# How to measure t0 with Waters2465 ECD?

<p>Hi,
We have started using Waters Electrochemical detector <strong>2465</strong> together with an Alliance and have a question regarding the determination of k’. In order to determine k’ we need a value/time for t0 .</p><p>Previously we have used an electrochemical detector from Agilent and then we used the first disturbance on the baseline for t0. The value for t0 was then around 0.8 min.</p><p>When using the Waters ECD the first disturbance on the baseline appeared around 0.2 min which didn’t seem reasonable.</p><p>Does anyone have a suggestion for how we could determine t0 while using Waters ECD?</p><p></p><p>/ Thomas</p>

• Hi Thomas

Most of the contribution to the t0 comes from the column. You can estimate the volume of mobilephase in the column by the simple formula : 0.5 x D2 x L. D = Column ID in mm, L = column lenght in mm.

This will give you the column volume in ul. If you add 50ul (contribution from the tubing) to this value you will hvae a good estimat of t0

best regards

Rune

• Thanks,

We need to be able to determine a value for t0 in every analysis we make. We have done a test using a mixture of water and mobile phase and tested with different injection volumes (2-30µl), see attached. The first disturbance on the baseline which correlates to the injection volume is a negative peak, see attached file.  Our idea was then to use the retention time for the negative peak as t0.

Is this a reasonable way to determine a value for t0? For UV-detection NaNO3 is used but we're not sure what to use for Electrochemical Detection.

• Hi

Yes this seems to be a good determination of t0.

best regards

Rune