In cosmetic products, hydrocarbons from mineral oil origin are used as ingredients in a wide variety of consistency, from liquid oil to solid wax. Refined mineral oil hydrocarbons consist of MOSH (mineral oil saturated hydrocarbons) and a low proportion of MOAH (mineral oil aromatic hydrocarbons). MOSH and MOAH comprise a variety of chemically similar single substances with straight or branched chains. In the context of precautionary consumer protection, it is crucial to determine hydrocarbons from mineral oil origin of inferior quality quickly and efficiently. This publication presents a rapid method for quantifying MOAH by proton nuclear magnetic resonance spectroscopy (1H qNMR) in anhydrous cosmetics such as lipstick, lip gloss, and lip balm. A sample clean-up using solid-phase extraction (SPE) was developed for the complete removal of interfering aromatic substances to improve the robustness of the method for analysing compounded cosmetics. In preliminary trials using silica gel thin-layer chromatography, the retention behaviour of 21 common aromatic compounds was tested in eluents with different solvent strength including EtOAc, MeOH, cyclohexane, and dichloromethane. Based on these results, the SPE sample cleanup with silica gel and cyclohexane as an eluent was suggested as best suitable for the purpose. The SPE cleanup was successfully achieved for all tested potentially interfering aromatic cosmetic ingredients except for butylated hydroxytoluene. The recovery for lipophilic cosmetics is more than 80% based on naphthalene as calculation equivalent. Furthermore, a specific sample preparation for the examination of lipsticks was implemented. The SPE cleanup was validated, and the robustness of the method was tested on 57 samples from the retail trade. The 1H qNMR method is a good complement to the LC-GC-FID method, which is predominantly used for the determination of MOSH and MOAH. Chromatographic problems such as migration of MOSH into the MOAH fraction during LC-GC-FID can be avoided.
The term “mineral oil hydrocarbons” summarizes a complex combination of numerous saturated and aromatic chemically similar hydrocarbons. Mineral oil raw materials are used in cosmetics in different consistencies, for example, as liquid oil or solid wax. They are classified according to their consistency into the groups listed in Table
Classification of mineral oil raw materials according to their consistency.
Common INCI name of mineral oil raw materials | Description (considering EC CosIng database) |
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Mineral oil | Typically used as a general term for derived products from raw oil refinement (often petrolatum). |
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Paraffinum liquidum | “White mineral oil (petroleum), a highly refined petroleum mineral oil consisting of a complex combination of hydrocarbons.” It mainly consists of saturated hydrocarbons (having carbon numbers in the range of C15–C50). |
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Hydrogenated mineral oil/distilled petrolatum | The end product of the controlled hydrogenation of hydrocarbons from mineral oil origin. |
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Paraffin | “A solid mixture of hydrocarbons obtained from petroleum characterized by relatively large crystals.” |
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Cera microcristallina/microcristalline wax | Hydrocarbon waxes and paraffin waxes of long, branched chain hydrocarbons. Predominantly saturated straight and branched chain hydrocarbons > C35. |
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Petrolatum | Complex combination of hydrocarbons. It mainly consists of saturated crystalline and liquid hydrocarbons (carbon number predominantly > C25). |
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Ozokerite | A complex combination of hydrocarbons. It mainly consists of saturated straight chain hydrocarbons (carbon numbers predominantly in the range of C20–C50). |
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Ceresin | “A complex combination of hydrocarbons produced by the purification of ozokerite.” |
Hydrocarbons from mineral oil origin are often used in cosmetics due to their different positive properties, such as good skin compatibility, good cleaning performance, and high stability. These substances are subject to mandatory declaration requirements and are indicated in the ingredients list as mineral oil, paraffin, paraffinum liquidum, petrolatum, cera microcristallina (microcrystalline wax), ceresin, or ozokerite (Table
