Passage IV
In high performance liquid chromatography (HPLC), a sample solution is injected into a continuous flow of solvent, which carries the sample through a column packed with an adsorbent (see Figure 1).
The components of the sample separate from each other in the column. As each component passes through the detector, a peak is plotted on a graph. The portion (fraction) of solvent containing each component of the sample can then be collected and analyzed. The retention time (RT) is the time it takes for half of the component to pass through the column (the time that corresponds to the top of the peak).
Two experiments were done to analyze foods for the presence of sugars (which have the suffix "ose") and sugar alcohols (which have the suffix "itol"）
Experiment 1
A 0.01 mL sample of a solution containing 1 g/L each of several sugars and sugar alcohols was injected into the HPLC apparatus. The flow rate (FR) of solvent through the apparatus was 1.5 mL/min. The detector readings were plotted, and the fraction corresponding to each peak was collected and analyzed to determine its composition. The procedure was repeated at different FRs (see Figure 2).
Experiment 2
For each of 7 foods, a 1 g sample was mixed with 500 mL of ethanol in a blender, then stored overnight. Each mixture was filtered and then diluted to 1.000 L with ethanol. A 0.01 mL sample of this solution was analyzed by HPLC at FR = 0. 5 mL/min (see Table 1).
22. Suppose a trial had been done in Experiment 1 at FR=2.0 mL/min. The RT of sorbitol would most
likely have been:
Your Answer is
Correct Answer is F
Explanation
From the three graphs in figure 2, it can be seen that the larger the FR, the smaller the RT of sorbitol. So when FR=2.0, the RT should be less than the RT in the first picture, that is, less than 9.5, and the F option is less than 9 min.