A flow cell assembly for use in a liquid sample analyzer, the liquid sample analyzer including a radiation source, a sensing device and a liquid sample source to supply a liquid sample, the flow cell assembly comprising: a joint member including an axially extending alignment bore, the alignment bore including a waveguide receiving bore section and an optical fiber termination receiving bore section; a liquid core waveguide mounted in the waveguide receiving bore section, the liquid core waveguide defining a waveguide bore; and an optical fiber assembly including an optical fiber and an optical fiber termination mounted on an end of the optical fiber, wherein the end of the optical fiber and the optical fiber termination are mounted in the optical fiber termination receiving bore section, the optical fiber having an exposed optical fiber end face adjacent and substantially flush with an end face of the optical fiber termination; wherein the alignment bore radially aligns the liquid core waveguide with the optical fiber termination and thereby radially aligns the optical fiber end face with the waveguide bore; and wherein the optical fiber is operative 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; characterized in that: the joint member is unitary; the alignment bore further includes an interface bore section axially interposed between the waveguide receiving bore section and the optical fiber termination receiving bore section; an end portion of the liquid core waveguide and an opposing portion of the optical fiber termination are each disposed in the interface bore section; and a mask member is disposed in the interface bore section between the end face of the optical fiber termination and the end face of the waveguide such that the end face of the optical fiber is located adjacent and outside of the waveguide bore, the mask member defining an aperture to permit transmission of light from the optical fiber end face into the waveguide bore. a joint member including an axially extending alignment bore, the alignment bore including a waveguide receiving bore section and an optical fiber termination receiving bore section; a liquid core waveguide mounted in the waveguide receiving bore section, the liquid core waveguide defining a waveguide bore; and an optical fiber assembly including an optical fiber and an optical fiber termination mounted on an end of the optical fiber, wherein the end of the optical fiber and the optical fiber termination are mounted in the optical fiber termination receiving bore section, the optical fiber having an exposed optical fiber end face adjacent and substantially flush with an end face of the optical fiber termination; wherein the alignment bore radially aligns the liquid core waveguide with the optical fiber termination and thereby radially aligns the optical fiber end face with the waveguide bore; and wherein the optical fiber is operative 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; characterized in that: the joint member is unitary; the alignment bore further includes an interface bore section axially interposed between the waveguide receiving bore section and the optical fiber termination receiving bore section; an end portion of the liquid core waveguide and an opposing portion of the optical fiber termination are each disposed in the interface bore section; and a mask member is disposed in the interface bore section between the end face of the optical fiber termination and the end face of the waveguide such that the end face of the optical fiber is located adjacent and outside of the waveguide bore, the mask member defining an aperture to permit transmission of light from the optical fiber end face into the waveguide bore. the joint member is unitary; the alignment bore further includes an interface bore section axially interposed between the waveguide receiving bore section and the optical fiber termination receiving bore section; an end portion of the liquid core waveguide and an opposing portion of the optical fiber termination are each disposed in the interface bore section; and a mask member is disposed in the interface bore section between the end face of the optical fiber termination and the end face of the waveguide such that the end face of the optical fiber is located adjacent and outside of the waveguide bore, the mask member defining an aperture to permit transmission of light from the optical fiber end face into the waveguide bore.