Analytically, hydrocarbons are usually divided into two groups: MOSH (mineral oil saturated hydrocarbons) and MOAH (mineral oil aromatic hydrocarbons). MOSH consists of saturated aliphatic and cyclic hydrocarbons and MOAH of aromatic partially hydrogenated and highly alkylated compounds. In general, MOSH and MOAH are determined as sum parameters using convention methods (e.g., by LC-GC-FID). Toxic polycyclic aromatic compounds may not be contained, specifically potentially carcinogenic 3–7 ring polycyclic aromatic hydrocarbons (PAH). They need to be removed by a comprehensive refining process to fulfil the prerequisites of the European cosmetics regulation EC/1223/09. Mineral oils used in cosmetics often also meet the purity requirements for medicinal products, i.e., they are in compliance with Pharmacopeia standards [
In terms of precautionary consumer health protection and in the light of a large variety of mineral oil containing cosmetics, there is a need for efficient methods for characterizing the profile of mineral oil in cosmetic products. The aim is to distinguish high-quality mineral oil hydrocarbons (pharmaceutical, cosmetic, or food-grade mineral oil) from less refined hydrocarbons (technical-grade mineral oil material) and to check the compliance with the European regulations. According to the current state of the art, different analytical methods are used, for example, online coupled high-performance liquid chromatography-gas chromatography-flame ionization detection (LC-GC-FID), comprehensive two-dimensional gas chromatography-mass spectroscopy (GCxGC-MS), and nuclear magnetic resonance spectroscopy (NMR). A recently published review provides an overview of the current state of literature about the methods for detecting MOSH and MOAH in food, food contact materials, tissues, and cosmetics [
From the available methods, LC-GC-FID is currently the most widely used procedure for the analysis of mineral oil hydrocarbons. This method uses the excellent separation performance of liquid chromatography (HPLC) to separate the hydrocarbons into saturated and aromatic hydrocarbons, predominantly MOSH and MOAH. Each single fraction is then separated by online coupled gas chromatography and detected by flame ionization detection (GC-FID) according to the volatility and carbon amount of the substances. As a result of the complex composition of mineral oils, no separated peaks but so-called humps are obtained, which still provide a relatively characteristic profile for the different mineral oil compositions [
The chromatographic methods described above separate mineral oil hydrocarbons by the different elution force of the compounds. The proton NMR spectroscopy separates a sample into different signal areas based on the individual atom’s electronic environment. For the MOAH fraction, the spectral aromatic region between
In our experience, the quantitative 1H NMR spectroscopy is a good complement to the LC-GC-FID method. It is useful as a simple screening tool to get information about the MOSH/MOAH distribution. By this evaluation, the MOSH/MOAH ratio can be estimated and migration of MOSH into the MOAH fraction as evident in the LC-GC method can be circumvented. The LC-GC-FID method elutes firstly MOSH and then MOAH. The typically large excess of MOSH in cosmetic products (>99.5% [
Nevertheless, the previously described NMR procedure [
Cyclohexane SupraSolv, TLC silica gel 60 F254 plates, and silica gel (40, 0.063–0.200 mm) were purchased from Merck (Darmstadt, Germany). Acetone-d6 from Eurisotop D009H (Gif sur Yvette Cedex, France). Syringe filters with PET membranes (Chromafil Xtra PET-20/25 0.2
TLC was used to determine the appropriate eluent for the solid-phase extraction (SPE) cleanup on the silica 60 stationary phase. As a test system, 21 common aromatic compounds were used (Table
Test compounds for the TLC investigation.
# | Substance | Function |
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1 | BHT | Antioxidant |
2 |
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Skin care agent |
3 | Retinol | Skin care agent |
4 | Coenzyme Q10 | Skin care agent |
5 | Dibutyl phthalate | Banned plasticizer |
6 | Benzophenone-3 | UV filter |
7 | 3-(4-methylbenzylidene)camphor | UV filter |
8 | Ethylhexyldimethyl PABA | UV filter |
9 | Amylcinnamal | Perfuming |
10 | Benzyl alcohol | Perfuming, preservative |
11 | Methyl eugenol | Perfuming |
12 | Coumarin | Perfuming |
13 | Sorbic acid | Preservative |
14 | Phenyl salicylate | Perfuming |
15 | Benzophenone | UV filter |
16 | Methylparaben | Preservative |
17 | Butylparaben | Preservative |
18 | CI 11710 | Colour |
19 | CI 26100 | Colour |
20 | CI 47000 | Colour |
21 | CI 61565 | Colour |
All 1H NMR measurements were performed using a Bruker Ascend 400 spectrometer (Bruker Biospin, Rheinstetten, Germany) equipped with a 5 mm SEI probe PA BBI 400S1 with Z-gradient coils and a Bruker automatic sample changer (Sample Xpress, Bruker Biospin). All spectra were acquired at 300.0 K. The spectra (for samples dissolved in 120
For the robustness of the 1H qNMR method, it is crucial that all aromatic compounds except mineral oil aromatic hydrocarbons are removed during sample preparation. The sample cleanup depends on the matrix, as shown in Table
qNMR-analysis of pure mineral oil cosmetics and lipophilic cosmetics with further aromatic ingredients.
