Passage
Electrospray ionization mass spectrometry (ESI-MS) employs a soft ionization technique that, unlike traditional ionization via electron bombardment, results in little to no fragmentation of target molecules. During electron bombardment, electrons collide with the analyte and cause the molecule to lose an electron whereas during ESI-MS, ions are produced by passing the analyte solution through an electrospray needle that has a potential difference applied with respect to a counterelectrode. This leads to the formation of charged droplets, which are repelled from the needle toward the counterelectrode and mass spectrometer, as shown in Figure 1.
Figure 1 ESI-MS ionization mechanismDuring the droplet's flight, the solvent is evaporated off analyte molecules. Ionization occurs through the protonation of basic sites on target molecules. Reaction 1 shows the number of protons n added to molecule M.M → (M + nH) ⁿ⁺Reaction 1Researchers used ESI-MS to quantify the formation of four pyridyloxobutyl-DNA (POB-DNA) adducts, shown in Figure 2. POB-DNA adduct formation involves highly mutagenic pyridyloxobutylating agents, which are formed from cytochrome P450-mediated hydroxylation of 4-(methylnitrosamino) -1-(3-pyridyl) -1-butanone (NNK) , an abundant N-nitrosamine carcinogen found in cigarette smoke. Adducts were produced in vitro by treating samples of calf thymus DNA with NNK. The DNA adducts were then separated by reversed-phase high-performance liquid chromatography (RP-HPLC) and analyzed via ESI-MS.
Figure 2 Molecular structure of POB-DNA adducts
Adapted from Lao Y, Villalta PW, Sturla SJ, Wang M, Hecht SS. Quantitation of pyridyloxobutyl DNA adducts of tobacco-specific nitrosamines in rat tissue DNA by high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry. Chem Res Toxicol. 2006.
-Which of the following would most likely be used as the mobile and stationary phases, respectively, for RP-HPLC separation of the POB-DNA adducts?

Question

Passage
Electrospray ionization mass spectrometry (ESI-MS) employs a soft ionization technique that, unlike traditional ionization via electron bombardment, results in little to no fragmentation of target molecules. During electron bombardment, electrons collide with the analyte and cause the molecule to lose an electron whereas during ESI-MS, ions are produced by passing the analyte solution through an electrospray needle that has a potential difference applied with respect to a counterelectrode. This leads to the formation of charged droplets, which are repelled from the needle toward the counterelectrode and mass spectrometer, as shown in Figure 1.

Figure 1 ESI-MS ionization mechanismDuring the droplet's flight, the solvent is evaporated off analyte molecules. Ionization occurs through the protonation of basic sites on target molecules. Reaction 1 shows the number of protons n added to molecule M.M → (M + nH) ⁿ⁺Reaction 1Researchers used ESI-MS to quantify the formation of four pyridyloxobutyl-DNA (POB-DNA) adducts, shown in Figure 2. POB-DNA adduct formation involves highly mutagenic pyridyloxobutylating agents, which are formed from cytochrome P450-mediated hydroxylation of 4-(methylnitrosamino) -1-(3-pyridyl) -1-butanone (NNK) , an abundant N-nitrosamine carcinogen found in cigarette smoke. Adducts were produced in vitro by treating samples of calf thymus DNA with NNK. The DNA adducts were then separated by reversed-phase high-performance liquid chromatography (RP-HPLC) and analyzed via ESI-MS.

Figure 2 Molecular structure of POB-DNA adducts
Adapted from Lao Y, Villalta PW, Sturla SJ, Wang M, Hecht SS. Quantitation of pyridyloxobutyl DNA adducts of tobacco-specific nitrosamines in rat tissue DNA by high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry. Chem Res Toxicol. 2006.
-Which of the following would most likely be used as the mobile and stationary phases, respectively, for RP-HPLC separation of the POB-DNA adducts?

Quizplus · Accepted Answer

11ecba2d_127e_8a4a_a3bf_21f8e4d7d5a0_MD0008_00 In general, separation in chromatography is accomplished as a result of different retention times, as determined by the degree of interaction between analyte molecules and the stationary and mobile phases. High-performance liquid chromatography (HPLC) is a type of chromatography in which a liquid solvent (mobile phase) carries the sample through a column filled with adsorbent material (stationary phase). The guiding principle for separation is polarity: Molecules with a polarity similar to the stationary phase have longer retention times than molecules with polarities similar to the mobile phase. In reversed-phase HPLC (RP-HPLC), the stationary phase is a nonpolar compound and the mobile phase is a polar solvent; polar molecules move faster through the column, and nonpolar molecules have longer retention times. Of the materials given, water (polar) would be appropriate for the mobile phase and C-18 alkyl hydrocarbon (nonpolar) would be appropriate for the stationary phase. (Choices A and B) When the mobile and stationary phases are both polar (water and silica) or both nonpolar (hexane and C-18 alkyl hydrocarbon), analytes will not be separated effectively. (Choice D) A nonpolar mobile phase (hexane) and a polar stationary phase (silica) are used in normal-phase HPLC. The polar adducts from the passage would likely remain in the polar stationary phase. Educational objective: High-performance liquid chromatography (HPLC) separates molecules according to polarity. In reversed-phase HPLC, the mobile phase is a polar liquid solvent that carries the analyte through a nonpolar stationary phase.

Passage Electrospray Ionization Mass Spectrometry (ESI-MS) Employs a Soft Ionization Technique