The Road to Calorimeter Master Vol.7: The Key to the Second DSC Measurement is Filling the Solution! (Part 1)
>
The characters and story herein are fictional.
The technical content is supervised by Professor Fukada, a guest researcher at Osaka Prefecture University.
You can download the “Memo to Confirm with Professor Fukada (DSC) and His Answers” compiled by Mr. Nakamura, which appears in the text, from the “Download” button below the page.
[Previous Story]
Mr. Nakamura of Maruban Pharmaceuticals conducted the VP-DSC measurement according to the manual. However, the measurement didn’t go well. He decided to visit Professor Fukada with questions he had compiled after finding “???” on Malvern’s homepage.
[This Story]
| Mr. Nakamura sent the following email to Professor Fukada beforehand. |
| Additionally, before the visit, he compiled the items he wanted Professor Fukada to confirm based on the content described on the homepage and the manual. It seems there are some differences from ITC measurements. |
 | |
 | Professor Fukada. It’s been a while. Thank you very much for your instruction on VP-DSC measurements today! |
 | Yes, thank you as well. |
 | As mentioned in the email before, the baseline in the water-water measurement was rising in an upward-right trend. Where do you think the cause lies? |
|---|
| The causes vary, but the main reasons cited are:
(1) Air bubbles mixed in the cell
(2) Dirt in the cell
(3) Difference in solution between the reference and sample cells
(4) Difference in liquid level between the reference and sample cells
(5) Sample precipitation.
Since it’s a water-water measurement this time, (3) and (5) are not applicable. However, looking at the data, the DP value starts from negative, which suggests that (1) and (4) might be the causes if the cells were properly cleaned. Although I haven’t seen the actual operation, did you adjust the liquid level with the filling adjustment syringe? |
|---|
| Yes, that’s correct. |
| You also degassed according to the manual, right? |
|---|
| Yes, I did. |
| In that case, the possibility of air bubble inclusion is still high. Since the amount of solution in VP-DSC is 500 uL, which is more compared to iTC200, it might have been hard to grasp the pumping sensation a bit. |
|---|
| Professor, regarding the solution filling method, do we absolutely have to use the filling funnel? |
| The filling funnel serves to prevent damaging the cell by hitting it with the Gastight syringe. When using the funnel, the syringe stops a few millimeters above the cell bottom, preventing it from hitting the bottom. |
|---|
 | Nevertheless, when removing the solution completely, I think the sample concentration might change… |
| Sharp observation, Mr. Nakamura! That’s correct. If the measurement objective is Tm, there’s no impact, but if you want to correctly determine the enthalpy, the concentration changes will have an effect. In such cases, remove the filling funnel to completely remove the solution. Also, if you become accustomed to the operation and can fill and pump the solution without the filling funnel, it is not essential. |
|---|
| I see. So, like with iTC200, it takes practice to get used to filling the solution. |
| That’s right. Conversely, solution filling is the only operation needed, so once that’s mastered, the measurement itself isn’t difficult. |
|---|
| So, if the filling is done properly, what should the DP value be? |
| DP stands for Differential Power. It looks at the difference between the reference cell and the sample cell. If the same solution is in the two cells, the difference should become as close to zero as possible. |
|---|
| Which means, when it was measured previously and was -6.5 mCal/min, it was incorrect. |
| Yes. As with ITC, it is necessary to properly confirm the stability of the baseline.
Causes for the DP value being negative include:
(1) Air bubbles in the cell
(2) Dirt in the cell
(3) Difference in solution between the reference and sample cells. |
|---|
| Speaking of which, Professor, in ITC we used ultrapure water for the reference cell, but why do we use buffer solution in DSC? |
| The heat capacity of water and buffer solutions differs. Also, the temperature dependency varies depending on the buffer components, which changes the baseline slope. In ITC, since the measurement is done at a constant temperature, the heat capacity difference doesn’t constantly change, so ultrapure water is fine for use. |
|---|
| I see, that’s how it is. Then, can we try conducting a water-water measurement using the system? |
| Yes, let’s begin. |
|---|
| First, turn on the system and PC. Launch the control software and confirm the system’s indicators are lit. Degas ultrapure water with ThermoVac for about 3–5 minutes. |
| We recommend degassing ultrapure water for about 15 minutes when checking baseline stability. With samples or buffer solutions, if degassed too long, water may evaporate changing the concentration, so keep it to around 3–5 minutes. |
|---|
| Understood. Degassing is complete, proceeding to clean the system. Remove the pressure cap, cover the pressure sensor with the pressure plug.
