A system and method for sampling fluid from a production wellsite are provided. The system includes an interface operatively connectable to the port and a separation circuit operatively connectable to the interface for establishing fluid communication therebetween. The separation circuit includes a pumping unit and at least one sample chamber. The pumping unit includes pumping chambers having a cylinder with a piston therein defining a fluid cavity and a buffer cavity. The fluid cavities define a separation chamber for receiving the fluid and allowing separation of the fluid therein into phases. The buffer cavities have a buffer fluid selectively movable therebetween whereby the fluid flows through the separation circuit at a controlled rate. The sample chamber is for collecting at least one sample of the phases of the fluid.