1. What is a fitting? I hear the term used all the time but I would like to know what the specific definition is?
2. What makes one fitting different from another?
3. Why do some fittings need ferrules and others do not?
4. What does the term 10-32 mean? What does it mean to a chromatographer?
5. How can my finger tight fitting be producing band broadening?
6. Can I use a PEEK finger tight fitting on stainless steel tubing? Can I use a SS fitting on PEEK tubing?
7. I am using TFA and someone told me that I might have a problem with my Delrin type fittings. Is this true?
8. What is the difference between a union and an adapter?
9. Should I use a 1-piece fitting or should I use a 2-piece?
10. What is the maximum temperature that the MicroSolv Classic Endure Fittings can be used in?
11. Do all fittings fit all receiving ports?

1.What is a fitting? I hear the term used all the time but I would like to know what the specific definition is. [top]
The dictionary defines a fitting as “a small often standardized part used to join other parts together properly.” This is very similar to what plumbers refer as fittings. For the use of chromatographers, fittings consist of nuts with internal and external threads for both high pressure and low pressure connections. Also, unions, crosses and tees and adapters are considered fittings for both high and low pressure connections.

2. What makes one fitting different from another? [top]
Of course, the quality of the manufacturing is important but besides that the most important features of all fittings are:

1. Geometry of the receiving port you are putting the fitting into.
2. Threads on the fitting and receiving port-Count per inch and total length of threads.
3. Material the fitting is made out of for purposes of chemical inertness, temperature the fitting will be used for.
4. Pressure the fitting will be required to hold.
5. Size of the tubing the fitting will be holding.

4.What does the term 10-32 mean? What does it mean to a chromatographer? [top]
This is a way of describing the threading on the fitting so that it will properly be matched to the receiving port. This is important for a good seal and long life of the fittings. Improper use will cause the fittings to cross thread and wear out prematurely.
The 10-32 description can be broken down into two parts. The first part (10 in this case) describes the diameter of the threaded part of the fitting. If you were to measure the width of the threads from side to side, this distance would be. For fittings above ¼” you would state the actual measurement. For example, if it were ¼” you would state ¼ . When the measurement is below ¼”, and for English measurements and not metric, you would report his number in gauge. In this case, we state 10 gauge.
The second number is number of threads per unit of distance. For our purposes, it is reported in threads per inch. If you were to take the length of the threads and count the number of threads per inch, that would be the second number, in this case 32. This means that there would be 32 threads per inch.

5. How can my finger tight fitting be producing band broadening? [top]
Most chromatographers may not realize it but if fittings are not properly set and a perfect connection is accomplished, a dead volume can occur that does not get swept. This extra volume can cause band broadening or ghost peaks or may decrease the sensitivity of your run by increasing baseline noise.

6. Can I use a PEEK finger tight fitting on stainless steel tubing? Can I use a SS fitting on PEEK tubing? [top]
Yes, you can very effectively use PEEK fittings on stainless steel tubing as long as you take into account the making pressure ratings of the fitting you are using and the expected pressures in your system. Generally speaking, a PEEK fitting is preferred for all HPLC applications up to 5,000 psi.
No, you should never use a stainless steel fitting on PEEK tubing.

7. I am using TFA and someone told me that I might have a problem with my Delrin type fittings. Is this true? [top]
That person is correct. Delrin is not compatible with Trifluoroacetic Acid. If it comes in contact with your fittings, it could become compromised and your connection might slip and become less than perfect.

8. What is the difference between a union and an adapter? [top]
The biggest difference is the price where a union is much less expensive than an adapter. For performance considerations, a union will make a connection between tubing and fittings that have the same thread size and thread count configurations. An adapter will connect two different thread sizes and thread count.

9. Should I use a 1-piece fitting or should I use a 2-piece? [top]
This is a matter of choice. The benefits of a 1-piece is that it is convenient and easy to use. The benefits of a 2-piece fitting is that the ferrule is the only piece that needs to be replaced when the unit is worn out. For most applications, they will both provide perfect connections. For higher pressures, it has been suggested that a 2-piece with a double cone ferrule will continue to hold even though pressures are above 6,000 psi.

10. What is the maximum temperature that the MicroSolv Classic Endure Fittings can be used in? [top]
150°C for Endure CarbonPEEK fittings and 100°C for most other PEEK fittings.