How to use temperature to assess if primary freeze drying is finished
The freeze-drying process is infamous for how much time the process consumes. Rather than having the time effect deter you from performing lyophilization, I’ve tried to give you some ideas on how to speed up the entire process. This time around, I’d like to zoom in on the most time-consuming part of freeze drying, the primary drying step. This post presents an effective approach for endpoint determination that shortens the time the intensive primary drying step requires.
A couple of weekends ago, we were having some friends over for a dinner party. We have one of those robot vacuum cleaners and we decided that it would be helpful to let the machine clean while we were grocery shopping. But once we came back, we found that the robot had shut himself off in the kitchen and had run out of battery power cleaning the same area repeatedly.
Well, I was not so amused. The robot had to be re-charged, so we couldn’t really use it anymore. So the other cleaning robot, me, had to step in and get the job quickly done with our regular vacuum cleaner. I couldn’t help but think of how much more economical and time-efficient it would be if the robot could turn itself off once it has vacuumed a certain area, even it couldn’t reach its charging station.
Well, automatic determination of an endpoint can greatly improve not only your robot vacuum at home, but also your freeze dryer in the lab.
I’ve already discussed ways to speed up lyophilization, ranging from shell freezing to heatable shelves to pressure gradients. Now I’d like to focus on one particular part of the freeze-drying process.
Think about it, primary drying is by far the longest step of the lyophilization process. It would undeniably bring great benefits if there was a way to decrease the amount of time this step requires, while ensuring the process is not terminated too early.
If my vacuum robot stops cleaning before he’s covered the whole floor, there would still be dirt spots resulting in a low-quality performance. Similarly, if we proceed to secondary drying before all the ice is removed from the product, we will likely end up with product defects such as collapse or eutectic melt.
The time it takes to clean the floors varies, as it is influenced by the amount of furniture, objects and dirt lying around. Similarly, the time required for the primary drying step during freeze drying varies. This time is affected by several parameters such as sample concentration, sample size and sample container.
An automatic stop to the cleaning process would save battery life, electricity and prevent loss of time. Similarly, an automated process to detect the endpoint of primary drying during each run would save time and resources.
Lucky for us, several analytical methods exist to assess the endpoint of primary drying.
The most basic and frequently used method of automatic endpoint determination involves measuring product temperature using thermocouples.
After this measurement, we compare the product temperature to the set temperature of the shelf on which the product sits. The product temperature is colder than the shelf temperature during sublimation, since heat from the shelf is needed for the phase change to occur. When sublimation of the ice is complete, the product temperature will increase and approach the value of the shelf temperature. Once product temperature equals shelf temperature within 1°C difference, primary drying is considered complete.
Importantly, the vial containing the thermocouple is not representative of the entire batch. As the wire conducts more heat, the sample in contact with the sensor will typically dry faster than the rest of the batch. In bulk drying, the area around the thermocouple will similarly dry more quickly than other areas of the tray. We should then add some additional drying time after the thermocouple temperature matches the shelf temperature. The additional drying time ensures that the ice in the entire batch of product has been completely removed.
Typically, between several minutes to a few hours of extra time need to be added, depending on sample characteristics.
Thermocouples should always be placed in the center and at the very bottom of the container (see figure below). This is because the product dries from the top down. If drying in vials, you should consider placing the vial containing the thermocouple in the middle of the shelf. This avoids edge vial effects which cause the product in the vial to dry quicker than the rest of the batch.
But what happens if you go ahead and perfrom the lyophilization run without endpoint determination? Let us look at some comparison experiments.
We ran two experiments using solutions of 10 wt% Trehalose. The method we set-up in the freeze dryer software involved a primary drying phase of 72 hours (see table below). The method was run with and without active endpoint determination. For the active endpoint determination, we programmed the software to start checking if the requirement of ΔT≤ 1 °C was met one hour after the start of the primary drying. The test passed if the difference of temperature of 1 °C or less between the shelf and the sample stayed constant for at least 20 minutes. Once this occurred, the software was programmed to automatically switch to secondary drying.