Pure mineral oil cosmetics [ |
Lipophilic cosmetics with further aromatic ingredients | |
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Cleanup step (SPE) | No | Yes. For lipstick/solid lip products, an additional preparation step to ensure homogeneity has to be carried out in advance. |
Solvent | CDCl3/TMSa | Cyclohexane |
Temperature | 55°C (bp CDCl3: 61°C) | 75°C (bp cyclohexane: 81°C) |
Sample solution for NMR | 600 |
480 |
Analytes | MOSH and MOAH | MOAHb |
a0.1% tetramethylsilane. bMOSH signals are interfered by cyclohexane suppression.
Sample preparation for pure hydrocarbons from mineral origin and hydrocarbon-containing cosmetics without further aromatic ingredients can be conducted as previously published [
Most cosmetic products contain, in addition to mineral oil aromatic hydrocarbons, other aromatic compounds, such as BHT, which would interfere with the 1H qNMR measurement (Table
As additional preparation step for lipstick, the following two steps have to be carried out to ensure homogeneity of the sample. A cross section of the lipstick is cut from the core of the product (2-3 mm from the edge), and a peanut-sized potion is scraped out (Figure
Additional preparation step for lipstick. (a) Removal from the lipstick; (b) filled with a spatula to homogeneity.
For the validation of lip cosmetics, 3 lip cosmetics with different consistency were chosen: an intensely colored lipstick (solid product), a lip balm (creamy product), and a colored lip gloss with glitter particles (liquid product). First, all cosmetic agents were analysed for their MOAH content by 1H qNMR spectroscopy. For all 3 products, this was below the detection limit of 0.03 g MOAH/100 g sample. Therefore, all 3 products were suitable for spiking experiments according to the preparation specified in Table
Creation of the validation series samples.
Matrix | Spiking procedure |
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Lip balm | Adding and melting in a water bath at 60°C. |
Lip gloss | Adding and melting in a water bath at 60°C. |
Intensive colored lipstick | 1. Weigh lipstick, melt, and cool |
2. Weigh vaseline and adding to the lipstick | |
3. Melting together in a water bath at 70°C. |
INCI for the matrices used for validation.
Matrix | INCI |
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Lip balm |
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Lip gloss | Polyisobutene, hydrogenated polyisobutene, paraffin, cera alba, cera microcristallina, tocopheryl acetate, parfum, limonene, linalool, [±]mica, silica, tin oxide, calcium aluminium borosilicate, aluminium hydroxide, CI 15850, CI 75470, CI 77491, CI 77492, CI 77499, CI 77891 |
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Intensive colored lipstick | Pentaerythrityl tetraisostearate, polybutene, octyldodecanol, bis-diglyceryl polyacyladipate-2, tridecyl trimellitate, cera microcristallina, polyethylene, trimethylsiloxyphenyl dimethicone, mica, |
A vaseline of known MOAH content was added to each matrix (additive weighing). The vaseline was stirred into the cosmetic product by melting the matrix (Table
Validation lip balm.
Validation points | Target value (MOAH) (g/100 g) | Weighted sample (mg) | Actual value (MOAH) (g/100 g) | Recovery (%) |
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P1 | 0.00 | 50.90 | 0.00 | 100.00 |
P2 | 0.08 | 49.70 | 0.07 | 88.71 |
P3 | 0.14 | 49.80 | 0.13 | 88.83 |
P4 | 0.22 | 50.60 | 0.20 | 89.64 |
P5 | 0.37 | 51.90 | 0.35 | 95.41 |
P6 | 0.51 | 49.40 | 0.49 | 94.57 |
P7 | 0.71 | 51.60 | 0.70 | 98.75 |
P8 | 0.90 | 51.00 | 0.86 | 95.90 |
P9 | 1.19 | 51.30 | 1.15 | 96.38 |
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P1 | 0.00 | 50.90 | 0.00 | 100.00 |
P2 | 0.08 | 51.10 | 0.07 | 88.58 |
P3 | 0.14 | 50.00 | 0.12 | 86.34 |
P4 | 0.22 | 50.50 | 0.20 | 89.02 |
P5 | 0.37 | 49.90 | 0.33 | 89.47 |
P6 | 0.51 | 50.90 | 0.47 | 92.13 |
P7 | 0.71 | 51.10 | 0.67 | 94.48 |
P8 | 0.90 | 50.80 | 0.79 | 87.47 |
P9 | 1.19 | 51.40 | 1.15 | 96.51 |
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P1 | 0.00 | 51.20 | 0.00 | 100.00 |
P2 | 0.08 | 50.90 | 0.04 | 50.31 |
P3 | 0.14 | 50.10 | 0.10 | 65.86 |
P4 | 0.22 | 52.30 | 0.18 | 79.93 |
P5 | 0.37 | 51.60 | 0.32 | 86.83 |
P6 | 0.51 | 51.00 | 0.48 | 93.54 |
P7 | 0.71 | 50.50 | 0.68 | 95.97 |
P8 | 0.90 | 51.90 | 0.91 | 100.62 |
P9 | 1.19 | 51.30 | 1.14 | 95.72 |
Validation lipstick.
