precision of SPME

[jiangds06]

the same samples were injected twice back to back. why the second injections always have around 30-40percent response factor increase (IS corrected). What could be the problems?

[rb6banjo]

I do a lot of SPME and I do not detect this phenomenon. My precision is generally better than this.

What is the concentration of your analyte? 30% of 100 parts-per-trillion is only 70 or 130 parts-per-trillion in the reported result. Either way, it's a ridiculously small amount.

[jiangds06]

concentration is around 20ppb.

I do a lot of SPME and I do not detect this phenomenon. My precision is generally better than this.

What is the concentration of your analyte? 30% of 100 parts-per-trillion is only 70 or 130 parts-per-trillion in the reported result. Either way, it's a ridiculously small amount.

[James_Ball]

the same samples were injected twice back to back. why the second injections always have around 30-40percent response factor increase (IS corrected). What could be the problems?

Have you done a blank injection using the same fiber right after the first injection? If so does it indicate any carryover?

[rb6banjo]

On "typical" things that are 20 ppb, I see better precision than +/- 30%. I agree with James_Ball. Is there something that's in your blank that is causing you trouble? Something coming from your injection (a siloxane from the fiber or the inlet septum) system?

[jiangds06]

I might need to inject blank inbetween.

On "typical" things that are 20 ppb, I see better precision than +/- 30%. I agree with James_Ball. Is there something that's in your blank that is causing you trouble? Something coming from your injection (a siloxane from the fiber or the inlet septum) system?

[jiangds06]

Hi Jame, I did not see carry over for the sample for blank injection. This is wired.

the same samples were injected twice back to back. why the second injections always have around 30-40percent response factor increase (IS corrected). What could be the problems?

Have you done a blank injection using the same fiber right after the first injection? If so does it indicate any carryover?

[jiangds06]

if this is the case, then why Internal standards in second injection always have lower peak area (almost decrease by half) than the first injection for all five standards. Analytes peak area remain very similar between two injections for the same samples.

On "typical" things that are 20 ppb, I see better precision than +/- 30%. I agree with James_Ball. Is there something that's in your blank that is causing you trouble? Something coming from your injection (a siloxane from the fiber or the inlet septum) system?

[jiangds06]

One thing I notice is that I have very noticeable column bleeding. Does that affect my reproducibility?

On "typical" things that are 20 ppb, I see better precision than +/- 30%. I agree with James_Ball. Is there something that's in your blank that is causing you trouble? Something coming from your injection (a siloxane from the fiber or the inlet septum) system?

[James_Ball]

One thing I notice is that I have very noticeable column bleeding. Does that affect my reproducibility?

On "typical" things that are 20 ppb, I see better precision than +/- 30%. I agree with James_Ball. Is there something that's in your blank that is causing you trouble? Something coming from your injection (a siloxane from the fiber or the inlet septum) system?

If you have air leaking at the injection port causing the column bleed then that could be causing problems.

[jiangds06]

i do not have leaking issue.
Actually, I solve the problem by decreasing the extraction time. probably it is the competitive adsorption.

One thing I notice is that I have very noticeable column bleeding. Does that affect my reproducibility?

On "typical" things that are 20 ppb, I see better precision than +/- 30%. I agree with James_Ball. Is there something that's in your blank that is causing you trouble? Something coming from your injection (a siloxane from the fiber or the inlet septum) system?

If you have air leaking at the injection port causing the column bleed then that could be causing problems.