I have an issue with silver on some of my Agilent 7700 and 7900 instruments. My calibration curve and recoveries on my QCs gottten progressivly worse over time. Calibration curve (done on a custom multistandard, 4% HNO3, 1 %HCl) is more or less quadratic now, instead of linear before, recoveries on my QCs are ranging between 30-50 %. This problem has gotten progressivly worse over time, just on certain instruments (i couldn't find any correlation on what matrices are ran on those certain instruments). I've tested following: followed Agilent's advice to do a clean-up of the front end of the instrument (3 different solutions followed by a nitric acid wash), changed the entire front-end including sample intake, lenses even the octapole, tested with just a single element solution with different acid concentrations ranging from 1% HCl - 20 % HCl, different wash out solutions and timings. All solution/different acids testing has been done with and without autosampler, as well as with self aspiration. My conclusion was, based on real time monitor, that silver has much longer stabilisation and wash out time (regardless the acid conc) than the other elements on the instruments with this problem. Apart from that, the issue dissapears temporarly after changing vacuum pump (not oil only, but the entire vacuum pump). The same calibration solutions, QCs are working fine on other instruments (both Agilents and PE instruments) which rules out the solutions. Increasing timings is not a favourable thing, due to high sample volumes. I'm in a bit lost for ideas on what it might be and was hoping to get some insights, did anybody have a similar issue?
Thanks in advance!
Eurofins Environment Testing Sweden AB
Development Chemist & Team Leader
Phone: +46 10 490 8133