Ligusticum chuanxiong Hort

Identification:

(1) Weigh 1 g of sample in 5ml of Petroleum ether ( 30-60 degree C) into 10 ml tube, shake the tube 2 or 3 times in 10 hrs. Let it still, pipet the upper clear solution 1 ml in to a evaporating dish. Allow the solvent to evaporate, add 1 ml MeOH, the residues dissolve.

(2) then add 2% 3,5-Dinitrobenzoic Acid (in MeOH) testing solution 2-3 drops, and 2 drops of Sodium Hydroxide Solution (saturated dissolves in Methanol), display Purple & red.

From China Pharmacopoeia 2005 - P28.

Mass Spectra of Ferulic Acid (CAS# 537-98-4)
C10H10O4
Source Temperature: 150 °C,
Sample Temperature: 140 °C,
DIRECT, 75 eV,
Mass of molecular ion: 194.

Peak Data:

    51.0       5.5
   77.0       7.0
  105.0       5.7
  133.0      13.6
  145.0       5.0
  161.0       7.4
  176.0       5.2
  177.0       8.6
  179.0      19.0
  193.0       6.1
  194.0     100.0
  195.0      11.1
Low down the flow rate and injection concentration.

Dandelion

Assay of Caffeic Acid in Dandelion

Dandelion (Herb Taraxaci)

Identification: TLC.

Column : C18, 250 x 4.6, 5 um
Mobile Phase A: 0.01 M NaH2PO4, pH 3.8-4.0.
B : MeOH. A/B is 70/30.
Flow Rate: 1.0 ml/min
Detector Wavelength: 323 nm, 30 degree C.

Standard Prep: 7.5 mg std in 50 ml MeOH, shake & dissolve well, pipet 2 ml to 1o ml volumetric flask, bring to volume with MeOH.
Sample Prep: Weigh 1 g in 50 ml, fill to volume with 5% HOAc in MeOH.

Results: HPLC assay of Caffeic acid NLT 0.020 %. Correct me if i am wrong, to my best knowledge, there is some connection between Caffeic acid and carcinogenicity.

Pesticides on the Cucumber/Strawberry/Carrot

Today, just like to do something to kill the time....

The Difficulty is How to isolate/remove the polar pigments (chlorophyll and carotinoids) /fatty acids, organic acids before LC-MS/ GC-MS?

Strongly recommend the combine of PSA and GCB (PSA= primary-secondary amine, GCB = graphitized carbon black)

Steps:

(1) Sample preparation and extraction

Sample: 10g of cucumber/strawberries were homogenized and placed in a 50mL PTFE centrifuge tube.

Solvent: 10mL of acetonitrile were added to homogenate Shake for 1 minute, until uniform

Salts: 4.0g MgSO4 (anhydrous powder or granular), 1.0g NaCl, 1.0g trisodium citrate dihydrate
0.5g disodium hydrogencitrate sesquihydrate

Salts were added and vigorously shaken for 1 minute. Sample was centrifuged and the supernatant removed for cleanup. Pesticides standards (200ng/mL) were spiked in at this point

(2) Sample extract cleanup ( Here, Do not recommend any brand to hurt "Fair Play Spirit" )

1mL of supernatant from the previous step was placed into several 2mL polypropylene centrifuge tubes, each containing one of the following adsorbent mixes:

• 500 mg PSA
• 250-300 mg GCB,
• 1.2 g MgSO4
• 4.0 mL Acetone/Toluene(3/1)
• Shake and Centrifuge

Samples were shaken with the adsorbents for 30 seconds (carbon for 2 minutes), then centrifuged to produce a clear supernatant for GC/MS analysis.

GC-MS:
Column: A 30m, 0.18mm ID, 0.14µm.

Sample: Custom pesticide mix 200µg/mL each pesticide,

Inj.: 1.0µL splitless (Hold 1 min.)

Inj. temp.: 250°C

Carrier gas: Helium

Flow rate: Constant linear velocity @ 40cm/sec

Oven temp.: 40°C (hold 1 min.) to 320°C @ 12°C/min.

Det: Aiglent 6890N-5973 MSD

Transfer line temp.: 300°C

Ionization: Electron ionization

Mode: Selected ion monitoring (SIM)

Results:
Should soak/wash the fruits before eating
email me if want the assay results (not public, not panic).

Electrospray Summary

1. Analyte type:

1.1 Preformed ions (acids and bases)
1.2 Polar neutrals
1.3 Multiply charged ions of biopolymers
1.4 NMT<100>

2. Typical flow rates: low down - 1.0 ml/min
3. Promote ionization:
3.1 Correct pH
3.2 Favorable HPLC solvent composition
3.3 Post-column addition of reagents

4. Soft ionization technique

5. Typical applications: Drugs, Sugars, Peptides, Proteins, Oligonucleotides

Here is another question: Why GC-MS have a NIST/EPA/NIH Mass Spectral Library 2005 or 2008.? that is "Standard" Mass Spectral for GC-MS, it help newbie chemist would master the elucidation skill of Mass Spectral in 3 weeks.

However, Why LC-MS do not have any LC-MS Mass Spectral Library?
Answer: give me one Coke, i will tell you..... or call the Agilent/Waters/Varian/AB/PE Technical Support, they would answer...

Tips: Look at above # 4: comparing the ionization technique.
for LC-MS: ESI, APCI, APPI ( they are Soft technique), the ionization energy@interface different, the mass fragment different, ---- so not a universal mass library. Or or call the Agilent/Waters/Varian/AB Technical Support, ask them why develop so many "New and Individual" Patent ( on their own instrumentation only) on LC-MS ionization technique...

For GC-MS: EI ( Hard ionization technique), the Ionization energy (from 5 to 241.5 eV) is stable, so the molecular fragment should be the same....that is the reason why NIST/EPA/NIH have Mass Library.

It is so simple: understand the basic ionization technique, should answer.

Maximizing High Flow ESI Sensitivity

Today, met a general question: how to improve the ESI Sensitivity? So I would like to answer this question from the preparation of sample.

(1) Select appropriate chromatography grade HPLC solvents
(2) Avoid exotic solvent mixes (MeOH, MeCN, Water, 0.1% formic work best for 98% of LC/MS applications)
(3) Avoid adding excessive modifiers (eg amm.acetate @ 10mM not 50mM)
Choose the right column chemistry (C-8 vs. C-18); change column chemistry before changing solvent mix or composition.
(4) 2.1mm column or lower, flow rates of 200-400 uL/min
(5) Peak widths for quantification not greater than 8-10 secs
(6) Dissolve sample in start mobile phase solvent (weakest solvent possible).

Here is a schematic drawing of the Finnigan MAT 900S electrospray ion source (kindly provided by EPA/Dr. Helmut Muenster.)