 3.11
n-Tridecane 79.71 77.77 75.02 3.04
N-Tetradecane 73.91 72.73 73.10 0.82
n-Pentadecane 73.29 80.63 74.61 5.13
n_Hexadecane 71.82 73.77 73.45 1.43
n_Heptadecane 72.41 68.05 72.55 3.60
n-Octadecane 70.98 77.32 74.93 4.30
n_Nonadecane 71.14 73.67 70.64 2.27
n-Eicosane 71.80 75.43 71.26 3.11
n-Heneicosane 70.77 73.14 72.86 1.79
n-Docosane 82.32 72.03 73.72 7.26
n-Tricosane 70.24 70.90 76.83 4.99
n-tetracosane 72.04 71.35 70.30 1.23
n-Pentacosane 77.32 71.52 81.43 6.49
n-Hexacosane 76.77 71.37 71.47 4.22
n-Heptacosane 77.48 74.35 76.92 2.19
n-Octacosane 76.18 79.61 71.11 5.65
Nonacosane 74.98 75.21 72.73 1.84
n-Triacontane 73.24 74.73 75.88 1.77
n-hentriacosane 70.36 82.13 74.32 7.92
n-Dotriacosane 71.86 75.61 77.89 4.05
n-Tritriacontane 76.66 70.04 75.58 4.79
n-Tetratriacontane 71.20 85.72 73.25 10.24
n-Pentatriacontane 77.55 83.32 71.01 7.97
n-Hexatriacontane 75.59 81.93 77.16 4.22
Heptatriacontane 70.79 85.50 75.18 9.79
Octatriacontane 81.73 73.01 72.05 7.06

Fig:1 Chromatogram of Blank vegetable oil

Fig:2 Chromatogram of vegetable oil spiked with hydrocarbon mixture

Contributed By: Piali Ganguly.


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