Proposed Mechanism for TFA Signal Suppression and the "TFA-Fix"

TFA can be displaced from the ion-pair complex by exposing the effluent to a higher concentration of a different acid post column and before the MS detector. This is referred to as the "TFA-Fix".That is to say: Signal Suppression due to Additives (ESI signal suppression by TFA)
Ion pairing with analyte --> surface tension effect

Solutions:
Post-column addition of a sheath liquid of propanoic acid (10%) in 2-propanol (TFA Fix)
Use low concentrations of TFA with acetic acid (TFA Light)
Replace TFA

Always remember: Achievement of gaseous analyte ionization at API interface is the key to MS detection.

Reference: Agilent LC/MS Method Development Resource.

APCI – Typical Operating Conditions

( Please look up Blog@July-06-2008 for the selecting of ionization methods for LC-MS)

Flow Rates: 50µL/min. - 2mL/min.
Vaporizer Temp (°C): 400-550 (600 max)
Discharge Current (µA): 5 (20µA max.)
Sheath Gas Flow Rate (arb): 35-80
Auxiliary Gas: 0
Capillary Temp (°C): 250-350C
Tube Lens Offset (V): 30-60V
Ensure that the APCI probe is hot enough so that the spray shield is not dripping wet.

(Note: For me, always assume that works better at higher flow rates, higher flow rate means more solvent for plasma production. Position of corona discharge needle is critical for sensitivity.)

Steps for APCI Optimization

If analyte’s pKa is unknown, evaluate 3 pH regions in positive and negative ion modes.
Acids – Negative Ion detection, adjust pH 2 units below pKa.
Decrease pH use formic acid , acetic acid, TFA.
Bases – Positive Ion detection, adjust pH 2 units above pKa.
Increase pH with NH4OH, TEA, TMA.
Adjust corona discharge voltage.
Adjust nebulization temperature.
Consider possible thermal decomposition of analyte.

Contamination Peaks - Positive Ion ES

Double check if following peaks consistently exist in the GC-MS chromatogram.
m/z Ion Compound
42 (M+H)+ Acetonitrile
59 (M+NH4)+ Acetonitrile
64 (M+Na)+ Acetonitrile
65 (2M+H)+ Methanol
79 (M+H)+ DMSO
83 (2M+H)+ Acetonitrile
85 (M+H)+ d6-DMSO
101 (M+Na)+ DMSO
102 (M+H)+ Triethylamine (TEA)
104/106 (M+Cu)+ Acetonitrile
105 (2M+Na)+ Acetonitrile
120 (M+Na+CH3CN)+ DMSO
122 (M+H)+ Tris
123 (M+H)+ Dimethylaminopyridine (DMAP)
130 (M+H)+ Diisopropylethylamine (DIPEA)
144 (M+H)+ Tripropylamine (TPA)
145/147 (2M+Cu)+ Acetonitrile
146 (3M+Na)+ Acetonitrile
150 (M+H)+ Phenyldiethylamine
153 (M+H)+ 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)
157 (2M+H)+ DMSO
159 (M+Na)+ Sodium trifluoroacetate
169 (2M+H)+ d6-DMSO
179 (2M+Na)+ DMSO
186 (M+H)+ Tributylamine
214 (M+H)+ Unidentified contaminant, maybe related to methanol
225 (M+H)+ Dicyclohexyl urea (DCU)
239/241 [(M.HCl)2-Cl]+ Triethylamine
242 M+ Tetrabutylammonium (C4H9)4N+
243 M+ Trityl Cation
257 (3M+H)+ DMSO
273 M+ Monomethoxytrityl cation (MMT)
279 (M+H)+ Dibutylphthalate (plasticiser)
301 (M+Na)+ Dibutylphthalate (plasticiser)
317 (M+K)+ Dibutylphthalate (plasticiser)
338 (M+H)+ Erucamide
360 (M+Na)+ Erucamide
391 (M+H)+ Diisooctyl phthalate (plasticiser)
413 (M+Na)+ Diisooctyl phthalate (plasticiser)
425 (M+Na)+ Unidentified contaminant (plasticiser)
429 (M+K)+ Diisooctyl phthalate (plasticiser)
449 (2M+H)+ Dicyclohexyl urea (DCU)
454 (M+Na+CH3CN)+ Diisooctyl phthalate (plasticiser)
798 (2M+NH4)+ Diisooctyl phthalate (plasticiser)
803 (2M+Na)+ Diisooctyl phthalate (plasticiser)

Thanks Dr.John Langley@University of Southampton

How to obtain a NICE GC Chromatogram with good peak profile?

To 1005ling: At the first look, seemingly found lots of impurities on the column.
(1) Did you condition the column according the GC Column manufacturer’s method? If No, Do IT now.
(2) If Yes, Double check that maybe your column was contaminated. Trim/cut the first 0.5 m of the inlet column or change another column.