Parameters for a freeze-drying process with and without endpoint determination
Phase | Primary Drying | Primary Drying | Secondary Drying | Secondary Drying |
---|---|---|---|---|
Duration [hh:mm] | 05:00 | 72:00 | 01:00 | 01:00 |
Shelf Temp. [°C] | 20.0 | 20.0 | 25.0 | 25.0 |
Shelf Temp. gradient [°C/min] | 0.17 | 0.00 | 0.08 | 0.00 |
Pressure [mbar] | 0.100 | 0.100 | 0.100 | 0.050 |
You can find the temperature profile of the process with endpoint determination (green line) and without endpoint determination (red line) in the graph below. After 20 hours, both sample and shelf had reached the sample temperature and the primary drying phase was completed. In the case where no endpoint determination was programmed, the machine kept running for the remaining 57 hours of the method before switching over to secondary drying. In contrast, when we programmed active endpoint determination in the freeze dryer, the freeze dryer automatically switched to secondary drying after 22 hours, once the sample and the shelf were at a similar temperature (ΔT≤ 1 °C for more than 20 minutes).
The results clearly demonstrate that
endpoint determination via temperature can optimize the freeze-drying process so that it runs for the smallest possible amount of time, helping increase productivity and save time and resources.
It might be then wise to invest in a freeze dryer with automatic endpoint determination of the primary drying using temperature measurement that can be directly programmed on the method. In such cases, the system measures temperature differences throughout the process. Once the difference is below a previously defined set point (normally around 1°C), the freeze dryer automatically switches to the next phase of the freeze drying process. I would also recommend adapting safety software features that reduce time and help prevent premature switching of phases if sample compositions vary slightly.
Although temperature is the most common method for endpoint determination of the primary drying step, other approaches are available. I will discuss another one of these with you soon. I hope you have re-charged with ideas after this post and keep coming back for more.
Till next time,
WANT TO STAY IN TOUCH?
Click on the button and receive the latest posts directly in your messenger!
Related Posts
15th February 2021
Happy birthday to me: The blog turns three and it’s all about the accessories!
Bart celebrates the blog's birthday with resources on accessories in chromatography and rotary evaporation →
27th January 2021
How to efficiently maintain a flash chromatography system
Bart details how to take care of the pump, detector and fraction collector of a chromatography system →
13th January 2021
Your 2021 chromatography and rotary evaporation crystal ball
Bart offers his outlook on how the chromatography and rotary evaporation markets will develop in 2021 →
23rd December 2020
Should I stay or should I go
Bart announces his retirement, but promises to continue writing for the blog →
18th December 2020
Let’s wrap up this unusual year with an unusual post
Bart says goodbye to 2020 with four chromatography and rotary evaporation videos for faithful blog readers to enjoy over the holidays →
25th November 2020
7 highly important factors for cannabinoid isolation
Bart lists seven factors that are important for successful of separation of cannabinoids using chromatography →
4th November 2020
Foam is foe in rotary evaporation. Here is how to prevent it.
Bart discusses why foam formation is dangerous and how to prevent foam in your evaporation flask →
21st October 2020
Slurry packing of chromatography columns can be just as fun as it sounds
Bart explains the slurry packing process for chromatography columns →
8th October 2020
Condenser loading should not be at 100% and here is why.
Bart discusses optimal condenser loading and why it is important →
24th September 2020
Dry packing of a chromatography column in three steps
Bart explains how to dry fill a chromatography column →
10th September 2020
Why 15 is the magic number for your recirculating chiller
Bart shows how to calculate cooling capacities and discloses how to set up your recirculating chiller to achieve sufficient condensation →
26th August 2020
How RFID technology lifeguards your chromatography process
Bart explains how and why RFID tags are used on chromatography cartridges and racks →
12th August 2020
Sizing up the importance of flask size in rotary evaporation
Bart discusses theory and experimental data on how flask size affects evaporation performance →
29th July 2020
Are peak splitting and peak fronting effects keeping you up at night?
Bart talks about peak fronting and peak splitting and how to eliminate these effects in chromatography →
16th July 2020
Why you should give the glass thickness of your evaporation flask a second thought
Bart discusses how the glass thickness of a flask affects evaporation performance and safety →
1st July 2020
The perfect peak shape: Five solutions to peak tailing problems
Bart explains how to analyze peak shape with the tailing factor and asymmetry factor and offers five causes and solutions for the peak tailing effect →
17th June 2020
Five ways to optimize the pressure values of your rotary evaporation
Bart offers five tips for finding the ideal pressure settings for rotary evaporation of a solvent →
3rd June 2020
What’s hidden behind your cosmetics labels? Chromatography!
