Extracted ion current

FIGURE 2 MEEKC APPI/MS analysis of five steroids. Total ion current (TIC) and extracted ion currents (XIC) of gestrinone (GES), canrenone (CAN), metolazone (MET), finasteride (FIN), and dexamethasone (DEX) and an EOF marker (N,N-dimethylformamide, DMF). 

When working with non-radiolabeled drugs the major challenge is to find metabolites in the biological matrices. Because the enzymes responsible for metabolism are quite well characterized metabolic changes can partially be predicted. For example hydroxylation of the parent drug is in many cases the principal metabolic pathway. From a mass spectrometric point of view it results in an increase of 16 units in the mass spectrum. In the full-scan mode an extracted ion current profile can be used to screen for potential metabolites. In a second step a product ion spectrum is recorded for structural interpretation. Ideally, one would like to obtain relative molecular mass information and the corresponding product ion spectrum in the same LC-MS run. This information can be obtained by data dependant acquisition (DDA), as illustrated in Fig. 1.39. 

Advances in high resolution mass analyzers (TOF, FT-ICR, orbitrap) have greatly improved the detection and identification of metabolites based on accurate mass measurements. In single MS mode accurate mass determination is mainly used to differentiate between isobaric ions. Combined with LC-MS, it allows the detection of predicted metabolites by performing extracted ion current profiles... 

The analytes are determined by acquiring a full mass scan and obtaining the extracted ion current profiles (EICP) for the primary mass-to-charge ratio and at least two secondary masses of each analyte. Ions recommended for this purpose are listed in the EMSL methods. 

Figure 9. Illustration of the use of extracted ion-current profiles obtained with LC-MS, moving-belt interface, for the detection of carbamate and other pesticides. T op, extracted ion-current profile for 17 major ions second from top, extracted ion-current profile for m/z = 151 to m/z = 181 third from top, extracted ion-current profile for m/z = 86 to m/z = 305 bottom, UV absorption detection at 220 nm. (Reproduced with permission from reference 53. Copyright 1982 Preston Publications.)...

GC-MS runs were stored as files by the data system on discs FORTRAN routines were written to compare selected parameters in file sets and to reduce the data to summary tables for hard copy output. These routines facilitated the determination of peak areas of components in extracted ion current profiles (EICP) for both total and selected ion chromatograms, calculated the removal of components of interest (e.g., those containing halogen isotopes) by treatment processes (GAC, CI2) or derivatization, summarized the occurrence of new components of interest in treatment or derivatization, and calculated the percent of the total ion current represented by a given component. The programs allowed operator discrimination between major and minor components in a file set by preselection of an ion current threshhold for data reduction. For data summarized herein, components were >4000 ion counts, which corresponds to a level >5 of the internal standard (decachlorobiphenyl) response. 

Fig. 8 HPLC-fo -UV Analysis of NDMA in beer. Extracted ion current profile, in the SIM mode for NDMA-acid complex (mlz 75) and that of its dissociative photolysis products, [(CH3)2NH2]+ (mlz 46) and [(CH3)(CH2)NH]+ (mlz 44). (Reprinted with permission from Ref. 86a. Copyright 1996, American Chemical Society.)...

Figure 1.4.3 An example of extracted ion current profiles for benzene, benzene-d6, and a mixture of benzene and benzene-d6. 

Isotope ratio is measured as the ratio of the area of the primary ion of the unlabeled compound to that of the labeled compound. When the area is zero, it is assigned a value of 1. The retention times of the analytes in most cases are the same as that of their labeled analogs. The isotope can be calculated from the extracted ion current profile (EICP) areas. An example of EICP for benzene, benzene-d6, and a mixture of benzene and benzene-d6 is presented inFigure 1.4.3. Calculation to determine the RR is given below ... 

Figure 6.11 The LC/MS extracted ion current profiles for 10 combinatorial drug candidate library components, using the bioaffinity screening procedure shown in Figure 6.6. (A) Before passing through a spin column. (.B) After one cycle. (C) After two cycles. The enhancement of tight-binding ligands is evident. (Reprinted with permission from Davis et al., 1999. Copyright 1999 American Chemical Society.)...

Figure 6.33 Representative HPLC chromatograms of human serum samples for the CP-80794 SIM LC/MS assay. Extracted ion current profiles for (A) Blank (B) Blank plus internal standard (C) 0.1 ng/mL CP-80,794 (.D) 0.5 ng/mL CP-80,794. (Reprinted with permission from Fouda et al., 1991. Copyright 1991 Elsevier.)...

