Characterization of an Unknown Compound Using the LTQ Orbitrap

Transcription

1 Characterization of an Unknown Compound Using the LTQ rbitrap Donald Daley, Russell Scammell, Argenta Discovery Limited, 8/9 Spire Green Centre, Flex Meadow, Harlow, Essex, CM19 5TR, UK bjectives unknown compound (compound X), compound X was provided and analyzed qualitatively and quantitatively. The following steps were taken to provide data: Accurately determine the mass of compound X and determine sum formulae proposals without any knowledge about the compound prior to mass analysis Exclude false positive hits by comparing the proposed sum formulae to the theoretical isotope patterns without any knowledge about the compound prior to mass analysis equivalent value (RDB equivalent value) by MS/MS using CID and HCD by gaining structural information Carry out a quantitative analysis by means of dilution series of compound X. The study follows an analytical approach in which the compound was unknown in the beginning; subsequently it column. Introduction As a drug, the quaternary ammonium salt Tiotropium is used to prevent wheezing, shortness of breath, and pulmonary disease (CPD, a group of diseases that affect the lungs and airways) such as chronic bronchitis (swelling of the air passages that lead to the lungs) and emphysema (damage to air sacs in the lungs). CPD is considered to be killers after heart attack, stroke, cancer, and Alzheimer's Disease. Tiotropium belongs to a class of medications called bronchodilators which works by relaxing and opening the air passages to the lungs to make breathing easier. For further information please see: uginfo/ medmaster/a html The pre-charged status of this compound makes it source-, ph-, and ionization yield- independent and is therefore a ideal candidate to study analyzer performances. Methods LC-ESI-MS and MS/MS Liquid chromatography-electrospray ionization (LC-ESI) mass spectrometry and tandem mass spectrometry in combination with high resolving power and accurate mass rbitrap system, a hybrid mass spectrometer consisting of a linear ion trap coupled to an rbitrap mass analyzer, is used as mass spectrometer. For quantitative analyses a stock solution was was prepared in 95 / 5 water / acetonitrile containing 0.1% formic acid. This solution was used to prepare a dilution Surveyor Hypersil GLD 2.1 mm column, 50 mm length, 1.9 µm dilution experiments. A 20 µl full loop injection and the below given gradient were applied to quantitative experiments. Time A% B% µl/min Table 1: LC gradient. MS Methods for Quantitative Experiments Targeted MS/MS rbitrap detection FTMS p norm res = 15, CID Collision Energy 35.0% Q 0.25 Time 30.0 ms IsoW 3.0 u Targeted MS/MS Ion Trap detection ITMS p norm CID Collision Energy 35.0% Q 0.25 Time 30.0 ms IsoW 3.0 u 284

2 Qualitative Results A Surveyor MS Pump HPLC system with Micro AS autosampler was used for the analyses. The previous given experiments shown. For qualitative results either direct infusion or injection via the autosampler was chosen. A typical qualitative experiment performed is illustrated in Figure 1. The inset into the base peak chromatogram in Figure 1 shows the reproducibility of mass measurements over the LC peak. More than 20 mass measurements can be performed over the LC peak. This structure is imported into Mass Frontier MS/MS data (CID and HCD) obtained from compound X. This is shown in Figure 5. Collision Induced Dissociation (CID) Figure 5a: m/z 392 using Collision Induced Dissociation (CID) was a fragmentation techniques detected in the rb itrap analyzer. The accurately determined m/z 152 and m/z 170, respectively, come up with a single sum formula proposal each. The labeling of proposed structures was done using Mass Frontier. Higher Energy Collision- Trap Dissociation (HCD) Figure 5b: m/z 392 using Higher Energy Collision-Trap Dissociation (HCD) as a fragmentation techniques detected in the rbitrap analyzer. The accurately determined m/z 152 and m/z 170, respectively, come up with a single sum formula proposal each. In the mass range below m/z 150 some more fragments are observed that can be assigned by sum formulae unambiguously. Labeling of proposed structures was done by Mass Frontier. Figure 1: Base peak chromatogram of a 1 pg/µl solution. Sum Formula Proposals by means of Accurate Mass Measurement, RDBE and Isotope Pattern Evaluation Compound X was measured at RP m/z 400 in order to resolve potential sulfur(s). An inset into a full scan is given in Figure 2. The inset at m/z 394 reveals the existence of sulfur (S). The sum formula proposals for m/z 392 is taking C, H,, and up to 2 S in a ± 5 ppm tolerance window into account. For elemental constraints see Table 2. Assuming the ion observed at m/z 392 is an MH ion, as this is typical for ESI, RDBE values can only be x.5 for a singly charged ion, as displayed in Table 3. These seven proposals are simulated and compared to the Sum formula proposals with RDBE values x.5 according to Figure 1 (bottom) simulated with resolution 135,000 at FWHM. Sum formula proposals with elemental constraints according to Table 2 are simulated with resolution 135,000 at FWHM. Proposals without S can be excluded ( 32 S and 34 S are responsible for splitting the signals starting with the A2 ion) right away, as proposals with a single S can be excluded (see A3 ion, A4 ion) by comparing to the raw data information. The comparison reveals that the correct sum formula of compound X as an MH ion is C 19 H S 2. A search for the structure of compound X and its name in a database by use of the previously determined sum formula C 19 H 22 4 S 2 was carried out. A search against reveals Tiotropium as the only hit which exists as a bromide salt at molecular weight (Figure 4). Figure 2: A mass spectrum of the region of interest m/z with an inset of m/z 394. Isotop e Min Max RDB equi v. Mass C H S Table 2: Elements in use. m/z Theo. Mass Delta (ppm) RDB equi v. Composition C 18 H C 11 H S C 10 H S C 19 H S C 23 H S C 19 H C 15 H S 2 Table 3: Elemental composition applying the nitrogen rule. 285

