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- Posts: 7
- Joined: Fri Jun 13, 2025 8:27 pm
Good evening,
I'm having some issues related to the PAH analysis on my GC-MSMS.
I'm trying to validate a method for PAH determination following the EPA3546+EPA8270D. I'm working with a Shimadzu GC2010-TQ8040, which i'm using ad a single quadrupole.
I've few questions about different issues i'm facing:
1) First of all, i've started to use this instrument in January. Everything worked almost perfectly although it had been used without paying much attention. Calibrations where very good, although nobody had ever provided to change syringe, septa or glass insert. The only issue I could complain about was the very weak stability of the calibration, which lasted just 5 or 6 days. During the last days of March I've tried using the automatic addition of the internal standard using the autosampler, anda also this function worked great. On 16th of April I've done a new calibration, whitout any problem: R^2 was higher than 0.99 for almost all the analytes (23 PAH + 3 surrogates) and internal standars areas where perfectly replicable. Well, on 28th of April, the instrument started having trouble. No replicable areas for internal standards nor for the analytes. Planned a PM done by Shimadzu technician, who cleaned everything, from the inlet to the detector, replacing the syringe too. Although this, the instrument hasn't come back to its previous performaces. Tried to do diffent calibration, but couldn't achieve the previous performances. Since the 28th of April, I've tried replacing the syringe, septa, glass inserts different times, but can't understand why areas, which were perfectly replicable (1/2% difference between injections) before that day, have a 5 to 10% difference now. Have you any idea about this?
2) Yesterday I've calibrated the instrument using RSD<20% as acceptability criterion. Today, I've tried to analyse a 10ug/L and a 25ug/L standard, to verify the calibration, and noticed that the analytes concentration rised from 10ug/L to 15ug/L, and from 25ug/L to 37ug/L for the heavier analytes of the mix (Indeno-1,2,3-c,d,fluoranthene, benzo(ghi)perylene and the 4dibenzopyrene). Consider that the solutions where prepared from a 200ppm solution for both PAH and Surrogates, stored at -8°C and left at room temperature for 20minutes to avoid poor solubility of the heavier compounds in the mix. I've spiked 50ul of both in 10mL of DCM, obtaining a 1ppm and then, from the 1ppm spiked respectively 200ul and 500ul to 10mL of DCM to obtain the 20ug/L and 50ug/L solutions. All the spikes where done using a 5190 Agilent syringe. Have you any advice about this problem?
Thank you so much in advance and thank for the amount of informations available on the forum!
Peppels
I'm having some issues related to the PAH analysis on my GC-MSMS.
I'm trying to validate a method for PAH determination following the EPA3546+EPA8270D. I'm working with a Shimadzu GC2010-TQ8040, which i'm using ad a single quadrupole.
I've few questions about different issues i'm facing:
1) First of all, i've started to use this instrument in January. Everything worked almost perfectly although it had been used without paying much attention. Calibrations where very good, although nobody had ever provided to change syringe, septa or glass insert. The only issue I could complain about was the very weak stability of the calibration, which lasted just 5 or 6 days. During the last days of March I've tried using the automatic addition of the internal standard using the autosampler, anda also this function worked great. On 16th of April I've done a new calibration, whitout any problem: R^2 was higher than 0.99 for almost all the analytes (23 PAH + 3 surrogates) and internal standars areas where perfectly replicable. Well, on 28th of April, the instrument started having trouble. No replicable areas for internal standards nor for the analytes. Planned a PM done by Shimadzu technician, who cleaned everything, from the inlet to the detector, replacing the syringe too. Although this, the instrument hasn't come back to its previous performaces. Tried to do diffent calibration, but couldn't achieve the previous performances. Since the 28th of April, I've tried replacing the syringe, septa, glass inserts different times, but can't understand why areas, which were perfectly replicable (1/2% difference between injections) before that day, have a 5 to 10% difference now. Have you any idea about this?
2) Yesterday I've calibrated the instrument using RSD<20% as acceptability criterion. Today, I've tried to analyse a 10ug/L and a 25ug/L standard, to verify the calibration, and noticed that the analytes concentration rised from 10ug/L to 15ug/L, and from 25ug/L to 37ug/L for the heavier analytes of the mix (Indeno-1,2,3-c,d,fluoranthene, benzo(ghi)perylene and the 4dibenzopyrene). Consider that the solutions where prepared from a 200ppm solution for both PAH and Surrogates, stored at -8°C and left at room temperature for 20minutes to avoid poor solubility of the heavier compounds in the mix. I've spiked 50ul of both in 10mL of DCM, obtaining a 1ppm and then, from the 1ppm spiked respectively 200ul and 500ul to 10mL of DCM to obtain the 20ug/L and 50ug/L solutions. All the spikes where done using a 5190 Agilent syringe. Have you any advice about this problem?
Thank you so much in advance and thank for the amount of informations available on the forum!
Peppels
