Real-Time Quantitative Analysis

To determine the concentrations of vapor phase alkaloids detected in ETS by APCI mass spectrometry, it is necessary to have vapor phase standards which can be used for instrument calibration. Gas dilution is perhaps the best way to calibrate for compounds in the gas phase. Gas dilution requires that a standard of known concentration and a method for accurately and reproducibly diluting the standard are available. Permeation tubes and diffusion tubes, housed in a constant temperature oven, are well suited for generating gas standards with known analyte concentrations. Table 1 includes the analyte, source, and typical source effusion rates used for investigating ETS along with the ion monitored for quantitative analysis of each analyte. 

It is not possible to distinguish among different isomers of the substituted pyridines listed in Table 1 by APCI-MS 3-picoline and 3-ethylpyridine were chosen for calibration because they are the predominant isomers of these compounds found in ETS. Although 3-ethenylpyridine is the most abundant ethenylpyridine isomer in ETS (there is a trace of the 2-ethenyl isomer and none of the 4-ethenyl isomer Ogden 1991), it is not commercially available. 4-Ethenylpyridine is used for calibration because it is the most stable of the two commercially available isomers. 

To generate a calibration curve for the determination of response factors, it is necessary to supply standards to the APCI ion source at different concentrations. The effluent from an oven containing permeation tubes is frequently too concentrated to be an effective calibration source. Furthermore, only one concentration is provided by a permeation tube in a constant temperature oven. To dilute the standard to working concentrations, a capillary dilution apparatus such as the one illustrated in Fig. 5 is used. The effluent from the oven is directed into the base of the apparatus. From here, the effluent can either pass through the capillary into a stream of dilution air 

There are a number of important considerations when using this method of instrument calibration. First, the concentration of the analyte exiting the 

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Since the pioneering work of Thome et al. (1986), many applications of APCI mass spectrometry to the detection and analysis of alkaloids and alkaloid-derived compounds in ETS have been developed. Qualitative analysis of alkaloids in ETS can be performed by APCI-MS/MS however, this technique will not be discussed here. Real-time quantitative analysis is a highly useful technique for determining instantaneous compound concentrations and investigating the reactivity of the title compounds and their relationship and interactions to other compounds found in the indoor environment. Real-time data can be combined with plethysmography to accurately determine inhaled alkaloid dose (deBethizy et al. 1989). Analysis of the decay kinetics of ETS alkaloids can be used to understand relationships between various ETS tracers (Nelson et al. 1990, 1991). Time-weighted... 

Branford S, Rudzki Z, Parkinson I et al. Real-time quantitative PCR analysis can be used as a primary screen to identify patients with CML treated with imatinib who have BCR-ABL kinase domain mutations. Blood 2004 104 2926-2932. 

Livak KJ, Schmittgen TD (2001) Analysis of relative gene expression data using real-time quantitative PCR and the 2(-Delta Delta C(T)) method. Methods 25 402-408... 

Analysis of minimal residual disease by Ig/TCR gene rearrangements guidelines for interpretation of real-time quantitative PCR data. Leukemia, 21, 604—611. 

Smith D, Spanel P, Herbig J, et al. Mass spectrometry for real-time quantitative breath analysis. J Breath Res. 2014 8 027101. 

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