A method for determination of particle magnetic susceptibility with analytical magnetapheresis

We recently developed a new method for simple determination of particle mag netic susceptibility using analytical magnetapheresis. This new method does not require laborious calibration plots and trial susceptibility values as do previous analytical magnetapheresis methods. The new method is based on balancing channel now rates and magnetically induced now rates for particl e deposition in analytical magnetapheresis. The maximal now rate for comple te particle deposition was determined experimentally and set to equal the m agnetically induced now rate for determining particle magnetic susceptibili ty. This magnetic susceptibility determination generally takes less than 20 min. Several magnetically susceptible and ion-labeled particles were teste d using this new method. The carrier magnetic susceptibilities were varied, and erbium ion-labeled particles were studied experimentally, resulting in successful susceptibility determinations of erbium ion-labeled particles a nd yeasts. The precision of each measurement was generally similar to 10%. Experimental determination of particle magnetic susceptibilities differed b y less than 10% from reference measurements taken using a superconducting q uantum interference device magnetometer. This method can determine minimal susceptibilities on the order of 10(-9) cgs. The minimum number of erbium l abeling ions per particle required for complete deposition of silicas and y easts was found to be 6.7 x 10(9). Analytical magnetapheresis shows good po tential for use in simple determination of particle magnetic susceptibiliti es and should become a useful technique.