LC/MS peaks

The maximum LC-MS peak capacity calculated fora DDA duty cycle of 1 s is shown in Table 12.3. The number of MS/MS scans exceeds 100,000 for lOh long 1D/2DLC experiment, but the number of identified peptides is typically lower. When considering the 25% success rate of a database search and the limited 2DLC orthogonality, the number of identified peptides is not more than 4500 in a 10 h experiment. 

Figure 12.5 illustrates a typical problem of analysis of minor components present in a matrix of highly abundant ones. Despite the availability of large LC-MS peak capacity (Table 12.3), the number of peptides detected in a semm/plasma digest does not exceed several hundreds (Kapp et al., 2005). These peptides typically match 30-50 high abundant proteins. We believe that the maj ority of remaining proteins/peptides in the sample are present at concentrations well below the LOD of MS instrument. 

Figure 20.4 Base-peak chromatogram of RNase B oligosaccharide alditols, acquired using a graphitized carbon column in LC-MS. Peak annotation (a)...

A UV-triggered purification system was described by Kibby [44] in support of the purification of combinatorial libraries generated at Parke-Davis. This system is operated in either reverse-phase or normal-phase mode, and is employed as well for chiral separations. Multiple column sizes allow the system to accommodate the purification of samples in weight up to 50 mg. The operational protocol involves an initial scouting run by analytical HPLC with APCI-MS detector. The conditions that are selected are based on structural information. Fraction collection is controlled by customized software, and sample identity, UV, MS data along with chromatographic data are imported from the analytical LC-MS. Peaks are collected only when the UV threshold is met within an appropriate collection window thus, the number of fractions obtained is limited. Postpurification loop injection mass spectra are collected on these fractions to determine the desired component from each sample. 

B) Positive-ion hill-scan mass spectrum of the LC-MS peak at 18.07 min. (C) Product-ion... 

Calibration (Standard) Curve A plot of instrument response (e.g., LC/MS peak area) vs concentration or amount (mass or moles) of analyte injected. The sensitivity (or response factor) is best defined as the slope of the calibration curve (change in signal for unit change in quantity/concentration), but sensitivity is often used in a colloquial sense to imply low LOD and/or LLOQ-When a SIS is used for maximum accuracy and precision, the ratios of instrument response (analyte SIS) are plotted vs the corresponding concentration ratio. The standard solutions used for calibration can be clean solutions of the analytical standard (possibly plus SIS), or matrix-matched calibrators, i.e., analytical extracts of a blank matrix spiked with known amounts of analytical standard (plus possibly also SIS)... 

Figure 5.35 Pharmacokinetic curves (LC-MS peak areas) for fexofenadine in human plasma analysed by LC-ESI-MS at (a) 0.6mL.min and (b) 60p.L.min Internal standard (Dg-analogue) response (for constant concentration) shown as open symbols, and analyte as closed symbols. Note that the suppression of the signal for the internal standard at the maximum concentration of analyte is much reduced at the low LC flow rate. Reproduced from Sojo, Analyst 128, 51 (2003), by permission of the Royal Society for Chemistry.

Fig. 6. Particle beam lc/ms analysis of a complex ha2ardous waste sample (a) TIC showing peak at 23.23 min (b) mass spectmm of 23.23 min peak of...

Figure 3.27 TIC trace obtained from the LC-MS analysis of a pesticide mixture, showing integrated peak areas and heights. From applications literature published by Micromass UK Ltd, Manchester, UK, and reproduced with permission.

Figure 3.32 Full-mass spectra at peak maxima of the constant-neutral-loss TIC trace shown in Figure 3.31(a), obtained after (a) 13.25 and (b) 15.9 min, from the LC-MS analysis of a mixture of atrazine and its degradation products. Reprinted from J. Chro-matogr., A, 915, Steen, R. J. C. A., Bobeldijk, I. and Brinkman, U. A. Th., Screening for transformation products of pesticides using tandem mass spectrometric scan modes , 129-137, Copyright (2001), with permission from Elsevier Science.

A solution oontaining 0.5 mg mM of an analyte gives a detector response (based on peak height) of 48 3 arbitrary units when analysed by LC-MS at a flow rate of 0.75 ml min". At a flow rate of 1.00 ml min", the detector response was 49 3 arbitrary units. Is the mass speotrometer behaving as a conoentration- or mass-flow-sensitive detector ... 

Once several target methods employing, e.g., LC/MS/MS techniques have been combined, a multi-residue method will evolve which includes the DEC S19 extraction procedures in combination with the generally applicable GPC cleanup and requires automatic multiple injections to circumvent the limitations of the limited HPLC peak capacity and the target-specific MS/MS methods. 

The methods described above generally produce recoveries in the 80-110% range with relative standard deviations of 10% or less, at the stated LOQ and higher levels. The LC/MS/MS traces are generally free of interference, especially for soil and water analyses. On rare occasions, an interfering peak may be observed at one of the transitions monitored for plant-based samples, but we have never seen interference on... 

Table 7.53 shows the main characteristics of LC-PB-MS. Of all LC-MS interface methods, LC-PB-MS comes closest to GC-MS (Scheme 7.7). The particle beam is an acceptable choice in cases where sensitivity, volatility and analyte polarity are not an issue. Usually, the function of UV is added to LC-PB-MS this allows the investigation of peak homogeneity. Drawbacks of LC-PB-MS are the low sensitivity and the nonlinearity... 

Principles and Characteristics The main reasons for hyphenating MS to CE are the almost universal nature of the detector, its sensitivity and the structural information obtainable, including assessment of peak purity and identity. As CE is a liquid-phase separation technique, coupling to the mass spectrometer can be achieved by means of (modified) LC-MS interfaces. Because of the low flow-rates applied in CE, i.e. typically below lOOnLmin-1, a special coupling device is required to couple CE and the LC-MS interface. Three such devices have been developed, namely a... 

Because online separations provide such a wealth of information about target proteins, interpretation becomes of critical importance in order to make full use of the data. The first step in any analysis of LC-MS data involves integration and deconvolution of sample spectra to determine protein mass and intensity. In manual analysis (Hamler et al., 2004), users identify protein umbrellas, create a total ion chromatogram (TIC), integrate the protein peak, and deconvolute the resulting spectrum. Deconvolution of ESI spectra employs a maximum entropy deconvolution algorithm often referred to as MaxEnt (Ferrige et al., 1991). MaxEnt calculates... 

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