Gow-mac Chromatograph 580 Manual

Prevention

Gas Chromatograph Hardware Reference Manual Part Number 3-9000-537 Revision K JULY 2010. Model 500 Gas Chromatograph System Reference Manual NOTICE ROSEMOUNT(“SELLER”) SHALL NOT BE LIAB LE FOR TECHNICAL OR EDITORIAL ERRORS IN THIS MANUAL OR OMISSIONS FROM THIS MANUAL. SELLER MAKES NO WARRANTIES. AGILENT TECHNOLOGIES 7890A OPERATING MANUAL Pdf Download. Gas Chromatographs. Series 59001019. Series 580 TCDR5. Series 580 FIDR8. Series AR720R8. Please contact customer service at 610-954-9000 ext 246 for manuals on Series 200, Series 826 and Series 8100 Manuals – GOW-MAC Instrument Company Gas chromatograph valves.

Many GC problems can be prevented if the column is properly installed and GC is maintained routinely. For example, replacing septa or liner at regular intervals and keeping the injector and detector clean and well-maintained shoud solve many problems. Regular preventive maintenance depends on particular model of GC and you should consult required operations in the operator's and service manuals.

For the problem identification we recommend to use electronic flowmeter and leak detector. Mac os x screen share app.

Baseline problems

Baseline problems could be divided into 5 categories: drift, noise, offset, spiking and wander.

Drift means slow baseline movement in one direction
Noise is rapid and random movement of the baseline position
Offset is sudden unexplained change of the baseline position
Spiking is presented by peaks with no width, either positive or negative
Wander is low frequency noise

Downward drift

Possible cause	Suggestions
Downward drift for a few minutes is normal after installing a new column	Increase the oven temperature to close to the maximum continuous operating temperature for the column. Maintain the temperature until flat baseline is observed. If the detector signal does not drop in 10 minutes, immediately cool the column and check for leaks.
Unequilibrated detector	Allow sufficient time for temperature equilibration of the detector.
Downward drift is frequently due to the 'back-out' of contaminants from the detector or other parts of the GC	Clean out contamination.

Upward drift

Possible cause	Suggestions
Damage to the stationary phase of the GC column	Determine the cause of the damage. It may be due to impurities in the carrier gas or to excessive temperatures. Replace column.
Drift in gas flow rates	Clean or replace flow or pressure regulator(s). Adjust pressure.

Noise

Possible cause	Suggestions
The column may be inserted too far into the flame of an FID, NPD or FPD detector	Reinstall the column. Be sure to insert the column into the detector exactly the correct distance specified in the instrument manual.
An air leak can result in noise in ECD and TCD detectors	Eliminate the leak.
Incorrect combustion gases or flow rates can generate nois in FID, NPD or FPD detectors.	Be sure yuor gases are the proper grade, as well as clean and dry. Reset the flow rates of the gases to their proper values.
Contaminated injector	Clean injector. Replace inlet liner, septa and selas.
Contaminated column	Bake out the column. Cut off first 10 cm of column. If it does not help, replace the column.
Defective detector	Clean and/or replace parts as necessary.
Defective detector board	Consult GC manufacturer.

Offset

Possible cause	Suggestions
Line voltage changes	Monitor line voltage for correlation with offset. If correlation is found, install voltage regulator or ensure stable power supply.
Poor electrical changes	Check electrical connections. Tighten any loose connections. Clean any dirty or corroded connections.
Contaminated injector	Clean injector. Replace inlet liner, septa and selas.
Contaminated column	Bake out the column. Cut off first 10 cm of column. If it does not help, replace the column.
Column inserted too fat into the flame of FID, NPD or FPD detectors	Reinstall the column. Be sure to insert the column into the detector exactly the correct distance specified in the instrument manual.
Contaminated detector	Clean the detector if possible.

Spiking

Possible cause	Suggestions
Electrical disturbances entering the chromatograph through power cables, even shielded cables	Try to correlate spikes with events in equipment near the chromatograph. Periodicity is often a clue. Turn off equipment or move it. If necessary, install a voltage regulator.

Wander

Possible cause	Suggestions
Baseline wandering may be caused by changes in environmental conditions such as temperature or line voltage	Try to correlate the wandering with environmental parameters. If a correlation is observed, you will know what to do.
Inadequate temperature control Check if variations can be correlated with changes in the baseline position.	Measure detector temperature.
Wandering while using isothermal conditions may be due to contaminated carrier gas	Change the carrier gas or the gas purification traps.
Contaminated injector	Clean injector. Replace inlet liner, glass wool and seals.
Contaminated column	Bake out the column. Cut off first 10 cm of column. If it does not help, replace the column.

Distorted peak shapes

All peaks redused in size

Possible cause	Suggestions
Sample validity	Check the concentration and stability of the sample.

Flattened top peaks

Possible cause	Suggestions
Detector overload. The broad peaks may have a rounded top or even valleys in the top.	Reduce sample volume, dilute with solvent or use higher split ratio.
Overload of the signal processing electronics. The peaks are clipped with flat tops.	Attenuate detector output or reduce sample amount (see above).

Fronting peaks

Fronting peaks are usually the result of column overloading. In this case, the effect should be a function of injection volume. Solutions include reducing the injection volume or using a column with greatr capacity. Columns with larger diameter or thicker stationary phase coatings generally have larger sample capacities, however, resolution may be reduced.