Bart highlights the role of chromatography in ingredient discovery for development of cosmetics →
20th May 2020
How the delta 20 rule can make all the difference in your rotary evaporation
Bart describes the golden delta 20 rule for finding optimal temperature values for laboratory evaporation →
6th May 2020
The joint relationship between chromatography and cannabis
Bart talks about the purification of cannabinoids like CBD from cannabis using flash chromatography and solvent recycling →
22nd April 2020
Five cases where the bigger the condenser, the better
Bart explores the relationship between condenser size and distillation rate with specific examples and experimental data →
8th April 2020
All about ELS detectors – part 002
Bart discloses valuable information on ELS detectors in his sequel post on the topic of ELSD →
25th March 2020
Eco-friendly rotary evaporation is possible and here is the evidence
Bart shares energy savings data from using eco-friendly features on a rotary evaporator →
11th March 2020
How to solve two challenges of UV detectors in chromatography
Bart gives advice on how to overcome two common challenges of UV detection in chromatography →
26th February 2020
Is your rotary evaporator well configured?
Bart jumps into rotary evaporation by discussing current applications and how to configure your own rotary evaporator →
14th February 2020
The blog turns two, but you get all the presents
Bart's Blog turns two, offers chromatography presents, introduces rotary evaporation as a regular topic →
29th January 2020
How to separate very polar substances without destroying your packing material
Bart shares how to separate very polar compounds using a stationary phase ideal for this purpose →
15th January 2020
What does liquid chromatography have in its 2020 fortune cookie?
Bart shares his predictions on where liquid chromatography is heading in 2020 →
19th December 2019
A look back at your favorite chromatography and freeze-drying posts from 2019
Year-in-review: Bart offers a summary of the most read freeze-drying and chromatography posts in 2019 →
29th November 2019
Why the retention factor needs to be kept in check
Bart offers the ideal retention factor range for achieving good resolution in chromatography while keeping running times and costs low →
14th November 2019
Why a bit of moisture in freeze-dried products can be a good thing
Bart discusses the danger of overdrying during the freeze-drying process and how moisture mapping can help achieve optimal moisture content in products →
23rd October 2019
Does anyone in chromatography give a load about the sample load?
Bart talks about sample overload in chromatography and how it affects plate height, column efficiency and resolution →
9th October 2019
A load of tips on how to prevent condenser overload
Bart describes how freeze-driyng rates, condenser ice capacity and other parameters can be used to prevent condenser overload →
25th September 2019
Five good reasons to attend my live Q&A chromatography webinar
Bart invites readers of his blog to join a live Q&A chromatography webinar where he personally answers their purification questions →
18th September 2019
Simple ways to take the edge off the edge vial effect in freeze drying
Bart draws attention to the edge vial effect and how to reduce its negative impact during the freeze-drying process →
11th September 2019
How to master chromatography in two days
Bart invites users to an advanced user chromatography training →
28th August 2019
The poster that could put Bart’s Blog out of a job
Bart offers a sneak peak into a free chromatography poster with the basic principles needed to perform perfect flash chromatography and prep HPLC →
22nd August 2019
What happens if you run your freeze drying process under direct sunlight
Bart experiments with the effect of direct sunlight on freeze drying performance and draws attention to how the environment can influence lyophilization →
31st July 2019
We need to talk about flow rate and column efficiency in chromatography
Bart discusses how an optimized flow rate helps improve the column efficiency of flash and prep HPLC chromatography →
17th July 2019
How to find a suitable pressure endpoint criterion for freeze drying
Bart discusses comparative pressure measurement and how to use it for endpoint determination of freeze-drying steps →
3rd July 2019
Three major ways to influence column efficiency in your favor
Bart explains how particle size, column packing and pore size affect column efficiency and resolution in chromatography →
5th June 2019
Why you should care about column efficiency
Bart explains how column efficiency, or the number of theoretical plates, affect resolution in chromatography →
22nd May 2019
Why pressure gradients are the main drivers in improving sublimation rates
Bart discusses why a good pressure gradient is the most efficient way to improve freeze-drying rates →
8th May 2019
Putting safety first during the chromatography process
Bart discusses how to maximize the safety of user, sample and the surroundings during the chromatography process →
18th April 2019
A pretty hot way to speed up the freeze-drying process
Bart offers theory and experimental data on how heated shelves can speed up the freeze drying process →
10th April 2019
Two essential aids for proper column maintenance
Bart discusses the role of pre-guards, column guards and RFID technology in proper cartridge and column maintenance →
27th March 2019
Shall we use shell freezing to speed up manifold freeze drying?
