LC Technical Note

GL Sciences Inc.Switching the mobile phase from Acetonitrile to Methanol

Example 1.Analytical Conditions:

System: LC800 HPLC

Column: Inertsil ODS-SP 5um, 150 x 3.0mmI.D.

Mobile Phase: CH3CN / H2O or CH3OH / H2O

Flow Rate: 0.4 mL/min

Column Temp.: 60C

Detection UV 360 nm

Injection Vol.: 10 uL

From the end of last year, the shortage of Acetonitrilesupply has been a topic in the HPLC industry. Oureconomy is now drawn into chaos, which was caused byAmerican financial crisis. All car industries are goingdown resulting in less production of Acrylonitrile as thecar industries uses a lot of Acrylonitrile during theirproduction of cars. Acetonitrile is a by-product ofAcrylonitrile and only from 2 to 3% Acetonitrile isgenerated when producing Acrylonitrile.We would like to introduce the important reminders onwhen switching the mobile phase from Acetonitrile toMethanol.

Attention!!!

1) The elution strength of an organic solvent may change.

=The elution strength of Methanol is weaker than

Acetonitrile.

2) The elution pattern may change.

= Conduct qualitative analysis again to confirm.

3） Back pressure will definitely increase.

= Use a column that offers low back pressure.

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0 2 4 6 8Time (min)

010

20mV

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0 2 4 6 8Time (min)

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0 2 4 6 8Time (min)

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60% Acetonitrile

60% Methanol

70% Methanol

= Mobile Phase Composition

1. Formaldehyde-DNPH( 100μg/L )2. Acetaldehyde-DNPH ( 100μg/L )

As you can see, the elution strengthbecomes weaker.

In addition, the elution pattern maychange depending on the sample.Back pressure will increase too.

The retention time can be optimized byincreasing the ratio (%) of an organicsolvent.

Back Pressure: 6.7 MPa (67 bar, 971 psi)

Back Pressure: 6.2 MPa (62 bar, 899 psi)

Back Pressure: 3.9 MPa (39 bar, 565 psi)

GL Sciences　LC　Technical　Note

Inertsil provides the lowestback pressure in the world!Therefore, it is totallycompatible with Methanolmobile phase condition.

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0 20 40 60 80 100

Methanol Concentration (%)

Bac

k P

ress

ure

(Mpa

)

When changing the mobile phase, the elution pattern may change depending on the sample.Please refer to the 2 chromatograms below.The ratio (%) of an organic solvent was adjusted to obtain the same retention time.

Inertsil ODS-3

Inertsil ODS-4Inertsil ODS-SP

* Analytical Conditions used in the above comparison dataColumn: 5um、250 x 4.6mmI.D.Col Temp: 40 ℃Flow Rate: 1.0 mL/min

Back pressure comparison using Methanol

Commercially available C18 column

Even if the column specification were the same, when the packing material changes, the column back pressuremay increase. When the column back pressure increases, the following phenomena can be experienced;-Short column lifetime-Frequent instrument maintenance as high column back pressure deteriorates the instrument

Example 2.

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72% Acetonitrile 80% Methanol : Alkylbenzenes

: Polyaromatics

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GL Sciences　LC　Technical　Note

When changing the mobile phase from Acetonitrile to Methanol, please make sure to set the flowrate lower than that of Acetonitrile.As you can see in the chart below, when using Methanol, maximal performance, minimum HETPcan be obtained when setting the flow rate at a low range.

Additional Information

Comparison of Organic Solvents

Theoretical Plates vs Flow Rate

Maximal performance can be obtained when setting the flow rate at a low range with Methanol

●：CH3OH / H2O = 85 /15▲：CH3CN / H2O = 65 /35