Chromatography Forum

I'm excited that it appears I am close to being able to reliably see 10 ppm DRO. Looks like the top of the curve is going to be about 10,000 ppm. Things become distinctly variable higher than that. From one injection to the next a 25,000 can vary 50%. Maybe best culprit is that 0.25um film thickness.

The first column I started out with was 50m and 0.33um film thickness. Too bad it embrittled and fell apart. I can't afford another column at the moment. I'll see how the next month comes out.

Too bad there is not a hack or something to trick the 7673 or 6890 series injectors into doing the solvent saving feature of the newer 7683 model. 3 rinses at 80% of 50uL drains the clean solvent vials remarkably quickly.

Too bad there is not a hack or something to trick the 7673 or 6890 series injectors into doing the solvent saving feature of the newer 7683 model. 3 rinses at 80% of 50uL drains the clean solvent vials remarkably quickly.

Yes, that is a big problem with the older autosamplers. I like in the new ones you can set it to x ul of rinse or even sample washes. I had to just use sample pumps without a sample wash using the older autosamplers if I used a small volume insert, otherwise after one injection most of the sample was gone.

We have been using a 5uL injection for a couple years now. With 5uL our effective MDL for DRO was 25ppm. But to pass the ERA PT tests for DRO in water we wanted a lower detection limit.

Last month we ordered in some 50uL syringes and decided to try for a larger injection volume. I can say its been a success. With the 20uL injection we have 10 ppm in the calibration and we are using 10 ppm DRO as our MDL. Our effective Response Factor range is from 10 ppm to 25,000 ppm with a 13.7% RSD. We can see down to 5 ppm but blanks are coming back at 1-4 ppm and that seems a bit too close to use 5 ppm as an effective MDL. We passed the DRO PT with a z-score of 0.703.