Response retention-time distribution

The application of this statement in the present context enables one to represent the process responsible for the retention of molecules by a chain of v catenary compartments, each of them associated with an exponential retentiontime distribution with parameter A. This compartment chain is well known as the pseudocompartment chain, but no physical or mechanistic meaning may be associated with this chain. It simply represents a formal way to take into account the Erlang retention-time distribution. 

Though collected editions of chemical engineering theory existed since the early 1930 s, as for instance by Eucken and Jakob (35) and by Berl (36), their generalizing land of thinking did not meet widespread response. The importance of retention time distribution (37) and of Damkohler s fundamental work on the influence of difiusion, fluid flow, and heat transfer on the degree of conversion (38), which still today represents the basis of chemical reaction engineering, was not realized properly until 1950. Ever since then the fields of heat transfer (39) and distillation generally have been dominated by chemists. 

The time at which a peak appears in the detector response is called the retention time of the solute it is the time it takes a given solute to travel the length of the column. For a Gaussian peak distribution, the retention time corresponds to the peak center. Mathematically, the retention time of component i is simply... 

Figure 8.2 NanoLC-chip-MS of replicate injections (n — 5) of an eight-protein digest, 250 fmol each, (a) Overlay of 5 total ion chromatograms for the corresponding analyses, (b) Scatter plot of intensity measurements for 5 replicates and 2230 peptide ion clusters, (c) Distribution of RSD values on retention time measurements, (d) Variation of MS response for different tryptic peptides according to sample amount loaded. Conditions enrichment/trap volume of 40nL LC separation channel of 43 x 0.075 x 0.050mm both packed with Zorbax Ci8 separation media a 5 pL injection of 80 ng tryptic digest of 8 proteins was performed except for (d) where variable amounts (1-1000 ng) of digest were injected.

The capacity factor k is essentially a corrected retention time (Equation [3.18]) that takes into account variations in mobile phase flow rate and thus provides a more robust indicator of analyte retention for a given combination of stationary and mobile phases. As is a unique property of a given solute A for a given stationary-mobile phase combination, the adjusted (corrected) retention volume V,a (Equation [3.15] (or the corresponding retention time) can be used as a tag for analyte identification. Thus the precision and accuracy of measurement of Vja become important and depend on those of the measurement of flow rate U since in practice retention times rather than volumes are the measured quantities. In response to this limitation of the V,a parameter, the capacity ratio of a solute (k) ) was defined as the ratio of its distribution (partition) coefficient to the phase ratio (Vm/V s) of the column with respect to analyte A ... 

The dinonyl-phthalates (DNP) create a special analytical challenge. The DNPs typically consist of a technical mixture of C9-isomers. Hence the response of DNP is distributed to individual isomers. The integration of the unresolved DNP peaks needs to be performed over a wider but constant retention-time range from the data processing software as shown in Figure 4.73. A linear calibration range for DNP of 0.4-4.0 mg/L could be achieved. 

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