Calculating Peak-to-Valley Ratio with OpenLab CDS

Answer

This Information Applies To: Agilent OpenLab CDS 

Issue

This article provides step-by-step instructions to calculate peak-to-valley ratio in OpenLab CDS.

Background

• The peak-to-valley ratio is calculated to indicate the quality of peak separation. It is calculated with the European and Japanese Pharmacopeia (EP, JP).
• This value is different from the peak-to-valley ratio that you set in the advanced integration parameters!
• The peak-to-valley ratio is computed for peaks separated by a valley:
  PV = peak height/ valley height
• If there are valleys to both left and right of a peak, the peak-to-valley ratio is computed for front and tail. The minimum p/v will be displayed.

Prerequisites

• The injection is linked to a processing method that supports System Suitability (Figure 1).

  
  
  Figure 1: System Suitability Feature in Processing Method
  
  

• To be able to carry out the procedure as described, you need the privileges Processing Method > Edit system suitability parameters. Privileges are configured in the Control Panel.
• The integrated peaks must share the same baseline. It is not possible to calculate if there is a separated baseline between peaks. In other words, if there are no peaks and valley, it will be impossible to calculate the peak-to-valley ratio.
  • Individual baselines (p/v ratio is not calculated) (Figure 2)

    
    
    Figure 2: Individual Baseline 
    
    

  • Shared baseline (p/v ratio is calculated) (Figure 3)

    
    
    Figure 3: Shared Baseline 
    
    

• Tangent skimming mode for integration is not used. It can be found from Processing Method > Integration Events ChemStation > Advanced (Figure 4).

  
  
  Figure 4: In this Example Tangent Skim Mode (Exponential) for Integration is Used, therefore the p/v ratio is not calculated
  
  

• Manual integration peak splitting is not used, or else the value of peak and valley cannot be calculated (Figure 5).

  
  
  Figure 5: Manual Integration - Peaks Splitting is not used
  
  

Steps to Follow

1. Optimize data integration. See articles on:
   • How to use Integration Optimizer in OpenLab CDS 2.5 and above
   • How to Do Manual Integration in OpenLab CDS 
   • How to Integrate Peaks using Integration Events in OpenLab CDS
     
     
2. Set system suitability parameters.
   In the Processing Method, select System Suitability > Properties node.
   
   
3. Under separation performance computation, select the following values:
   • Column performance: Select All peaks.
   • Tangent calculation mode:
     • Select Standard for backward compatibility with results generated with OpenLab CDS 2.5 or lower. With noisy data, the application may not be able to calculate the number of plates.
     • Select Advanced to use more data points for the tangent calculation. Use this option especially for very noisy data.
   • Pharmacopeias: Select the required pharmacopeia or pharmacopeias.
     • Choose the European and/or Japanese pharmacopoeia options (EP or JP).
     • Attention: United States Pharmacopeia (USP) does not calculate peak-to-valley ratios.
       
       
4. Click Reprocess.
   
   
5. In the Injection Results window, click show column chooser on the left and select columns p/v ratio. The p/v ratio column contains the peak-to-valley ratio as calculated with the chosen algorithm (Figure 6).

   
   
   Figure 6: Selecting P/V Ratio column in Injection Result
   
   

   If the peak does not appear in the Injection Results, the filter might be applied. Click the Injection Results window and ensure Show identified peaks and Show not identified peaks are selected. For more details, see Show or hide specific compounds in injection results.
   
   
6. To report peak-to-valley ratio in a report, click and drag the desired item into the report. It can be found from Report Items > Fields > Peak > Peak Valley Ratio (Figure 7).
   

   
   
   Figure 7: Reporting Peak Valley Ratio 
   
   

Figure 8 shows a video on how to calculate peak-to-valley ratio in OpenLab CDS 2.6 as an example. 

Figure 8: How to Calculate Peak-to-Valley Ratio via OpenLab CDS 2.6

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