Overview

TCPSIM analyzes samples for some of the same target compounds as 8260, but it measures analyte recovery in parts per trillion (ppt) instead of parts per billion (ppb). In other words, this method measures concentrations at 1000x the regular method (so very sensitive).

There is a separate SOP for this method that you need to read before you perform this analysis. You also need to run IDOC (4 LCS) before analyzing samples.

Running QC

Before Starting

Because SIM is such a sensitive method, we set up the GC/MS to selectively scan for specific ion abundances. As a result, trying to analyze BFB using the same settings as the QC/samples would yield no peaks. To solve this, we have a standard scan method used specifically for tune checks before starting the sequence for the day. This scan method shares the same name as the method name but with an A appended to it.

Ex: SIM method for analyzing QC/samples is named VOF5J06. The scan method for analyzing BFB is named VOF5J06A.

It’s very important that we don’t overwrite the scan method if we need to make adjustments to the ICAL. This isn’t usually an issue, but it’s something to keep an eye out for nonetheless.

Standards

We have specific stock standards we use to prepare TCPSIM standards. They’re in a plastic rectangle box labeled SIM alongside the standards for TCPSIM. Check the standard logbook for instructions on how to prep.

Prepping QC

To spike TCPSIM (25mL):

• 25mL DI water
• 1.0uL TCPSIM IS/SS (2.5ppm)
• 1.0uL TCPSIM (1°) (2.5ppm)
• 1.0uL TCPSIM (2°) (2.5ppm)

For SIM, the percent recovery for target analytes needs to be within 20% of expected value. Higher can be tolerated, but analytes cannot be lower than 20%.

Evaluating Data

A lot of folders will say 8260SIM on the front, but the actual target list is for TCPSIM. To check if a folder is actually 8260SIM or TCPSIM, look at the surrogate list.

• If the surrogate list has d4 or 4BFB, run 8260SIM
• If the surrogate list has d8, run as TCPSIM

Sometimes, a sample will have heavy matrix interference so integrations aren’t picking up correctly. Make sure you check the peaks for all compounds to see if they’re being improperly integrated or completely missing. If you’re not sure whether a sample needs to be run at a dilution, ask Diem.

ICAL

Use a previous TCPSIM ICAL as reference for spiking. You don’t need to use SmartWater when running TCPSIM ICAL so I just use the sink water.

Unlike 8260, we only run eight levels for ICAL. This means we finish running the ICAL sooner, but it also means we have less wiggle room when processing the ICAL. Check the ICAL carefully when it’s done. If you’re running quarterly MDL, run LOD at 2.5ppt for 1,2,3-TCP.