[Simultaneous determination of saturated and aromatic hydrocarbons in soil by on-line high performance liquid chromatography-gas chromatography].

To strengthen regulation for mitigating the risk posed by petroleum contaminants in soil, the Ministry of Ecology and Environment of the People's Republic of China has classified petroleum hydrocarbons as a key monitoring item for regulatory contamination monitoring. Petroleum is principally derived from petroleum and synthetic fuels, which contain an extremely high content of hydrocarbon compounds that have varied boiling points. These compounds are chemically classified primarily as saturated and aromatic. Aromatic hydrocarbons are typically highly alkylated monocyclic, bicyclic, and polycyclic, which are more toxic to human and animal life than saturated hydrocarbons. Because of the significant toxicological differences among the various hydrocarbons, it is difficult to accurately assess their environmental toxicity by only determining the total content of petroleum in soil. However, there are no analytical methods for the simultaneous determination of saturated hydrocarbons and aromatic hydrocarbons in soil according to Chinese standards. In this study, extraction and purification procedures were completely optimized depending on the matrix of the soil samples. The advanced analytical technique of on-line high performance liquid chromatography-gas chromatography (HPLC-GC) was performed after sample preparation for the simultaneous determination of saturated hydrocarbons and aromatic hydrocarbons in soil. For the extraction, n-hexane/ethanol (1∶1, v/v) was chosen as the extraction solvent. The ratio of solid sample (soil) to the solvent was chosen as 1∶4, and extraction was performed once at room temperature, for 1 h. Water was then added and mixed to remove ethanol from the extracts, and the upper n-hexane layer was separated; thus, the petroleum hydrocarbons in the samples were completely extracted. However, the oils and fats in the matrix of the soil sample were also simultaneously extracted. Because of the limited retention capacity of the HPLC column, the presence of oils, fats, and other interferents would affect the subsequent determination of saturated hydrocarbons and aromatic hydrocarbons. Therefore, an additional purification step is required before sample injection into the HPLC-GC equipment. In this study, purification was performed using a lab-made silica gel column, which is commonly used for the determination of saturated hydrocarbons and aromatic hydrocarbons in food. The purification column was conditioned and eluted with an 8∶2 ratio (v/v) of n-hexane to dichloromethane after sample loading. Subsequently, the eluent was concentrated and injected into the HPLC-GC equipment for analysis. The flame ionization detector (FID) is ideal for petroleum hydrocarbons quantification because of its nearly identical responses to all hydrocarbons; hence, with the FID, reference standards are not required for quantification, and internal standards are typically used for quantifying the total hydrocarbon content. In this study, cyclohexylcyclohexane (Cycy) and 2-methylnaphthalene (2-MN) were used as internal standards for determining the saturated and aromatic hydrocarbons, respectively. The limit of quantification (LOQ) of this proposed method was 0.4 mg/kg. Moreover, the suitability of the method was verified by comparing the obtained content against the soil petroleum hydrocarbon standard (SQC-116); the measured value was found to be within the credible interval provided by the standard. The relative error (RE) was 10.6% with a relative standard deviation (RSD) of 1.4%, which indicates that the proposed method is accurate and reliable, and the precision meets analytical requirements. Finally, the method was applied to the determination of hydrocarbons in five soil samples from the Beijing area. Saturated hydrocarbons (C10-C40) were detected in all five samples, with contents ranging from 3.3 to 32.1 mg/kg, while aromatic hydrocarbons (C10-C40) were detected in four samples, with contents ranging from 0.8 to 4.3 mg/kg. HPLC-GC combines the high selectivity of HPLC with the high separation efficiency of GC, and as demonstrated in this study, can be used for the simultaneous determination of saturated and aromatic hydrocarbons in soil. The source of hydrocarbon contamination can also be preliminarily identified by chromatographic analysis.

Survey of mineral oil hydrocarbons in Chinese commercial complementary foods for infants and young children.

