Question

1.Sketch a schematic showing the key parts of the Dionex ion chromatography unit. Label the key parts and briefly explain their purpose. Indicate what the key ions are in the eluent as it passes through the system.

2.Use a sketch and descriptive labels to show how a single titration is able to determine the carbonate, bicarbonate, and total alkalinity. Where do the 4.5 and 8.3 numbers the method uses come from?

3.Explain how potentiometry and coulometry differ. Sketch example data on how each could be used to measure the copper ion concentration in solution. For each, would they measure the free or total concentration of the ion (assume that any complex formation is reversible.

Answer 1

1.A sample of the mixture to be examined (analyte) is injected into a carrier fluid (the eluent)

2.the combination is passed through a column containing a stationary fixed material (adsorbent)

3.Compounds contained in the analyte are then partitioned between the stationary adsorbent and the moving eluent/analyte mixture

4.Different dissolved materials adhere to the adsorbent with different forces

4.The ones that adhere strongly are moved through the adsorbent more slowly as the eluent flows over them

5.As the eluent flows through the column the components of the analyte will move down the column at different speeds and therefore separate from one another.

6.A detector is used to analyze the output at the end of the column. There are various detectors, our IC has an electrical conductivity detector.

7.Each time analyte molecules/ions emerge from the chromatography column the detector generates a measurable signal which is usually printed out as a peak on the chromatogram.

8.A suppressor is being used to reduce the background conductance of the Eluent and at the same time enhance the conductance of the sample ions

9. Detection of ions:

The chromatogram is a record of detector output (electrical conductivity) versus time as the analyte passes through the chromatography system. It consists of a series of several peaks equivalent to the different times in which components of the analyte mixture occur from the column. The number of peaks corresponds to the minimum number of different substances (compounds or ions) contained in the analyte.

Ion: an atom or a group of atoms that has both an additional or a absence of electrons
main ions in water, positive charge (cations), negative charge (anions):

H+, Na+, K+, Ca2+, Mg2+, OH-, Cl-, SO42-, NO3-, HCO3-, PO43-