Chromatographic bandwidth

Ghrist, B.F., Stadalius, M.A., Snyder, L.R. (1987). Predicting bandwidth in the high-performance liquid chromatographic separation of large biomolecules. I. Size-exclusion studies and the role of solute stokes diameter versus particle pore diameter. J. Chromatogr. 387,1-19. 

The continuous annular chromatograph can be described mathematically by a theoretical plate approach similar to the one developed by Martin and Synge [40] and exemplified by Said [41] for stationary columns [5]. The mathematical description results in algebraic expressions for the elution position of each solute relative to the feed point and for the bandwidth of the eluting zone as a function of the elution position or other system parameters. However, a series of simplifications have to be made in order to describe the CAC with the theoretical plate concept ... 

Residue chemists would be most interested in comparable confidence bands or confidence bandwidths. These values become a performance characteristic for any detection system. The values indicate the precision of not only the prepared standards but also the precision of the overall operating detection system. It is ultimately envisioned that a given system of a separation column in a chromatograph with a certain type of detector should give bands of standardized values. If a chemist finds he has not met... 

They were also typical when the regression model chosen was first order. Mean-level bandwidths greater than 20-30% are probably indicative that errors have been made in the analysis process that should not be tolerated. In this case techniques would be carefully scrutinized to find errors, outliers, or changing chromatographic conditions. These should be remedied and the analysis repeated whenever possible. Certain manipulation can be done to reduce the bandwidth values. For example, they would be... 

And he continues, The confidence bandwidth of a calibration problem does not adequately describe the solution of unknowns, but it could give information about the status of the analytical instrument, such as a gas chromatograph. It could tell how efficient it was running on a particular day. For the solution of unknowns, one needs, in addition to the confidence bandwidth, information about the response bandwidth which provides the more important portion of the error estimations in a calibration situation. ... 

An overview of HPLC instrumentation, operating principles, and recent advances or trends that are pertinent to pharmaceutical analysis is provided in Chapter 3 for the novice and the more experienced analyst. Modern liquid chromatographs have excellent performance and reliability because of the decades of refinements driven by technical advances and competition between manufacturers in a two billion-dollar-plus equipment market. References to HPLC textbooks, reference books, review articles, and training software have been provided in this chapter. Rather than summarizing the current literature, the goal is to provide the reader with a concise overview of HPLC instrumentation, operating principles, and recent advances or trends that lead to better analytical performance. Two often-neglected system parameters—dwell volume and instrumental bandwidth—are discussed in more detail because of their impact on fast LC and small-bore LC applications. 

Bandwidth. Column efficiency may also be expressed in terms of a bandwidth. The bandwidth is defined as the volume of mobile phase containing 95% of an eluted compound, or, equivalently, four standard deviations of a statistical distribution of the same shape as the chromatographic peak ... 

In chromatographic systems, the various contributions to peak broadening are generally independent. This means that the variance of the system is the sum of the variances from each contribution. Combining this relationship with Equation 1 yields an expression for the system bandwidth ... 

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 5-vim gel GPC columns are seen to produce tremendous e.fficiencies, but these efficiencies are only realized when the chromatographic system is optimized with respect to bandwidth. This also holds true to a lesser degree for a well-packed lO-ym gel column. 

A chromatographic property of interest is the separation between spots (solutes). The most simple definition is resolution R= z ( - - z 2 H2 (J2 (5 ) with a, the bandwidth of the developed spot. Assuming ai=cj2 and using zJo= NRf [2] N is the plate number) the formula becomes ... 

The resolution of two chromatographic peaks has been defined in terms of retention times and bandwidths in chapter 1 ... 

Lor a particular analytical separation, each biosolute will have an optimal k] value for maximum resolution with a designated column, flow rate, and mobile phase composition. Similar criteria apply in preparative (overload) chromatography with multicomponent mixtures, where resolution is similarly enhanced following optimization of chromatographic selectivity and zone bandwidth. The conventional approach to process purification with low molecular weight solutes has frequently been based on linear scale-up of the performance of an analytical column system. In these cases, high-resolution separations can be achieved often without the burden of conformational or... 

Uni-uni pathway Typified by simple distribution process and kinetics, narrow bandwidth with high mass and biological recovery may be characterized by very rapid interconversion kinetics as the solute transverses the chromatographic bed as a single, time-averaged structure. 

Once the retention volume of a solute is calculated for a particular gradient profile, corresponding bandwidth and resolution can be determined by introducing the appropriate instantaneous retention factor A, at the elution of the peak maximum calculated from the gradient function tpf = /(Tr) and from the retention equation A, = f chromatographic mode and gradient function used [851 ... 

When the sample is introduced into the column, usually in the form of a zone of vapor, it takes the form of a narrow band. During transit through the column, various factors influence the width of this band, which is continuously increased due to various dispersion processes. These include diffusion of the solute, resistance to mass transfer between and within phases, and the influence of flow irregularities and pertur-bations.f A simple concept, the theoretical plate, carried over from distillation processes, has been used to compare columns and account for the degree of dispersion that influences bandwidth. A chromatographic column may be considered to consist of numerous theoretical plates where the distribution of sample components between the stationary and mobile phase occurs. Hence, a measure of the efficiency of a GC column may be obtained by calculating the number of theoretical plates, N, in the column from ... 

Resolution (RJ is a measure of a successful chromatographic separation and requires that two peaks have different elution times for the peak centers and sufficiently narrow bandwidth to eliminate or minimize overlap (Figure 6-6). It is expressed mathematically as follows ... 

Figure 6-6 Schematic diagram of a chromatogram obtained from a column and open-bed chromatograph (planar). In open-bed chromatography (bottom), strongly retained compounds (B) move more slowly than less strongly retained compounds. In column chromatography (top), compound B is eluted later than compound A, again because of stronger retention, Rj, Resolution Vr A), retention volume for solute A V,(B), retention volume for solute B w A), bandwidth (units of volume) measured at base for solute A w(B), bandwidth (units of volume) measured at base for solute B V , volume between Injector and detectors d(A), distance traveled by solute A A, solute A B, solute B.

This paper addresses the operating characteristics and performance of a 30pi TCD when coupled with a high resolution capillary gas chromatograph. Differences in the peak shape, peak symmetry, electronic bandwidth, column flow rates, and column bleed Invoke different responses for the TCD with a capillary column as opposed to a packed column. These differences raise several questions which will be addressed in this paper ... 

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