Recently, mineral oil hydrocarbons (MOH) in various foods have raised significant concern, especially for infants and young children due to their potential adverse health effects. Two fractions can be distinguished by certain analytical techniques, mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH). The toxicological profile of MOSH and MOAH differs greatly. The toxicity of MOSH is linked with long-term accumulation of some hydrocarbons. MOAH with three to seven, non- or simple-alkylated, aromatic rings may be mutagenic and carcinogenic. However, data on the occurrence of mineral oils in commercial complementary foods for infants and young children are lacking in China. In the present study, 100 commercial food samples were collected, including 26 pureed or paste canned foods, 21 high-protein ground cereal foods (rice flour), 25 raw cereal foods (noodles), and 28 cereal-based molar sticks and biscuits. The content of MOSH and MOAH in those samples was determined by optimised sample preparation methods combined with on-line high-performance liquid chromatography coupled with gas chromatography and flame ionisation detector (HPLC-GC-FID), with a limit of quantification of 0.5 mg/kg. The results indicated that there were no MOAH detected in any of the foods, but MOSH and polyolefin oligomeric saturated hydrocarbons (POSH) existed in most of the food samples, at <0.5-23.68 mg/kg. Moreover, the data and chromatograms of the MOSH and POSH also indicated that these contaminants were closely correlated to their ingredients and manufacturers. The current study provides basic data to understand MOH exposure and consequent health impact.

Contribution of packaging materials to MOSH and POSH contamination of milk powder products during storage.

Mineral oil hydrocarbons (MOH) in milk powders, particularly in infant formulas, have been and continue to be a major concern to the public worldwide. These contaminants are likely derived from environmental pollution, manufacturing process and packaging materials. In this study, 23 Chinese commercial milk powder products packaged in four types of materials, i.e. metal cans, paper containers, paperboard boxes with internal bags, and aluminium foil-plastic bags, were collected and stored for 1 year. The total and surface MOH in these samples were detected and compared before and after storage to understand the MOH migration during storage, despite no mineral oil saturated hydrocarbons (MOAH) were detected. The contents of mineral oil saturated hydrocarbons (MOSH) and polyolefin oligomeric saturated hydrocarbons (POSH) in metal cans were the least among the four packages and changed little during storage, which suggested that little MOH migration occurred in metal material. Despite all the food contact materials in the other three packagings were the aluminium foil-plastic composite, the similar low migration occurred in the aluminium foil-plastic bags and internally contained composite bag(s) in paperboard boxes. However, both total and surface MOSH and POSH easily migrated from the paper-plastic-aluminium composite of paper containers during storage. These findings are helpful for the selection of packaging materials in manufacturing milk powder products or other foods.

Mild mixed-solvent extraction for determination of total mineral oil hydrocarbon contaminants in milk powder products.

A mild mixed-solvent of n-hexane/isopropanol is proposed for extracting total mineral oil hydrocarbons (MOH) from commercial milk powder products. Unlike acid-hydrolysis, the mixed-solvent extraction was performed at ambient temperature and the low-boiling-point hydrocarbons were retained to the greatest extent. After extraction, total MOH was determined by on-line liquid chromatography-gas chromatography with a flame ionization detector (LC-GC-FID). The validation of the proposed extraction method revealed a recovery efficacy of 83.0-107.5% and a limit of quantification of 0.5 mg/kg. Then, the total MOH in ten commercial milk powders was determined and mineral oil saturated hydrocarbons (MOSH)/polyolefin oligomeric saturated hydrocarbons (POSH) were found to be within the range of 0.61-5.46 mg/kg. The comparison of the total and surface MOSH/POSH indicated that a major part of the contamination was derived from sources before packaging. The present study provides a robust method for the extraction and determination of total MOH in milk powders.

Concentrations of migrated mineral oil/polyolefin oligomeric saturated hydrocarbons (MOSH/POSH) in Chinese commercial milk powder products.

Mineral oil contaminants migrated from food contact materials have raised much concern in the past few decades. However, survey data of the occurrence of mineral oils in foods are only available for a limited variety of foods, which do not include the contaminants in Chinese milk powders. Thus, to conduct an analysis of mineral oils migrated into milk powder products from different packaging materials, 50 Chinese commercial samples (including 38 infant formulas), which were packaged in metal cans, paper containers, paper boxes and aluminium foil-plastic bags, were analysed. Mineral oil saturated hydrocarbons (MOSH), polyolefin oligomeric saturated hydrocarbons (POSH) and aromatic hydrocarbons (MOAH) migrated into those samples were extracted and quantitatively analysed by on-line liquid chromatography coupled with gas chromatography (LC-GC). The results indicated no surface MOAH was detected in any of the samples, while 33 samples contained MOSH/POSH with surface contents of 0.10 ~ 5.09 mg kg-1. Moreover, the amounts of those MOSH/POSH are closely related to packaging materials, among which the surface contamination values of products in metal cans were the lowest, followed by products in paper containers and boxes, and the values of samples in aluminium foil-plastic bags were the highest. In addition, the surface MOSH/POSH content exhibited a positive correlation with fat content in the samples due to their similar polarities.

