Effective peak number

Band Asymmetry. The peak asymmetry factor AF is often defined as the ratio of peak half-widths at 10% of peak height, that is, the ratio b/a, as shown in Fig. 11.2. When the asymmetry ratio lies outside the range 0.95-1.15 for a peak of k =2, the effective plate number should be calculated from the expression... 

The analytical capability of a SEC column is sometimes judged by the peak capacity, which is the number of unique species that can be resolved on any given SEC column. This number will increase with decreased particle size, increased column length, and increased pore volume. Because small particlesized medium generally has a lower pore volume and a shorter column length, peak capacities of ca. 13 for fully resolved peaks can be expected for high-resolution modern media as well as traditional media, (see Eig. 2.5). It was found that SEC columns differ widely in pore volume, which affects the effective peak capacity (Hagel, 1992). 

The peak broadening for the entire chromatographic system,. columns plus the instrument, may thus be estimated from the bandwidth contribution of each component of the system. The effective plate number of the system may then be calculated from Equation 1. 

The alcohol plot (Fig. 13) shown top right reveals a peak centred on 1.2nm 1 and having a FWHM of 0.25 nm 1. Relative to its comparatively low effective atomic number, estimated using HETRA to be 5.3, it scatters profusely as shown by the peak... 

The water plot (Fig. 13, top left) shows a much broader peak of lower peak amplitude at the lower x value of 0.75 rim The effective atomic number derived from HETRA is 6.3. Of particular interest is that these two peak structures are maintained in the plot of German liquor (centre bottom) indicating that the molecular structure of water and alcohol are preserved even when they are dissolved in one another. This possibly surprising conclusion is well known in the literature [28],... 

In Section 2.3.1., the diffraction profile was fitted to IAM atomic scatter cross-sections in the region where the molecular interference function is practically unity. This procedure yields the effective atomic number and, particularly for liquids, several further parameters derived from peaks in the molecular interference function. With... 

Capacity Requirements The operating capacity of a transfer station must be such that collection vehicles do not have to wait long to unload. In most cases, it will not be cost-effective to design the station to handle the ultimate peak number of hourly loads. An economic trade-off analysis should be made between the annual cost for the time spent by the collection vehicles waiting to unload against the incremental annual cost of a larger transfer station and/or the use of more transport equipment. Because of the increased cost of transport equipment, a trade-off analysis must also be made between the capacity of the transfer station and the cost of the transport operation, including both equipment and labor components. 

Solid-probe mass spectrometric analysis (31) showed that the benzene-ether extracts consist mainly of organic acids. Therefore, these extracts were deriva-tized with dimethylsulfate-de to yield methyl-da-labeled derivatives. The derivatives were analyzed by GCMS and high resolution MS using techniques that have been described previously (31). Authentic samples of phenolic acids deriva-tized with dimethylsulfate-dg or diazomethane were also analyzed by GCMS for reference. The distribution of the organic acids as methyl esters was determined by measuring areas of GC fiame ionization detector peaks with a correction for the effective carbon number for each compound. 

Rel. (18) shows how N depends on chromatographic retention time tp, and since tp is compound related (index i" omitted), it also shows that N (as well as n) are compound dependent. Both rel. (17c) and (18) can be used to measure the theoretical plate number or effective plate number based on experimental data obtained with a given column. This measurement is useful in practice to select columns (higher n gives lower peak broadening) and also to assess the loss in performance of a column after a certain period of usage. 

Fig. 21 Steady state incoherent intermediate scattering functions d> (r) as functions of accumulated strain yt for various shear rates y the data were obtained in a col loidal hard sphere dispersion at packing fraction

The use of a number, N, of different chromatographic mechanisms in sequence is known as column switching. Assume each mechanism has the same effective peak capacity. In its simplest form, the use of such a chromatographic sequence expands the... 

From equations (12), (13), and (14), it can be seen that the plate number is a measure of the relative peak broadening that has occurred while the sample component passed through the column in time tR. As retention time increases, the value of W increases, that means the peak broadens. If the adjusted retention time, tR, is used, the peak number is called the effective plate number and written as ... 

Figure 4.10 Effect of flow rate and gradient time on the separation of styrene oligomers in molded poly(styrene-co-divlnylbenzene) rod. Conditions column, 50 X 8 mm ID (a) mobile phase, linear gradient from 60 to 30% water in tetrahydrofuran within 200 min flow rate, 1 mL/mln (b) mobile phase, linear gradient from 60 to 30% water in tetrahydrofuran within 20 min flow rate, 10ml7min UV detection, 254 nm peak numbers correspond to the number of styrene unit in the oligomer. (Reprinted from [401] with permission of the American Chemicai Society).

ITsecond point suggested by the Table is the fact that where there are many favorable frequencies in the pattern, a randomly selected candidate is likely to have at least one that will approximately match one element of the pattern. This is no doubt the reason why 25.3% of the 2577 compounds tested by the U.S.D.A. attracted the medfly which has a seven element pattern. This contrasts with the fact that of 2618 compounds tested as attractants for the Mexican fruit fly, only 7.8% were effective (9). For this insect the Peak Number Plot shows only three favorable frequencies which makes it less probable that any given chemical will attract. 

---