the Different between ESI and APCI sources

Update @ Friday

(MRL) Maximum Residue Levels for Pesticides in or on food and feed of plant and animal

On the regulation of (MRL) Maximum Residue Levels for Pesticides in or on food and feed of plant and animal:

I think European Union and Japan really did a good job on that.

It is really dilemma to the using of the Pesticides: Some "Environmental-concern" people always want to Pesticides free in all everything. Some"Profit-oriented" always try to use all high efficient Pesticides without caring the impact.

As for me, European Union and Japan: from the regulation view, they are good example for USA and China.

http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2008:058:0001:0398:EN:PDF

( LC-MS/MS) Contamination of Detergents/Surfactant

Which detergent used in the Lab now? Look like the contamination of the detergent/surfactant which was used for the glassware.

Did you notice the m/z different of all the peaks in the mass spectrum?

Tips:
Calculated the most dominant five peaks in the mass spectrum.
305,349,393,437,481,525,569 -> there is 44 different in m/z.
Also checked the less dominant peaks:
333, 377, 421, 465, 509,553 -> there is also 44 different in m/z.
The m/a difference between the first line and second line is 16, look like [M+Na]+, for the second like [M+K]+.

As the m/z = 44.
I think that may be the PEG （polyethylene glycol）:-[-CH2-CH2-O-]-n .
The monomer of PEG is C2H4O ( m/z is 44).
That are the evidences why I doubt that is from the contamination of detergents/surfactant.

Decent HPLC Assay Method for Melamine

(From FDA: Melamine found in baby formula made in China.)

I am really feel sorry for the innocent baby. Feel shame for the authority in SFDA in China. They are not doing any professional jobs.

Sample Pre-treatment:
Transfer an accurately weighted quantity (5 g) of Baby (Infant) formula or milk powder sample to 50-mL volumetric flask. Add some amount of grade MeOH and mix well, sonicate it 10 min. Bring to volume with MeoH. Filter through a membrane filter (0.22 um) before injection.

Standard Preparation:
Using an accurately weighted quantity (50 mg) of USP Melamine RS, prepare a solution in MeOH having a known concentration of about 1 mg/ml.

Column: C18 4.6×250mm，5um.
Buffer:10mM Citric Acid, 10mM 1-Heptanesulfonic acid. using 1M NaOH adjust pH to 3.0.
Mobile Phase: Buffer:MeCN=85:15.
Injection Volume: 10uL.
Flow rate: 1.0mL/min.
Column Temp: 30℃.
Detector Wavelength: 236nm or DAD.

two Papers of Neutral Loss Scan LC/MS/MS Method

To Erics**, Here are two good papers about the Neutral Loss Scan LC/MS/MS Method.
Good luck for your Qualify. (I think the Boss is nice for the Qualify: didn't require 1st year should pass, but NO ONE is failed for the qualify yet in the group, all you need is relax and 100% focus on that).

(1) Screening and Sequencing of Glycated Proteins by Neutral Loss Scan LC/MS/MS Method. Anal. Chem., 79 (15), 5991 -5999, 2007. 10.1021/ac070619k S0003-2700(07)00619-1.

http://pubs.acs.org/cgi-bin/abstract.cgi/ancham/2007/79/i15/abs/ac070619k.html

(2) Multiple Neutral Loss Monitoring (MNM): A Multiplexed Method for Post-Translational Modification Screening. Journal of the American Society for Mass Spectrometry:Volume 17, Issue 3, March 2006, Pages 307-317.

http://dx.doi.org/10.1016/j.jasms.2005.11.002

the Different among the Q1 Full Scan, Product Ion Scan, Precursor Ion Scan

Q1 Full Scan (Start – Stop) : Q1 always used as single MS analyzer. Used primarily for identification of precursor ions.

SIM - Selected Ion Monitoring: Used to optimize analyzer for specific ions. SIM used for quantitative analyses. Q1 SIM used to “optimize” precursor ion. Maximize signal in preparation for MS/MS.

Product Ion Scan: After identification, the precursor ion is sent into the collision cell and fragmented by CID. Q1 is fixed, Q3 sweeps a given mass range. Used for structural elucidation. First step to developing quantitative methods:
m3 + scanned or m1+ fixed.

Precursor Ion Scan: Q1 sweeps a given mass range, Q3 is fixed.
Used to determine the “origin” of particular product ion(s) created in the collision cell.
Frequently well used for drug metabolite identification (common product ion observed in the metabolites).

Why Q-TOF can not perform neutral loss scanning, however precursor ion scan is OK?

To Erics**, That is a "no ending" topic if you allow me to elucidate: once a man walk into bar. (Just my 2 cents)

Precursor Ion Scan: (select a specific m/z in Q3)
Scan Q1, obtain all the precursor ions which could product the specific m/z ion in Q3.
Q1 masses Q3masses
from to from to 300 (m/z) or 400 (m/z) to the same -> 191 (m/z).

Neutral Loss Scanning: perform Q1 and Q3 at the same time.
The only different is that always keep a specific mass different
(the m/z is neutral loss)
Could locate the precursor ions that could product ions of neutral loss.
Q1 masses Q3 masses: from to from to
200 (m/z) -> 182 (m/z): loss 18 (m/z)
420 (m/z) -> 402 (m/z): loss 18 (m/z)
is good for identification of some functional groups ( -OH, -NH2)

So for Q-TOF: it is MS-MS too, but different Q-Q. The 1st MS is a Quadruple, the 2nd mass is TOF.
As I said above, neutral loss scanning requires the 100% exact same scan mechanism happening in 2nd mass. Simultaneous scan at the same ion:
The 1st mass for M, the 2nd mass is for M-m.
Separately Quadruple and TOF could not do that at the same time.

For both of them, MS1 full scan is not necessary: Full scan is only basic scan process, is not a requisite for all the neutral loss scanning and precursor ion scan.

For example, for product ion scan process: Q1 would allow you choose the specific m/z precursor ions, (just change RF/DC is ok), then Q2 CID, Q3 is for product ions scanning.

Nice Picture and Vedio from Varia* 240 Atiomic Absorption Spectrometer

Very Interesting Experimental Phenomenon happened Varia* 240 FS AAS.

Will update the video later.

Infants Milk Powder Contaminated with Toxic Melamine

Updated FCC Developmental Melamine Quantitation (HPLC-UV) and GC-MS Screen for the Presence of Melamine. The sample pre-treatment really matters a lots on the assay result.

Call me if want the detail Method (Adapted from FDA/ORA Forensic Chemistry Center SOP T015) .

Molecular ion of CH3I ??

I am not sure what is your question? So sorry if my answer is wrong, the molecular ion should be 127. But I had no idea of the second Mass Spectrum. Do then have any relationship? or you sent me a wrong Mass Spectrum?

Thanks for your update...