Validation points | Target value (MOAH) (g/100 g) | Weighted sample (mg) | Actual value (MOAH) (g/100 g) | Recovery (%) |
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P1 | 0.01 | 48.70 | 0.01 | 96.59 |
P2 | 0.05 | 50.50 | 0.05 | 102.21 |
P3 | 0.14 | 51.70 | 0.15 | 106.20 |
P4 | 0.20 | 50.90 | 0.18 | 94.97 |
P5 | 0.34 | 49.60 | 0.34 | 100.11 |
P6 | 0.51 | 50.00 | 0.48 | 95.22 |
P7 | 0.70 | 52.30 | 0.66 | 95.63 |
P8 | 0.90 | 50.40 | 0.84 | 93.38 |
P9 | 1.19 | 51.50 | 1.08 | 91.09 |
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P1 | 0.01 | 51.20 | 0.01 | 72.89 |
P2 | 0.05 | 50.30 | 0.02 | 42.31 |
P3 | 0.14 | 51.00 | 0.07 | 53.03 |
P4 | 0.20 | 50.50 | 0.14 | 69.88 |
P5 | 0.34 | 52.50 | 0.30 | 86.73 |
P6 | 0.51 | 50.20 | 0.43 | 84.59 |
P7 | 0.70 | 51.10 | 0.59 | 84.70 |
P8 | 0.90 | 51.20 | 0.72 | 80.21 |
P9 | 1.19 | 50.80 | 0.95 | 80.16 |
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P1 | 0.01 | 50.20 | 0.01 | 126.14 |
P2 | 0.05 | 50.20 | 0.04 | 90.86 |
P3 | 0.14 | 51.70 | 0.11 | 75.07 |
P4 | 0.20 | 51.30 | 0.14 | 74.08 |
P5 | 0.34 | 48.60 | 0.29 | 87.17 |
P6 | 0.51 | 50.70 | 0.48 | 95.50 |
P7 | 0.70 | 51.10 | 0.68 | 97.58 |
P8 | 0.90 | 52.30 | 0.88 | 97.78 |
P9 | 1.19 | 53.20 | 1.07 | 90.17 |
Validation lip gloss.
