Hi to all,
I also have a problem with fluctuations of perylene-d12 signal. The problem with the perylene-d12 signal (m/z 264) affects the analytical calibration (internal standard calibration) and also the two control standards analyzed after the calibration standards (one control standard closer to instrumental quantitation limit of 0.1 µg/mL and the second control standard with concentration at the middle of instrumental working range (1 µg/mL)). I use the signal of perylene-d12 (264 as quantitation ion and 260 as confirmation ion) to calibrate the PAH benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(e)pyrene, benzo(a)pyrene, perylene, indeno(1,2,3-cd)pyrene, dibenzo(a,h,)anthracene and benzo(g,h,i)perylene. When I calibrate these PAH using chrysene-d12, the calibration works very well and I have also seen improvements in the calibration of these PAH when I use as internal standard the perylene-d12 quantifyed by m/z 260.
I tried, without any improvements in the perylene-d12 signal, in the calibration and in the analysis of control standards:
- changing the guard column. The injection mode used is on column (1 µL injected volume);
- cutting around 50 cm of column (side attached to guard column);
- conditioning again the column (60ºC to 325ºC - 10ºC/min and 325ºC for 20 min);
- injecting a standard with only target PAH (without internal standards - deuterated PAH: naphtalene-d8, acenaphtelene-d10, phenanthrene-d10, chrysene-d12 and perylene-d12) to verify any interference of the these PAH in the signal of perylene-d12;
- changing the column (DB-5MS 30m x 0.25 mm x 0.25µm) to another one new (DB-5MS 60m x 0.25 mm x 0.25µm);
- analyzing new calibration and control standards prepared from a new standard ampoule, opened for this purpose and within the validity. The ampoule contained naphtalene-d8, acenaphtelene-d10, phenanthrene-d10, chrysene-d12 and perylene-d12;
- changing acquisition conditions (final temperature of the oven program changed from 310ºC to 320ºC; ion source temperature from 230ºC to 250ºC).
- cleaning ion source
Information:
- Calibration and control standards prepared in n-hexane with any problems in the past with the same column type, acquisition method and GC-MS instrument;
- GC- 6890N Agilent; MS - 5975B Agilent
- Acquisition method:
- injection: on column (1 µL)
- with guard column (fused silica deactivated 0,53mm ID)
- column: DB-5MS 30m x 0.25 mm x 0.25µm
- helium: 1.1 mL/min
- oven program: 60ºC (1min); to 100ºC at 9ºC/min; to 310ºC at 5ºC/min; 310ºC (30min)
- interface: 300ºC
- ion source: 230ºC
- quadrupole: 150ºC
- selected ion mode
Could anyone give me some suggestions to identify and solve what is happening? Thank you all.