Equipping an Analytical Chemistry Lab at Minimal Cost

Part 2. Some Completely Subjective Opinions on Purchasing and Maintaining Used Instrumentation 11/15/2024

• Prior familiarity is very helpful. If possible, try to work with items that you have used in the past. That is the best way to know what the potential issues are. For example, some HPLC pumps that I bought a few years ago were so old that they qualified as antiques, but they were very popular in their time, I was familiar with and had used the equipment, and I knew that they were built like tanks with a relatively simple control system. The weak parts are the check valves, pistons and piston seals, but new replacements are still available online for each of those. Also sometimes inoperable check valves are just stuck from nonuse and can be restored by dissasembling and sonicating in acetonitrile or methanol. For the more adventurous it is sometimes possible to fabricate a part by 3D printing or simple machining. That will be discussed in another post.


• Buying brands that were popular in their time is usually an advantage since more systems are available and replacement parts are usually easier to find.


• Another advantage with a known instrument is that you are less dependent on an operator or service manual being available. Manuals are rarely provided with used equipment and for older systems they can be nearly impossible to find (note: see the list of manuals available for free download on this site). Occassionaly, an old manual might be offered for sale that is priced higher than the equipment itself. But if you already know the system and have at least some mechanical and electronics skills it can be much easier to get and keep things working.


• Focusing on known systems can also be an advantage as a buyer since the seller (on ebay at least) is most commonly a general used equipment dealer who might have little or no knowledge of what they are selling. That is why many items are listed simply as “powers on” or "for parts only". It doesn't necessarily mean the item doesn’t work or is only good for parts, but rather commonly it means that they don't know how to or simply don’t want to properly test it so it is being sold as a black box in terms of operability. I have seen listings describing non-functioning equipment offered at a very reasonable price where the pictures showed what the problem likely was which might require only a changed setting or very simple repair.


• Of course the internet is a rich information source, but not always a good one for old equipment. A younger person reading this may find it hard to believe, but some older equipment may have no information available at all on the internet, even on the Wayback Machine. That’s because some stuff is so old that the company never had a website for it since the internet hadn’t been invented yet.


• Warranties and returns. The former are not common, and the latter if available are at your own shipping expense. At todays rates, shipping is always a significant consideration for all but the smallest items. Some sellers try to game the system by advertising an item at an unusually low price to move it up in search listings, but then add on an exorbitant shipping charge to make back the difference. This ploy is easily avoided by searching with the “price + shipping” sort option on ebay.


• This is a highly subjective opinion, but for me, and as a very general rule, analog is usually GOOD and digital is often BAD. That might seem counterintuitive considering the many advantages of newer digital equipment, but the difference in accessibility and in making repairs can be quite important. For example, a defective analog switch such as a thumb wheel rotary encoder to control a pumps flow rate is very simple to repair or replace whereas an electronic controller may be impossible to fix without at least the schematics for the board which you are not likely to find. This means that you may be dependent on cannabilizing another system.


• Another major problem with newer digitial equipment is that many instruments have no direct controls and can only be operated via software. Software is another item that is rarely included with a used instrument and without it the instrument may be completely useless. Sometimes software can be located but it is often very expensive and/or requires a license which may not be available.


• Many other repairs can be simple to make if you are patient and careful in disassembling the equipment as needed to find the problem. For example, a non-functioning centrifugal evaporator may simply require locating and reattaching a loose tubing connection buried deep within the device.


• Know the limits. For example, if you plan to develop liquid chromatography separations that are demanding, then used systems are more likely to be troublesome in part because more can go wrong. If gradient rather than isocratic elution is required then the cost and difficulty in finding and maintaining a system will be higher, and older systems are usually not compatible with newer techniques such as ultra high pressure columns. Simple gas-liquid chromatographs with a FID can be relatively cheap and very useful, but the cost of He is currently very high, and a hydrogen source is needed for the detector. Substituting nitrogen as the carrier will greatly degrade resolution, whereas substituting hydrogen as a GLC carrier gas may wind up degrading both you and your lab.


• Make sure that you are aware of what replacement parts you will likely need and what they will cost. That should be an important consideration before deciding to purchase a used item. Major functional parts like motors are often not a big problem since they may be widely available, easily substituted, or you may be able to buy another instrument cheaply and cannabilize it. However, common replacement items such spectrophotometer and detector UV lamps can be a problem. UV lamps wear out of course, and they can age and go bad even in a system that has not been used much. Some lamps can be purchased for only a few hundred dollars, but others may be quite sophisticated and specialized and can cost thousands if you can find them at all. On the other hand, visible tungsten lamps are usually fairly cheap to replace.


• Don’t hesitate to inquire about an item when necessary. For example, a used spectrophotometer on ebay was described as having a working light source, but it was not clear if that included the deuterium lamp or just the visible source. After contacting the seller and explaining how to start and check for a functioning deuterium lamp, he tried it, it was, and I bought it. The lamp works fine.


• Although instruments relying on digital control via software are usually something to avoid, your OWN digitial control devices sometimes can be nicely integrated to upgrade an older instrument. For example, any detector with an analog output can be used with a home constructed data system. 16-, 24-, or 32-bit precision ADC boards can be purchased realtively cheaply and integrated via an old computer, an SBC, or other controller with some simple programs to provide a functional data system that can be used to collect and process information. You need to be aware of noise reduction and signal shielding aspects, but this approach is feasible. Simple GC and LC chromatographic data is really just a stream of time/volatage points. There also are some inexepensive chromatography data systems that may be useful and those will be discussed in a future article.

So that’s a general overview. Some of the points will be discussed in future postings. If you disagree with any of the above, or just have your own views on what to look for and what to avoid in evaluating used equipment, please leave a comment describing them.