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Determination of nitrosamines in skin care cosmetics using Ce-SBA-15 based stir bar-supported micro-solid-phase extraction coupled with gas chromatography mass spectrometry
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
xCe-SBA-15 sorbents were used in SB-µ-SPE of nitrosamines in cosmetic. 5-Ce-SBA-15 showed better extraction performance. All extraction parameters were fully optimized. Satisfactory analytical figures of merit were obtained.
Abstract
Improvement for nitrosamine detections, particularly in consumables and products applied to skin is a growing area of research due to implications of nitrosamines on human health. In this study, mesoporous silica, SBA-15 was doped with various ceria loadings and used in the stir bar-supported micro-solid-phase extraction (SB-µ-SPE) of nitrosamines in cosmetic samples. The synthesized sorbents were characterized using field emission scanning electron microscopy and energy dispersive X-ray spectrometry. The effects of extraction variables (sorbent type and amount; desorption time, solvent, and volume; extraction time; and ionic strength) were determined. This newly improved method provides good linear range (R2 value up to 0.9985) and trace detection (2.7–3.4 ng mL−1). Relative standard deviation (RSD) values determined at different concentration levels ranged between 2.3 and 8.0%, and the screened sorbent shows excellent regeneration ability for four cycles. With this developed Ce-SBA-15 based stir bar-supported micro-solid-phase extraction, trace levels of nitrosamines can be detected in matrices that are commonly encountered by humans.
Keywords
Stir-bar supported micro solid phase extraction
Nitrosamines
Cosmetic samples
Mesoporous silica
GC/MS
1 Introduction
Nitrosamines (NAs) are class of highly carcinogenic (IARC, 1999) organic compounds with the structural formula RN⚌(—R′)—N⚌O. With risk index of grade B2 for human health damage, the Environmental Protection Agency (EPA) of the United States reported that NAs, particularly N-nitrosodimethylamine, are carcinogenic at concentrations even as low as 0.7 ng L−1 (N-Nitrosodimethylamine). Since NAs are invariably present in many foods and consumables, and because their synthesis occurs via both in vitro (chemical pathway) and in vivo (biological pathway), there is urgent need for increasing research in their detection.
The rising social and societal disquiet about health and beauty has recently resulted in a remarkable increase in the use of cosmetic products. Although many international regulatory bodies have banned the use of NAs in cosmetic products, research have shown that trace levels of NAs still exist in cosmetics. Because nitrogen containing compounds such as amino acids and amides are ingredients in cosmetics, it is of no surprise that these trace amounts of NAs are being detected in the cosmetics (Choi et al., 2016; Liu et al., 2016). In addition, the preservatives used in cosmetics are mostly nitrogen containing compounds which could also undergo nitrosation to form NAs. Though the NAs may not be directly used in the production of these cosmetics, these carcinogenic organic compounds may still come into contact and be absorbed via human skin, thus posing a great health threat to individuals (Ma et al., 2011).
Until recently, the primary focus for NAs detection has mainly been on food, potable water, and environmental matrices (Andrade et al., 2005; Herrmann et al., 2014; Huang et al., 2013). The conventional detection method has been gas chromatography coupled with various detectors such as flame ionization detector (FID), thermal conductivity detector (TCD), nitrogen-phosphorus detector (NPD) and mass spectrometry (MS). Additionally, the use of liquid chromatography coupled with MS has also been reported (Ripollés et al., 2011; Kim and Shin, 2013). However, due to the low concentration levels and sample matrix complexity, there is need to develop methods for extraction and preconcentration of the target NAs prior to their instrumental analyses.
Traditional extraction methods are limited both in their efficacy in their costs and time. Typically, liquid-liquid extraction (LLE) and solid-phase extraction (SPE) and the equilibrium-based solid phase microextraction (SPME) and micro solid phase extraction (µ-SPE) have been used to detect NAs, but LLE and SPE consume a large quantity of toxic solvents and are generally tedious and time-consuming. On the other hand, SPME and µ-SPE are both characterized by low solvent usage and are less time consuming, but SPME is relatively more expensive (Shen et al., 2006; Shi and Lee, 2010).