Validation points | Target value (MOAH) (g/100 g) | Weighted sample (mg) | Actual value (MOAH) (g/100 g) | Recovery (%) |
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P1 | 0.00 | 51.70 | 0.00 | 185.71 |
P2 | 0.04 | 53.70 | 0.02 | 50.60 |
P3 | 0.11 | 49.60 | 0.06 | 52.03 |
P4 | 0.19 | 50.30 | 0.14 | 74.14 |
P5 | 0.34 | 49.80 | 0.30 | 89.09 |
P6 | 0.49 | 51.30 | 0.41 | 84.12 |
P7 | 0.69 | 52.60 | 0.60 | 87.44 |
P8 | 0.88 | 50.90 | 0.79 | 89.25 |
P9 | 1.19 | 53.70 | 1.03 | 86.91 |
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P1 | 0.00 | 49.40 | 0.00 | 64.29 |
P2 | 0.04 | 52.20 | 0.02 | 44.80 |
P3 | 0.11 | 51.20 | 0.09 | 81.92 |
P4 | 0.19 | 50.00 | 0.15 | 79.02 |
P5 | 0.34 | 51.70 | 0.29 | 86.12 |
P6 | 0.49 | 49.60 | 0.47 | 96.10 |
P7 | 0.69 | 49.80 | 0.63 | 91.07 |
P8 | 0.88 | 51.20 | 0.78 | 88.33 |
P9 | 1.19 | 50.30 | 1.07 | 90.29 |
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P1 | 0.00 | 51.40 | 0.00 | 314.29 |
P2 | 0.04 | 50.90 | 0.02 | 39.68 |
P3 | 0.11 | 51.20 | 0.07 | 64.49 |
P4 | 0.19 | 51.90 | 0.15 | 74.91 |
P5 | 0.34 | 51.20 | 0.26 | 77.18 |
P6 | 0.49 | 50.30 | 0.40 | 81.00 |
P7 | 0.69 | 50.50 | 0.55 | 79.79 |
P8 | 0.88 | 51.00 | 0.68 | 77.24 |
P9 | 1.19 | 51.60 | 1.00 | 83.97 |
The retention behaviour of 21 frequently used aromatic ingredients (Table
Based on the results of thin-layer chromatography, the SPE cleanup for silica gel/cyclohexane was developed. To check the robustness of the SPE cleanup, the breakthrough rate was screened for some frequently used cosmetic ingredients (Table
Breakthrough rates of aromatic ingredients frequently used in cosmetics with signals in the chemical shift region integrated for MOAH determination (
INCI | Function in cosmetics | Breakthrough rate (%)a |
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Benzyl benzoate | Antimicrobial, perfuming, solvent | 0.2 |
BHA | Antioxidant, masking | 0.0 |
BHT | Antioxidant, masking | 90 |
Tocopherol | Antioxidant, masking, skin conditioning | 0.5b |
Phenoxyethanol | Preservative | 0.0 |
Methylparaben | Preservative | —c |
Ethylparaben | Preservative | —c |
Propylparaben | Preservative | —c |
Benzophenone-3 | UV filter/absorber | 0.0 |
Octocrylene | UV filter/absorber | 0.0 |
Ethylhexyl methoxycinnamate | UV filter/absorber | 0.0 |
aDetermined by comparison of 1H NMR results with and without SPE cleanup. bDetermined in a mixture of 70% tocopherol and 30%
The breakthrough rates of these critical ingredients provide information about the robustness of the implemented SPE cleanup step. As shown in Table
NMR spectra of a mineral oil sample containing 5% of 3-(4-methylbenzylidene)camphor. The blue 1H NMR spectra show the signals of a direct measurement in cyclohexane/acetone-d6, while the red spectra represent the result of the same sample following SPE cleanup. The aromatic light filter is not detectable following SPE.
NRM spectra of a lip gloss sample. The blue 1H NMR spectra show the signals of a direct measurement in cyclohexane/acetone-d6, while the red spectra represent the result of the same sample following SPE cleanup. The interfering signals in the range 8.2–7.2 ppm are completely removed.
This situation is different with butylated hydroxytoluene (BHT), a frequently used antioxidant with additional masking functions. It can reduce oxidant reactions and the intrinsic smell and taste (lipstick) of a product to improve its storage life and scent. Owing to the two tert-butyl groups strongly shielding the hydroxyl group, BHT elutes almost entirely resulting in more than 90% breaking through. The steric hindrance leads to visible signals for BHT even at the commonly low concentrations in cosmetic products. A comparison to the structural and functional similar butylated hydroxyanisole (BHA) shows that the steric hindrance is obviously only given with more than one tert-butyl group as the aromatic BHA signals were missing after the cleanup (Figure
Comparison of BHT (a) and BHA (b). The blue 1H NMR spectra show the signals of a direct measurement in cyclohexane/acetone-d6, while the red spectra represent the result of the SPE cleanup. While BHA is completely removed by SPE, a considerable amount of BHT remains.
Lipsticks were found to be challenging to analyse due to homogeneity issues. These may arise during the production process of lipsticks. The shape of lipsticks is achieved by pouring the hot mass into special silicone or metal casting molds. When the lipstick cools down in the casting mold, different temperature zones are created, which can lead to inhomogeneity with respect to the composition of the pencil as a result of the flow behaviour. The process of shaping itself can also contribute to the inhomogeneity of the surface. The potential inhomogeneity within a lipstick is irrelevant to the user of the product, but may be relevant to the comparability of analytical results. In an experiment, 12 lipsticks and 12 lip care sticks were examined with regard to the homogeneity of MOSH and MOAH. For this purpose, for each lip product, at 3 different points of the lipstick, a sample was taken (from the surface of the lipstick to the core). Figure
Homogeneity experiment of 36 samples from 12 lipsticks. MOSH (a) test statistic = 7.27, f(0.95) = 2.22, and the result is highly significant inhomogeneous; MOAH (b) test statistic = 1.09, f(0.95) = 2.22, and the result is homogenous.
