Good chromatographic practices
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Transcript of Good chromatographic practices
Introduction
Chromatography is a physical method of separation in which the components to be separated are distributed between two phases
one of which is stationary (stationary phase) while the other (the mobile phase) moves through it in a definite direction.
The chromatographic process occurs due to differences in the distribution constant of the individual sample components.
Mobile phase Stationary Phase Solvent Management system Sample Management system Routine startup Pre analysis checks Sample set sequence Bracketing standards System failures & Incidents Integration & Re-integration Processing Empower Reporting Post analysis check
Contents
Mobile PhaseWater used for HPLC Always use Purified water / Milli Q water as both
inorganic and organic contaminants are removed. Do not use RO water / de-ionsed water for HPLC. Due to existence of impurity, deionized water
shows higher absorption.
Mobile PhaseWater used for HPLC Ghost peak will be appeared in gradient elution if
water is of bad quality!
Mobile PhaseSolvents used for HPLC Always use HPLC/ Chromatographic grade
solvents. Do not use analytical grade solvents.
Mobile PhaseSolvents used for HPLC – Precautions for using THF Analytical grade THF contains butylated
hydroxytoluene (BHT) as an oxidation inhibitor. As BHT has strong UV absorption, it is not added for HPLC grade THF.
As such, HPLC grade THF must be stored in cool and dark places to reduce oxidation to form peroxides. Accumulation of large amount of organic peroxides may lead to explosions.
Mobile PhaseSolvents used for HPLC – Precautions for using Chloroform Analytical grade chloroform contains 3% ethanol
to prevent generation of phosgene, a highly toxic gas.However, ethanol, like water, may deactivate silica gel used in normal phase separation and thus lead to unstable retention times.
HPLC Grade chloroform therefore does not contain ethanol as a stabiliser.
Once seal is opened, it should be stored in dark and cool places to reduce the possibility of generation of phosgene.
Mobile PhaseBuffers used for HPLC All the solutions should be clear, homogenous & free
from particulate matter. Buffer solutions must be filtered through 0.45µm filter
or as specified in the method by using Solvent Filtration Kit.
Mobile Phase Do not keep mobile phase under the suction for
more than 4 to 5 minutes as the composition of mobile phase change especially if highly volatile solvents are used.
Mobile PhaseBuffers used for HPLC Buffer solutions must not be left in system to
avoid crystalisation. effect on pump -- damage plunger and seal effect on column -- creation of column voids effect on flow line -- corrosion of stainless
steel lines Possible bacterial growth especially phosphate
buffers -- good medium for bacterial and fungus growth.
Ideally, solutions should be prepared fresh everyday.
Mobile PhasePremixing of solvents For isocratic systems, different solvents are
premixed. They are to be measured separately for accuracy in measuring.E.g. To prepare 1000 mL of 50:50 mixture of water/methanol,Measure 500 mL of water, transfer into a bottleand 500 mL of methanol, transfer into same bottlethen mix them together & sonicate for about 15 minutes.
Mobile PhaseMaterial of the container Use glass bottle Use Plastic bottle for high sensitivity inorganic
analysis.Always cover the container To prevent evaporation of solvents To prevent dust enter the mobile phase To reduce the vapors in the roomDo not cover the mobile phase bottle with parafilm.
The leachable from the parafilm may contaminate the analysis.
Mobile Phase Do not expose the bottle to direct sunlight/wind.
Always keep reservoir above solvent delivery system
Always use a suction filter Prevent particulates from reaching pumps Clean the suction filter by sonicating in isopropanol
or 1N nitric acid and water.
Mobile Phase
Label all the mobile phase and Solvents bottles. Write all the details on the label clearly. Use the mobile phase before expiry period. Establish the validity of the Mobile Phase.
Mobile Phase Changing Over of Mobile Phase.
Do not keep the channel tubing directly in another mobile phase.
Mobile Phase Changing Over of Mobile Phase.
Do not keep the channel tubing directly from buffer solution to aqueous organic solvent.
Do not keep the channel tubing directly from aqueous organic solvent to Non aqueous organic solvent.
Mobile Phase Changing Over of Mobile Phase.
Before changing to totally organic phase in the system, the whole system should be flushed with water/organic (1:1) mixture to remove the buffers used.
Otherwise, crystallisation may occur when the organics come into contact with leftover buffers in system.
Mobile PhaseDegassing Degas the Mobile phase before use & use online
degasser while running the HPLC.
Mobile Phase
Degassing Do not use Online degasser while using THF in
the Mobile phase as it may degrade the Teflon tube which is connected to vacuum chamber.
Stationary PhasePrecautions to be followed Avoid pressure shocks on the column. Pressure shocks lead to channeling in the
column, which results in peak splitting in corresponding chromatogram.
Always keep both ends of the column closed, after usage.
Keep the columns in the designated column cabinets after use.
Use the pH range of 2 to 8 or follow the manufacturers instructions.