Ghost peaks

Possible cause	Suggestions
Remmants of previous samples in the inlet or column. Ghost peaks due to remmants are most likely to occur when increasing inlet or column temperatures.	Increase the final temperature and lengthen the run time to allow for complete elution of previous samples. If ghost peaks continue to occur, clean the inlet. Condition the column at temperature higher than has been used but lower than the maximum continuous operation temperature for the column. Cut 10 cm off the inlet end of the column and/orreverese it before reconditioning it. If it does not help, replace the column.
Backflash may cause remmants. Backflash refers to vapours from the sample which expand to exceed the volume of the injector liner. These vapours may come in contact with colder spots, such as the septum and gas inlets of the injector. Less volatile components may condense. These condensates may vaporize later and interfere with subsequent analyses, sometimes producing 'ghost peaks'.	Use septum purge Lower injection volume Enlarge injector liner Optimize injector temperature Use pressure pulsed program
Bleed from the septum or fragments of the septum lodged in the inlet or liner.	Clean the inlet. Replace the inlet liner, glass wool and seals.

Irreproducible peak heights or areas

Possible cause	Suggestions
Inconsistent injection	Develop a reproducible injection technique. Use autosampler.
Distorted peak shapes can adversely affect quantitative determinations	Correct any problems that result in the distortion of peak shape. See Peak shape problems.
Baseline disturbances	See Baseline problems.
Variations in GC operating parameters	Standardize operating parameters.

Negative peaks

Possible cause	Suggestions
Incorrect polarity of the recorder	Reverse polarity of recorder connections.
Incorrect setup in the software	Set-up right parameters in your chromatography software.
Sample compound has greater thermal conductivity than the carrier gas and you are using a TCD or µTCD detector	If possible, change carrier gas. Otherwise there is not a solution.
Detector overload in element-specific detectors such as ECD, NPD, FPD, etc., can produce both positive and negative peaks	Have the compound of interest arrive at the detector at a different time from the solvent or other compounds in high concentration. H₂ produces negative peaks with TCD (µTCD) and helium carrier gas.
Dirty ECD detector can give negative peak after a positive one	Clean or replace the ECD detector.

No peaks at all

Possible cause	Suggestions
Defective syringe	Try a new or proven syringe.
'Blown' septum or massive leaks at the inlet	Find and fix leaks.
Problems with carrier gas flow	Adjust gas flow. Check the column flow ath the column outlet by immersion to methanol.
Broken column or column installed in the wrong way	Replace or reinstall the column.
The detector is not functioning or not connected to the recorder or integrator.	Ensure that detector is working properly. E.g.: Is the flame in a FID on? Check connection to the output device.

Selective sensitivity loss

Possible cause	Suggestions
Contamination of column and/or liner can lead to loss of sensitivity for active compounds	Clean liner. Bake out the column or replace it.
Injector leaks reduce the peak height of the most volatile components of a sample more than less volatile	Find and fix any leaks.
Initial column temperature too high for splitless injection which can prevent refocusing of sample. This affects the more volatile components most.	Initial column temperature should be below the boiling point of the solvent. Decrease the initial column temperature or use less volatile solvent.
Inlet descrimination. Injector temperature is too low. Later eluting and less volatile compounds have low response.	Increase injection temperature.

Split peaks

Possible peaks	Suggestions
Fluctuations in column temperature	Repair temperature control system
Mixed sample solvent for splitless or on-column injections	Use single solvent
When using injection techniques that require 'solvent effect' refocusing such as splitless injectiion, the solvent must form a compact, continuous flooded zone in the column. If the solvent does not wet the stationary phase sufficiently as might be the case for methanol used with a nonpolarstationary phase, the solvent flooded zone may be several meters long and not of uniform thickness. This will result in broad and distorted peaks because the solutes will not be refocused into a narrow band near the beginning of the column.	Installing a retention gap (5 meters of uncoated but deactivated column) ahead of the crhomatographic column may reduce or eliminate this problem.

Tailing peaks

Possible cause	Suggestions
Contaminated or active injector liner, seal or column	Clean or replace injector liner. Do not use glass wool in the liner. If necessary, replace the column.
Dead volume due to poorly installed liner or column.	Confirm by injecting inert peak (methane). If it tails, column is not properly installed. Reinstall liner and column as necessary.
Ragged column end	Score the tubing lightly with a ceramic scoring wafer or sapphire scriber before breaking it. Examine the end using magnifying glass. If the break is not clean and the end square, cut the column again. Point the end down while breaking it and while installing a nut and ferrule to prevent fragments from entering the column. Reinstall the column.
A bad match between the polarities of the stationary phase and the solvent	Change the stationaryphase. Usually polar analytes tail on no-polar columns, or dirty columns.
A cold region in the sample flow path	Remove any cold zones in the flow path
Debris in the liner or column	Clean or replace the liner. Cut 10 cm off the end of the column and reinstall it.
Injection takes too long.	Improve injection technique.
Split ration is too low	Increase split ratio to at least 20:1
Overloading the inlet	Decrease the sample volume or dilute sample
Some types of compounds such as alcoholic amines, primary and secondary amines and carboxylic acids tend to tail.	Try a more polar column. Make a derivative of the dsample.

Retention time shifts

Possible cause	Suggestions
Change in column temperature	Check GC oven temperature
Change in gas flow rate (linear velocity)	Inject a detectable unretained sample such as methane to determine the linear gas velocity. Adjust gas pressure or flow to obtain proper values for your analytical method.
Leak in the injector	Check the septum first. Change, if necessary. Find the leak and fix it.
Change of solvent	Use the same solvent for standards and samples.
Contaminated column	Bake out the column. Cut 10 cm off the end of the column. If necessary, replace the column.

Loss of resolution