Bart discusses the benefits of shell freezing over bulk freezing in speeding up the manifold freeze drying process →
13th March 2019
Beware: Protecting yourself and the environment against chromatography hazards
Safe, green chromatography? Yes, you can! →
20th February 2019
How to effectively use organic solvents in lyophilization
Bart offers advice on how to incorporate challenging organic solvents into your laboratory freeze drying process →
14th February 2019
The blog gets older, falls in love and branches out
Bart's blog celebrates its first birthday by welcoming a new guest to the party. Lyophilization will now get regular coverage on the blog! →
7th February 2019
Three chromatography problems the new Pure system solves
There are challenges in chromatography when it comes to user, sample and environmental safety. See how the Pure chromatography system sets out to solve them →
10th January 2019
Four Fab Lab New Year’s Resolutions to live by in 2019
The chromatography team at Büchi lists their chromatography resolutions for 2019 and how they plan to remain funny, innovative, safe and green →
18th December 2018
It’s time we separate from 2018 and flash in a brilliant 2019
Büchi's chromatography team gets ready to bring in the new year by talking about their favorite moments of 2018 and their plans for 2019 →
10th December 2018
How to optimize your mobile phase to improve selectivity and resolution in chromatography
Discover methods for choosing the most suitable solvent to achieve better selectivity and resolution in your separations→
10th December 2018
How to choose a stationary phase, optimize selectivity and get better resolution in chromatography
See the effects of selectivity on separation quality and get some great tips on how to optimize resolution by finding the ideal stationary phase for your application→
29th November 2018
The fastest, easiest and smartest way to select a flash cartridge
Discover a brand new digital tool for flash cartridge selection. Read how the FlashPure Scout app can provide you with tips on finding the ideal cartridge, as well as technical information for method optimization→
30th October 2018
All you need to know about using TLC data for flash method optimization
Convert your TLC results into optimized separations and learn about how certain software can convert TLC data into better purifications →
18th September 2018
Clever ways to speed up laboratory evaporation
This post is a giant turbo button for your laboratory evaporation performance. Read on to gain fresh ideas on how to make your evaporation process faster →
30th August 2018
How to quicken laboratory freeze drying procedures
The freeze drying process in the lab can be fun, but as with all common chemistry methods, the sooner it is done, the better. Learn how to quicken it and download the poster →
3rd August 2018
Top tips on how to save time in chromatography
Get some great suggestions on how you can speed up your chromatography runs and save valuable time →
18th July 2018
The most important factors to consider when selecting a flash chromatography cartridge
See what important parameters you should consider when choosing a flash cartridge and get insights into how to simplify the selection process →
5th July 2018
How to overcome limitations in flash chromatography with an ELSD
Find out how ELSD functions and what benefits this detector can bring to your chromatographic experiments compared to UV detectors alone →
22nd June 2018
World Cup Fever: How to Score Purer Compounds by Improving Resolution in Chromatography
Soccer fans or not, all chemists want to give impurities a red card. Read today how to improve resolution and score purer compounds →
3rd April 2018
How to do sample introduction in Flash Chromatography?
When introducing a sample in flash chromatography, are you going for Wet or Liquid Loading? Learn about the two sample introduction techniques and how they influence the sample loss during the purification process →
7th February 2018
Warm and Colorful Welcome from Bart
Hello there and welcome on the blog!
This place is for all colorful researchers out there who are looking for their next adventure in science. Let's introduce ourselves →
31st January 2018
What might happen if you don’t equilibrate your flash cartridges.
"To equilibrate or not to equilibrate" flash Silica cartridges prior to loading the crude material and what possible risks you might face if you skip this step, read here →
24th January 2018
“Alien vs. Predator”… or in other words “Silica vs. Alumina”
The rivalry between Silica and Alumina looks a lot like "Alien vs. Predator" movie, don't you think? Read more about how we can benefit from their "competition" →
17th January 2018
The “Golden Mean” in Flash Chromatography
Which system describes perfectly the balance ratio between productivity and cost in flash chromatography? Open columns, automated or semi-automated systems?
Very good information on lyo
Thank you very much for your kind words Iranna.
Regards,
Bart