A method of sample processing, comprising: providing a microfluidic device with at least one separation channel in fluid communication with a background electrolyte (BGE) reservoir , a waste reservoir connected to the separation channel through a waste channel , and a sample reservoir connected to the separation channel through a sample channel that connects to the separation channel at a junction; injecting a fluid sample from the sample reservoir into the at least one separation channel by concurrently applying pressurized gas to the BGE reservoir and the sample reservoir, and a lower pressure to the waste reservoir; delivering fluid from the BGE reservoir into the at least one separation channel to define a plug (Sp) of the sample in the at least one separation channel downstream of the junction by reducing the gas pressure (P1) in the sample reservoir , so that the gas pressure in the BGE reservoir is greater than the gas pressure in the sample reservoir; electrophoretically separating an analyte component of the sample from other sample components in the at least one separation channel by generating an axial electric field within the separation channel; and performing at least one of: (a) electrospraying the separated analyte component from at least one emitter in fluid communication with the at least one separation channel ; and (b) measuring an electrical signal corresponding to the separated analyte component in or emerging from the separation channel. providing a microfluidic device with at least one separation channel in fluid communication with a background electrolyte (BGE) reservoir , a waste reservoir connected to the separation channel through a waste channel , and a sample reservoir connected to the separation channel through a sample channel that connects to the separation channel at a junction; injecting a fluid sample from the sample reservoir into the at least one separation channel by concurrently applying pressurized gas to the BGE reservoir and the sample reservoir, and a lower pressure to the waste reservoir; delivering fluid from the BGE reservoir into the at least one separation channel to define a plug (Sp) of the sample in the at least one separation channel downstream of the junction by reducing the gas pressure (P1) in the sample reservoir , so that the gas pressure in the BGE reservoir is greater than the gas pressure in the sample reservoir; electrophoretically separating an analyte component of the sample from other sample components in the at least one separation channel by generating an axial electric field within the separation channel; and performing at least one of: (a) electrospraying the separated analyte component from at least one emitter in fluid communication with the at least one separation channel ; and (b) measuring an electrical signal corresponding to the separated analyte component in or emerging from the separation channel. (a) electrospraying the separated analyte component from at least one emitter in fluid communication with the at least one separation channel ; and (b) measuring an electrical signal corresponding to the separated analyte component in or emerging from the separation channel. <EOS>