Translator for HPLC HINTS and TIPS for Chromatographers

Saturday, August 8, 2020

Resetting or Clearing the TCP/IP stack to Resolve Connection Problems

  • Warning: These commands should only be used by experienced users who both accept and understand the risks involved. Before using any system commands or utilities, please backup all systems, programs, applications, data and files.
BACKGROUND: A TCP/IP Stack Reset or 'clearing' will flush the computer’s stored Internet Protocol settings back to their default values. Flushing or resetting these values may solve some types of Internet connection issues where screen messages such as; "This Site Can’t be Reached” or “Unable to Connect to the Internet” are observed. 

EXAMPLE 1: To reset the TCP/IP stack in Windows O/S, you can use the Command Prompt. You MUST use and run the Command (CMD) prompt screen with Administrator's Privileges (or it may not work). 


   In Windows 10 O/S, from the CMD prompt screen, type and run the following commands:

  •     netsh winsock reset and press Enter.
  •     netsh int ip reset and press Enter. (*this command rewrites two registry keys)
  •     ipconfig /release and press Enter.
  •     ipconfig /renew and press Enter.
  •     ipconfig /flushdns and press Enter.
  •  Exit out of the CMD screen (exit) and recheck your connection. A re-boot, restart should not be needed.
  
   In Windows 7 O/S, from the CMD prompt screen, type and run:
  • netsh int ip reset resetlog.txt 
  • Exit the CMD.
  • Restart the computer and check your connection.

EXAMPLE 2: For most MacOS, the TCP/IP stack reset can be run by renewing the DHCP Lease.
  • Click on System Preferences then Network. Click on the Internet connection with status Connected. Next, click the Advanced button. Open up the TCP/IP menu and click on Renew DHCP Lease followed by the OK button.


Saturday, July 11, 2020

Cannabis, Cannabinoid (Hemp, THC, CBD, CBN, Marijuana) HPLC Analysis and Testing, Areas for Improvement [*Updated 8/2021]

Over the past few years we have observed an exponential growth in the number of state-level, legal businesses (in the USA) who offer Cannabis Analysis (e.g. Potency Analysis or Profiles) and/or related businesses such as Hemp Oil Extraction. Most related products which incorporate Marijuana, CBD, THC, Cannabinoids, Terpenes and/or other related compounds require formal analytical laboratory testing which should follow good laboratory practices. This article is targeted to help many of the people involved in this new analysis business (or anyone using chromatography as the analytical technique of choice for the same goals).

As a professional chromatography consultant, I have seen a large increase in the number of requests for my services to this new market. Most of these new businesses have questions about obtaining professional training, correct analysis procedures, improving reproducibility, documentation, optimizing method development, how to receive professional training in maintenance of the HPLC system(s) and need hands-on help to optimize the procedures used. Many users are not achieving acceptable results and need help finding out why. They want to know where they can take a class to learn HPLC method development and how to perform the required tests. 

These new businesses would benefit greatly from professional guidance EARLY in their setup and establishment, to improve the internal methods and procedures of analysis used. Time spent on the "front-end" of any process is always time spent wisely (in this context, knowledge and practical experience = confidence). A chromatography professional can quickly identify areas which may need improvement and/or suggest changes that can directly improve your company's accuracy, reproducibility, increase efficiency and of course, impact your bottom-line too. Focus is placed on the exact areas that will benefit you (rather than wasting time with non-targeted approaches, sales biased classes and trial-and-error approaches). 

  • Please note that there are NO SCIENTIFICALLY LEGITIMATE ONE DAY, ONE WEEK or ONE MONTH LONG TRAINING CLASSES THAT CAN TEACH YOU HOW TO PERFORM HPLC METHOD DEVELOPMENT or ANALYSIS. NONE AT ALL. Most types of "Certification" offered are completely without scientific merit or value. The training needed takes many years of hands-on experience, in an industrial laboratory (not a school), to acquire just a basic level of proficiency (*Emphasis on 'Basic", not intermediate or expert). Be very cautious of anyone who claims to be able to provide you with all the training you need in a short time period.
Generating accurate and reproducible analytical data, esp. with HPLC, SFC or GC requires a great deal of knowledge, formal training and practical hands-on experience (not something which is taught at most university or school programs). These complex techniques require years of bench time and professional hands-on experience to learn). Shipping or selling products which contain unacceptable levels of impurities or which do not meet basic testing or regulatory qualifications could pose a health and/or liability risk. Hire people who have the needed training from industry before setting up the laboratory.

