A spectroscopic measurement system for measuring a material composition of a mixed phase fluid flowing through a process pipe, the fluid having a gas phase dispersed in a liquid phase or vice versa, the measurement system comprising: an insert configured to be inserted into the pipe, the insert including: a measurement chamber defined on at least one side by a phase separating membrane, the phase separating membrane adapted to enable the gas phase of the fluid flowing through the pipe to diffuse into and out of the measurement chamber and to facilitate coalescing of the liquid phase of the fluid outside the measurement chamber, wherein the gas phase within the measurement chamber defines a gas sample; and a collector disposed adjacent the measurement chamber such that the coalesced liquid from outside the measurement chamber drains into the collector, wherein the collector includes a drain in fluid communication with the pipe such that the coalesced liquid collected by the collector flows through the drain and returns to the fluid flow of the pipe, and wherein the coalesced liquid flowing through the drain defines a liquid sample; a first probe mounted onto the insert, the first probe including a first probe tip extending into the measurement chamber and configured to transmit excitation light into the measurement chamber and to receive a gas Raman signal emanating from the gas sample within the measurement chamber; a second probe mounted onto the insert, the second probe including a second probe tip extending into the drain and configured to transmit excitation light into the drain and to receive a liquid Raman signal emanating from the liquid sample flowing through the drain; and an excitation light generation and signal evaluation unit configured to generate the excitation light, provide the excitation light to the first probe and the second probe, receive the gas Raman signal from the first probe and the liquid Raman signal from the second probe, and determine the material composition of the fluid based on the gas Raman signal from the first probe and/or the liquid Raman signal. an insert configured to be inserted into the pipe, the insert including: a measurement chamber defined on at least one side by a phase separating membrane, the phase separating membrane adapted to enable the gas phase of the fluid flowing through the pipe to diffuse into and out of the measurement chamber and to facilitate coalescing of the liquid phase of the fluid outside the measurement chamber, wherein the gas phase within the measurement chamber defines a gas sample; and a collector disposed adjacent the measurement chamber such that the coalesced liquid from outside the measurement chamber drains into the collector, wherein the collector includes a drain in fluid communication with the pipe such that the coalesced liquid collected by the collector flows through the drain and returns to the fluid flow of the pipe, and wherein the coalesced liquid flowing through the drain defines a liquid sample; a measurement chamber defined on at least one side by a phase separating membrane, the phase separating membrane adapted to enable the gas phase of the fluid flowing through the pipe to diffuse into and out of the measurement chamber and to facilitate coalescing of the liquid phase of the fluid outside the measurement chamber, wherein the gas phase within the measurement chamber defines a gas sample; and a collector disposed adjacent the measurement chamber such that the coalesced liquid from outside the measurement chamber drains into the collector, wherein the collector includes a drain in fluid communication with the pipe such that the coalesced liquid collected by the collector flows through the drain and returns to the fluid flow of the pipe, and wherein the coalesced liquid flowing through the drain defines a liquid sample; a first probe mounted onto the insert, the first probe including a first probe tip extending into the measurement chamber and configured to transmit excitation light into the measurement chamber and to receive a gas Raman signal emanating from the gas sample within the measurement chamber; a second probe mounted onto the insert, the second probe including a second probe tip extending into the drain and configured to transmit excitation light into the drain and to receive a liquid Raman signal emanating from the liquid sample flowing through the drain; and an excitation light generation and signal evaluation unit configured to generate the excitation light, provide the excitation light to the first probe and the second probe, receive the gas Raman signal from the first probe and the liquid Raman signal from the second probe, and determine the material composition of the fluid based on the gas Raman signal from the first probe and/or the liquid Raman signal.