trouble with the spe cartrige bad weight

[melike]

Hi to everybody,

I'm confused about how to choose the right bed weight of a spe cartrige.

My sample is 10 ml and my analyte (pestiside) consantration is between 5-35 ppm (it is not an original wastewater, it is synthetic). I tried different cartriges (C18, 6ml, 350mg), (C18, 6ml, 500mg) but the recovery of my analyte was too low. I thought that something is wrong with my cartrige .And also I'm not clear about how to choose correct cartrige.

Can you explain me please,
I look forward to your comments.
Thank you for your contribution...

[X]

The capacity for C18 sorbent is about 1-5%, which means you can load at least 3.5 or 5 mg of your target analytes and matrix components onto the cartridge before breakthrough occurs.

What pesticides are you analyzing? Are they acidic, neutral or basic? or very polar? if you can provide these info, I can suggest you a suitable cartridge with SPE procedure.

X

Hi to everybody,

I'm confused about how to choose the right bed weight of a spe cartrige.

My sample is 10 ml and my analyte (pestiside) consantration is between 5-35 ppm (it is not an original wastewater, it is synthetic). I tried different cartriges (C18, 6ml, 350mg), (C18, 6ml, 500mg) but the recovery of my analyte was too low. I thought that something is wrong with my cartrige .And also I'm not clear about how to choose correct cartrige.

Can you explain me please,
I look forward to your comments.
Thank you for your contribution...

[melike]

There is some information about malathion (my target compound);
Vapor pressure2,3,4: 1.78 x 10-4 mmHg at 25 ºC or 5.3 mPa at 30 ºC; also 1.2 x 10-4
to 8 x 10-6 mmHg at 20 °C
•• Octanol-Water Partition Coefficient (log Kow)5,6: 2.75, 2.36-2.89
•• Henry’s constant may be estimated or derived experimentally. An experimental
value of 2.0 (± 1.2) x 10-7 (n = 6 experimental values, dimensionless
units) is reported based on a wetted-wall column, concentration/concentration
method.7 This value has been cited elsewhere as 4.9 x 10-9 atm·m3/mol.2
Additional estimated values range from 2.4 x 10-7 to 1.0 x 10-6 at varying temperatures.
7 An additional value of 5.68 x 10-8 mmHg has been reported.8
•• Molecular weight3: 330.4 g/mol
•• Solubility (water)3: 145 mg/L

thanks for your help...

[X]

Malathion is a neutral compound and can be extracted by either C18 or DVB sorbents, I have a customer got 88% recovery using C18 and 97% using DVB for this compound. Here's the procedure:

1. Wash SPE cartridges with 3 x 5 mL dichloromethane (DCM).
2. Condition with 10 mL methanol (MeOH), and 10 mL reagent water.
3. Load sample at 10-15 mL/min.
4. Dry cartridges under full vacuum for 10 min.
5. Elute with 5 mL acetone and 10 mL DCM (bottle rinse); and 5 mL DCM into cartridge.
6. Dry eluate with DCM pre-rinsed anhydrous sodium sulfate.
7. Rinse eluate vial with 5 mL DCM, pass the rinse through sodium sulfate; repeat with 5 mL DCM.
8. Evaporate the dried eluate to 0.5 mL, rinse the wall with 3 mL n-hexane, continue concentrating to 1 or 2 mL.
9. Inject 2 µL to GC/FPD, GC/NPD or GC/MS for analysis.

Please let me know if this works, you can email me at xwang@unitedchem.com, I have some applications for you.

Xiaoyan

[melike]

Thank for your help firstly...

so you think that , 6ml 500mg cartridge is enough for my target compound (sample is;10 ml and my analyte (pestiside) consantration is between 5-35 ppm) and all problem is about the process. Am I right?

[X]

Thank for your help firstly...

so you think that , 6ml 500mg cartridge is enough for my target compound (sample is;10 ml and my analyte (pestiside) consantration is between 5-35 ppm) and all problem is about the process. Am I right?

The sorbent amount is enough for your target analytes, however if your sample matrix (waste water in this case) contains high amount of organic interference, it may cause analyte breakthrough as the interference also counts for capacity.

To check if the sorbent capacity is enough for your analysis, you can connect a 2nd SPE cartridge under your SPE cartridge with a cartridge adaptor and run the extraction, if you find your analyte in the eluate from the bottom cartridge, which means breakthrough occurs. If not, then your sorbent amount is fine, you may need to adjust your procedure.

One more thing, do you know how much organic content is in your sample, if too high you would see low recovery, you can dilute your sample with water to decrease the organic content.

X

[melike]

Okey, I see..

There is only organic solvent of malathion technic solution (%95malathion in xylen) and no more organic material in my sample becouse I prepare it with %95 malathion and pure water.

and also I will send you a mail from my mail for application notes. Thank you very much for your help..
Now Im working with HPLC in another labroratuary and so I couldn't try your application becouse there isn't any gc ms, but as soon as I try I will share the results with you...

have a good day...

[X]

OK, please see my email.

Okey, I see..

There is only organic solvent of malathion technic solution (%95malathion in xylen) and no more organic material in my sample becouse I prepare it with %95 malathion and pure water.

and also I will send you a mail from my mail for application notes. Thank you very much for your help..
Now Im working with HPLC in another labroratuary and so I couldn't try your application becouse there isn't any gc ms, but as soon as I try I will share the results with you...

have a good day...