Traditionally, in µ-SPE, a small amount of adsorbent is packed in a polypropylene (PP) membrane and then sealed with a heater, and this construction allows extraction even in a complex matric system since only target analyte diffuses in and out of the PP membrane. After extraction, the target analyte is desorbed by dipping the PP membrane into a suitable desorption solvent by sonication. Although µ-SPE is an ideal method for extracting NAs, it still could be improved upon by eliminating the problems associated with the floating of the packed sorbent on the surface of adsorbate-containing solution or its sticking to the wall of flask. To overcome these issues, A recently improved approach of µ-SPE, termed stir-bar supported µ-SPE (SB-µ-SPE) was introduced. In this approach, a mini-stir-bar is packed inside the PP membrane along with the sorbent. This has not only solved the aforementioned problems but has also increased the rate of mixing of the adsorbate with the packed sorbent through continuous stirring and rotating of the sorbent due to the inserted stir-bar. Overall, an increased adsorption efficiency was reported through this approach (Sajid and Basheer, 2016).
Porous silica materials such as SBA-15 (Jahandar Lashaki et al., 2017) and zeolites (Alver and Metin, 2012) have proven to be excellent materials for adsorption of both liquid and gaseous analytes in various complex matrices. These favorable adsorption properties are due to their large surface area; porosity; and chemical, thermal and mechanical stabilities. In addition, SBA-15 is exceedingly cheap and easily accessible. Modification of the SBA-15 through functionalization or metal loading have shown significant improvement in its adsorption properties. Wang et al. reported the functionalization of SBA-15 with amino groups using aminopropyltriethoxysilane and the advantage of using it for removal of lead (Wang et al., 2015). Because of their basic properties, a series of primary, secondary, and tertiary amines were also grafted on SBA-15 and utilized in the adsorption of CO2 in several recent studies. For example, by using in situ FTIR spectroscopy to elucidate the surface species formed on the amine-grafted SBA-15 following adsorption of CO2, it was confirmed that monomeric and dimeric carbamic acid species were formed on secondary amines (Foo et al., 2017). Hydrothermal stability of triamine-grafted SBA-15 for CO2 adsorption was also studied using steam stripping, and it was reported that steaming resulted in reduced surface area of the functionalized SBA-15, although no amine leaching was recorded from FTIR and thermogravimetric analysis (Jahandar Lashaki et al., 2017). In addition, CO2 adsorption on triamine-grafted SBA-15 was found to be dependent on the textural properties (pore size and volume) of the SBA-15 support (Jahandar Lashaki and Sayari, 2018). Two-step modification of SBA-15 nanoparticles by first coating with anionic surfactant sodium dodecyl sulfate followed by immobilization of diphenylcarbazone forms a nanocomposite that was used to remove trace amount of Cu2+ and Zn2+ in water, herbal and food samples (Mirabi et al., 2018). Xu loaded Mn and AgMn on SBA-15 by impregnation method and used it in the adsorption and catalytic conversion of toluene (Xu et al., 2016). The CO2 adsorption capacity of SBA-15 has also been significantly enhanced after loading the SBA-15 with zirconia (Thunyaratchatanon et al., 2017). The enhanced performance is attributed to the increase in the microporous surface area and microporous volume that was created by the incorporation of zirconia into the Zr-SBA-15. Similarly, ceria, a lanthanide series element, can be incorporated to the framework of SBA-15 and employed in the SB-µ-SPE method for extraction of the following nitrosamines: N-Nitrosodiethylamine (NDEA), N-Nitrosodipropylamine (NDPA), N-Nitrosopiperidine (NPP), N-Nitrosodibutylamine (NDBA) and N-Nitrosodiphenylamine (NDPhA).
2 Experimental
2.1 Chemical and materials
All the studied nitrosamines standards were purchased from SUPELCO Analytical. ACS reagent grade ceric ammonium nitrate was procured from Riedel-de Haen AG, USA. Tetraethylorthosilicate (reagent grade 98%) was purchased from Sigma-Aldrich. Accruel polypropylene (PP) sheet membrane (pore size of 0.2 µm, 157 µm thickness) was purchased from Membrana (Wuppertal, Germany). Analytical-grade high purity solvents (dichloromethane, methanol, acetone, n-hexane, cyclohexane and carbon tetrachloride) were obtained from Fisher (Loughborough, UK).
