Effect of Source Temperature on 2,4-DNP Response at Low Concentrations

Last year, Michelle wrote a blog highlighting the effect of source temperature on peak shape and recoveries. I was having my own problems with terrible PAH peak shape on the same instrument (a 7890a/5975C with an inert source). While the inert source has a maximum programmable temperature of 350 degrees, I made sure to heed Michelle’s warning and stayed well below the maximum. Unfortunately, I was having problems at the same temperature Michelle picked for her optimum.

Starting at 250 degrees, I tuned the MSD at 10 degree intervals, using the same targets for each tune file. As you can see, there was a drastic increase in the response of the late eluting PAHs as the source temperature was stepped up.

But how did 2,4-dinitrophenol (2,4-DNP), that key SPCC, respond relative to its associated internal standard?

 

Response vs Ion Source Temperature

The graph on the left makes it look like Acenaphthene-d10 experienced a dramatic increase while 2,4-DNP barely saw any gains, but the reality is they both a little more than doubled their responses over the 50 degree temperature range. Since both Acenaphthene-d10 and 2,4-DNP responded similarly to the temperature increases, you would not expect the relative response factor to 2,4-DNP to be negatively impacted, and that is the case. Below, in the second graph, you can see the trend line for 2,4-DNP is flat, indicating no change in the relative response factor as the source temperature was increased. In fact, the slope of the trend line was .0001, indicating an extremely slight increase in relative response as source temperature was increased.

Relative Response vs Ion Source Temperature

The preceding data was collected from a series of 10 ug/mL injections at 10:1 split. I also ran 20 ug/mL and 32 ug/mL standards through the temperature range with similar results…and negligible effect on 2,4-DNP relative response factors. However, as Michelle mentioned in her post, you can’t have your cake and eat it too (well, she really said “all great things come at a cost”). The problem I ran into was that the DFTTP tune evaluation would not meet 625 tune criteria reliably above 260 degrees. At 270 degrees, the 625 criteria were met about half the time, above 270, the criteria weren’t being met.

We'll revisit source temperature effects on tune evaluations and target tuning in another post.