Rapid screening of mineral oil aromatic hydrocarbons (MOAH) in grains by fluorescence spectroscopy.

On-line high-performance liquid chromatography coupled with gas chromatography with flame ionization detector (LC-GC) has become an important technique for the determination of mineral oil aromatic hydrocarbons (MOAH) in foods. However, the analysis is complicated and time-consuming. The present study aimed to develop a fluorescence spectrophotometry approach for the fast screening of MOAH in grains. A reference material, which is a mixture of diesel oils and lubricants, was selected for MOAH calibration. The excitation/emission wavelength of EX230 nm/EM330 nm was determined and the linear range was 0.125-2.5 mg/kg with an R2 of 0.999. The MOAH content determined by the fluorescence method showed good correlation with that determined by LC-GC (r = 0.946). This result suggested that the performance of these two methods was comparable, and thus fluorescence spectroscopy can be used for screening MOAH. A MOAH content of >0.1 mg/kg in grains could be rapidly determined by fluorescence spectroscopy.

Offline Solid-phase Extraction Large-volume Injection-Gas chromatography for the Analysis of Mineral Oil-saturated Hydrocarbons in Commercial Vegetable Oils.

An offline solid-phase extraction (SPE) approach combined with a large-volume injection (LVI)-gas chromatography-flame ionization detector (LVI-GC-FID) is improved for routine analysis of mineral oil saturated hydrocarbons (MOSH) in vegetable oils. The key procedure of the method consists in using offline SPE columns for MOSH purification. The SPE column packed with 1% Ag-activated silica gel was used to separate MOSH from triglycerides and olefins in variety of vegetable oils. The eluent of MOSH fraction was only 3 mL and the concentration step was quick with little evaporation loss. The limit of quantification (LOQ) of the method was 2.5 mg/kg and the linearity ranged from 2 to 300 mg/kg. The accuracy was assessed by measuring the recoveries from spiked oil samples and was higher than 90%. Twenty-seven commercial vegetable oils were analyzed, and different levels of MOSH contamination were detected with the highest being 259.4 mg/kg. The results suggested that it is necessary to routinely detect mineral oil contamination in vegetable oils for food safety.

[Detection of Sulfur Dioxide in Preserved Fruits with High Resolution Continuum Source Atomic Absorption Spectrometry Assisted with Distillation].

The CS diatomic molecules can be transformed from sulfur in fuel-rich air acetylene flame. The absorbance of CS can be detected with atomic absorption spectrometry as the CS line profile is similar to the atomic absorption. A novel method was established to detect the sulfur dioxide in preserved fruits with high resolution continuum source atomic absorption spectrometry. The sulfate ions can be transformed from the SO2 in preserved fruits after the experience of acidity, distillation and oxidation with H2O2.The instrumental parameters influencing on the sensitivity of SO2 determination were optimized, including the velocity of acetylene, the flame height, etc. And the interference of different S species, such as SO2-4, S2O2-3, etc on the SO2 recovery was observed. In the optimal conditions, the limit of detection under the wavelength of 257.961 nm was 52.4 mg·kg-1, and the relative standard deviation was below 10%. The average spiked recoveries between 85.7% and 115.7% were achieved when this method was used for real preserved fruits samples analysis. It's proved that this method has the merits of high accuracy rapid analysis and low interference, and the application areas of atomic absorption spectrometry were extended.

Rapid detection of authenticity and adulteration of walnut oil by FTIR and fluorescence spectroscopy: a comparative study.

Fourier transform infrared (FTIR) and fluorescence spectroscopy combined with soft independent modeling of class analogies (SIMCA) and partial least square (PLS) were used to detect the authenticity of walnut oil and adulteration amount of soybean oil in walnut oil. A SIMCA model of FTIR spectra could differentiate walnut oil and other oils into separate categories; the classification limit of soybean oil in walnut oil was 10%. Fluorescence spectroscopy could differentiate oil composition by the peak position and intensity of emission spectrum without multivariate analysis. The classification limit of soybean oil adulterated in walnut oil by fluorescence spectroscopy was below 5%. The deviation of the prediction model for fluorescence spectra was lower than that for FTIR spectra. Fluorescence spectroscopy was more applicable than FTIR in the adulteration detection of walnut oil, both from the determination limit and prediction deviation.