2.2 Synthesis of SBA-15 and Ce-SBA-15
2.2.1 Synthesis of SBA-15
Highly ordered mesoporous SBA-15 silica was synthesized in a highly acidic medium (pH < 1) as reported by Zhao et al. (1998). Briefly, 2 g of Pluronic (123) was dissolved in a mixture of 2 M HCl (60 g) and de-ionized water (15 g) at 40 °C. After complete dissolution of surfactant in acidic medium, 4.16 g of tetraethylorthosilicate (TEOS) as silica precursor was added and stirred for 20 h to complete the hydrolysis and condensation before hydrothermal synthesis. The whitish solution of silica was then transferred into Teflon autoclave for hydrothermal synthesis at 80 °C for additional 24 h before centrifuging and drying at 80 °C for 10 h. The as-prepared SBA-15 was subjected to calcination at 500 °C (ramping at 10 °C/min) for 5 h to remove the template and achieve highly ordered hexagonal mesoporous SBA-15.
2.2.2 Synthesis of ceria modified SBA-15
A series of cerium-modified SBA-15 at different Ce weight percent loading (1–10) was synthesized by incipient wetness impregnation of cerium precursor into the pores of SBA-15 at room temperature. The required amount of ammonium cerium(IV) nitrate was dissolved in de-ionized water and stirred at room temperature for 10 min before addition of calcined SBA-15. The mixture was stirred for additional 3 h at the same temperature before drying and calcination at 100 °C (8h) and 500 °C (5h), respectively. The final product after calcination was denoted x-Ce-SBA-15, where x represents the Ce weight percent.
2.3 Characterization
Morphology of adsorbents were recorded on a Field Emission Scanning Electron Microscope FESEM (TESCAN, LYRA 3) using a secondary electron (SE) and the back scattered electron (BSE) mode at an accelerating voltage of 20 kV. An attached energy dispersive X-ray spectrometer (EDS, Oxford Inc.) detector was employed for the subsequent determination of the elemental composition of the samples.
2.4 SB-µ-SPE procedure and optimization
SB-µ-SPE fabrication was followed according to Sajid and Bashir methodology (Sajid and Basheer, 2016). Briefly, a mini-stir-bar and 5.0–40.0 mg of SBA-15 and x-Ce-SBA-15 sorbents were packed inside a PP envelope of dimension 2.2 cm × 1.0 cm, and the edges were later sealed. Before extraction, the sorbents-packed SB-µ-SPE was suitably conditioned by sonicating for 5 min in toluene solvent. Later, the conditioned sorbents were dropped each in a 25 mL glass vial containing 10 mL of the sample solution of 100 µg L−1 concentration. The glass vials were then placed on a magnetic stirrer at a rate of 800 rpm for 30 min after which the sorbents were removed from the vials with forceps. The sorbents were then thoroughly mixed with water and dried with a tissue. Later, the sorbents were placed in a desorption vials followed by addition of 300 µL of methanol as desorption solvent. The desorption vials were then ultrasonicated for 20 min to elute the analytes in the desorption solvent. After desorption, the eluted analyte was injected into the GC–MS for analysis.
Optimization experiments were carried out using ultrapure water spiked at 100 µg L−1. Each optimization experiment was conducted for the five nitrosamines: NDEA, NDPA, NPP, NDBA and NDPhA. The amount of sorbent; desorption solvent, volume, and time; salting effect, and extraction time parameters were all optimized using a univariate approach. Extraction efficiency was evaluated based on chromatographic peak areas of the target analytes.
2.5 GC–MS
An Agilent 7890A GC-System coupled with MS-5975C inert MSD with a triple axis detector was used for identification and quantification of target analytes. The system is equipped with an Agilent (GC-Sampler 80) autosampler and injector. An Agilent 19091J-413 MS column with thickness of 0.25 µm, length of 30.0 m, and diameter of 0.32 mm was employed for separation of target analytes. High purity helium gas was used as carrier gas at a flow rate of 1.00 mL min−1. The GC injection port and GC–MS interface temperature were maintained at 250 °C, and the ion source temperature was fixed at 230 °C. The oven temperature was programmed as follows: initial temperature of 50 °C was held for 0.5 min and then ramped at 30 °C min−1 to 180 °C. The temperature was further increased to 210 °C at 7 °C min−1 and held for 1 min for a total run time of 10.119 min. Splitless injection mode was used to introduce analytes into the GC column throughout the study. For qualitative analysis, data acquisition was performed in scan mode to confirm the retention times of the target analytes, and for quantitative analysis, selective ion monitoring (SIM) mode was employed. The retention times and selected target ions are listed in Table S1.
Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.arabjc.2018.06.004.
An Agilent 7890A GC-System coupled with MS-5975C inert MSD with a triple axis detector was used for identification and quantification of target analytes. The system is equipped with an Agilent (GC-Sampler 80) autosampler and injector. An Agilent 19091J-413 MS column with thickness of 0.25 µm, length of 30.0 m, and diameter of 0.32 mm was employed for separation of target analytes. High purity helium gas was used as carrier gas at a flow rate of 1.00 mL min−1. The GC injection port and GC–MS interface temperature were maintained at 250 °C, and the ion source temperature was fixed at 230 °C. The oven temperature was programmed as follows: initial temperature of 50 °C was held for 0.5 min and then ramped at 30 °C min−1 to 180 °C. The temperature was further increased to 210 °C at 7 °C min−1 and held for 1 min for a total run time of 10.119 min. Splitless injection mode was used to introduce analytes into the GC column throughout the study. For qualitative analysis, data acquisition was performed in scan mode to confirm the retention times of the target analytes, and for quantitative analysis, selective ion monitoring (SIM) mode was employed. The retention times and selected target ions are listed in Table S1.
Supplementary data 1
Supplementary data 12.6 Method validation and analysis of real samples
The linearity, limit of detection (LODs), repeatability, and relative recoveries studies were performed in order to validate the optimized experimental conditions. Six-point calibration points for plotting all target analytes were generated by using ultrapure water samples spiked with known concentrations (10–1000 µg L−1) of NAs. The developed method was used for analysis of nitrosamines in cosmetics. For real sample analysis, 5 g of the cosmetic samples was dissolved in ultra-pure water. Similarly, the spiked cosmetic samples were prepared and extracted. This sample solution was used for extraction of nitrosamines using the previously described sorbents.
3 Results and discussion
3.1 Field emission scanning electron microscope (FESEM)
The morphology of two adsorbents, SBA-15 and 5-Ce-SBA-15 were recorded from the FESEM analysis. The image of 5-Ce-SBA-15 Fig. 2) shows increased particle density when compared to Fig. 1 which has only SBA-15. This is an indication that ceria has been loaded to the SBA-15. Percent composition of the components obtained from the EDS result of the FESEM is presented alongside their images. Mapping of the elemental analysis of 5-Ce-SBA-15 shows that ceria is evenly distributed on the SBA-15.
Scanning electron microscope image of SBA-15 and the electron dispersive X-ray spectroscopy image showing the morphology and elemental composition of SBA-15 respectively.
Scanning electron microscope image of 5-Ce-SBA-15 and the electron dispersive X-ray spectroscopy image showing the morphology and elemental composition of 5-Ce-SBA-15 respectively.
3.2 Optimization of Ce-SBA-15 packed SB-µ-SPE
3.2.1 Sorbents screening
Four adsorbents, SBA-15, 1-Ce-SBA-15, 5-Ce-SBA-15 and 10-Ce-SBA-15 were subjected to PP membrane sorbent extraction of NAs, and their extraction efficiency was determined. The incorporation of ceria to SBA-15 continue to increase the extraction efficiency with ceria loading up to 5 wt% (Fig. S1). However, the efficiency decreased when the ceria loading reached 10 wt%. These efficacy patterns of increase in extraction efficiency due to ceria loading is most likely due to the Lewis acidity generated by incorporation of ceria to the SBA-15. However, at 10 wt% the ceria might have blocked the pores of the SBA-15, thereby hindering the diffusion of NAs compound to and from the adsorbents.
Four adsorbents, SBA-15, 1-Ce-SBA-15, 5-Ce-SBA-15 and 10-Ce-SBA-15 were subjected to PP membrane sorbent extraction of NAs, and their extraction efficiency was determined. The incorporation of ceria to SBA-15 continue to increase the extraction efficiency with ceria loading up to 5 wt% (Fig. S1). However, the efficiency decreased when the ceria loading reached 10 wt%. These efficacy patterns of increase in extraction efficiency due to ceria loading is most likely due to the Lewis acidity generated by incorporation of ceria to the SBA-15. However, at 10 wt% the ceria might have blocked the pores of the SBA-15, thereby hindering the diffusion of NAs compound to and from the adsorbents.