It has been my professional experience that some of the most common training areas that client's would benefit from are: GLP (Good Laboratory Practices/Procedures and SOPs) and additional instrument operational training to demonstrate proficiency in analytical chromatography. Address these areas early on and continuously update them to reduce errors and improve results. Training should continue on a regular basis to gain experience.
 
While each confidential consultation visit I have with a client may show different key issues which need to be addressed, many labs can start to improve their analytical results by addressing and improving how they address:

  1. Documentation: Laboratory methods and sample analysis must be conducted using clearly written documentation. This should initially include having Standard Operating Procedures (SOPs) in place for all methods, procedures, qualification, verification and tests used. They should include SOPs, Document Control and Policy documents which also address: Training, Calibration, Maintenance, Frequency of the same, Mobile phase preparation, pH measurement, use of the balance and so on... I find that it is best to create an initial SOP Template to insure document uniformity (i.e. include such fields as: Business Name, SOP #, review/approval date(s)/names, Rev #, materials & tools needed, purpose, procedure steps, pass/fail definitions... plus any needed supporting documents).
  2. Sample Preparation Methods: Be sure to document, test, review / standardize specific sample preparation methods, for each sample type. Variations in: temperature, extraction solvent or the solution(s) dissolved in, homogenization or grinding methods, mixing, times used, glass or plastic containers used may result in significant variation of the final reported results.
  3. Correct Poor Reproducibility and/or Baseline Instability Issues: In chromatography analysis, if the method(s) used are not stable and reproducible, every time they are run, then little to no scientific value can be obtained from them. Methods used must follow basic good chromatography fundamentals and meet basic guidelines. Baseline noise or instability may directly impact integration results (which directly impacts reported results). Instrumentation must be operated in clean, climate controlled rooms. Failure to reproduce a result within acceptable limits (these will vary per method type) will invalidate the method used. Make sure that SOP's are followed, mobile phase solutions are made fresh each day (do not pre-mix solutions with acids and let them sit for several days before use; do not "top off" bottles), solutions should be degassed, HPLC columns are properly washed and re-equilibrated before each analysis, instruments are maintained (per a SOP) and serviced on a regular basis. 
  4. Develop HPLC methods that follow good chromatography fundamentals: Retain, separate and resolve ALL peaks. Insure peak K primes are 2.0 or higher. If you have co-eluted peaks in your method, then method development is not finished. If you have ghost peaks or changing retention times, then you need to stop running samples and find out why. Be careful whose method(s) you use. A method that is "Validated" may not be scientifically valid method to use. Have the method checked by an experienced chromatographer.
  5. Continuous Training is Required to become Proficient: To be proficient, at a basic level in chromatography, takes most chromatographers several years working in an industrial environment to gain practical hands-on time. That assumes that they have had professional training outside of college, in an industrial lab, and can demonstrate an understanding of the fundamentals of good chromatography. Note, that method development skills require a much higher level of understanding and hands-on training to acquire the needed skill set. Make sure your scientists have the needed level of training to operate, run analysis methods and troubleshoot any issues that come up (and issues will come-up, even under ideal conditions). Please do not make the mistake of thinking they will "figure it out" on their own. Hire people who already have several years of industrial chromatography experience, then provide them with additional training opportunities to advance their skills in the application areas that your business needs.  Get them help NOW, you will save money and time, plus get back on track moving forward with your project.
If you want to surpass your competitors and provide clients with the most accurate data, then investing in your employees professional knowledge and hands-on technical training is the fastest route to do so. This is an experience based technique where decades of practical knowledge are needed to improve your skill set. A professional can quickly provide you with practical information and show you techniques that will help you move forward. 1-2 days of on-site training often translates to nearly one years worth of knowledge. What is one-years worth of lost time worth to you?
  
Additional Resources:

Saturday, April 25, 2020

HPLC Column Cross-Sectional Area and Scaling

Here is a simple formula to use when scaling up or down Internal Column Diameter to maintain retention values (under constant linear velocity). Flow rate must be adjusted to account for any changes made to the column's cross-sectional area. We usually refer to these types of changes as the "Scaling Factor". To determine the scaling factor, we need to know the internal column diameters of the two columns we are scaling from (actually, we need to know the radius, but once we have the diameter, we simply divide the diameter by 2 to obtain the radius). *In this discussion, changes in cross-sectional area are the only parameters we are concerned with as column length does not affect scaling.


  • Scaling Factor = (S);
  • Column #1 Radius =  (R1);
  • Column #2 Radius =  (R2).

     S = R22 / R12


Example #1: 250 x 4.60 mm column scaled down to a 250 x 2.10 mm column. 
          Answer = 0.208. 

