Hello,

I´m looking for a flow splitter, which should be installed between LC column and MS. The splitting ratio should be around 10.
I have an offer from LCPackings. They sell two different splitters; one with a fixed splitting ratio and one with a variable ratio.
Has anybody experience with those or other flow splitters (e.g. from ASI) regarding reproducibilty etc.?

Thanks in advance

How much are they charging? You can make your own with a simple peek or stainless "tee" and some peek tubing. First connect your tubing from LC to tee, then from tee to MS so that you have the length you need. Then connect a length of tubing to the third port on the tee, which will go to waste. Turn on your LC pumps at the expected flow rate and have the eluent flowing into the MS, and measure the flow rate out of the waste line. If the split ratio is close to what you want, keep it. If it's not right, adjust the length of the waste tubing until it's close enough. This has worked best for me using the same ID tubing for tee--->MS and tee---->waste. Once you're set up, you'll have a constant split ratio unless your MS inlet or waste line becomes obstructed, as long as you don't change the tubing going to the MS or waste.

I have a variable splitter from Upchurch that has a little dial on it. It has the advantage of being able to more easily adjust the flow rate, but you still have to measure the flow rate if you want to know the split ratio after adjustment.

Don't know what your column configurations are and what flow your MS can tolerate. In general, you loose sensitivity, if you split. If you don't split, all your mass goes to the MS.
Often the trick is simply to use a smaller column. In most MS systems you can work easily to 0.5 mL/min. The standard LC flow rate on a 4.6 mm column is 1 mL/min. Use a 3 mm column at 0.4 mL/min and you get the same results without splitting together with higher sensitivity.

2 comments:

Remember that when you build a splitter as described above, your split ratio will change as your back pressure changes. Back pressure changes when you run gradients.

Splitting does not really affect sensitivity in electrospray MS. Mass specs are concentration detectors, not mass detectors, concentration does not change with split ratio. Further to that ESI response is much higher at lower flow rates. In many cases splitting increases sensitivity.

Last Anon: You keep your sensitivity even when splitting 100% to waste?

Hello,

thank you very much for your response.

Anonymous, you´re right, Í forgot to add some important parameters: I use a RP-C18 column (250 x 3.0 mm), the LC flow is 0.5 ml/min. Of course my MS can tolerate high flow rates, the sensitivity will increase by conducting 0.05 ml/min flow to the MS.

An accurate and reproducible splitting is quite important me.
As I do not know what the difference is between a simple "tee" splitter (Mr. Garnder mentioned) and an expensive splitter form ASI I would be appreciative for more information regarding different splitter types!

Thanks in advance!

Mr. Mueller, if you are splitting 100% to waste, then you are not splitting the flow. Splitting implies that some amount of flow goes on both sides of the splitter!

All joking aside, of course you need some level of flow into the MS probe. Electrospray wworks extremly well very low flows (nL/min). As a matter of fact nanoflow chromatography into MS is a very common practice in the life sciences.

Which means a mass detector is a mass detector, it becomes a concentration detector when calibrated. Also, because of this one would expect a optimum flow for an optimum sensitivity.

Could someone explain to me the basis behind a MS turning from a mass senstitive detector to a concentration sensitive detector. This has always boggled me. I understand the differences between the two catagories, but not why MS can be in both, or either catagory. I was always of the understanding that a mass senitive detector destroyed the sample (MS or E chem) and a concentration sensitive detector did not (UV/fluoresence).
Thanks

LC-MS/MS usually operates in two modes, namely APCI and ESI. In APCI, MS is mass dependent. In ESI, MS can be mass dependent (very low flow), concentration dependent (high flow) or something between.

I had previously recommended not to split. The reason is the following (and this works the same, whether you're using a UV detector or a MS): if you inject the same amount of sample onto a smaller i.d. column, you dilute the sample less, and the sensitivity increases. Unless something else speaks against this, I would do this rather than splitting. Yes, the sensitivity of MS detectors is not completely independent of flow, but the gains at slow flow are rather small compared to the approach of injecting the same amount onto a smaller i.d. column.

Forgot to say of course that the use of the smaller i.d. column combines the potential gains from the lower flow into the MS with the lower dilution in the column.