3.2.2 Amount of sorbent
The amount of sorbent is expected to have some effect on the efficiency of adsorption. Therefore, a range of 5–40 mg of 5-Ce-SBA-15 sorbent were packed in the PP membrane and their adsorption efficiency evaluated. The peak areas of the NAs increased up to 30 mg and then became constant for most of the nitrosamines, even though a slight decrease was observed for others Fig. 3). Hence, 30 mg was selected for further optimizations. This amount is relatively easy to pack inside the PP membrane along with a mini-stir-bar.
Effect of Amount of sorbent material, (5.0–40.0 mg): Conditions: Sample volume 10.0 mL, concentration 100 ng mL−1, salt addition 20% w/v, extraction time 30 min, desorption solvent methanol, desorption solvent volume 300 μL, desorption time 20 min.
3.2.3 Desorption solvent
The type of desorption solvent is a pre-requisite for efficient desorption. The primary factor to be considered in choosing such a solvent is its polarity. A good match between the polarities of the target analytes and the desorption solvent will result to efficient desorption. In this study, six desorption solvents: methanol, acetone, dichloromethane, tetrachloromethane, hexane and cyclohexane, with varying degree of polarity were used as desorption solvents. The best extraction performance was achieved with dichloromethane (Fig. S2) for all the NAs except NDPhA which was best extracted by acetone. The effects of the desorption solvents can be arranged in the following order based on their extraction efficiency taking into account all the desorbed analytes: dichloromethane > acetone > methanol > carbon tetrachloride > n-hexane > cyclohexane. This trend of solvent desorption is likely associated to the non-polar nature of the first four NAs as compared to NDPhA.
The type of desorption solvent is a pre-requisite for efficient desorption. The primary factor to be considered in choosing such a solvent is its polarity. A good match between the polarities of the target analytes and the desorption solvent will result to efficient desorption. In this study, six desorption solvents: methanol, acetone, dichloromethane, tetrachloromethane, hexane and cyclohexane, with varying degree of polarity were used as desorption solvents. The best extraction performance was achieved with dichloromethane (Fig. S2) for all the NAs except NDPhA which was best extracted by acetone. The effects of the desorption solvents can be arranged in the following order based on their extraction efficiency taking into account all the desorbed analytes: dichloromethane > acetone > methanol > carbon tetrachloride > n-hexane > cyclohexane. This trend of solvent desorption is likely associated to the non-polar nature of the first four NAs as compared to NDPhA.
3.2.4 Volume of desorption solvent
The volume of solvent used in desorbing analytes affects the efficiency and reproducibility of the desorption. In this work, volume of desorption solvent was evaluated in the range of 100–500 µL. Highest analytes desorption was obtained using 200 µL for all the nitrosamines (Fig. S3). For desorption volumes above 200 µL, the desorption efficiency decreased proportionally with increase in volume (Fig. S3). This decreased desorption is likely due to the fact that at a desorption volume <200 µL, there may be incomplete and poor immersion of the SB-µ-SPE device, and at 200 µL there is complete immersion of the sorbent device which result in preconcentration of the analytes. Desorption volumes >200 µL result in dilution of the analytes, hence the decreased desorption efficiency. Thus, 200 µL was selected as optimum desorption solvent for further experiments.
The volume of solvent used in desorbing analytes affects the efficiency and reproducibility of the desorption. In this work, volume of desorption solvent was evaluated in the range of 100–500 µL. Highest analytes desorption was obtained using 200 µL for all the nitrosamines (Fig. S3). For desorption volumes above 200 µL, the desorption efficiency decreased proportionally with increase in volume (Fig. S3). This decreased desorption is likely due to the fact that at a desorption volume <200 µL, there may be incomplete and poor immersion of the SB-µ-SPE device, and at 200 µL there is complete immersion of the sorbent device which result in preconcentration of the analytes. Desorption volumes >200 µL result in dilution of the analytes, hence the decreased desorption efficiency. Thus, 200 µL was selected as optimum desorption solvent for further experiments.
