Base peak definition

Example The 70 eV El mass spectra of methyl propyl ether and diethyl ether are shown below (Fig. 6.7). Although being isomers, their spectra are clearly different. In case of methyl propyl ether, a-cleavage can occur by H loss, m/z 73, and definitely preferable by C2H5" loss, m/z 45, which gives rise to the base peak. The advantage of C2H5 loss over CH3 loss becomes evident from the diethyl... 

The gas phase pjnrolysis of alkyl hahdes has been extensively reviewed 58>, and in general the unimolecular gas phase reactions of alkyl halides parallel their reactivity in a mass spectrometer. For example, ethylchloride yields ethylene and HCl on thermolysis 5 >, and the ethylene ion in the mass spectrum of ethyl chloride is significantly more intense than the molecule ion. 1,2-dichloroethane also eliminated HCl thermolytically and the corresponding ion is the base peak in its mass spectrum. Elimination of HCl is also common to the mass spectra and thermochemistry of chloroprene dimers.Although in this case the major ion at mje 91 had no definite analog in the thermochemistry. This is probably due to the fact that mje 91 was a tropylium ion which would not be stabihzed as a neutral. 

As the third option was one where considerable hands-on experience was available, our chromatography-based procedure definitely had to be kept alive in the sense that development resources were justified for improving the performance. However, a forecast of 5 kg production simply by linearly extrapolating data from the A kg batch, resulted in a really frightening scenario where considerable manpower (peak values of 20-30 people during certain stages) had to be allocated over... 

Since ABA is a minor component in crude extracts of plant material, extensive purification is necessary prior to identification and quantification [8,31]. The definitive method for identifying ABA as its methyl ester. Me-ABA, is combined gas chromatography-mass spectrometry (GC-MS). Negative chemical ionization causes very little fragmentation, so that the molecular ion is the base peak. This technique has been used extensively in studies with 0-labeled ABA to determine the location of the atoms within the ABA molecule [32]. GC-selected ion monitoring (SIM) is a very sensitive method for quantifying ABA, but requires ABA labeled with a stable isotope, usually H, as internal standard to compensate for losses. 

L4.3.1 Chromatography Although the final detection is based on the mjz ratios, optimized chromatographic separation is crucial to obtain high-quality data since it is directly related to peak definition and subsequent data... 

As a rule, a GC peak should he defined by at least 15 points to offer good peak definition. Thus, in a GC peak of 3 s base width, each isotope should be measured in an interval of a maximum of 200 ms. Provided that three different isotopes are measured, a maximum dwell time of 66 ms per isotope should be applied. Consequently, for narrower peaks and/or more isotopes to be measured, dwell times must be reduced. Thus, in GC-ICP-MS, GC parameter optimisation should not aim for extremely narrow peaks. 

Now, we must consider the relative abundances of each peak. The peak at m/z = 423.0647 is the base peak, because it has a relative abimdance of 100% (it is, by definition, the most abundant ion). The peak at 424.0681 has an abundance of 22.5%, relative to the most abundant ion. This is consistent with an ion having 21 carbon atoms, because the natural abundance of is 1.07%. [21x1.07% = 22.5%]... 

In principle, any type of sample can be analysed by SEC provided that it can be solubilised and that there are no enthalpic interactions between sample and packing material. By definition then, this technique cannot be carried out on vulcanisates and even unvulcanised fully compounded rubber samples can present problems due to filler-rubber interactions. The primary use of SEC is to determine the whole MWD of polymers and the various averages (number, viscosity, weight, z-average) based on a calibration curve and to allow qualitative comparisons of different samples. Many commercial polymers have a broad MWD leading to strong peak overlap in the chromatography of complex multicomponent systems. 

This chapter examines another measure of the space used by 2D separations subject to correlation. Some researchers use the words, peak capacity, to express the maximum number of zones separable under specific experimental conditions, regardless of what fraction of the space is used. By definition, however, the peak capacity is the maximum number of separable zones in the entire space. No substantive reason exists to change this definition. The ability to use the space, however, depends on correlation. In deference to previous researchers (Liu et al., 1995 Gilar et al., 2005b), the author adopts the term, practical peak capacity, to describe the used space. The practical peak capacity is the peak capacity, when the separation mechanisms are orthogonal, but is less than the peak capacity when they are not. The subsequent discussion is based on practical peak capacity. 

Quantification of the limits of detection (LOD), or minimum detectable levels (MDL statistically defined in Section 13.4), is an important part of any analysis. They are used to describe the smallest concentration of each element which can be determined, and will vary from element to element, from matrix to matrix, and from day to day. Any element in a sample which has a value below, or similar to, the limits of detection should be excluded from subsequent interpretation. A generally accepted definition of detection limit is the concentration equal to a signal of twice (95% confidence level) or three times (99% confidence) the standard deviation of the signal produced by the background noise at the position of the peak. In practice, detection limits in ICP-MS are usually based on ten runs of a matrix matched blank and a standard. In this case ... 

The term resolution essentially describes the same the small difference being that its definition is based on the resulting signals. The resolution R is defined as the ratio of the mass of interest, m, to the difference in mass. Am, as defined by the width of a peak at a specific fraction of the peak height. [1]... 

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