A flow cell assembly for use in a liquid sample analyzer including a radiation source, a sensing device and a liquid sample source to supply a liquid sample includes an entrance joint member, a liquid core waveguide, a liquid sample feed tube, and an input optical fiber. The entrance joint member includes a waveguide receiving bore and a feed tube receiving bore. The liquid core waveguide is mounted in the waveguide receiving bore and defines a waveguide bore. The liquid sample feed tube is mounted in the feed tube receiving bore such that the liquid sample feed tube is in fluid communication with the waveguide bore to fluidly connect the liquid sample source to the waveguide bore. The input optical fiber is mounted in the entrance joint member to transmit radiation from the radiation source to the waveguide bore, which radiation is transmitted through the waveguide bore and the liquid sample therein to the sensing device.