Measurement and Results - Measuring Cs with ICP-OES

I am attempting to observe Cesium with ICP-OES. I recently created a calibration curve that consisted of 10, 100 and 1000 ppb Cesium. I observed little to no response for these solutions. My question has to do with ionization buffers. To measure Cesium, it appears that a Lithium ionization buffer would be ideal. Do you sell this solution and what concentration would be recommend adding? Also, does this ionization buffer lower the detection limit considerably or perhaps just an order of magnitude? Thank You.