Da Wu

Analysis of amino acids in tobacco by derivatization and dispersive liquid–liquid microextraction based on solidification of floating organic droplet method

A new one-step derivatization and microextraction technique was developed for determination of amino acids in tobacco samples. In the proposed method, amino acids were derivatized with isobutyl chloroformate (IBCF) in aqueous solution. The derivatives were extracted by dispersive liquid-liquid microextraction based on solidification of floating organic droplet (DLLME-SFO). Parameters affecting the extraction efficiency were investigated in detail. The optimum conditions were as follows: a mixture of 500μL acetone, containing 40μL 2-dodecanol, was rapidly injected by syringe into the 2mL water sample. After centrifugation, the 2-dodecanol droplets were floated at the top of the tube. Then, the tube was cooled in an ice bath. After 5min the solvent had solidified and was then transferred into a conical vial; it melted quickly at room temperature and it was injected into a gas chromatograph for analysis. Under the optimum conditions, the limits of detection were of the order of 0.12-2.82μg/mL. The calibration curves showed good linearity over the investigated concentration range between 0.5 and 200μg/mL with a coefficient of estimation (R(2))>0.9887 for GC-MS (SIM). The proposed method is an alternative approach to the quantification of amino acids in tobacco samples.

Development of solvent micro-extraction combined with derivatization

Solvent microextraction (SME), such as single-drop microextraction (SDME), hollow-fiber liquid-phase microextraction (HF-LPME) and dispersive liquid-liquid microextraction (DLLME), has been explored for its ability to cover a wide range of analytes. Microextraction, combined microextraction with derivatization can greatly improve separation, detectability and compound identification, expand its scope of application, and improve the effect of analysis. In this view, the article not only highlights the development of the microextraction technology such as SDBE, HF-LPME and DLLME, but also improves the key strategies of microextraction coupled to derivatization in analytical chemistry. In order to encourage further development of microextraction-derivatization, its coupling with different analytical techniques such as GC or GC-MS, HPLC, and the other technique has also been discussed.

Determination of the volatiles from tobacco by capillary gas chromatography with atomic emission detection and mass spectrometry

A new gas chromatograph-atomic emission detector (GC-AED) coupled with Deans switching technique for analyzing volatiles from tobaccos were developed. The detector operating parameters (reagent gas pressure and make-up gas flow rate) were optimized. The detection limits for the elements carbon (193 nm), hydrogen (486 nm) and oxygen (171 nm) ranged 0.05-0.2, 0.05-0.3 and 1-11 ng, respectively, depending on the compound. The sensitivity and linearity for the elements carbon (193 nm), hydrogen (486 nm) and oxygen (171 nm) decreased in the order O>H>C. Calibration curves were obtained by plotting peak area versus concentration, and the correlation coefficients relating to linearity were at least 0.9359. Elemental response factors measured on these channels, relative to the carbon 193-nm channel, were hydrogen, 0.38-0.48 (mean %RSD=5.64), and oxygen, 0.085-0.128 (mean %RSD=14.9). The evaluation was also done for the new technique and for an established GC-MS technique for the same real samples. The results of GC-AED and GC-MS showed that there was a relatively good agreement between the two sets of data.

A novel fully automated on-line coupled liquid chromatography-gas chromatography technique used for the determination of organochlorine pesticide residues in tobacco and tobacco products.

In this study, a novel fully automated on-line coupled liquid chromatography-gas chromatography (LC-GC) technique was reported and applied for the determination of organochlorine pesticide residues (OCPs) in tobacco and tobacco products. Using a switching valve to isolate the capillary pre-column and the analytical column during the solvent evaporation period, the LC solvent can be completely removed and prevented from reaching the GC column and the detector. The established method was used to determinate the OCPs in tobacco samples. By using Florisil SPE column and employing GPC technique, polarity impurities and large molecule impurities were removed. A dynamic range 1-100ng/mL was achieved with detection limits from 1.5 to 3.3μg/kg. The method exhibited good repeatability and recoveries. This technology may provide an alternative way for trace analysis of complex samples.

Evaluation of compound-independent calibration using gas chromatography with atomic emission detection.

The evaluation of compound-independent calibration (CIC) using gas chromatography (GC) with atomic emission detection (AED) is demonstrated by the identification of several sulfur or nitrogen compounds. Among other GC detectors, the advantage of using the AED is the selectivity of detection. Because contradictory results have been reported for the determination of numeric atomic ratios of elements, we set up a study with the objectives not only of applying these techniques but of determining under which conditions they will yield satisfactory results. The column pressure dependence of AED response is demonstrated through studies performed with constant pressure of 20, 30, and 40 psi. Moreover, the data collected in this study are evidence that inter-elements response factor ratios, particularly for the C/S, is very dependent on the molecular mass and concentration of the chemicals analysed whereas molecular structure seems to have less effect on the AED signal. We therefore suggest the use of a reference set of compounds covering a large chromatographic window, which enables the selection, within this set, of the most appropriate reference compound for calibration and for determination of the raw formula of an unknown analyte.

