So how many times do you need to rinse a syringe?
Well, I can tell you the answer for the experiment we did. Let me first refresh your memory on specifically what we did.
Sequence of manual syringe rinsing:
1. 20 µL draw of a 500 ppm hydrocarbon standard and expel it
2. 20 µL draw of acetonitrile – eject into sample vial – test via GC-FID
3. Repeat step 2 many times
Each “rinse” was tested via GC-FID.
How many 20 µL acetonitrile rinses were needed to show no signal (FID)?
The answer is 4.
I want to thank everyone that commented when I posed the question. Most people were right on track with about 4 rinses. It is also funny that people tended to do “extra” rinsing regardless of what they thought was required. I still do this with about 6 to 10 rinses depending on the situation.
I wanted to share some helpful hints from people who commented:
- Use more than one rinse solvent especially in situations were analytes have a wide range of polarity
- Use more than one rinse vial
- Use the same solvent for rinsing as is used for the sample and standard solutions
Here is a chromatogram of a 50 ppm hydrocarbon standard followed by chromatograms of consecutive rinses. The 50 ppm chromatogram can be used as an intensity reference because the y-axis is the same for all chromatograms.
Interesting tips (again)
But…do I see some signal again after 5 rinses? :-)
As I read the data, the answer is three. Three rinses and then you have a clean syringe. Just like we learned in school.
I suspect the syringe volume would have an impact on the rinsing efficiencie, with a larger volume syringe posessing greater surface area that has to be cleaned. What was the volume of the syringe used for your experiment?
Thanks,
Scott
Hi Scott,
thank you for reading the blog.
For this experiment, i used 20 uL…the same volume as the sample
“2. 20 µL draw of acetonitrile – eject into sample vial – test via GC-FID”
This isn’t really typical as most people use more that the volume of the sample but in some cases if you are using most of the capacity of a syringe, this would be similar. I considered it the “worse case scenario”.
thanks again
Julie
HI I OFTEN WONDERED WHY NO ONE EVER PUPLISHED THIS TYPE OF STUDY. I also found using a 10 ul syringe injecting 1ul of a 5% solution in dichlormethane and rinsing the 10 ul syringe with 10 ul dichlormethane it took three 10ul rinses to basically have a clean needle. Interestingly if I rinsed the needle first and then rinsed the needle I could have gotten away with one less rinse. SOP in this lab is 5 10ul rinses flowed by drying in a vacuum line for 5 min.
The number of rinses would depend upon the nature of the solutes and solvent. Acetonitrile is not a very good solvent for hydrocarbons. We use chloroform and then hexane. Remember freshman chemistry: like dissolves like! ;-) Also, the number of rinses needed depends upon your objective, how close your work is to your instrument’s LOD, are you making a qualitative or quantitative analysis? Several factors to consider!