Ph.Eur. HS parameters for water as solvent:

oven: 80°C 60min; needle,valve, transfer line 85°C; pressurization 30sec; injection volume 1ml (this is for a loop based system). For pressure balanced injection : oven 80°C 60min; needle 85°C; transfer line 90°C ; pressurization 1 min; inject 0.04 min; vent 20 sec; withdraw 1 min

vial pressure should be higher then 50kPa

You will have troubles to make a 1000 ppm solution of dichloromethane in water , try to dilute from a dichloromethane in DMSO solution.DMSO and water produce heat on mixing so take care not to loose volatiles. As alternative You can use DMSO or DMF as solvent (other parameters).

Ph.Eur. GC parameters for wax column:

30m; 0.53 or 0.32 mm ID;film 0.25µm;carrier 35 cm/s(He is best N2 will work); split 1/5; injector 140°C; detector 250°C; oven 50°C 20 min, 6°C/min to 165°C, 165°C 20 min.

In your case you can change the oven program to 50°C 10 min, 40°C/min to 165 min for 20 min.

methanol~ 3.2 min, dichloromethane ~3.7 min

A 624 column will give a better separation.

Headspace is a very nice and clean technique but what happens in the vial is quit complex so you will have to build up some expertise

A good place to start is the 'European Pharmacopeia'. In the chapter 'limit tests' there is a complete protocol for the control of residual solvents(section2.4.24). Sample preparation, choice of dilutant and corresponding parameters are explained.

You should also try to find 'B. Kolb, Leslie S. Ettre, Static Headspace Gas Chromatography: Theory and Practice' (available from Perkin Elmer or book store).

Without the complete description of the used device, parameters and solutions used it is difficult to have a decent opinion about the peak splitting, but the first guess would be a temperature problem causing part of your analyte to condense with a 'second injection' as concequence

1000 ppm? Really? That is very high - you are probably overloading the column. If that is the concentration range that you need, you will need to use a pretty high split ratio, say on the order to 50-100. Also, in HS as well as other gas phase injections you absolutely MUST use a split injection. If you do not split the injection you will most assuredly have very poor chromatography.

1000 ppm is not necessary the problem. We used 4000 ppm of ethanol in water without problems. It depends on how much sample you bring into the vial and at witch temperature you equilibrate. It is however possible to run into troubles with much lower concentrations if the temperature/pressure settings are wrong for the solvent used.

I do agree with the split remark: it is difficult to obtain good separation and peak shape without split although it is possible with some implementations.

Dear Sir

I am taking 2 ml sample in Vial. I am using water as a diluent. So will you provide information regarding GC-HS parameters for this type of analysis.

You can change the temperature program and folw rate, start with low temperature with low folw rate of mobile phase

Ph.Eur. HS parameters for water as solvent:

oven: 80°C 60min; needle,valve, transfer line 85°C; pressurization 30sec; injection volume 1ml (this is for a loop based system). For pressure balanced injection : oven 80°C 60min; needle 85°C; transfer line 90°C ; pressurization 1 min; inject 0.04 min; vent 20 sec; withdraw 1 min

vial pressure should be higher then 50kPa

You will have troubles to make a 1000 ppm solution of dichloromethane in water , try to dilute from a dichloromethane in DMSO solution.DMSO and water produce heat on mixing so take care not to loose volatiles. As alternative You can use DMSO or DMF as solvent (other parameters).

Ph.Eur. GC parameters for wax column:

30m; 0.53 or 0.32 mm ID;film 0.25µm;carrier 35 cm/s(He is best N2 will work); split 1/5; injector 140°C; detector 250°C; oven 50°C 20 min, 6°C/min to 165°C, 165°C 20 min.

In your case you can change the oven program to 50°C 10 min, 40°C/min to 165 min for 20 min.

methanol~ 3.2 min, dichloromethane ~3.7 min

A 624 column will give a better separation.

Headspace is a very nice and clean technique but what happens in the vial is quit complex so you will have to build up some expertise

Kris's answer is good, but I will expand it a bit. You will not only have trouble making a 1000 ppm methylene chloride in water standard; you will have created a biphasic system. HS depends upon the analytes being in solution in the bulk matrix so that the variable to be controlled is the partition coefficient between the solid/liquid phase and the gas phase. You will not get reproducible results out of water for methylene chloride at 1000 ppm - you need to dilute your samples (which presents its own problems). You also need to carefully control the ionic strength of the bulk matrix (water, in your case) so that you don't get variations in the partitioning coefficients. I'd recommend adding salt to your vials.