Establishment of a two-dimensional liquid chromatography-tandem mass spectrometry system for detection of four tobacco-specific N-nitrosamines

In this work, we developed a system for the qualitative and quantitative analysis of four tobacco-specific N-nitrosamines (TSNAs). This system was based on strong cation exchange/reversed phase liquid chromatography-tandem mass spectrometry (SCX/RPLC-MS/MS). Benefiting from an efficient two-dimensional separation, the system could well circumvent tremendous matrix effects and provide excellent detection of ultra-low concentrations of TSNAs (ng mL−1 level, after pretreatments) in Chinese Virginia cigarette mainstream smoke samples. Based on the features of TSNAs, one heart-cutting was used to transfer fractions from the first dimension to the second. A side flow was added between the two dimensions to gain retention in RPLC of TSNAs from SCX fractions. The system was evaluated using standard TSNA samples and mainstream cigarette smoke samples. The total separation time was within 20 minutes. The limits of quantitation (LOQs) for N′-nitrosonornicotine (NNN), 4-(methylnitrosoamino)-1-(3-pyridyl)-1-butanone (NNK), (R,S)-N-nitrosoanatabine (NAT) and (R,S)-N-nitrosoanabasine (NAB) were 39, 47, 58 and 9 pg mL−1, respectively, which could well meet the requirements of all kinds of commercial cigarette samples. With Kentucky reference cigarettes as a standard sample, the relative deviations (r) of the measured values of TSNAs from the standard values were between −1.6% and 4.6%. And the relative standard deviations (RSD) of intra- and inter-day analysis were below 4.9% and 5.9%, respectively. These results revealed that the SCX/RPLC-MS/MS system we built could efficiently achieve minimal sample matrix effects and make highly sensitive analysis of pg mL−1 level TSNAs in extremely complicated samples easy, fast and accurate. Finally, we successfully applied the system to the evaluation of TSNA yields in Chinese Virginia cigarettes.

Development of Multiple Heart-Cutting Two-Dimensional Liquid Chromatography Coupled to Quadrupole-Orbitrap High Resolution Mass Spectrometry for Simultaneous Determination of Aflatoxin B1, B2, G1, G2, and Ochratoxin A in Snus, a Smokeless Tobacco Product

The combination of multiple heart-cutting two-dimensional liquid chromatography (MHC-LC/LC) and quadrupole-orbitrap high-resolution mass spectrometry (HRMS) for simultaneous determination of the aflatoxins and ochratoxin A in snus is presented in this work. A C18 capillary column was used as the first dimension (1D) to isolate the aflatoxins and ochratoxin A from the complex matrices; then, a 2-position/10-port high-pressure valve equipped with two 60 μL loops was employed to transfer the heart-cuts of 1D-LC into a pentafluorophenyl (PFP) column for the second dimension (2D) separation. With the better separation of the MHC-LC/LC system, the sensitivity of the method was improved, which is essential for the trace mycotoxins analysis. Furthermore, HRMS performed in parallel reaction monitoring mode was employed to eliminate the interferences, and the sample pretreatment procedure was simplified. A new approach utilizing ethyl acetate with 1% formic acid/water solution was adopted to extract aflatoxins and ochratoxin A in snus, which provided parallel recoveries for aflatoxins and ochratoxin A with higher responses in comparison with the QuEChERS method. A dynamic range between 0.2 and 20 μg/kg was achieved with LOQs of 0.05 μg/kg for aflatoxin B1, 0.1 μg/kg for aflatoxin B2, G1, G2, and 1.0 μg/kg for ochratoxin A in dry mass of product. The results revealed that the established method exhibited good repeatability and recovery and could be used as a rapid and reliable approach for routine analysis of aflatoxins and ochratoxin A in snus.

Development of microwave-assisted extraction and liquid chromatography-tandem mass spectrometry for determination of maleic hydrazide residues in tobacco

Herein, an effective and rapid method involving microwave-assisted extraction (MAE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed for the determination of maleic hydrazide residues in tobacco. In order to completely extract the free and bound maleic hydrazide, MAE was employed to accelerate the hydrolysis of maleic hydrazide glycoside, which was proved to be a powerful extraction method in comparison with conventional extraction methods. Then the obtained extract was filtered and directly analyzed by LC-MS/MS without further pretreatment, and d2-maleic hydrazide was used as the internal standard to reduce the matrix effects. A dynamic range of 50–5000 ng mL−1 was achieved with a limit of detection of 0.16 mg kg−1 for maleic hydrazide. The established method exhibited good repeatability and recovery for maleic hydrazide, and could be used as a rapid and reliable approach for routine analysis of maleic hydrazide in tobacco.

Identifying the tobacco related free radicals by UPCC-QTOF-MS with radical trapping method in mainstream cigarette smoke

Tobacco related free radicals (TFRs) in the cigarette smoke are specific classes of hazardous compounds that merit concern. In this study, we developed a hybrid method to identify TFRs directly based on ultra-performance convergence chromatography with a quadrupole time-of-flight mass spectrometry (UPCC-QTOF MS) combined spin trapping technique. The short-lived TFRs were stabilized successfully in situ through spin trapping procedure and UPCC was applied to facilitate efficient separation of complex derivative products. Coupling of orthogonal partial least squares discriminant analysis (OPLS-DA), UPCC-QTOF MS system enabled us to identify specific potential TFRs with exact chemical formula. Moreover, computational stimulations have been carried out to evaluate the optimized stability of TFRs. This work is a successful demonstration for the application of an advanced hyphenated technique for separation of TFRs with short detection time (less than 7min) and high throughput.