The sampling approaches using solid phase microextraction (SPME) were evaluated for the analysis of tobacco alkaloids Because of their low volatility and ionic nature, sampling alkaloids from the headspaee of dry or wet tobacco samples often required more effort to improve extraction efficiency. Directly dipping the SPME fiber coated with polydimethylsiloxane film into the tobacco extract was proved to be a simple, effective tool for sampling alkaloids from tobacco. When combined with the practice of fast GC and nitrogen-phosphorus detection, nicotine and a group of selected minor alkaloids (i.e., nornicotine, myosmine, anabasine and anatabine) were separated with baseline resolution within 3 min. The detection limits for these alkaloids are below 0.1 lag mL -1. In addition, the carry-over problem frequently occurred in alkaloids analysis was eliminated. The influence of tobacco matrix and fiber aging on the partition of alkaloids, as well as the use of an internal standard to compensate these deviations, were also studied.Short Communication 0009-5893/98/04
In this study, two microextraction methods, viz. continuous-flow microextraction (CFME) and static liquid-phase microextraction (s-LPME), were optimized and compared for the determination of p-toluidine in water and Chlamydomonas reinhardtii samples. The calibration curve for p-toluidine was linear in the concentration range of 0.01-5 microg/mL, and the squared regression coefficients (r(2)) for the lines were up to 0.999 for both CFME and s-LPME treatments. Detection limits in CFME and s-LPME were 8.2 ng/mL and 4.9 ng/mL, based on a signal-to-noise (S/N) ratio of 3, respectively. The precision was tested, in five replicates, by analysis of a 100-ng/mL standard solution of p-toluidine and the relative standard deviations were 5.43 and 3.08% for CFME and s-LPME, respectively. The concentration factors were 5.5 and 14.4 for CFME and s-LPME, respectively. s-LPME has a higher extraction efficiency, lower detection limit, and higher concentration factor than that of CFME. Additionally, the s-LPME method is precise and reproducible, and requires only a 3.0-microL microdrop of extraction solvent. Therefore, this procedure is more convenient in use, and viable for qualitative and quantitative analysis of p-toluidine in water and biota samples.
Biological thin films may form on a surface by specific molecular interactions. The fixed polarizer ellipsometer (FPE) is a sensitive instrument that detects biological thin films either qualitatively or quantitatively. The design is simple and inexpensive. The assays are formatted on an optical surface, and the FPE detection is based on the phase shift of linearly polarized light after reflection through a thin film. We have constructed mathematical models of the FPE response to reflection through single-layer and two-layer films that agree closely with experimental data. Several biological assays have been measured with the FPE to demonstrate the application of this technology to clinical targets, including ultrasensitive immunoassays for hepatitis B surface antigen (0.1 ng/mL) and α-fetoprotein (0.01 ng/mL) and DNA hybridization (0.5 fmol/μL target probe). A clinical study for detection of group A streptococcus from patient throat swabs demonstrated the qualitative application of the FPE to infectious disease targets. The flexibility and sensitivity of the FPE makes this technology suitable for numerous target analytes and applications.
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