The Road to Calorimeter Master Vol.5 – Troubleshooting on Your Own Part 1 & 2

The characters and story in this article are fictional.
For technical content, we have received advice from Professor Fukada, a visiting researcher at Osaka Prefecture University.

Related materials can be downloaded from the bottom of the article. Please have a look.

This is the final guidance on ITC. Has the information been helpful in your research?
This time, I would like to show you how to deal with irregular data by presenting real data.

Mr. Nakamura, today is the end of the ITC training, right? Have you gained some confidence?

Yes! Thanks to Professor Fukada, I think I’ve become able to handle the experimental operations and analyses. Thank you very much!

That’s good to hear. So today, I would like to talk about possible measurement troubles that you might experience in the future, while showing actual data.

I’m looking forward to it.

Part 1

Common ITC Troubles: Let’s Consider the Root Causes!

You’ve already experienced some troubles, haven’t you?

Like when the titration syringe couldn’t be cleaned, or when the DP value didn’t match the set value.

That’s right. Now, let’s list some possible troubles regarding the system, or rather, the data.

There are quite a few.

You’re right. But, Mr. Nakamura, if you understand why such phenomena occur, you can troubleshoot on your own. Let’s think about it together.

Yes, let’s do.

Part 2: Baseline Position Anomaly! Why!?

Let’s review why the signal in ITC shows upward or downward trends?

When a heat change occurs in the sample cell due to the interaction of samples, a temperature difference arises from the reference cell. To compensate, if an exothermic reaction occurs, feedback works to lower the temperature, causing a downward signal. Right?

Exactly. The ITC system controls to eliminate the difference between the sample cell and the reference cell. Therefore, if the DP value of the baseline before sample measurement is lower than the set value, it suggests that the sample cell is warmer than the reference cell. This could be caused by the factors shown here.

I have heard about the air conditioning issue before. If the temperature in the sample cell changes due to the titration syringe, this affects the DP. So, is this the titration syringe?

No, in this case, the titration syringe would “physically” hit the cell.
Physically hit??
If the titration syringe bends and hits inside the cell, frictional heat will be generated, right?

Such a thing can happen!?

Moreover, in the case of the iTC200, if the nut part of the titration syringe becomes loose, the syringe may not be set in the proper position and may hit the bottom of the cell.

Additionally, in VP-ITC, if the syringe is bent or height adjustment is not done properly, similar phenomena can occur. Furthermore, even if the measurement has started, if the DP continues to show negative values, it could be that the syringe is bent or hits.

How about the rotation speed?

The faster the rotation speed, the more likely friction occurs, thus the DP tends to decrease accordingly.

I see! So, if the baseline decreases, should I assume that it is because the temperature in the sample cell has risen due to some cause? How about the effect of temperature settings?

This data was obtained with VP-ITC, setting Referene Power to 11 μcal/sec, and plotting the DP value of the baseline at different measurement temperatures. You can see that DP values tend to be lower as the measurement temperature increases. However, it is also clear that there is no effect at room temperature during actual measurement, right?

That’s correct.

So far, we have seen the system-derived influences on baseline position anomalies. So, Mr. Nakamura, can you think of anything other than system-derived causes that might affect the baseline position?

From my experience, air bubbles might enter the solution, or the cell might be dirty.

That’s correct. By monitoring the DP value before titration begins, you can tell which cell has air bubbles. Normally, the DP value should be within ±1 μcal/sec for the set Reference Power. If there are air bubbles in the sample cell, the DP value is low; if there are air bubbles in the reference cell, the DP value is high. Is that clear?

Yes! If the sample cell is dirty, the DP value will also be low, right?

That’s correct. In most cases where the DP value does not stabilize, the cause is often the contamination of the sample cell. As I mentioned earlier, maintaining a habit of cleaning the sample cell with 14% Decon 90 (or 20% Contrad 70) after each measurement will help keep the system in good condition. Do not skimp on effort, and make sure to carry out maintenance.

Yes, I understand!! By the way, professor, what kind of data can be obtained when there are air bubbles in the sample on the titration syringe side?

To be continued…