Injection volume, maximum allowed

For several reasons, the drastic effect predicted by eqn.(7.25) is not usually observed. In the first place, the maximum allowable injection volume may not only be determined by the amount of stationary phase, but also by the amount of mobile phase present in the column (or, to be precise, the volume of mobile phase that occupies one plate in the column). ... 

The equations also make clear that the sample mass, i.e. the product C U should be large. The column may be overloaded with regard to the main component as long as the resolution of the trace peak is not affected (Figure 19.2). However, the injection volume is restricted if band broadening needs to be avoided. The maximum allowed injection volume which restricts band broadening to 9% is given by " ... 

In the analytical chromatogram the injected sample volume is so small that the peak widths are not influenced. Moreover, the sample mass is too low to give overloading. The maximum allowed injection volume has been calculated in Section 19.2 and the... 

A diluted solution contains component A, which is required to be isolated by preparative HPLC amongst accompanying impurities. The separation factor of A to the nearest adjacent peak is 1.5 and its retention factor is 4. The analytical column used has a theoretical plate number of 6400 and a void volume of 2 ml. Calculate the maximum allowed injection volume at which peak A actually touches its nearest neighbour. 

The maximum allowed injection volume, Vj, to avoid an excessive broadening of the first peak is defined as ... 

Usually the injection quality can be assumed to correspond with K=2 but for excellent injection it is lower, thus allowing larger sample volumes. However, it is more important that the maximum injection volume depends on the retention volume of the solute therefore, for capillary columns with their extremely small retention volumes (since Ur decreases with the square of the capillary diameter), the allowed injection volume has values in the nanolitre range. 

Conventional packed column injection ports are used for the sample introduction on packed and megabore columns. In case of capillary columns, unless a special injection technique is used, the low maximum allowable sample volume which may be introduced on the column negatively affects the experimental detection limits as only a tiny fraction of the derivatized extract is finally processed in the hyphenated system. Online preconcentration and injection of derivatized organolead species can solve that problem. It consists of three consecutive processes taking place in the injection hner sample injection, solvent venting and release of the analytes on to the column. Up to 25 fil can be processed at a time and larger amounts can be handled by successive injections of 20 to 25 /a1 volumes at 1 min intervals to remove the solvent. 

Of course the later eluted peak is diluted more than the early eluted one. However, if only the peak with 10 is important, the injection volume can be increased to 157 pi as shown in the discussion of equation (10). In this case the dilution factor of this second peak is as small as that for the first peak with an injection volume of 28 pi, namely 4.2. Therefore, the peak maximnm concentrations will be the same in both cases, 0.24 x 10 gml Note that this is only true if the respective maximum allowed injection volume is used for both peaks. In this case, Cp is independent of the peak retention volume (i.e. of the column inner diameter or of the k value) or the plate number of the column. 

Inject the desired volume of specimen into the gas chromatograph and record the peaks on the sensitivity setting that allows the maximum peak height and minimum baseline noise. The injection volume should be small enough to produce symmetrical gaussian shaped peaks. Fig. I illustrates a typical analysis. 

If the mobile phase is a liquid, and can be considered incompressible, then the volume of the mobile phase eluted from the column, between the injection and the peak maximum, can be easily obtained from the product of the flow rate and the retention time. For more precise measurements, the volume of eluent can be directly measured volumetrically by means of a burette or other suitable volume measuring vessel that is placed at the end of the column. If the mobile phase is compressible, however, the volume of mobile phase that passes through the column, measured at the exit, will no longer represent the true retention volume, as the volume flow will increase continuously along the column as the pressure falls. This problem was solved by James and Martin [3], who derived a correction factor that allowed the actual retention volume to be calculated from the retention volume measured at the column outlet at atmospheric pressure, and a function of the inlet/outlet pressure ratio. This correction factor can be derived as follows. 

Usually, one has obtained an estimate for the elimination constant and the distribution volume Vp from a single intravenous injection. These pharmacokinetic parameters, together with the interval between administrations 0 and the single-dose D, then allow us to compute the steady-state peak and trough values. The criterion for an optimal dose regimen depends on the minimum therapeutic concentration (which must be exceeded by and on the maximum safe... 

The flow cell is the most important component of a flow injection manifold for CL measurements since maximum radiation should be generated while the solution is flowing in front of the detector. Other attributes of the flow cell are the small dead volume of the cell to allow fast and effective washing between injections... 

Kinetics. The reaction of N-dodecyl 3-carbamoyl pyridinium bromide (I) with cyanide ion in the microemulsions was observed by following the 340 nm absorption maximum of the 4-cyano adduct (II). See equation (1). Following the work of Bunton, Romsted and Thamavit in micelles ( ), a 5/1 mole ratio of KCN to NaOH was employed to prevent cyanide hydrolysis. The pH of each reaction mixture was measured on a Coleman 38A Extended Range pH meter to insure that the system was sufficiently basic to allow essentially complete ionization of the cyanide. The appropriate amounts of cyanide and hydroxide were added to the mlcroemulslon sample within 10 minutes of running a reaction. Cyanide concentration varied between 0.02 and 0.08 M with respect to the water content. Substrate was Injected via a Unimetrics model 1050 syringe directly into a known volume of the yE-nucleophlle mixture in a 1.0 cm UV quartz cell. Absorbance at 340 nm was followed as a function of time on a Perkln-Elmer model 320 spectrophotometer at 25.0 + 0.3 C. Since the Initial bulk concentration of substrate was 10 M, cvanide was always present in considerable excess. 

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