Contamination problem

bgreer
bgreer
in Instrumentation and Mass Spectrometry
<p>Afternoon all</p><p></p><p>I was wondering if anyone could help me out with a problem I am having with my system. The details are as follows:</p><p></p><p>While running a baseline check injecting water & monitoring with UV, there is a small peak (contaminant) at RT approx. 0.8 min. After isolating the problem to the pumps/lines, I was advised to prime the lines several times with 30% Phosphoric Acid and then flush them several times with water. After doing this I ran another set of water injections and there was no sign of the peak for the 1<sup>st</sup> four runs, however, it then reappeared and got stronger in intensity for the next few before levelling out at around injection 8. </p><p></p><p>The peak (contaminant) has a UV<sub>max</sub> of approx. 214 nm and these are the conditions used:</p><p></p><table border="1"><tbody><tr><td><p>Time (mins.)</p></td><td><p>Flow Rate (ml/min)</p></td><td><p>%A</p></td><td><p>%B</p></td></tr><tr><td><p>0</p></td><td><p>0.4</p></td><td><p>100</p></td><td><p>0</p></td></tr><tr><td><p>1.5</p></td><td><p>0.4</p></td><td><p>38</p></td><td><p>62</p></td></tr><tr><td><p>2.0</p></td><td><p>0.4</p></td><td><p>100</p></td><td><p>0</p></td></tr><tr><td><p>3.0</p></td><td><p>0.4</p></td><td><p>100</p></td><td><p>0</p></td></tr></tbody></table><p></p><p>A - 95:5 (H<sub>2</sub>0:ACN) with 0.05% TFA</p><p>B - 100% ACN</p><p>Weak Wash - 9:1 (H<sub>2</sub>O:ACN)</p><p>Strong Wash - 1:1 (H<sub>2</sub>O:ACN)</p><p>Full loop - 5 ul injection with overfill factor of 1.</p><p></p><p>I have also ran an MS scan and the only thing that is showing up around this RT is a peak at 214Da which I believe is plasticiser. Could this be the contaminant or has anyone else had a similar problem and know what it could be. </p><p></p><p>Thanks in advance</p>

Answers

  • dougm
    dougm

    Hi Brett,

    I was wondering if you could run a quick and very simple experiment.

    Would it be possible to run the following gradient profiles a two or three times each?

    Gradient 1:

    Time (min.)

    Flow Rate (ml/min)

    %A

    %B

    0

    0.4

    100

    0

    1.5

    0.4

    38

    62

    2.0

    0.4

    100

    0

    4.0

    0.4

    100

    0

    Gradient 2:

    Time (min.)

    Flow Rate (ml/min)

    %A

    %B

    0

    0.4

    100

    0

    1.5

    0.4

    38

    62

    2.0

    0.4

    100

    0

    2.5

    0.4

    100

    0

    Does the contaminant peak get bigger or smaller?

    There are other things that I am sure people will suggest, but this test is simple and does not require changing any solvents.

    Thanks,

    --Doug

  • bgreer
    bgreer

    Afternoon Doug

    thanks for your reply regarding the contaminant. I did as you suggested and ran the 2 gradients you listed, making several 'blank' injections. However, the peak intensity did not change at all.

    Any other suggestions?

    Thanks in advance

    Brett

  • dougm
    dougm

    Hi Brett,

    Have you tried another column to rule out/implicate that? Also, instead of injecting a blank, would it be possible to inject either your mobile phase A or B?

    My suggestion was aimed at mobile phase A contamination. In a gradient you are 'loading' mobile phase A onto the head of the column, much like loading sample in solid phase extraction. Then you eluting this off with the gradient. Load more 'stuff' on and a contaminant peak from your aqueous mobile phase gets bigger; load less and it gets smaller.

    I hope this makes sense.

    --Doug

  • bgreer
    bgreer

    Hi Doug

    sorry for the very late reply regarding my problem. We had a few things wrong with the instrument, such as the injector pod being replaced and the problem is long gone thankfully!

    Thanks again for your advive and apologies for the delay in responding

    Regards

    Brett

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