Chromatography Forum

Hi there,

newer chemist here.

I'm wondering why my recoveries are so bad for spikes <60% in water samples. What kind of recoveries are typical for you all?

I'm using MeCl2..(having trouble with emulsions, and getting it out of solution). Also there is the long 'blow down' time.

I'm wondering if you all have had similar issues. Someone here suggested Hexane. ??

Have any of you experienced chemists found the best ways for liquid-liquid extraction method? or any other method for that matter.

thanks.

Hey, here are a few tricks i've learned to help you with recoveries of 8270 waters. First off, if you are having trouble with emulsions, one way to minimize this is to put salt into the sample, i usually put around 100 grams or so for 1000 ml samples. You can always put more as long as it dissolves in the sample no problem. I'm not sure of the procedure you use either? One thing to do is start off with the acid extraction then the base extraction. The reason for this is that usually the first extraction will get neutral compounds also and since putting base in the sample is usually what causes the emulsion you are putting yourself at a disadvantage right off the bat. As far as the analysis part, you will always get lower recoveries on acid compounds, such as phenols. You shouldn't have a problem with basic or neutral compounds. How much spike to you use to spike your sample? I suggest using at least 1ml.......we use 1ml of 4000ppm spike and it works well. Let me know if you want to know anything else, i've been doing this for a while.

Mickygd,

A couple more suggestions to add to sidd80's excellent suggestions. Regarding emulsions, put part of the solvent and the emulsion in an erlenmeyer and put it in the freezer for a bit, sometimes that helps the separation. Better yet, spin it down in a centrifuge with a balance centrifuge tube (or split sample between two tubes.) Sometimes you can simply stir them out with a glass rod, simple if it works. If it is a particular sample stream think about using liquid liquid.

Regarding blow down, consider micro-KD as one option. Can do this pretty easily. Also, make sure you are keeping the samples a little bit warm when blowing down to help them evaporate. Don't use too high a nitrogen flow for blowdown since this will decrease recoveries (although if it is taking a long time it does not sound like you are doing that.) Finally, don't blow it down too far because this also reduces recoveries.

Best regards.

What kind of salt are you using? Regular NaCl?