Meet Low ng/L Detection Limits for Volatiles in Drinking Water Using Coconut Charcoal Cartridge SPE and a 50 µL Injection in an Unmodified Agilent Split/Splitless inlet – Find out how at the NEMC Drinking Water Section Thursday Afternoon

 

I’ve been working on combining EPA methods 521 and 522 for a while. Both methods use the same SPE cartridge and very similar extraction procedures. In order to meet extremely low PPT detection limits required by 521 on my 7890A-5975C, I had to resort to a 50 µL injection. Generally,a special injection port such as a PTV injector is required for this type of injection. With the PTV inlet temperature set near the boiling point of the solvent, the sample is introduced at a high split ratio and as the solvent evaporates the analytes of interest are concentrated in the inlet. After a predetermined time, the split valve is closed and the inlet temperature is increased to transfer the concentrated sample and remaining solvent onto the column. This solvent-venting, analyte-concentrating step requires a relatively large difference in boiling points between solvent and solute, more than 100 ⁰C, in order to prevent loss of analytes of interest to the split vent. This rules out using a PTV type injection port for the analyte list covered here due to inadequate differences in boiling points.

I made a few trial runs with my MMI operating in PTV solvent vent mode. I was not able to recover a detectable amount of THF-D8 (the 522 internal standard) when injecting a total mass of 50 ng until I set the oven temperature below the boiling point of dichloromethane, solvent focusing the analyte in question. The following figures are of 50 µL injections of 1.0 µg/mL standard

Slide3 Slide4

Now lets look at a 50 µL CSR-LVSI injection of the same 1 µg/mL standard in an unmodified split/splitless inlet on the same 7890A-5975C

Slide4

If we overlay the MMI and CSR-LVSI runs, the difference in mass transfer to the column is significant.

CSR-LVSI vs the MMI in PTV solvent vent mode

Finally, the labeled chromatogram of the high point of my calibration curve.

ical 8 correct units

 [ng/mL] ICAL 1 ICAL 2 ICAL 3 ICAL 4 ICAL 5 ICAL 6 ICAL 7 ICAL 8 R
THF-d8 100 100 100 100 100 100 100 100
THF 0.10 0.20 0.50 1.0 2.5 5.0 25 50 0.998
1,4-Dioxane-d8 200 200 200 200 200 200 200 200 1.90%
1,4-dioxane 0.50 1.0 2.5 5.0 25 50 0.999
n-nitrosodimethylamine-d6 20 20 20 20 20 20 20 20 3.60%
n-nitrosodimethylamine 0.025 0.050 0.13 0.25 1.3 2.5 0.998
n-nitrosomethylethylamine 0.10 0.25 0.50 2.5 5.0 0.998
n-nitrosodiethylamine 0.010 0.020 0.050 0.10 0.25 0.50 2.5 5.0 0.998
n-nitrosodi-n-propylamine-d14 10 10 10 10 10 10 10 10
n-nitrosopyrrolidine 0.010 0.020 0.050 0.10 0.25 0.50 2.5 5.0 0.997
n-nitrosodi-n-propylamine 0.050 0.10 0.25 0.50 2.5 5.0 0.997
n-nitrosomorpholine 0.010 0.025 0.050 0.13 0.25 1.3 2.5 0.994
n-nitrosopiperidine 0.010 0.020 0.050 0.10 0.25 0.50 2.5 5.0 0.997
n-nitrosodi-n-butylamine 0.020 0.050 0.10 0.25 0.50 2.5 5.0 0.997

I’ll be presenting the details at 3:30 on Thursday in the drinking water section at NEMC. I’ll be posting the details here on the blog over the next few weeks too.

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