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Purospher® STAR RP-18 Endcapped for LC-MS Applications

Base peak intensity

"Ghost" mass peaks present a challenge frequently encountered in gradient LC-MS. It is impossible to determine whether ghost peaks originate from an unknown compound in the sample, from an impurity in the mobile phase, or from bonded phase leaching. However, a three-step procedure can help you avoid spurious LC-MS peaks and ensure consistent ghost-peak-free HPLC separations. The simple process includes cleaning the columns and choosing appropriate solvents for LC-MS. These steps increase ionization efficiency, thus improving the sensitivity and reproducibility of LC-MS results.

Simple, 3-Step Process for Optimized Performance in LC-MS

  1. Flush the column for 60 minutes with a special solvent mixture to remove possible trace impurities. The recommended LC-MS wash solvent is 2-propanol with 0.1% formic acid at a flow rate of 0.5 mL/min (for 3 mm ID columns).
  2. To reduce the LC-MS background signal, work with extremely high-purity solvents. The recommended solvent is LiChrosolv® Hypergrade with special MS specifications.
  3. Finally, the column must be re-equilibrated with the mobile phase. Best results are obtained when two blank solvent gradients (without sample injection) are run prior to analysis. Purospher® STAR RP-18 endcapped HPLC columns produce very low and stable background signals in LC-MS, simply after washing with 2-propanol / 0.1% formic acid.

Extracted Ion Chromatograms of "Profens" in Negative Ion Mode Separated on Purospher® STAR RP-18 Endcapped

The combination of LiChrosolv® Acetonitrile Hypergrade solvents and Purospher® STAR RP-18 endcapped columns demonstrates ghost-peak-free MS spectra for Ketoprofen, Fenoprofen, and Ibuprofen (100 ng).

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Purospher® STAR RP-18 endcapped (3µm) LiChroCART® 55-2 HPLC column
Mobile Phase A
0.1% acetic acid in acetonitrile
Mobile Phase B
0.1% acetic acid in water
From 25% A to 50% A in 3 min, then isocratic
Flow rate
300 µL, without split
UV 220 nm, Ion Trap MS
Temperature Ambient
Inj. volume
1 µL
Sample Ketoprofen, Fenoprofen, Ibuprofen; 0.1 µg/µL
MS Conditions
Ionization ESI(-)
Nebulizer 36 psi
Dry gas 8.5 L/min
Dry temperature 330°C
Smart mode
Target mass 205
Ion charge control
Target 50.000, max 50 ms
Scan mode Standard/Normal
Scan range 50-600 m/z
 Merck:/Freestyle/LE-Lab-Essentials/Chromatography/Diagrams/LE-Extracted ion chromatograms-400x485-11192013.jpg
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