3.2.5 Salting out effect
Salting out effect is another important parameter that is optimized in the microextraction procedures. It involves addition of salt to the sample solution which leads to decrease in the solubility of the target analytes in the aqueous phase. This effect is more pronounced when the target analytes are polar compounds. In this study, 0.5–3 g of NaCl was added to the sample solution, and it was observed that maximum extraction of target analytes is achieved with 2.5 g of NaCl in all the NAs (Fig. S4). In addition, it was observed that the salting out effect is greater for NDPA and NDPhA, and this may be because of their chemical structure.
Salting out effect is another important parameter that is optimized in the microextraction procedures. It involves addition of salt to the sample solution which leads to decrease in the solubility of the target analytes in the aqueous phase. This effect is more pronounced when the target analytes are polar compounds. In this study, 0.5–3 g of NaCl was added to the sample solution, and it was observed that maximum extraction of target analytes is achieved with 2.5 g of NaCl in all the NAs (Fig. S4). In addition, it was observed that the salting out effect is greater for NDPA and NDPhA, and this may be because of their chemical structure.
3.2.6 Extraction time
For an equilibrium-based technique, the extraction of target analytes is generally expected to increase with an increase in extraction time until equilibration is achieved. After equilibration, extraction time should have no significant effect on the extraction process. In this study, the extraction times of 10–50 min were used to establish the optimum extraction time. Maximum extraction was achieved at 40 min Fig. 4). After that, no further increase in extraction was observed, therefore 40 min was adopted as the optimum extraction time.
Effect of extraction time (10–50 min): Conditions: Sample volume 10.0 mL, concentration 100 ng mL−1, desorption solvent volume 200 μL, desorption time 20 min, salt addition 25% w/v, weight of sorbent material 30 mg, Solvent: Dichloromethane.
3.2.7 Desorption time
Like extraction, the desorption time is also an important parameter in optimization of microextraction procedure. The desorption was performed by immersing the analyte-bound SB-µ-SPE in an organic solvent and sonicating. A time range of 5–30 min was used to investigate the effect of desorption time. Desorption efficiency increased with increasing time up to 15 min and then remained slightly stable Fig. 5; therefore, 15 min was chosen as the optimum desorption time.
Effect of desorption time (5–30 min): Conditions: Sample volume 10.0 mL, concentration 100 ng mL−1, desorption solvent volume 200 μL, extraction time 40 min, salt addition 25% w/v, weight of sorbent material 30 mg, Solvent: Dichloromethane.
3.3 Method validation and analysis of real samples
Good linearity was obtained for all the NA compounds under the optimized extraction and desorption conditions, with coefficient of correlation (R2) value between 0.9956–0.9985 Table 1). The limit of detection (LOD), which was determined based on the signal to noise ratio (S/N = 3), is between the range of 2.7–3.4 ng mL−1. Method precision was assessed by extracting samples spiked at 50, 250 and 750 ng mL−1 (n = 7), and their calculated relative standard deviations (RSDs) were recorded in the range of 2.3–8.0%. The enrichment factor of the studied NAs was within the range of 34–47. In addition, relative recoveries were also calculated from the cosmetic samples A and B to determine the matrix effect. The extraction ability was tested by spiking ultra-pure water and the cosmetic samples at 100 ng mL−1 (n = 3). Figs. 6 and 7 show the spectra of the spiked and unspiked cosmetics A and B respectively. Relative recoveries of all studied nitrosamines ranged between 80.5 and 100.5% as shown in Table 2. Compared to previous studies Table 3), the optimized extractions in this study result in better LOD, linear range, and percent recovery which means these techniques can extract nitrosamines at trace amount better than the previously reported methods. Additionally, this setup allows for NAs to be detected within a wide concentration range while also maintaining high percent recovery.
