Migration time

Migration Time A solute s total velocity is given by... 

Examining equation 12.41 shows that we can decrease a solute s migration time (and thus the total analysis time) by applying a higher voltage or by using a shorter capillary tube. Increasing the electroosmotic flow also shortens the analysis time, but, as we will see shortly, at the expense of resolution. 

Figure 6.13 SEE-MEKC electropherogram of the pesticide carbaryl in a tomato sample the peak assigned number (4) coiresponds to the migration time of carbaryl. (from ref. 58).

An example of the results obtained in the form of a chromatoelectropherogram can be seen in Figure 9.6. The contour type data display showed the three variables that were studied, namely chromatographic elution time, electrophoretic migration time, and relative absorbance intensity. Peptides were cleanly resolved by using this two-dimensional method. Neither method alone could have separated the analytes under the same conditions. The most notable feature of this early system was that (presumably) all of the sample components from the first dimension were analyzed by the second dimension, which made this a truly comprehensive multidimensional technique. 

Table 11-3. Migration times for piperoxan enantiomers for four eonseeutive runs on the same agarose gel using sulfated eyelodextrin as the ehiral seleetor.

The determination of acifluorfen in soybean was performed using CE," under the following conditions capillary column (total length 83 cm, 65 cm to the detector, with a 3-mm pathlength, 75-p.m i.d.) absorbance detector, 240 nm capillary oven temperature, 20 °C mnning buffer, 50 mM ammonium acetate buffer (pH, 4.75) applied voltage, 17 kV injection, 0.4 min at 4 mbar migration time, 20 min. 

As concluded by Menzinger et CE will only fully augment chromatographic techniques in the routine determination of pesticide residues when software becomes capable of compensating for the intrinsic variability in analyte migration times. This... 

A common criticism of CE is the poor consistency of migration times for peaks compared with HPLC or GC. The effects of matrix components and small differences in ionic strength and pH can have significant effects in the separation. The use of a... 

The separation of charged compounds is based on the differences in migration velocity (v) when the electric field is applied. Migration velocity is derived by dividing the length of the capillary from injection to detection (1) by the measured migration time (t) ... 

CE can be used for both qualitative and quantitative analysis. Good reproducibility in migration times... 

FIGURE 15.5 Close-up of a 3.5 min. long stretch of the data of Fig. 15.4. Two components are migrating from the first capillary and are outlined with dashed curve. The components are transferred over 6 cycles. They have different migration times in the second dimension separation, which allows their resolution. 

Log k appears to correlate with log P for standards between log P —0.5 to 5.0. One limitation of this method is that solutes must be electrically neutral at the pH of the buffer solution because electrophoretic mobility of the charged solute leads to migration times outside the range of Tm and TEof- Basic samples are therefore run at pH 10, and acidic samples at pH 3, thus ensuring that most weak acids and bases will be in their neutral form. This method has been used in a preclinical discovery environment with a throughput of 100 samples per week [24]. 

Fan et al. [106] developed a high performance capillary electrophoresis method for the analysis of primaquine and its trifluoroacetyl derivative. The method is based on the mode of capillary-zone electrophoresis in the Bio-Rad HPE-100 capillary electrophoresis system effects of some factors in the electrophoretic conditions on the separation of primaquine and trifluoroacetyl primaquine were studied. Methyl ephedrine was used as the internal standard and the detection was carried out at 210 nm. A linear relationship was obtained between the ratio of peak area of sample and internal standard and corresponding concentration of sample. The relative standard deviations of migration time and the ratio of peak area of within-day and between-day for replicate injections were <0.6% and 5.0%, respectively. 

Mobile Phase Stationary Phase Migration Time (min,) Ref,... 

From the migration velocity of a compound and the migration distance one can derive its migration time (tj). The migration distance (/) in CE is equal to the length of the capillary from the inlet (injection site) to the point of detection. 

The migration time increases with increasing capillary length and reduces with increasing mobilities of the compounds and applied voltages. 

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