Chemistry Investigatory Project

CHEM. RES. CHINESE UNIVERSITIES
China Abstract A sensitive, simple, and low-cost method based on capillary electrophoresis(CE) with electrochemical(EC) detection at a carbon fiber microdisk electrode(CFE) was developed for the determination of nicotine. The effects of detection potential, concentration, and pH value of the phosphate buffer, and injection time, as well as separation voltage, were investigated. Under the optimized conditions: a detection potential of 1. 20 V, 40 mmol/L phosphate buffer(pH 2. 0), a sample injection time of 10 s at 10 kV and a separation voltage of 16 kV, the linear range obtained was from 5. 0? 10–7 mol/L to 1. 0? 0–4 mol/L with a correlation coefficient of 0. 9989 and the limit of detection(LOD, S/N=3) obtained was 5. 0? 10–8 mol/L. The method was also used to determine the nicotine in cigarettes. Nicotine amount ranged from 0. 211 mg/g to 0. 583 mg/g in the pipe tobacco of seven brands of cigarette and the amount in one cigarette varied from 0. 136 mg/cigarette to 0. 428 mg/cigarette. Keywords Capillary electrophoresis; Electrochemical detection; Nicotine; Tobacco Article ID 1005-9040(2012)-03-415-04 1 Introduction Nicotine accounts for about 98%(mass fraction) of the total alkaloids and presents in a concentration of 0. %? 8% (mass fraction) in tobacco. And nicotine addiction is related to a higher risk for many kinds of diseases such as Alzheimer’s, Parkinson’s, and even suicide. Thus it’s necessary to control the nicotine amount in tobacco products. The determination of nicotine is very important in both the tobacco industry and the toxicology area. A lot of analytical methods have been established for the analysis of nicotine and related alkaloids, such as radioimmunoassay, spectrophotometry, near-infrared spectroscopy, and recently flow injection(FI) with electrochemiluminescence(ECL) detection.
The most frequently used analytical techniques for nicotine and its relative compounds determination are high-performance liquid chromatography(HPLC) and gas chromatography (GC) with mass spectrometry(MS). Besides, HPLC coupled with UV-visible absorption(UV)\ or GC with flame ionization detector(FID) and atomic emission detector(AED)\have also been developed to determine nicotine and related alkaloids. Capillary electrophoresis(CE) is characterized by high separation efficiency, short analysis time, and a small amount of reagent consumed.

Moreover, the capillary column is flexible for use, easy to be treated with, and cost-effective. CE has been considered as an efficient alternative for the HPLC technique. Up to now, various detectors have been combined with CE separation for nicotine analysis, such as CE-MS, nonaqueous CE(NACE)-MS, CE-U, microchip micellar electrokinetic chromatography(microchip MEKC)-UV, and CE with dual light-emitting diode induced fluorescence (LEDIF) and ECL detection. Electrochemical(EC) detection has received more attention due to simple manipulation and good selectivity.
EC experiment was conducted with a Voltammetric Analyzer(CHI 800, USA). A conventional three-electrode system was employed with a 33-? m CFE as a working electrode, a Pt wire as a counter electrode, and an Ag/AgCl electrode as a reference electrode. An uncoated fused-silica capillary with i. d. of 25? m and length of 45 cm(Ruifeng Chromatogram Equipment Co., Ltd., Hebei, China) was used for sampling and separation. The Capillary was rinsed in 0. 1 mol/L NaOH overnight before use. Every day before experiments, it was flushed with doubly distilled water for about 10 min and balanced with running buffer for about 15 min.
CE-EC was conducted on a self-assembly instrument including a Voltammetric Analyzer(CHI 800, USA) and a high voltage supplier(MPI-A, Remax Electronics Co., Ltd., Xi’an, China). The sample injection was performed electrokinetically for 10 s at 10 kV. Fig. 2 HDV investigation of nicotine c(Nicotine)=1. 0? 10–5 mol/L; sample injection: 10 s at 10 kV; separation voltage: 20 kV; CE buffer: 40 mmol/L PBS(pH 2. 0); cell buffer: 0. 1 mol/L PBS(pH 8. 0). 3. 3 Optimization of CE-EC Conditions 3 3. 1 Results and Discussion Cyclic Voltammetry(CV) CV was used to investigate the electrochemical behavior of nicotine.
A dramatic current increased from 0. 70 V was observed for nicotine(Fig. 1, curve b) compared with that of background electrolyte(Fig. 1, curve a), indicating that nicotine had high electroactivity at CFE. The adsorption property of CFE for nicotine was also investigated under the CV experiment, however, no adsorption phenomenon of nicotine was observed. Since the oxidation potential of nicotine was not high at CFE, CE coupled with EC at CFE is practical for nicotine determination. Some other important factors including buffer concentration and buffer pH as well as separation voltage were investigated.
In consideration of the detection sensitivity, pH 2. was selected as the proper CE buffer pH value. Separation voltage is an important factor that influences the detection sensitivity and the migration time. When the separation voltage was changed from 10 kV to 20 kV, the migration time decreased from 14 min to 7 min correspondingly. No. 3 SUN Jin-ying et al. 417 As for EC response, when the separation voltage increased from 10 kV to 18 kV, the EC intensity of nicotine increased quickly, after that it decreased quickly from 18 kV to 20 kV(shown in Fig. 4). Detection sensitivity at 16 kV was higher than that at 18 kV.
In consideration of the detection sensitivity, 16 kV was selected as the optimum separation voltage. supermarket. Pipe tobacco of 0. 1 g was weighed and placed in a polyethylene tube, in which 10 mL of solvent was added for nicotine extraction. Then, 10 µL of the extraction solution was transferred into a new polyethylene tube and diluted 100 times by doubly distilled water and the diluted extraction solution was used for analysis. 4. 2 Investigation of Extraction Solvents Fig. 4 Effect of separation voltage on detection of nicotine Applied detection potential: 1. 20 V; other conditions are as those in Fig. . 3. 4 Linear Range and LOD To obtain high extraction efficiency, solvents including water, methanol, chloroform, and ethyl acetate were investigated. The current response of nicotine extracted with different solvents is shown in Fig. 5. The current response of nicotine was the highest when water was used as the solvent. Methanol was also efficient for the extraction of nicotine from pipe tobacco. However, when methanol was used as a solvent, migration time prolonged and the baseline shifted. When chloroform was used for extraction, the current response was about 36% of that when water was used for extraction.