Temporarily use the filling funnel to remove the solution inside the reference cell. Similar to ITC, after completion of measurement, the cell must be filled with ultrapure water before finishing. |
| Yes, that’s correct. |
|---|
| Then remove the filling funnel, set the cell cleaning device. Flow 300 mL of 14% Decon90 (or 20% Contrad70), followed by 300 mL of ultrapure water for cleaning. Remove the device, remove the remaining ultrapure water in the cell with the Gastight syringe, then set the filling funnel. Fill about 700 uL of degassed ultrapure water into the Gastight syringe and eliminate air bubbles. Insert the Gastight syringe into the sample cell and slowly inject until the solution is visible through the filling funnel hole. Once the liquid level appears, pump a few times. Remove the solution overflowing from the cell entrance, remove the filling funnel, and adjust the cell liquid level with the filling adjust syringe. Repeat the same procedure for the sample cell. Remove the pressure plug and close the pressure cap tightly. Verify the Pressure on the monitor! You’ll check if it hasn’t fallen far below 27 psi, right? |
 | Yes, though this value varies by system, check the engineer’s measurement data from the time of delivery. |
|---|
| How can I find it? |
| Open the raw data text file with extension “.dsc” in Notepad. You’ll find a number indicating pressure in the real measurement section.
If it’s below 20 psi, the pressure cap may be worn. Occasionally, debris inside the cap or on system screw threads may also reduce Pressure, so please be cautious. |
| ![]()  |
| By the way, Mr. Nakamura, how long did it take to clean and fill the sample cell? |
| I didn’t measure exactly, but about 10 minutes? |
| Not bad. The reason for checking the time taken for operation is that in VP-DSC measurements, you must not stop the measurement when switching samples. |
|---|
| Yes, it was mentioned in the operating instructions. It’s related to thermal history. |
 | Let me add to thermal history. In DSC, due to the device’s nature, data from the initial scan after measurement begins appear in different positions and forms than subsequent data. This occurs because pre-scan “thermal history” differs from subsequent scans. Before the scan starts, the device is at a constant temperature. In contrast, for the second scan and beyond, it initiates after lowering the temperature from the previous cycle’s heating scan back to the starting measurement temperature. Thus, since the state before commencement differs, the response obtained from the first scan differs from others. Repeated scanning tends to increase inter-scan reproducibility. In DSC measurement, the data is acquired as a set of control (both cells filled with buffer) and sample measurement (buffer in reference cell and sample in sample cell). To perform the sample measurement in a stable thermal history state, control measurement is recommended to be conducted overnight from the day before. |
 | Indeed. To conduct measurements in a stable thermal history, conduct the measurement without interrupting continuous scans, swiftly filling the sample after the control measurement cooling phase reaches an appropriate temperature. Depending on your familiarity with the operation, expect removing, cleaning, and filling to take about 10–15 minutes on average. Even if you haven’t completed the operation, the system will start heating. Therefore, it’s recommended to practice with water before measuring actual samples to get a feel for the operation. |
|---|
| Thank you, I am feeling a bit nervous. |
| Once accustomed, you’ll be fine. When filling the sample, using a dry Gastight syringe reduces concentration discrepancies. If it was delivered with a needle connectable to a luer-lock type syringe, use it for removing solutions or simple cleaning, and use the Gastight syringe only for filling samples. Also, after using the Gastight syringe, well washing it and storing it with the plunger removed is good practice. I’ve heard stories of plungers not coming out due to residue buffer solution components. |
|---|
| Got it! Very insightful. By the way, Professor, is cleaning also necessary when switching from buffer to sample? |
| No, it is not necessary. |
|---|
| The filling of ultrapure water is completed, setting parameters in the control software according to the operating instructions. |
| ![]()  |
| Addendum. This time, Mr. Nakamura is conducting a system check with Number of Scans set to 10. However, precisely knowing how many control scans can be performed in one night during actual sample measurement might be challenging. Depending on the measurement conditions, estimate the time it takes for the scan, for instance, about 30 minutes until the baseline stabilizes for a 90°C/Hr scan from 10–100°C, and calculate how many measurements can be minimally performed until the next morning. Input the number of scans plus some extra into Number of Scans. The Number of Scans> can be adjusted during measurement. Upon arrival the next morning, if the scan is higher than the measurement number, for example, set at 20 but completing at 15, adjust the input to 15, then confirm with Update Run Param.. Ending the measurement forcefully might result in data retrieval problems, so changing the number of scans is recommended. |
| ![]()  |
| Let’s start the measurement. |
| Yes, but before that, let’s take a short break. |
|---|
Continue to Part 2Download the “Memo to Confirm with Professor Fukada (DSC) and His Answers” featured in the text from the “Download” button below.Download