Fig. 8 Various chromatograms (from D to A mjz 170, APCI + TIC, UV at 280 nm, APCI — TIC, extracted ion current profile from APCI+) from APCI LC/MS analyses of an elastomer solvent extract.

Fig. 3 Various chromatograms (C) TIC (B) UV at 254 nm (A) m/z 722 extracted ion current profile) from the positive ion ESI LC/MS impurity profile analysis of a drug product. Note the two unknown trace level impurities in the m/z 722 extracted ion current profile.

Fig. 5 shows a comparison based on extracted ion current profiles of ionization efficiencies for Nifedipine. Included are positive ion APCI and ESI, along with negative ion chloride ion attachment APCI. As predicted. Nifedipine can be readily ionized by all three LC/MS ionization processes. The mass spectra of Nifedipine obtained using these three ionization processes are shown in Fig. 6. Positive ion ESI and APCI both show [M + H] at m/z 347 (note the [M + Na] ion at m/z 369 in the ESI spectrum) with some fragmentation (the ion at m/z 315 likely results from loss of methanol from one of the methyl ester groups). The negative ion chloride ion attachment spectrum shows the anticipated [M + Cl] at m/z 381, along with a [M + Cl - HCl] ion at m/z 345. Note that there is also a relatively small [M + TFA] (TFA) ion at m/z 459. If TFA is present in the HPLC...

Fig. 5 Extracted ion current profiles from LC/MS analyses of equal quantities of Nifedipine (A) m/z 347 from positive ion APCI (B) m/z 347 from positive ion ESI (C) m/z 381 from negative ion chloride ion attachment APCI.

The electrospray stability of this device was studied with two different samples 1 pg mL 1 imipramine- 3 directly dissolved in 75% methanol, 25% water and 0.1% formic acid and extracted urine sample containing only methylphenidate-d3, which corresponds to the blank calibration standards. Figure 6.13A shows the total ion current of full mass range scan (m/z 250 to 350) of the imipramine-J3 sample over 15 min with a scan speed of 1.16 s per scan while Figure 6.13B shows the extracted ion current of the base peak (m/z 284.2) from Figure 6.13A. The RSD for the total ion current over the 15 min periods was 10.7% and the protonated molecule ion was even more stable with an RSD of 5.7%. Figure 6.13C shows the total selected ion current for the SRM data (m/z 234.2 > m/z 84.1, m/z 234.2 > m/z 84.1) from 150ngmL 1 methylphe-nidate-fi 3 sample. The SRM mode was also very stable with an RSD of 3.05% over a period of 5 min. 

Figure 6.13 Electrospray stability of the device. (A) Total ion current of m/z from 250 to 350 with solution of lpgmL-1 imipramine-d3 in 75% methanol, 25%water and 0.1 % formic acid. (B) Extracted ion current of imipramine-d3 (m/z 284.2) from (A). (C) Selected reaction monitoring of extracted urine sample containing 150ngmL 1 methylphenidate-<73 (from ref. 13).

Figure 1. Extracted ion current profiles (EICPs) of the molecular ions for the Z = —22 AHD for a marine sediment. Arrowheads indicate the (M + 2)+ ions of compounds with MW = 228.

Prednisolone along with other corticosteroids could be separated within 6 min by El SFC/MS. The packed column SFC/MS was applied for the analysis of a TLC scrape of a urine sample collectd two hours after the intramuscular administration of 100 mg of prednisolone to a horse. The extracted ion current profile for the abundant fragment ion at m/z 122 and the molecular ion at m/z 360 easily identify the prednisolone in this sample. Packed-column SFC/MS... 

Figure 9.3 Ion current chromatogram of a BSA digest analyzed by LC-MS. (a) Total-ion current chromatogram and (b) extracted-ion current chromatogram of a spectral feature with m/z =1163...

FIGURE 18.3 Extracted ion current profiles of the water-soluble vitamins detected in a green kiwi extract (see reference [138] for the details). The LC—SRM (standard reference material) chromatogram was acquired by a high-flow ESI source (TurboIonSpray source). Each analyte was identified on the basis of the retention time, the two selected SRM transitions and their relative abundance. Only the most intense SRM ion current is reported in the figure. 

FIGURE 18.4 Extracted ion current profiles of the fat-soluble vitamins detected in a green kiwi extract. This is an example of NARP chromatography (see Table 18.1, reference [137], for the details) a nonaqueos mobile phase was chosen as the best compromise between chromatographic resolution and support to positive APCl ionization of analytes. 

---