Stationary Phase
Equilibration of Column The amount of mobile phase which should be
flushed through a column before it is ready to use is usually expressed in terms of the column volume i.e. the amount of mobile phase required to fill the column.
When a column has just installed on a reverse phase HPLC system then it will typically require 10 to 20 column volumes. (with few exceptions like methods which include on pairing agents & chiral methods).
Stationary PhaseEquilibration of Column This column volume is more correctly called as
void volume (Vm). This is the volume of the HPLC column that s not
taken up by the stationary phase. This is typically approximately 70% of the total column volume.
Methods to calculate Vm Volume of a cylinder V = π r2 L
By injecting an unretained solute to obtain t0
Void volume, Vm = F x t0
Where F is flow rate expressed n mL/[email protected]
Stationary Phase Storage of HPLC Columns Do not store HPLC columns in buffers. A buffer may precipitate
inside the column, resulting in plugged hits and packing material. A buffer may also encourage bacterial growth, which can plug both the column frit and packing material. This is more likely to occur with mobile phases which have close to or 100% buffer. Bacteria may also affect your analytes, and organic products from the dead bacteria may cause "ghost peaks" in chromatograms.
Do not store HPLC columns in solvents that degrade easily tetrahydrofuran (THF), triethylamine (TEA), trifluoroacetic acid (TFA). Unstabilized THF can form peroxides which may degrade the column. TEA and TFA are more likely to become contaminated from the lab environment and should be refrigerated during storage. Contamination may change the chromatography or change the column.
Stationary PhaseStorage of HPLC Columns For short term storage, i.e. over night, columns can be
stored in the eluent used in last analysis. For middle term storage, i.e. 2 days or over the
weekend, columns should be flushed with pure water to prevent microbial growth.
For long term storage, silica based columns should be stored in an aprotic solvent.
The water content should not be higher than 50%. The best storing solvent is Acetonitrile.
Make sure that all buffers are washed out of the column before flushing with Acetonitrile. Buffer salts are mainly not soluble in Acetonitrile and can block the capillaries and the [email protected]
Log book
Record the column usage in Column usage log books / sheets of respective column.
Make entry of relevant details in HPLC log book before using the system.
Solvent Management System
To prevent damage to the Separations Module, be sure to use needle wash and plunger seal wash solutions that are miscible with the mobile phase you are using.
Use separate solutions and containers for plunger seal wash and needle wash. Because the functions of these solutions differ, the use of one solution for both functions may compromise the effectiveness of either needle washing or plunger seal washing.
Plunger Seal Wash
Seal wash is used to rinse the backs of the piston seals in the pump of a HPLC system.
The piston is the part of the pump which moves back and forward in the pump head drawing in and pushing out the mobile phase solvent with each movement. Because it is a moving part, a seal around this piston is required to prevent the liquid leaking out the back of the pump.
Plunger Seal Wash
Over a period of time small amounts of mobile phase solvents seep through the seal to the back of the pump head.
If these solvents contain buffers then the salts may precipitate out forming deposits which can shorten the life of the seal.
Seal wash is used when the mobile phase contains buffers. The wash flushes the back of the piston seals removing any deposits and maximising the lifetime of the seal.
Seal wash - Composition
It follows that the composition of the seal wash should be aqueous to dissolve buffers.
A small amount of organic solvent is added to prevent bacteria growth and also to reduce the surface tension of the water (this helps the wash solvent cling to surfaces).
Typical seal wash composition is 80% water and 20% organic solvent.
The organic solvent may be methanol, acetonitrile or isopropyl alcohol (IPA)
Solvent Management System
Prime the solvent management system by: Dry prime option when the solvent lines are dry
Opens the fluidic path (from the selected solvent reservoir to the prime/vent valve) to replace air with solvent, then performs a prime.
Wet prime option when you want to change between miscible solvents.
Sample Management SystemPurge the sample management system whenever Prime the solvent management system Change solvents See bubbles in the syringe Start using the Separations Module at the beginning of
each day.To purge the sample management system: In the Main screen, press Menu/Status to display the
Status screen. Enter the appropriate solvent composition in the
Composition fields. Press Direct Functions to display the Direct Functions
menu. Select Purge Injector, then press Enter.
Needle wash The needle-wash pump flushes the needle in the sample
management system, preventing carryover of sample between injections.
The needle-wash also extends the life of the injector seals by removing buffered mobile phase and sample from the needle.
The needle in the HPLC system is used to introduce the sample into the mobile phase so that it can be separated on the HPLC column.
The needle wash is used to clean the needle after an injection.
Use “Extended needle wash” from the instrument method if the carry over is expected, especially during the analysis of Related [email protected]
Needle wash The composition of the needle wash needs to be
matched to the sample since this is what you want to clean off the needle.
Typically a composition of needle wash which matches the proportions of aqueous and organic solvents in the mobile phase will be appropriate.
Adjust seal packAdjust the seal pack whenever: Start up the Separations Module for the first time. The
Separations Module does not perform injections or compression checks until the seal pack has been adjusted.
