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...

Agilen* 1100: Pump Preventive Maintenance

Today, firstly finished a "Preventive Maintenance" on the pump @ Agilen* 1100 system at Sept-08-2008. ( the fourth PM on the Agilen* LC system since 2004)

The system is working well, except a high frequency noise come from the Quan-Pump -> when the pump delivery mobile phase, the Sapphire Plunger forward and back -> a scratching noise from the pump.

-> found lots of dark matter in the pump, use the MeOH and H2O to wash ->

-> use the IPA to prime the LC system for 30 min. done!!!

Next step: should order the Preventive Maintenance kit and finish the PM task on the autosampler and VWD.

Note: some catalog #01018-68722, # G1311-68710.

Poor Response of p-Chlorophenol in Tandem LC-MS?

That is really a good example for Triple Quadrupole LC-MS.
Poor response at Positive ESI (+) mode, however, acceptable response at Negative ESI (-) mode.

Here, let's us assume that Tandem LC-MS instrument is under 100% perfect tuning mode ( just want to exclude the uncertainty of the Tandem LC-MS, just want to discuss about the nature of analyte in LC-MS)

General the Mass Response depends on the stability of molecular ion. -> look at the structure of p-Chlorophenol -> Positive ESI (+) mode, would very unstable due to the -Cl element (Cl element is EWG, that is to say, -Cl belongs electron withdrawing group. However, under Negative ESI (-) mode, the molecular ion would be more stable due to the present of Cl element. ( When this center is an electron rich carbanion or an alkoxide anion the presence of the Cl has a stabilizing effect.) that is the delocalization effect in the physical chem.

That is the reason why I always ask for the pKa value of each analyte @ Tech. For me, I NEVER under estimate the importance of pKa value.

So we always could change pH value to alter the disassociation of analyte in ESI mode. ( With ESI, convert the molecular ion from liquid phase into gas phase, enable the analyte evaporate into ion status -> obtain a decent response).

From the pKa, we know about the nature of analyte: basic,acid or neutral.

Then for basic analyte -> add some Acetic Acid/ Formic Acid ( pH ≈ pKa－2 ) -> enable the analyte generate positive (+) ion in solution for Positive ESI (+) mode. or for acid analyte -> add some ammonium to increase the pH ≈ pKa＋2 -> analyte is molecular ion with negative (-) for Negative ESI (-) mode.

Next time, will update my Tech Notebook about how to trouble-shooting the Poor Response of the Analyte based on the API 3200 Tandem QQQ LC-MS . (that is a golden treasure I learnd from Tech, U definetely need to buy me a drink for that)

Normalized Peak Area

Talked about this issue so many time, need to assume that response factor of each component is identical. However, we always negelect that at the assay of total impurities in the samples were performed by normalization method.
So I only recommend to use this method to estimate the relative amounts of small impurities or degradation compounds in a purified component at the specific detector wavelength, that is chromatographic purity.
From my view, the Second maybe ensure a better Repeatability for your results.
or if I were you, I will use manual integrate to get a decent result with batch options.
At the same time, I always double that the column maybe over-load, that mass of analyte per injection is too high, don't you think so?

What is Batch Review in ChemStation?

Huge Time saving with this Batch Review option.
And I also need to learn how to write Excel Macros/Excel VBA, hope john** you could give me some basic knowledge, thanks a lots.

Assay of Vitamin e

H2O + Vitamin D3 (Internal Standards) + Vitamin C Solution (in MeOH) + Sodium Hydroxide. Water bath 30 min, extract with ethyl ester and evaporate to dry, and then dissolve in MeOH. The peak @ rt=2.8 is the problem?(1) Double check the contamination from the needles and HPLC volumetric flash, vials.

(2) If doesn't work, -> what is the concentration of the Sodium Hydroxide? 0.1 N? Do you make sure that the internal standard (Vitamin D3) would not discomposed with the present the anti-oxidant (Vitamin C) during the saponification process?
(3) The final method is that follow the USP method to troubleshooting.

Constitutional Isomers (Structural isomer) by HPLC

To Ren***, I am a newbie on the separation on the Constitutional Isomers (Structural isomer). I 100% knew that you might try all the combination of mobile phases and C18 Column. Here are my suggestions:
(1) Try to call the Column Supplier for some info of Chiral column. Maybe they have more information for your analyte. Or if you are lucky, ask them give you a favor -> provide a free chiral column for trial analysis.
(2) If the chiral column is not available, try to put some Quatemary Ammonium Salt in the mobile phase, it maybe obtains a better separation.

Good Luck, also thanks for your question and any update of your results in advance.

How Important to Tune LC/MS system (Agilen* 6410)

At the first half of 2007, always complained on the poor / False Negative ESI mode on the Agilen* 6410.
At the on-site setup@Feb-2007, already learned how to tune up the 6410. At March 2007, Mr. B-Cousin** just occasional stopped by Atlanta: then asked him for an update of Mass-Hunter Software. Then I performed an auto-tune on the 6410. After that, the nightmare on the Negative ESI happened. -> Found poor selectivity on the Negative ESI mode ->However the Positive ESI mode worked perfect with a good pass results of tuning. Tried to cal Agilent Tech, but faile to find out a solution.
Lots of unknown biofuels in the lab need to identified by PosESI and NegESI, felt huge pressure from the Co-works. Every morning, almost want to smash on the Agilen* 6410 when entered into the lab.
When cool down, checked with the old tune reports with new tune reports: for old tuning solution b4 upgrade the 6410 Masshunter software, tuning peaks@ 112.99, 431.98, 601.98, 1033.99, 1633.95, 2233.91. However when upgrade the software, the tuning m/z is: 112.99, 302.00, 601.98, 1033.99, 1333.97, 1633.95.
Then found out problem: maybe did not use the new tuning solution after upgrade the 6410 Masshunter software. Changed the new tuning solution, OMG, perfec. Huge response value for the MET** in the biofules.
Used the old tuning solution after upgrade the 6410 Masshunter software.: expected 302.00m/z , but only found @ 290.26 m/z.
So when the m/z of the analyte is from 230- 350 at NegESI, almost got poor results, made the catalyst guys crazy and cry everyday.

See an good GLP on LC/MS tune report @ FDA :http://www.cfsan.fda.gov/~comm/fluoroqu.html#attachb