| Compound | Linear range (ng/mL) | R2 | LOD (ng/mL) | RSDs (%) (n = 7) | Enrichment Factors | ||
|---|---|---|---|---|---|---|---|
| 50 ng/mL | 250 ng/mL | 750 ng/mL | |||||
| NDEA | 10–1000 | 0.9963 | 3.2 | 8.0 | 3.7 | 4.5 | 38 |
| NDPA | 10–1000 | 0.9956 | 3.1 | 6.6 | 2.8 | 4.1 | 34 |
| NPP | 10–1000 | 0.9985 | 2.9 | 6.2 | 2.3 | 5.8 | 45 |
| NDBA | 10–1000 | 0.9971 | 3.4 | 7.6 | 4.3 | 6.6 | 42 |
| NDPhA | 10–1000 | 0.9980 | 2.7 | 7.3 | 4.0 | 5.4 | 47 |
- Cosmetic product A analysis: Unspiked (solid line) and spiked (dotted line). Conditions: 5.0 g product homogenized in 30.0 mL water, sample volume taken 10.0 mL, concentration spiked 100 μg mL−1, desorption solvent volume 200 μL, extraction time 40 min, salt addition 25% w/v, weight of sorbent material 30 mg, Desorption solvent: Dichloromethane, desorption time: 15 min.
- Cosmetic product B analysis: Unspiked (solid line) and spiked (dotted line). Conditions: 5.0 g product homogenized in 30.0 mL water, sample volume taken 10.0 mL, concentration spiked 100 μg mL−1, desorption solvent volume 200 μL, extraction time 40 min, salt addition 25% w/v, weight of sorbent material 30 mg, Desorption solvent: Dichloromethane, desorption time: 15 min.
| Nitrosamines | Matrix effect and extraction efficiency (Mean relative recoveries n = 3) |
|
|---|---|---|
| Cosmetics A Spiked 100 ng mL−1 (%) |
Cosmetic B Spiked 100 ng mL−1 (%) |
|
| NDEA | 80.5 | 99.5 |
| NDPA | 98.6 | 83.2 |
| NPP | 82.5 | 92.5 |
| NDBA | 95.6 | 90.5 |
| NDPhA | 100.1 | 100.5 |
| Compound | Choi et al. (2016)a | Liu et al. (2016)b | This studyc | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Correlation coefficient | LOD (ng/mL) | Recovery ± RSD 50 ng/mL | Correlation coefficient | LOD (ng/mL) | Linear range (ng/mL) | Correlation coefficient | LOD (ng/mL) | Linear range (ng/mL) | Recovery ± RSD 50 ng/mL for cosmetic A | |
| NDEA | 0.9983 | 36.08 | 63 ± 12 | 0.993 | 15 | 3–200 | 0.9963 | 3.2 | 10–1000 | 80.5 ± 8 |
| NDPA | 0.9977 | 2.30 | 82 ± 1 | 0.999 | 7 | 1–200 | 0.9956 | 3.1 | 10–1000 | 98.6 ± 6.6 |
| NPP | 0.9953 | 1.37 | 88 ± 2 | 0.995 | 7 | 1–200 | 0.9985 | 2.9 | 10–1000 | 82.5 ± 6.2 |
| NDBA | 0.9986 | 15.64 | 54 ± 9 | 0.996 | 7 | 1–200 | 0.9971 | 3.4 | 10–1000 | 95.6 ± 7.6 |
| NDPhA | – | – | – | 0.998 | 10 | 3–200 | 0.9980 | 2.7 | 10–1000 | 100.1 ± 7.3 |
4 Sorbent regeneration
Regeneration ability of 5-Ce-SBA-15 sorbent was studied by first washing the used sorbent with water and methanol, and the washed sorbent was later dried at 70 °C. It was observed that the recycled sorbent showed excellent extraction ability Fig. 8). This entails that the nitrosamines extraction properties were still retained after the regeneration treatment.
Regeneration of sorbent material: Conditions: sorbent material 30 mg, sample volume 10.0 mL, concentration of nitrosamines 100 μg mL−1, desorption solvent volume 200 μL, extraction time 40 min, salt addition 25% w/v, Desorption solvent: Dichloromethane, desorption time: 15 min.
5 Conclusion
Series of ceria doped SBA-15 has been synthesized and used as sorbents for the extraction of nitrosamines by SB-µ-SPE method. The sorbents were characterized using FESEM and the elemental composition was verified by EDS. All the parameters that can affect extraction performance of SB-µ-SPE were optimized. The extracted samples were analyzed by GC–MS. The LODs ranged between 2.7 and 3.4 ng mL−1. The SB-µ-SPE method also provides satisfactory precision with RSDs ranging between 2.3 and 8.0%, and excellent regeneration ability even after four cycles.
Acknowledgements
The author acknowledge support provided by King Fahd University of Petroleum and Minerals for funding this work through Project DSR NUS15105.
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