مگنتو کروماتوگرافی مایع با کارایی بالا High-performance liquid magneto-chromatography

۱٫ Introduction The separation of different compounds according to their magnetic properties is common practice in the manufacturing and mining industries [1,2]. However, in recent years the use of this technique has expanded to other areas such as biotechnology and analytical chemistry [3]. Given its benefits including speed, simplicity and selectivity, magnetic separation has promising applications in the field of separation techniques. Industrial magnetic separators[4,5] are used to separate ferromagnetic or paramagnetic particles, that is, substances with a positive magnetic susceptibility value (χ). Nevertheless, most biological molecules such as amino acids and proteins have diamagnetic properties (i.e., negative susceptibility) or are weakly paramagnetic (they are not affected by a magnetic field). Thus, magnetic supports need to be used to promote their retention. These magnetic supports are usually polymer particles doped with magnetite or with colloidal suspensions of paramagnetic compounds. The development of new methods of separating magnetic particles has been the goal of several research teams. These efforts have resulted in the emergence of a series of analytical separation techniques, designated magnetophoresis, used to characterize particulate and polymeric materials [6–۸]. Thus, the field flow fractionation (FFF) system developed by Giddings in the mid 1960s and marketed in the late 1980s was initially based on gravitational, thermal and electrical forces. However, the incorporation at the start of 1980 of a magnetic field [9] turned this system into a high resolution and reliable analytical method for particles and polymers from a few nm to 1
m in the normal mode and from 0.5 to 100
m in the steric mode [8]. The split- flow thin fractionation (SPLITT) method based on differences in transport rates can be applied to gravitational [10] or magnetic [11] fields among others, and is useful for the separation of macromolecules, colloids and particles. The SPLITT procedure is particularly useful for the preparative separation of large molecules (FW > 106). The technique known as magnetapheresis [12] evolved from ferrography, an analytical method based on the magnetic deposition of particles in a free-flowing, open stream closed to a magnetic field, and generates a deposition pattern of magnetically susceptible particles from the suspending medium under carefully controlled flow and magnetic field conditions. In electromagnetophoresis (EMP), whose theory was developed by Kolin [13], particles migrate through an electrolyte solution in a direction perpendicular to a magnetic field and an electric current, when the electric current is applied through the conductive fluid and the homogeneous magnetic field is perpendicular to the current [14]. Finally, high-gradient magnetic separation (HGMS) is a powerful separation process with a great potential for industrial wastewater treatment. HGMS relies primarily on a magnetic force as the mechanism for the capture of particles on collectors [15,16]. In this paper, we advance one more step to develop a chromatography system in which the stationary phase is made up of particles with paramagnetic properties. These particles, along with the analytes eluted by the mobile phase, are subjected to a low intensity external magnetic field, which plays a key role in the separation process. We, therefore, consider that the term high-performance liquid magneto-chromatography (HPLMC) fittingly describes the technique developed. Herein, we derive a theoretical expression describing the effect of the magnetic field on the analyte retention time, and illustrate its use by determining the magnetic susceptibility of copper-labelled amino acids. ۲٫ Theory The model proposed is based on the presence of a stationary phase of paramagnetic particles subjected to an external magnetic field. In these conditions, lines of induction occur around these particles (Fig. 1). The paramagnetic analytes would drive into the randomly distributed high gradients around the magnetized packing particles. The paramagnetic analytes could be attracted then into the slower moving fluid close to the surface of the paramagnetic stationary phase rather than being carried by the faster moving fluid in the larger spaces between particles. The separation takes place due to the difference in the attraction force exerted by the high gradients.