[Authentication and adulteration analysis of sesame oil by FTIR spectroscopy].

It's common in edible oil market that adulterating low price oils in high price oils. Sesame oil was often adulterated because of its high quality and price, so the authentication and adulteration of sesame oil were qualitatively and quantitatively analyzed by Fourier transform infrared (FTIR) spectroscopy combined with chemometrics. Firstly, FTIR spectra of sesame oil, soybean oil, and sunflower seed oil in 4,000-650 cm(-1) were analyzed. It was very difficult to detect the difference among the spectra of above edible oils, because they are all mixtures of triglyceride fatty acids and have similar spectra. However, the FTIR data of edible oils in the fingerprint region of 1,800-650 cm(-1) differed slightly because their fatty acid compositions are different, so the data could be classified and recognized by chemometric methods. The authenticity model of sesame oil was built by principal component analysis (PCA) and soft independent modeling of class analogy (SIMCA). The recognition rate was 100%, and the built model was satisfactory. The classification limits of both soybean oil and sunflower seed oil adulterated in sesame oil were 10%, with the chemometric treatments of standard normal variation (SNV), partial least square (PLS) and PCA. In addition, the FTIR data processed by PCA and PLS were used to establish an analysis model of binary system of sesame oil mixed with soybean oil or sunflower oil, the prediction values had good corresponding relationship with true values, and the relative errors of prediction were between -6.87% and 8.07%, which means the quantitative model was practical. This method is very convenient and rapid after the models have been built, and can be used for rapid detection of authenticity and adulteration of sesame oil. The method is also practical and suitable for the daily analysis of large amount of samples.

[Raman spectroscopy combined with pattern recognition methods for rapid identification of crude soybean oil adulteration].

In the present paper, a non-destructive, simple and rapid analytical method was proposed based on Raman spectroscopy (Raman) combined with principal component analysis (PCA) and support vector machine (SVM) as pattern recognition methods for adulteration of crude soybean oil (CSO). Based on fingerprint characteristics of Raman, the spectra of 28 CSOs, 46 refined edible oils (REOs) and 110 adulterated oil samples were analyzed and used for discrimination model establishment. The preprocessing methods include choosing spectral band of 780-1,800 cm(-1), Y-axis intensity correction, baseline correction and normalization in succession. After those series of spectral pretreatment, PCA was usually employed for extracting characteristic variables of all Raman spectral data and 7 principal components which were the highest contributions of all data were used as var- iables for SVM model. The SVM discrimination model was established by randomly picking 20 CSOs and 95 adulterated oils as calibration set, and 8 CSOs and 35 adulterated oils as validation set. There were 4 kinds of kernel function algorithm (linear, polynomial, RBF, sigmoid) respectively used for establishing SVM models and grid-search for optimization of parameters of all the SVM models. The classification results of 4 models were compared by their discrimination performances and the optimal SVM model was based on linear kernel classification algorithm with 100% accuracy rate of calibration set recognition, a zero misjudgment rate and the lowest detection limit of 2.5%. The above results showed that Raman combined PCA-SVM could discriminate CSO adulteration with refined edible oils. Since Raman spectroscopy is simple, rapid, non-destructive, environment friendly, and suitable for field testing, it will provide an alternative method for edible oil adulteration analysis.

[Study on the processing of leech by FTIR and 2D-IR correlation spectroscopy].

The chemical differences of traditional Chinese medicine leech before and after processing were analyzed by FTIR and two-dimensional correlation infrared (2D-IR) spectroscopy. The result showed that the leech was high in protein, with characteristic peaks of amide I, II bands. Comparing the IR spectra of samples, the primary difference was that the characteristic peak of fresh leech was at 1 543 cm(-1), while that of crude and processed leech was at 1 535 cm(-1). A 2D-IR spectrum with heating perturbation was used to track the processing dynamics of leech In the 2D-IR correlation spectra, fresh leech exhibited stronger automatic peaks of the amide I and II bands than that of processed leech, which indicates that the protein components of the fresh leech were more sensitive to heat perturbation than the processed one. Moreover, the result of FTIR and 2D-IR correlation spectra validated that the 3-dimensional structure of protein was damaged and hydrogen bonds were broken after processing, which resulted in the inactivation of protein. The fatty acids and cholesterol components of leech were also oxidized in this process.