To evaluate the performance of optical chromatography, a number of equations are theoretically derived using a ray-optics model. These mathematical formalisms are experimentally verified by determining the relationship between the velocity of motion of a polystyrene bead with respect to the intensity of an applied radiation force under the condition where there exists no applied fluid flow. The force is confirmed to be at a maximum at the focal point and to decrease with increasing distance from this position. The radiation force is verified to be proportional to the square of the particle size when the particle diameter is much smaller than the beam diameter. In addition, the radiation force is ascertained to be proportional to the laser power. These results are in excellent agreement with the proposed theoretical model, which is based on ray optics. Furthermore, by analogy with conventional chromatography, fundamental parameters such as retention distance, selectivity, theoretical plate number, and resolution are calculated, and optimum conditions for chromatographic separation are discussed. Based on the results obtained, the dynamic range can be extended by increasing laser power and decreasing flow rate. Peak broadening is primarily caused by variations in laser power and flow rate of the medium for large particles (< 1 microm). It is possible, in theory, to distinguish particles whose diameters differ by less than 1% for particles with a diameter larger than 1 microm. Three sizes of polystyrene beads are well separated at a flow rate of 20 microm s(-1) and a laser power of 700 mW. This technique is also applied to the separation of human erythrocytes. Two fractions, one consisting of cells ranging from 1.5 to 2.4 microm in diameter and another consisting of cells ranging from 3.5 to 5.7 microm in diameter, are observed. Optical chromatography is useful for separation and size measurement of particles and biological cells.

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This paper reports the first demonstration of a multiplex sample injection technique in capillary electrophoresis. The sample was injected into a capillary (effective length, 4 cm) as a pseudorandam Hadamard sequence by a photodegradation technique using a high-power gating laser, and the fluorescence signal, which was measured using a probe excitation beam, was decoded by an inverse Hadamard transformation. The signal-to-noise ratio was improved by a factor of 8, which was in good agreement with the theoretically predicted value of 8.02. This approach is potentially useful for the enhancement of the sensitivity by 3 orders of magnitude in high-resolution capillary electrophoresis, combined with fluorescence detection.

Halogenated benzenes and phenols are measured by multiphoton ionization mass spectrometry using femtosecond (150, 500 fs) and nanosecond (15 ns) laser pulses. The molecular ion is strongly enhanced for monohalobenzenes when the pulse width of the ionization laser is shorter than the lifetimes of their excited states. This is attributed to the reduction of intersystem crossing by a spin−orbit interaction, the so-called internal heavy-atom effect, and to rapid dissociation from the triplet state. A femtosecond laser pulse was deemed to be useful for the efficient ionization of dichlorobenzene and trichlorobenzene although their lifetimes are unknown, since polychlorinated benzenes are thought to have shorter lifetimes as the result of a stronger spin−orbit interaction. The ionization efficiencies of o-chlorophenol and p-chlorophenol are also obtained using femtosecond and nanosecond pulses. In the case of o-chlorophenol, intersystem crossing occurs more efficiently by stabilization of the triplet state by intramolecular hydrogen bonding, and as a result, the femtosecond pulse is more effective in ionizing o-chlorophenol, which has a shorter lifetime. These results indicate that an ultrashort laser pulse is very useful in improving the ionization efficiency for a molecule with a short lifetime, such as polychlorinated dioxins and their precursors.

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Hadamard transform capillary electrophoresis, which is based on a multiple sample injection technique, was combined with laser-induced fluorometry and utilized in the determination of analytes at subpicomolar levels. The sensitivity was substantially improved by increasing the order, i.e., the number of elements, of the Hadamard matrix. In fact, the signal-to-noise ratio was enhanced 18-fold by the use of a matrix of order 2047. A feasibility study was carried out by computer simulation to study the detection of an average of less than a single molecule in a single injection volume. The signal peak was clearly observable even under conditions at which only 0.3 molecule is present in the volume. Thus, this approach is potentially useful for ultratrace analysis, in which conventional single-injection capillary electrophoresis cannot be applied.

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