3 Figure 3: All seven proposals vs. raw data information. Inset into full isotope pattern (left); insets into the A1, A2, A3 and A4 ion (right). Figure 4: Search for the structure of compound X. Tiotropium is the only hit with sum formula C 19 H S 2 of double bonds / unpaired electron pairs given for this sum formula in Table 3, RDB equiv. =

4 FTMS p ESI Full ms @cid35.00 [ ] C 9 H RDBE -3.2 ppm C 9 H RDBE -2.6 ppm H S H S m/z i S H S m/z rh R m/z Proposed fragmentation pathway for fragment ion m/z m/z Figure 5a: m/z 392 using Collision Induced Dissociation (CID) as a fragmentation techniques detected in the rbitrap analyzer. FTMS p ESI Full ms @hcd [ ] C 6 H RDBE -3.4 ppm C 7 H ppm -3.5 ppm H C 6 H RDBE -3.1 ppm C 8 H RDBE -2.8 ppm C 9 H RDBE -2.9 ppm C 9 H RDBE -2.7 ppm C 9 H C19 H S RDBE ppm 9.5 RDBE -1.0 ppm H m/z m/z Figure 5b: m/z 392 using Higher Energy C-Trap Dissociation (HCD) as a fragmentation techniques detected in the rbitrap analyzer. 287

5 Quantitative Results The dilution series applying two different targeted MS/MS methods was carried out. Results of three data sets are shown in Figure 6a for targeted MS/MS and rbitrap detection. The calibration graph on the right gives an overview over all measurement points (10 fg/µl to 10 pg/µl). The inset (in blue) shows the calibration graph between 10 fg/µl (200 fg on column) and 100 fg/µl (2 pg on column) in detail. For details on the graph also see the table displayed in Figure 6b. Results for targeted MS/MS and ion trap detection is shown in Figure 7. Retrieval from 3 data sets Figure 6a: Dilution series applying a targeted MS/MS method, results of three data sets. Targeted MS/MS rbitrap detection, FTMS p norm res = 15,000/7,500, CID Collision Energy 35.0% Q 0.25 Time 30.0 ms IsoW 3.0 u. Figure 6b: Result table in detail for the three data sets from Figure 6a. Figure 7: Quantitation results for targeted MS/MS method, results of a single data sets. Targeted MS/MS ion trap detection, ITMS p norm, CID Collision Energy 35.0% Q 0.25 Time 30.0 ms IsoW 3.0 u. 288

6 Conclusions An accurate mass measurement of compound X combined with RDBE evaluation and isotope pattern recognition revealed a sum formula C 19 H S 2 for compound X. An Internet accessible database search using the previously determined sum formula revealed Tiotropium as single hit. MS/MS information obtained by Collision Induced Dissociation (CID) and Higher Energy C-trap Dissociation (HCD) combined with the fragmentation Tiotropium. CID and HCD fragments are assigned by Mass Frontier. A dilution series - applying a targeted m/z 392 method detecting the fragments at m/z 152 and m/z 170, respectively, in the ion trap or the rbitrap analyzer - revealed that reliable calibration curves can be acquired down to total column load of 200 fg of Tiotropium. This is equivalent to a 20 µl full loop load of 10 fg/µl solution of Tiotropium. 289

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