If above tip doesn’t work, highly recommend you look back the Oven Temp Ramp: change the temp ramp by lowing down the initial temp, and hold for 5 min.

Or Double check the polarity different between your column and analyte.
Here is some information about the stationary phases of GC column with its applicability:
①SE-30: (100% Dimethylpolysiloxane), alternative to HP-1,HP-101, CP-si15CB,SPB-1, RTX-1,OV-1,007-1, ( similar with OV-101), is suitable for assay of amine, hydrocarbons, phenols, sulfides, flavor. Temperature Limits: 0 to 325/350°C.

② SE-52: (5%-Phenyl)-methylpolysiloxane. Or equivalent with SE-54.

③ SE-54: (5%-Phenyl)(1%-Vinyl)-methylpolysiloxane. Equivalent with HP-5,DB-5, CP-si18CB, RTX-5, OV-5, SPB-5,007-2 column. Good for assay of alkaloids, medicines, aliphatic acids, methyl ester, halide, aromatic. Temperature Limits: 0 to 350°C.

④ PEG-20M: are polymers of ethylene glycol, 20 meter. Highly cross-linked resulting in excellent peak. Alternative to HP-INNOWAX,HP-20M,CP-WAX52CB,DB-WAX,BP-20,007-CW for the assay of alcohol, aromatic, volatile oils, solvents. Temperature Limits: 0 to 250°C.

⑤ FFAP: Nitroterephthalic acid modified polyethylene glycol column. High polarity, Designed for the analysis of volatile fatty acids, ketone, nitrile and phenols. Bonded and cross-linked with solvent rinsable. Can be used at operating temperatures at 60-250ºC. Alternative to HP-FFAP, B-FFAP,CPWAX58CB,SP-1000,STABIL-PA,OV-351,007-FFAP Close equivalent to USP Phase G35.

⑥ XE-60: modified cyanoethylmethylpolysiloxane XE 60 (25% cya-. noethyl, 75% methyl)
Good for aliphatic acid，carborane, acryl amide, organophosphorus pesticides, cocaine, phenols, aromatic amine. Temperature Limits: 0 to 250°C.

⑦ OV-1701 : 14% cyanopropylphenyl-86% methyl polysiloxane. alternative to HP-1701,RTX-1701,SPB-7,SPB-1701,007-1701，good for environmental, food and beverages, pesticides, herbicides. Temperature Limits: 0 to 300 °C.

Reference: Phenomenex, Agilent, Restek Cross Reference for Similar GC Columns.

Note: Next time, pls enclose more detail of GC assay parameters, being a good questioner will help us answer well, NOT just guess. Thanks for your question, Best.

How to improve this Deltamethrin GC chromatogram?

(YJ007, thanks for your question, highly appreciate your trust.)

Column: HP-5.
Oven Initial Temp: 150℃ hold 2min, then to 270℃@ 10℃/min for 23min.
Injection: Splitless @ 280, 1 ul.
Carrier gas: Helium @ 6ml/min.
ECD Temp: 300.
Make-Up gas: 30ml/min.
Deltamethrin Conc.: 0.1mg/L.
My answer to YJ007:
From this first chromatogram, the second peak in the 1st chromatogram should be the peak of Deltamethrin. However, that is NOT good one.

My first doubt was drawn by that flow rate (6ml/min): what is the diameter of that HP-5 column? Maybe 0.32 mm ( correct me if I am wrong) , so why use so high flow rate?
Any specific reason?
Tips: Increase the ECD Temp to 300 degree C, low down the initial temp to 110 degree C, adjust to flow rate according the diameter of the column. That maybe helps.

Here is my method used @ Feb-2005:
Column : HP-1, 5 m X 0.53 mm X 2.5 um
Inlet Temp: 280 ℃
ECD: 300 ℃
N2: purity NMT 99.99%, 13 ml/min
Then the retention time of Deltamethrin peak is 7.3 min.

Any Versatile Tool for Drug Residu Analysis?

Today, had a talked with Co-Worker "Is there any versatile Instrument for Residues Analysis ?"

As far as I know, the answer is NO for the residues analysis of following veterinary drug.

GC-MS: Terbutaline、Clenbuterol、Salbutamol、Ractopamine ( Clenbuterol , Clenbuterol, Spiropent; Planipart）、Cimaterol.

GC: Chloramphenicol，Chloromycetin and Polychlorinated biphenyl (PCBs)

LC-MS: Chlortetracycline，Aureomycin、Sulfonamides(SAs)、Ciprofloxacin、Enrofloxacin、clopidol、Tetracycline Tablets、Furazolidone、Olaquindox、Sudan yellow( oil orange), Stilbestrol.

