Baseline separation, peak-counting

Band width, and plate number, 38 Baseline peak, computer-simulated chromatograms, I8,20f Baseline separation, peak-counting methodology, 17,18 Benzenethiol, RPLC, 99f Benzo(e)pyrene, excitation spectra, I9lf,l92f Bls(chloromethyl) ether, air monitor, 20>lf... 

Two methods of peak counting were used In this study. Both methods were based on visual Inspection of the synthesized chromatograms. The criteria used to differentiate between peaks were baseline separation and resolution between maxima. The former was used to test directly the validity of the model Independently of any empirical adjustment. The simulated chromatograms were synthesized with a flat and clearly discernible baseline before the first and after the final peak (see Figure... 

All events that lay between departure from and return to the baseline were counted as one peak. Our peak capacity calculations were based on - 1.5 for the baseline separation case. 

Table III. Comparison of average simulation baseline peak counts and theoretical expectation. Amplitude range 100 1800. Component standard deviations 12,10,8,6, and 4 sec.. Separation space 175 minutes. Noise is given in terms of amplitude units. a = m/n. = 1.5.

Table I. simulation results for in using baseline counting. Amplitude range 100-1800. Separation space 175 min. Values of in are calculated from simulations at five different peak capacities based on peak standard deviations of 12, 10, 8, 6, and 4 sec. Noise Is given In terms of amplitude units. Total peak capacity range 146-438. S = in value from slope.

Another recent innovation deals with the chemistry of the capillary wall. For example, capillaries have been improved by coating their inner surfaces with novel chemistries, or by adding a replaceable dynamic coating solution, allowing better resolution of analytes (109-114). Carrier solutions or background electrolytes can be enriched with a variety of additives, permitting the separation of closely related substances at baseline resolution (see Refs. 115-118 and Sec. II). These improvements have lead to better precision, selectivity, and accuracy of separated analytes. Precision and accuracy is improved for both peak migration and peak area counts for the simple and complex analytes. 

Equation (2.79) also is the basis for the temperature dependence of reten-. tion. Furthermore, it can be used to calculate adsorption energies. We can, for. example, calculate the minimum difference in adsorption energy needed for a separation. To obtain baseline resolution between two adjacent peaks at a plate count of 10,(X)0, we need a relative retention of about 1.1. Combining Equations (2.77) and (2.79), we obtain... 

Figure 13.11. Comparison of ion current stability between NanoESI and high-flow ESI and APCI techniques. The RSD of the baseline count rate is a measure of the high-frequency ion current fluctuations. The area counts were calculated over 3-s windows, approximating chromatographic peak width, taken at 10 separate segments of the 1.6-min trace from beginning to end. Only one segment is shown for each trace to illustrate the measurement. This is a measure of the low-frequency noise reflected in baseline drift. Similar experiments at intermediate flows under the conditions of Figure 13.1 A (not total consumption nanoESI conditions) verified the trend.

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