I am currently using a Solid Phase extraction method for the determination of catecholamines and get very large spikes in my DHBA internal standard when a plasma sample is extracted. These spikes sometimes appear and sometimes the sample comes out perfect. The spikes in DHBA do not appear in non-extracted standards or extracted standards. Only in plasma samples do these large spikes occur.

I feel that some component in plasma is interacting/binding with the DHBA, causing it to read higher than it should be (about 5-10X higher than what it should be).

Any thoughts

Here are my extraction methods using solid phase extraction with a vacuum manifold:

1) Condition Supelclean LC-WCX tube with 500 ul 0.5 hydrochloric acid.

2) Wash tube with 1 ml DI water to remove excess acid.

3) Load sample (500 ul plasma sample with 500 ul DI water), pass through tube at 250 ul/min.

4) Two washes (1 ml each) using DI water.

5) Add internal standard (50 pg DHBA in 250 ul water), pass through tube at 250 ul/min.

6) Elute with 250 ul perchloric acid.

7) Injection into Eicom H-TEC 500 is 20 ul of eluent.

Again, any ideas on why some plasma samples have large spikes in DHBA and others do not?