The temperature program recommending by the EU is extremely slow. If your only analytes are methylene chloride and methanol you can run isothermal at 60C on your wax column; assuming that you have no interfering peaks. We don't have enough information about your analysis to make that determination; you'll have to make that.

For these two analytes you're better off with your wax column than a 624 phase - stick with the wax The peak shape (refocusing) of methanol on a 624 phase is problematic.

Mark, If you increase the temperature to 60°C on a wax then the separation of methanol and CH2CL2 will be problematic, there is less then 0.5 min between them at 50°C on a wax column , It is not necessary to preform the complete Ph.Eur. program for those components , after 10 min one can recondition the column. If No other solvents (like DMSO) are in use you even can reduce the 165°C cleaning time with a very short run as a result specially compared to the equilibration time witch also can be reduced to 30 min if nothing else then methanol and dichloromethane are present . For the 624 you have to start at 40°C, there is a good separation but methanol has a very short retention time.

I consider salting out as the last thing to try out, specially in this case as dichloromethane and water are incompatible. In headspace the matrix is the problem and adding salts just make's it more complex and less controllable.

The biphasic situation has indeed to be avoided, that's why U use DMSO,it acts as a bridge between water and CH2CL2, it is possible to make 1000 ppm of CH2CL2 in DMSO but I do not know how much water one can add. If you go this way you have to ensure that the amout of water and DMSO in the vial are constant, water can be used to modifie the CH2CL2 response in a DMSO solution ( changes up to a factor 100).

On the other hand if the real sample in this topic is water based then there should never be a problem as the maximum ch2cl2 content in the sample can not be higher then the solubility limit

Respected Friend

I am using wax column for analysis. The diluent is water. Oven temp is 45°C hold time 5 minutes, rate 10° per minute increase upto 210°C. The injected temp is 230°C and detector temp is 250°C. I am getting peak of Methanol and Dichloro methane at same RT and more over getting split in both peaks. Is the method i am using is appropriate for residual solvent analysis. Please give me your valuable suggestion.

Both solvents are very volatile. In HS analysis injection times are large, and the volatile compounds start to migrate along the column while the injection is completed. That causes splittet peak shapes. One way to improve the chromatogram is to reduce injection volume. This helps to reduce injection times and column overloading.

Also, Carbowax columns are very susceptible to degradation caused by water. If water is your diluent, you are injecting large amounts of water. If your stationary phase is already damaged, peaks will always be ugly. Try cutting a few meters from the column, and change diluent or work with undiluted samples

Dear Mr. Tiwari,

For most of the cases Residual solvents determination is done on DB-624 Column ( See USP/ASTM) These columns are specifically used for residual solvents. u may got the separation of up to 2 minute on DB-624 column. Also as the KRIS communicated the Head spce requires only suitable solvents which dissolve your solvents.

It is better to use DMSF/DMF or The best suitable solvent is Sulfolane which is very high boiling point solvents and most of the organic solvents are soluble in this solvents.

We are using the columns described over here:

http://www.bioszeparacio.hu/_user/downloads/Alltech%20GC/083_ataquawax_aquawaxda.pdf

for most of our residual solvent work. As you can see in the description they are developed to deal with high amount of water. The research we are doing asks for high oven temperatures even with water, our headspace allows us to inject at a much higer pressure then required for the gc run so we even work above 100°C with water but Elena is correct, normal wax column's have a bad reputation considering water. The lower your column oven starts the longer the water stays on the column, I have a set of experiments where you can modify the retention time of a component by the amount of injected water. Depending on witch wax column you use it is indeed a possibility that part the column is gone. Do a direct injection with the calibration mix and system witch normally accompany's your column and if the spec's are not met follow Elena's suggestion and cut of a piece from the injection end.

Also You don't have to go up to 210°C, for a lot of wax column's this is close to the maximum allowable temperature, the reconditioning temperature should be high enough to remove all you injected but as low as possible.

Even with a good wax column the separation between the two compounds of interest is only 0.5 min so consider to use a less polar column, this would also reduce the water problem

Try to use Non polar columns like 100 % dimethyl siloxane (HP-1 or DB-1) or (HP-5 or DB-5) columns or mid-polar columns like DB-624 or HP-624 to separate the methanol , ethanol, acetone, MDC,ethyl acetate, heptane, pyridine and toluene. And also use the diluent as N-methyl pyrolidone. The oven temperature start from 50°C.