  • If the original flow rate was 1.000 mL/min, the the scaled down flow rate would be 0.208 of the original or 0.208 mL/min for the 2.10 mm ID column. *For practical use and application, we often use either 200 ul/min or 210 ul/min to simplify the value.


Example #2: 250 x 4.60 mm column scaled up to a 250 x 10.00 mm ID semi-prep column.
          Answer  = 4.726. 

  • If the original flow rate used was 1.000 mL/min with the 4.60 mm ID column, then we would increase the flow rate to 4.726 mL/min on the 10.00 mm ID column to maintain the same relative velocity (and relative retention). *For practical use and application, we often use 5 mL/min to simplify (round off) the value. 
Notes:
  1. Flow rate optimization should always be carried out by running a standard at different flow rates and plotting the plate height (N) vs the flow rate. Test flow rates that are slightly below the predicted linear velocity and up to 2 times higher than that rate to find and optimize the flow rate for your sample (it must be determined through experimentation for your specific method). 
     
  2. HPLC Columns packed with sub 2 micron supports may have optimum flow rates 2 to 5 times more than the predicted std linear flow rate so actual testing is critical to determining the most efficient flow rate. I recommend optimizing the flow rate used with analysis methods which use any particles which are 2.5 microns or smaller in diameter.


Saturday, March 14, 2020

Changing from Reverse Phase (RP) to Normal Phase (NP) Mode (or vice versa) in your HPLC System

Two closely related HPLC questions which have the same answer are commonly found in my email folder each week. Both questions deal with concerns about switching mobile phase solutions used in HPLC. Here are the two questions with an explanation regarding what information is needed to answer them:


  1. Can I switch-over an HPLC system which has reverse phase (RP) columns and RP solvents installed to one with Normal Phase (NP) columns and solvents (e.g. such as a C18 column with water and acetonitrile switched over to a silica column with Heptane and IPA )?
  2. What is the best way to switch or change-over from a reverse phase (RP) mobile phase made up of water with buffer and acetonitrile to one that is all organic for normal phase (NP)?


To answer these questions we first must review the specified materials used in the HPLC system that are in contact with the mobile phase solutions (the 'wet' parts). 

If you have a system rated for use with most RP solutions, then you will want to verify that the same system is also rated for use with the NP liquids you are considering too (Refer to the manufacturer's product manual or specification sheet).
Some HPLC systems may require no changes at all, while others may not be compatible for use. Some systems have seals, tubing and/or valve components that may NOT be chemically compatible with the proposed solvents. Use with incompatible solvents (or additives) may result in damage or destruction of the system. The instrument manufacturer will often provide the needed information inside the specific instrument's Operator / User Manual (*always contact the manufacturer if you have any questions regarding the safe use of the system). In some cases, the vacuum degasser, pump piston seals, tubing, injector seals and/or other parts may need to be replaced with chemically compatible parts before use.  The newer seals or parts may also have different operational limits (e.g. pressure) or specifications than the ones they replace. For example, the maximum pressure ratings with the different parts may be different (some RP to NP conversions result in much lower max pressure ratings and reduced part lifetimes). Many of the newer vacuum degasser units may have no chemical compatibility with the proposed HPLC solvents or additives. Proceed with caution. Check and verify compatibility first.

Anytime you switch from one liquid type to another, you must insure that the new solution is fully soluble (miscible) with the old solution being displaced from the system. The solutions used must be miscible and must not result in precipitation of any contents or contamination of the flow path (and/or plugging of lines) may result. 

Basic guidelines: 

  • If any buffers or additives have been used, begin by flushing the system with the same solution, but without the buffer or additives dissolved. We want to remove those buffers and salts first. Flush the entire flow path. Flushing out these salts will greatly reduce the chances of system contamination or plugging. In the case of aqueous buffer solutions, initially flushing with ultra pure water will remove them. 
  • Next, if the new solvent is not fully miscible with the old solvent (e.g. Water to Hexane...), then flush the system with an intermediate solvent that is fully soluble with both liquids (in the Water to Hexane example, IPA would be an excellent choice). In fact, for many aqueous to normal phase conversions, IPA provides the miscibility needed to change back and forth from a highly polar aqueous mode to a non-polar organic mode. *Consult a table of Solvent Physical Properties for guidance


Summary: 

Verify instrument chemical compatibility and the possible need to replace any seals or parts.
With the proper precautions and checks, many research grade analytical HPLC system can be routinely switched between RP and NP modes.

To switch from NP to RP mode (or RP to NP), flush the system of any salts, buffers or additives, verify liquid miscibility of the solvents, then use an intermediate solvent if needed to change over. 
A table of commonly used HPLC Solvent Properties will help you determine which liquids can be used as intermediate solvents for this purpose.