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Split Injections… The Good, The Bad and The Ugly

23 Jun 2011

While I’m not necessarily a fan of the old spaghetti western film with Clint Eastwood, I thought it was an appropriate title for what I have seen with my work using a split injection for EPA Method 8270 extracts.  You may recall an earlier blog that I wrote about the benefits of a split injection titled "Split Injections Increase your Throughput for Semivolatiles Analysis by EPA Method 8270".

for these dirty extracts.  So let’s start with the good.  Using a split injection can allow for an increased initial oven temperature (80°C) versus a splitless injection (45°C) because of the faster transfer of analytes through the injection port onto the head of the column.  This gives faster analysis times and much faster oven cool-down times, meaning more samples analyzed in a 12hr period.  I also noticed increased injection-to-injection repeatability and held a continuing calibration longer before instrument maintenance was needed.

This brings me to the bad...  Of course with a 10:1 split there is a compromise in sensitivity.  With an Agilent 5975 MSD I was able to get a nice linear calibration curve from 5 – 160 µg/mL (0.5 to 16 ng on-column).  Going down to 1 µg/mL was possible for most compounds with a few exceptions for those troublemaker phenols (2,4-dinitrophenol - I am talking about you!).  On a positive note, by decreasing the sample amount injected onto a 0.25mm ID x 0.25µm column, sample overloading is minimized. So maybe bad is a little harsh, but it goes with the theme.

Finally, let’s finish with the ugly, and I do mean ugly!  After injecting over 300 soil extracts from an underground storage tank site I performed maintenance on my split gas line.  When I took off the line that goes from the injection port to the EPC I couldn’t believe my eyes.  Not sure ugly cuts it here, I think my words were more like disgusting!  A simple rinse with some methylene chloride shined it right back up to looking new. Anyways, lesson learned, there are great benefits to using a split injection for Semivolatiles analysis if you can afford to lose some sensitivity, but make sure to do some routine maintenance on your split lines.
split vent line