wanted: info on old Spinco rotor

David F. Spencer DSpencer at Dal.CA
Tue Nov 26 11:54:37 EST 2002

In article 
<Pine.SOL.4.33.0211221658290.22651-100000 at mcmail.cis.mcmaster.ca>, Kyle 
Legate <legatek at mcmail.cis.mcmaster.ca> wrote:

> Hi, I wonder if someone with some _old_ lab equipment can help me out. I'm
> looking for spec info on the Spinco SW-39 rotor. It holds ~5 ml/tube and
> I'm assuming it's functionally equivalent to Beckman's SW-55 rotor, but I
> want to make sure before I overspin/underspin all my samples. What I am
> trying to do is replicate some data from the early 70s by separating
> ribosomal subunits from intact ribosomes on a sucrose gradient. I have the
> assay working beautifully in a SW-28 but I'm looking to drastically scale
> down. A 3 hour spin vs a 16 hour spin is also very appealing. The paper I
> have gives rpm and time for the SW-39 and I'd like to adapt it to the
> SW-55. Unfortunately, the Beckman site doesn't have a historical records
> section!

The Spinco/Beckman SW 39 was discontinued in the late 50's or early 
60's. The lab in which I was a PhD student 30 years ago had an old, 
unused SW 39 with the coupling nut on the top that allowed it to be run 
(preparatively of course) in the Model E (Analytical); it would have 
been called an SW 39E. It took the 1/2 by 2 inch (ca. 5 ml) tubes still 
used today. The successor to the SW 39 was the SW 50L (discontinued in 
1972) and a variation on the 39 and 50 was the SW 65Ti (discontinued in 
1994). In the early 70's the 6 bucket SW 50.1 was introduced 
(discontinued in 1997) and in the mid 80's the current SW 55 appeared. 
Not surprisingly when the rotor went from 3 buckets to 6 buckets the 
buckets had to be moved further from the centre of rotation. The 
geometries of the 50.1 and 55 are very similar, r_min about 60 mm and 
r_max about 108 mm. The SW 65 Ti had an r_min of 41.2 mm and an r_max of 
89 mm.

The oldest Spinco catalogue I have is from Nov. 1975 [PL-174Z] and the 
SW 50L was already history and the SW 39 a museum piece, so no specs in 
it for the 39. However I do have an old and faded photocopy of a Spinco 
publication [DS-327] called 'Factors in Selecting High Performance 
Rotors' in which there is a discussion of the k factor, an index of 
functional rotor performance. The k factor is normally calculated at the 
rotor's maximum speed and includes a variable based on the ratio of 
r_max to r_min. The k' [k prime] is based on the k factor but typically 
is used for calculations of run times for specific particle densities 
travelling through specified sucrose gradients.

The k factors for a number of rotors, gleaned from DS-327 and several 
Spinco catalogues are:

SW 39    112
SW 50L    68
SW 50.1   59
SW 55     48
SW 65Ti   46
SW 28    246
SW 28.1  276

In addition, at 40,000 rpm the SW 65 has a k factor of 122 (essentially 
identical to the SW 39, so their geometries were probably virtually 

For your purposes, you should be able to go from the protocol given for 
the SW 39 and multiply the times by 0.43 (48 divided by 112) if you want 
to use the SW 55. That assumes that the old paper used the SW 39 at 39K 
of course and you do your run at 55K. You could go from your current SW 
28 protocol to the SW 55 by reducing run time to about 0.2 of the 
original (also assuming the speeds are both max). If you are actually 
using the SW 28.1 then the factor is obviously .17. For speeds less than 
the rotors' max you can correct the k factor by knowing that the k 
factor is inversely proportional to omega squared (where omega is 
0.10472 times the rpm).


David F. Spencer, PhD
Dept. of Biochemistry and Molecular Biology
Dalhousie University
Halifax, Nova Scotia, Canada

DSpencer at Dal.CA

More information about the Methods mailing list