A “Compression Check Failed” error appears on the screen. A “Missing Restrictor” alarm appears during a diagnostic
procedure. Change the seal pack. Rebuild the seal pack.Before you adjust the seal pack, purge the sample
management system to ensure that there is no air in the syringe. Air in the system may cause Alarm Seal Geometry or Alarm Missing Restrictor dialog boxes to (erroneously) appear.
Sample Treatment Always filter sample with 0.2μm or 0.45μm filters
before injection. If the sample contains a lot of solid, centrifuge it,
and the filter the solution.
Sample Treatment
Check that the filter type you are using is compatible with the sample solvent.
Extractable components from the filter may show up as ghost peaks in a run. Incompatible filter types, which may partially dissolve in your solvent, introduce material into a column, which can cause plugging.
Use the filters which are mentioned in the validated method
Injector Maintenance Purge flow line at least once a day. Change purge liquid frequently. Never use salt solutions as purge liquid. Use septums for sample vial recommended by
manufacturer only. Septums should not be reused. Do not fill vials to the brim.
Waste Bottle Maintenance Remember to empty waste bottles regularly. Do not mix concentrated nitric acid with organic
solvents. Do not immerse the drain tubing in the waste
liquid as this may create back pressure on the flow cell.
Pre-analysis checks Filter mobile phase Sonicate the Mobile phase. Wait for mobile phase to reach room temperature Purge all the flow lines with mobile phase Replace mobile phases as necessary If the solvent tubing is not completely filled with
mobile phase, purge the flow line After periods of disuse or changes in ambient
temperature, purge the flow line
Routine start up Dry prime Place the solvent reservoirs Switch-on the degas Wet prime Purge injector Equilibrating the system Conditioning column Check for leaks Check the pump pressure Perform a baseline check
Empower Use your own log in ID for any software. Don’t share your password to any body.
Sample set Prepare all the solutions viz. blank, system
suitability, working standard & Sample solutions as per the method.
Equilibriate the column before sample set. Inject the Bracketing standard to ensure the
system condition during the sample run. Define the no. of samples to be injected for
bracketing and calculation for bracketing standard in the SOP.
Sample set
For linearity include the amounts during the preparation of sample set method
Sample set For linearity include the amounts during the preparation
of sample set method
System failures If HPLC / GC system fails during analysis due to
System over pressure Communication error Failure of system suitability Peak splitting Lost prime error Bracketing standard failure
System failures
Define the procedure to record Lab incidents. Record the incident as per defined procedure. Process all the injections including the
disregarded sets and enclose with the Raw data. Investigate the root cause for the sample set
failure. Rectify the problem, document the reason for
failure. Repeat complete sample set of injections in case
of 1 injection failure of Assay / dissolution / [email protected]
A chromatogram is a series of detector responses, sampled uniformly across a length of time. The elution of a compound results in a characteristic chromatographic peak profile.
Integration is the process of calculating an area that is bounded in part or in whole by a curved line. The goal of chromatographic peak integration is to obtain retention times, heights, and areas of these peaks.
Peak integration uses two key algorithms: one that detects peaks and one that determines their baselines. Once the peak apex and baseline are known, the retention time (RT), height, and area can be calculated.
Definitions
Processing Processing is the manipulation of data to determine
the identities and/or amounts of separated components. It most often involves integrating chromatographic peaks to calibrate standards and generate a calibration curve, and to quantitate the source components.
Processing methods define how Empower detects, integrates, calibrates, and quantitates unprocessed, raw data from a 2D channel or a 2D-derived channel.
In Review, you start with unprocessed data acquired from a known standard (Channels). You then create a multipoint calibration curve by using a range of standard concentrations. Adding a processing method to a method set allows the software to process raw data while it is being acquired.
Integration Do not integrate any peak manually. Integrate all the sample sets batch wise. Always use same processing method for
processing of blank, standard & sample chromatograms in case of Assay & dissolution tests.
Verify the processing parameters like threshold, width, system suitability, Peak names etc.
Save the processing [email protected]
Integration
Integrate all the injections including set failures. For System suitability injection for which Tailing
factor, Resolution or Theoretical plates are to be checked, consider only the first injection of the sequence. (Do not consider this criteria for average of all the standard injections unless otherwise specified.)
Re-integration
Do not re-integrate the chromatograms without documenting.
Document reason for reintegration.
Post analysis check
To remove buffered mobile phase from the fluidic path of the Separations Module:
Replace the buffered mobile phase with Milli-Q water and wet prime the system for 10 minutes at 3 mL/min.
Flush the system with Milli Q water & solvent after use to prevent salt deposition & precipitation of crystals & microbial growth.
Perform three injector purge cycles to ensure that the sample loop is clean.
Replace the plunger seal-wash solvent with a fresh solution of 80% water: 20% methanol or a miscible solvent, and prime the plunger seal-wash pump.
Replace the needle-wash solvent with a solution of 90% methanol: 10% water or a miscible solvent, and perform a needle-wash [email protected]
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