Testosterone background in UPLC

<p> I am developing an assay for low-level testosterone (low pg/mL range) and am seeing a significant testosterone signal, complete with spot-on retention time and ion transitions,  that we are reasonable certain is coming from the Acquity UPLC. The basal level quants out to 20-40 pg/mL, which is to high for us. We have tried:</p><p>1. Changing the needle wash solutions</p><p>2. Changing the needle</p><p>3. Changing the injection modes</p><p>4. The signal is present if you do a 0 uL injection at the same levels as a 10 uL injection.</p><p>5. It is present regardless if you inject solvent straight out of a bottle, or an extracted blank at nearly identical levels.</p><p>6. Waters has come in and basically rebuilt the entire injection path.</p><p>7. You can wash the entire system with straight ACN for an extended period of time and then re-equilibrate under initial conditions and get a yet stronger signal than you had before.</p><p>8.The signal is strongest on the first injection and then diminishes to a 'basal level' by the second and subsequent injections.</p><p></p><p>If anyone has successfully dealt with this problem, please let me know.</p><p></p><p>THanks,


  • MCLong

    Thank you for your input. We generally use Optima grade water, but it couldn't hurt to replace everything again. We did have to revert to house DI for a week or so. I'll let you know how it turns out.

    Have a good day!