The results are shown for 3 lipsticks that in the first experiment exhibited results strongly deviating from each other. It turns out that the same lipstick leads to homogeneous results with suitable sample preparation (Figure
Homogeneity experiment of 3 strongly scattering lipsticks from the previous experiment (Figure
Three experimental runs were carried out, each at nine concentration levels with varying different parameters (first, matrix; second, NMR spectrometer; and third, sample preparation). For each particular run, an individual blank matrix was used for spiking: a liquid product (lip gloss), a creamy lip balm, and a solid product (lipstick). The validation series were measured on two different NMR spectrometers (400 MHz) to include the variation of the devices during validation (second robustness criteria). The 3rd robustness criterion takes into account the sample cleanup (as described in Section
Linear weighted regressions for the matrices lip gloss, lip balm, and lipstick. Plot: detected content of MOAH in g/100 g as a function of spiked content of MOAH in g/100 g, 0.95 prediction bands.
Linear weighted regressions for the matrices lip gloss, lip balm, and lipstick. Plot: MOAH recovery (%) as a function of spiked content of MOAH in g/100 g.
MOAH uncertainty (%) as a function of result of MOAH in lip products.
A 95% prediction band of 0.02 to 0.05 g MOAH/100 g for a spiked MOAH content of 0.05 g/100 g and a 95% prediction band of 0.91 to 1.27 g MOAH/100 g for a spiked MOAH content of 1.19 g/100 g are shown in Figure
In order to determine the purity and quality of raw materials from mineral oil origin, photometric methods are still often applied, e.g., Ph. Eur. [
Figure
Comparison of the methods Ph. Eur. 9 and 1H qNMR for 13 vaseline samples (blue: pharmaceutical quality; red: technical quality).
All samples appeared to be in conformity with the Ph. Eur. standard requirements although the MOAH contents varied between 0.06 and 1.10 g/100 g. This goes in line with the Ph. Eur. labelling of 9 of the examined vaseline (blue). The remaining four were of technical grade (red) usually containing more aromatic compounds than highly refined mineral oil raw materials.
There is no obvious correlation between the two differing methods as higher MOAH contents do not always correspond with high absorbance maxima and vice versa. Furthermore, technical-grade products do not stand out with higher MOAH contents as this is, e.g., also influenced by the degree of alkylation of aromatic rings in NMR measurements.
Different lip products from the retail trade were purchased as test products, and their MOAH content was analysed. As already presented in the validation concept (Section
MOAH content in g/100 g sample for a selection of retail lip products. Classification according to the consistency (red–liquid; blue–creamy; green–solid).
Figure
Categorization of MOAH content among lip cosmetics.
MOAH (g/100 g) | Number of lip products | Percentage | Percent solid/creamy/liquid |
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≤0.1 | 36 | 63 | 58/14/28 |
0.1–0.4 | 13 | 23 | 54/31/15 |
≥0.4 | 8 | 14 | 0.0/13/88 |
As demonstrated, most of the polar aromatic compounds such as aldehydes, carboxylic acids, and their esters, as well as alcohols differ significantly from MOAH in their chemical structure or polarity and hence are well retained during SPE due to their interactions with the hydrophilic groups of the deployed silica gel and can be removed by a matrix-based cleanup. Only for sterically very demanding compounds, a breakthrough rate is recorded. The comparative investigation of BHT and BHA shows that BHA retards well despite a sterically demanding tri-tert-butyl group. Only the strongly shielded BHT with two tri-tert-butyl groups shows poor elution behaviour and cannot be separated from MOAH by the SPE cleanup.
In conclusion, the proposed SPE cleanup enables the determination of MOAH for anhydrous cosmetic agents (e.g., lip care products) by 1H qNMR spectroscopy as an important element amongst others such as LC-GC-FID to quantify MOAH-equivalents. In future, it will be essential to characterize MOAH fractions using those elements and hopefully gaining more information about the composition of those fractions by more specific methodologies.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
The authors are grateful to Jürgen Geisser for excellent technical assistance. The authors thank Andreas Scharinger for compilation of NMR figures.