A review of the Biohit mLine low-volume multichannel pipettor

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A review of the Biohit mLine low-volume multichannel pipettor

Summary: Low-volume multichannel pipettors often do not form an even seal across all channels. The decrease in accuracy from a poor tip seal is far greater than that from poor calibration. Poor tip seal can plague experiments where large numbers of small volumes (0.5 - 10 ul) must be pipetted. Over the years, I've developed a few tricks to improve tip seal and a watchful eye to lessen the effect this has on my experiments. However, the Biohit mLine (m10) mechanical multichannel pipettor addresses this problem by employing a spring system on each channel to ensure an even tip seal. I've used the pipettor for a few weeks now, and I find the spring system works brilliantly. This is by far the best-performing and most consistent low volume multichannel pipettor I've ever used.

Article created: Oct 11, 2007
Article by: Jeremiah Faith

Over the last two years, I've run over 30,000 qPCR reactions to verify transcription factor targets using chromatin immunoprecipitation. Because of the large number of reactions and the expense of qPCR master mix, I run these qPCR reactions with low-volumes (10 ul total) in 384-well plates on an ABI 7900HT qPCR machine. I've learned to tolerate the tedium of filling each of these plates, but I've never learned to tolerate my low-volume multichannel pipettor (i.e. 0.5 ul - 10 ul). I fill the plates with 5.5 ul of master mix, 3 ul of template, and 1.5 ul of primer, so I really get a feel for how the pipettor operates across a wide-range. And until a few weeks ago, my opinion was that all low-volume pipettors are mediocre at best.

Calibration accuracy versus real world accuracy

Every multichannel pipettor with an operating range of 0.5 ul - 10 ul has about the same accuracy (typically +/- one or two percent). This performance is measure by the pipette calibration folks who very carefully make sure that each tip is evenly sealed onto each channel and slowly aspirate each sample. They do this with a number of samples and use a very sensitive scale to judge (and adjust) the pipettor's accuracy.

For the larger volume multichannel pipettors (>10 ul), I think this is a pretty decent way to judge a pipettor. But for the low volume multichannel pipettors, I find that in practice the experimental pipetting error does not correlate with the accuracy of the pipettor in this ideal calibration scenario. The problem is that when you are filling plates and you don't have all the time in the world or the muscles of a professional boxer, the error from poor tip sealing is much greater than that from poor calibration. After trying a couple different models from different companies, I had resigned myself to the belief that it is impossible to have a small volume multichannel pipettor that easily, evenly, and consistently seals all of its tips.

How I obtained consistent results with mediocre pipettors

Since life must go on even in an imperfect world that lacks good low volume multichannel pipettors, I developed a number strategies to improve the consistency.

First, every three to four 384-well plates I would apply a very thin layer of silicon grease to each channel and carefully wipe it off (like waxing a car). This drastically improves the seal of the tip. However, the pipette calibration folks told me this isn't terribly good for the pipettor, as if you aren't careful and you glob the grease on, some can get aspirated into the channel and gum everything up.

Second, I use only the tips recommended by the pipette's manufacturer, and I apply very firm pressure to the center, left, and right of the pipettor to seal the tips (but I DO NOT bang the pipettor on the tips; banging the pipettor on the tips can easily break, crack, or warp a channel). The problem with this tight seal is it really wears you out (both to seal the tips and to eject them). By the end of a plate or two, I sometimes break a sweat. But come on this is a lab not a track, I'm not supposed to be sweating.

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