One more phobia for the food:" why this chemicals matters? Just want to improve the meat products, NOT thinking about the side effect for our generations? Maybe is is time to re-evaluate this additives now, as least for me, thinking more greener if we could.

5973 Mass Spec failed to Pump (2)

Remove the side cover of vacuum room: pull out 70 C, hold firmly, lift it slowly.Remove the vacuum room and pump:Agilent always took it apart separately But for me, recommemed remove them together by un-screw the six screws

Trun left a little bit, put the EGM back to remove the EGM

Remove the slot and vacuum line on the pump: anti-clickwise to take it down
Ask Co-worker for help : hold the whole vacuum room first, to pull out the turbo pumpReplace the new end-cap, careful put them back. Enclose a back view of all the connections.
<See (1) at May-16-2008>

Hamilton Syringes Clogged on 6890N GC

After finishing the assay of methylbenzene residue in Taxol (Paclitaxel), found the 10 uL syringe clogged.
The injection concentration is 0.2 g/ml. Maybe the high injection concentration is the reason why the syringe clogged.

Option 1: Try to put the syringe into MeOH with ultrasonic bath. But failed, the MeOH had difficulty to penetrate and dissolve the blockade.

Option 2: Put the needle in DMF bath for 2 hours, then if doesn’t work well, put ithe boiling water ( Boiling IPA) for 30 min. It worked.

Option 3: (learned it from Hamilton Tech Service) Put the clogged needle into MeOH or EtOH with ultrasonic bath over night.

Today, got a calling from a friend @ A****

He commented that my Sample Pre-treatment by Solid-Phase Extraction is GOOD, but complained for a average of 15 $ on the SPE per sample.

Ok, here is another alternative for Sample Pre-treatment, I named it as dispersive solid-phase extraction.

(1 ) Extraction: Transfer 15 g of ample, accurately weighted, in 50-mL PS Centrifuge tube. Add 15-mL Glacial Acetic Acid-Acetonitrile (1:1), 6 g of anhydrous Mg2SO4, 1.5 anhydrous Na2SO4, then shake it mechanical 1 min, centrifuge the mixture for 5 min under 5000 r/min for further purify.

(2) Purification: Weight 0.1 g PSA，0.1 g C18，0.3 g of anhydrous Mg2SO4 into a 5-mL glass centrifuge tube, then pipet 2-mL of clear solution into the tube.Mixing the solution by using multi-function mixer whirlpool for 1 min, centrifuge the mixture for 1 min under 5000 r/min . Pipet 1-mL of the upper clear solution into 1 ml volumetric flask for the assay preparation.

To ensure the precision of the assay results, highly recommend the follow steps.
(3) Add the internal standard and protective agents: Put the 1 ml volumetric flask onto a Nitrogen blowing Instrument, blow with N2, concentrate the solution volume is less than 0.8-mL at room temp.Transfer an accurately weighted quantity 100 100 µL internal standard of TPP and 100-µL of protective agent’s mixture solution. Bring to the volume with Acetonitrile. Homogenize the solution on a vortex 5 min for GC-MS analysis.

Would you please update me if it works. Thanks.
Appreciate your comments.

Note:Working 200% well with the vegetable juices and fruit juices. For the Grains, Beans, Nuts, Seeds, please add more water and increase extraction time with vigorous mechanically shake, it also works.

Extraction Melamine Methods from Pet Foods (diluted 100 times) Comment (Just my 2 cents)

There are at least up to 3 prevailing assay methods for Melamine.
(1) Sublimatography
(2) HPLC Method
(3) HPLC-MS（FDA，SGS) and GC-MS(FDA)Sample Preparation:
1. Homogenize the pet foods into the shape of structural pudding.
2. Weigh 2 g of sample into 10mL MeOH/H2O( 60:40)， shake it vigorously.
3. Sonicate 1 min.
4. Mixing the solution by using multi-function mixer whirlpool, let it still 5 min, allow aqueous phase and organic phase separate.
5. Centrifuge it 5 min under 3000 g.
6. Filter the solution with whatman glass fiber filter paper and collect the filtrate.
7. Pipet 0.1 mL of filtrate and dilute with 1.9 MeOH/H2O( 60:40) and 20 mM PBS.
8. Pipet 100 uL for further GC-MS analysis.

Results: Using this sample pre-treatment method assay 8 commercial cat foods ( 15 ppm melamine label claimed, No-FDA recall Porducts), the recovery ratio is from 75%-117%.

http://www.fda.gov/oc/opacom/hottopics/petfood.html

Why the sample pre-treatment matter? the answer is obviously for those chemist whose had nightmare with extraction Melamine from aqueous phase. VIP tips: when obtained a poor recovery result, DO NOT blame the GC-MS, pay attention to the that Melamine solubility in H2O vary under different temperatures.

Note: this method is for products screening only, NOT for any other purpose.