Split Injections… The Good, The Bad and The Ugly
23 Jun 2011While 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.