Retention of ions in a magnetic chromatograph using high-intensity and high-gradient magnetic fields

The control of the retention and separability of samples to be analyzed with high performance liquid chromatography systems is difficult, and usually requires exchanging of the. mobile phase and/or the column. We developed a magnetic chromatography (MC) system, which does not require re gular exchanging of the mobile phase and/or the column, and uses a continuous-flow system to separate, multiple ionic species with different magnetic properties. To demonstrate experimentally the feasibility of such an MC system, we measured the retention of ions in the MC system for aqueous solutions of either pure NaI, CuSO4, NiCl2, CrCl3, or CoCl2. We applied magnetic fields varying from 0 to 3 T to the aqueous solution of transition element cations and anions flowing in an MC system, and demonstrated that the retention time was delayed by about 20 min, and that for Co(II) the chromatogram broadened with increase in the applied magnetic field intensity (H). Furthermore, our results suggest that for ionized transition elements with a larger Bohr magneton number, the retention time in MC systems becomes longer. We derived experimentally a retention factor, k, that can be simply expressed in terms of an MC parameter, p(MCH), which is the product of the Bohr magneton number, the concentration of the cations, and H. The MC parameter can be used to correlate all experimental data in terms of k, as k = 0.0014p(MCH)(1.47). Hence, k is proportional to about 3/2 power of the MC parameter. We therefore confirmed that there is a significant effect of high-intensity, high-gradient magnetic fields on the behavior of paramagnetic cations in water.