Plastic contaminations are common in many analytical labs. A ultrapure water system and an oven for baking glass ware are especially needed for ultra trace analysis with LC-MS and GC-MS. In reality it is sometimes hard to avoid all plastics, because the process can start with chemicals in plastic containers, dirty solvents, contaminated gloves and multiple other sources.

This is a structure elucidation process using multiple stage tandem mass spectrometry (MS^8 or MS/MS to the eight) for finding core structures of molecules in plasma. The Finnigan LTQ can obtain such spectra in an automated manner for hundreds of peaks in data dependent mode. Chip based Nano Electrospray Ionization (nanoESI) is a very sensitive method and is used with the infusion robot Advion Nanomate.

Sample (Kwang-Hyeon Liu/FiehnLab - Data Evaluation Tobias Kind)
Plasma_Pos_LowMS_60MSMS_CE45_01.raw Friday, April 03, 2009

(Click picture to enlarge or download source)

MS2 precursor 664.00
|__MS3 precursor 607.32
| |__MS4 precursor 551.33
| | |__MS5 precursor 495.34
| | | |__MS6 precursor 439.26
| | | | |__MS7 precursor 383.17
| | | | | |__MS8 precursor 327.06
| | | | | | |__Composite spectrum MS8 664.00,607.32,551.33,495.34,439.26,383.17,327.06
| | | | | | |__Single spectrum MS8 664.00,607.32,551.33,495.34,439.26,383.17,327.06 (190)
| | | | | |__Composite spectrum MS7 664.00,607.32,551.33,495.34,439.26,383.17
| | | | | |__Single spectrum MS7 664.00,607.32,551.33,495.34,439.26,383.17 (189)
| | | | |__Composite spectrum MS6 664.00,607.32,551.33,495.34,439.26
| | | | |__Single spectrum MS6 664.00,607.32,551.33,495.34,439.26 (188)
| | | |__Composite spectrum MS5 664.00,607.32,551.33,495.34
| | | |__Single spectrum MS5 664.00,607.32,551.33,495.34 (187)
| | |__Composite spectrum MS4 664.00,607.32,551.33
| | |__Single spectrum MS4 664.00,607.32,551.33 (186)
| |__Composite spectrum MS3 664.00,607.32
| |__Single spectrum MS3 664.00,607.32 (185)
|__Single spectrum MS2 664.00 (184)

m/z 664 , 607 ,551 ,495 ,439 ,383 ,327
accurate masses see above

Precursor (ESI+) 664.00 Da --> 607 --> 551.2 --> 495.26

MS^8 (ESI+) of precursor m/z 327.06 Da

Use LipidMaps Tools!

CE(18:2(Ep)) 18 2 663.5711 0.4289 C45H75O3+
CE(18:2(Ke)) 18 2 663.5711 0.4289 C45H75O3+
CE(18:3(OH)) 18 3 663.5711 0.4289 C45H75O3+
CE(18:1(Ep))-cyclo 18 1 663.5711 0.4289 C45H75O3+
CE(18:1(Ke))-cyclo 18 1 663.5711 0.4289 C45H75O3+
CE(18:2(OH))-cyclo 18 2 663.5711 0.4289 C45H75O3+
Sphingosine CerP 18:1 644.5013 0.5013 C36H71NO6P+
Sphingosine HexCer 12:0 644.5096 0.5096 C36H70NO8+
Sphinganine Cer 24:4 644.5976 0.5976 C42H78NO3+

Problem our mass accuracy 0.04 Da (78 ppm) but all calculated results are 0.4 Da apart.

Google it!

Current mass accuracy with LTQ iontrap around 78 ppm. No need to fire up the LTQ-FT-Ultra (yet).

On the lipid composition of human meibum and tears: Comparative analysis of nonpolar lipids Igor A. Butovich; 10.1167/iovs.08-1889

Analysis of Additives in Polyethylene with Desorption Chemical Ionization/Tandem Mass Spectrometry

S. W. CHEN and G. R. HER*
Appl. Spectrosc. 47, 844-851 (1993)
http://www.opticsinfobase.org/abstract.cfm?URI=as-47-6-844
Also Oxidized Naugard 524: Mass spectrometric analysis of additives in polymer extracts by desorption chemical ionization and collisional induced dissociation with B/E linked scanning
Analytica Chimica Acta; Volume 311, Issue 2, 31 July 1995, Pages 153-164; C.G. Juo, S.W. Chen and G.R. Her
http://dx.doi.org/10.1016/0003-2670(95)00183-Z

Possible Solution

Irganox or Irgafos or Naugard oxidized plastisizer MW= 662.44
InChIKey: AZSKHRTUXHLAHS-UHFFFAOYSA-N and CID 14572930
Is that the final solution? Possibly yes, but: No, because for the formula = C42H63O4P the exact mass = 662.446397016.
The [M+H]+ would be 663.4542 Da and not 664.0. In this case an ultrazoom investigation or infusion into FT-ICR-MS with 50,000 to 100,000 resolving power would probably help. MS/MS on isotopic peak, ion suppression of isobars, overlap with
multiple ceramides or cholesterol and oxycholesterol species also possible. EDIT: the accurate mass was later determined to be 663.46117 Da, with 10 ppm deviation on the LTQ. Chapter closed.

LINKS

- List of common LC-MS contaminants
- ESI contaminants (A. Schlosser)
- Seven Golden Rules MS-MS-Fragmentation
- Interferences and contaminants encountered in modern mass spectrometry see XLS in supplement
("List of potential interference- or contaminant ions in modern mass spectrometry, positive mode")
- Nonylphenol series, m/z 463, 507. 551. 595, 639, 683, 727, 771, 815 Da = delta 44 Da
RCM 2002,16,1243 [DOI]

Downloads (provided for your convenience) CC-by license unless copyrighted material used.
- Powerpoint presentation [PPT]
- Mass Spectrum (MS8) of Naugard [MSP]
- Compressed and uncompressed pictures, mass spectra and RAW file with MS8 and all PPTs [ZIP]

Written on a sunny Friday in California Anno 2009
Filed under Anecdotal Mass Spectrometry