It would really help if you could share some more information on the gas flows and instrument parameters (such as the RF power) being used.
And could you also give some background on the sample types you're running and how you prepare them.
Torch melts can occur if the wrong combination of conditions are used, or if there is a nebulizer blockage.
For example, using high RF power and very low plasma gas flow can contribute to short torch life or a potential melt.
A partial blockage of the nebulizer and/or the injector in the torch could also contribute to a torch melt due to overheating. Have you checked the nebulizer for any blockage?
No nebuliser blockage is registering. Currently I'm involved in method development work on the OES. The lab plans to use the instrument for analysis of biological samples, i.e. blood serum, for the presence of macro, meso & trace elements - Na, P, K, Ca, Mg, Fe, Zn. The samples wont be acid digested but instead its hoped to dilute out the physical matrix effect through development of a dilute and shoot method. The diluent solution used for the calibration standard and sample make-up will be a mixture of 1% HNO3 & 0.01% Triton X.
However we are just at the initial stages of the development looking at wavelength selection and using the 'Timescan' & 'Read' functions to determine wavelength performance and optimise the emission intensity / analyte signal by altering the Measurement Conditions. We are only using known concentration standards from pure stocks ranging from 0.01 ppm to 0.5 ppm. The measurement conditions which were in use during the torch meltdown are given below.
Coincidentally a similar instance has occurred again today whereby the torch has again melted but this time the melt is not as severe and seems to be only on one side as you can see from the pictures below. Having contacted Agilent technical services the agent advised that when the torch is cleaned by soaking in aqua regia, removed, rinsed and left to air dry that if placed lying down that the drying on the torch isn't uniform and can produce 'salt hot spots' which cause the torch to melt when in contact with the high temperature plasma. So they recommended drying the torch standing upright. However I'm not sure that this is the case I've experienced as we aren't running any high salt samples at the moment only pure standard solutions which take 3-4 only daily. Plus I've also worked with ICP-MS and never had any torch drying issues or melts.
Any thoughts on likely causes are welcome.
I would like to reconfirm the gas flows.
Plasma Flow: 8L/min
Aux Flow: 0L/min
Is this correct?
Yes that is correct. I've found that it allows me to achieve optimum analyte signal intensity for Zn at those settings.
Due to the construction of the torch, it is not recommended that you air dry the torch.
Although the quartz parts can dry effectively, water may still be trapped in the internal gas channels in the torch.
It is recommended that you dry the torch by holding this inverted (with the ball joint connector at the top) and blowing clean compressed air, argon or nitrogen through the gas ports on the base and through the opening of the ball joint.
This will ensure all the moisture is removed.
However as Daniel has questioned, the most likely cause for the problem with the torch melt is that the aux flow has been set to 0.
This flow controls where the plasma sits in the torch with respect to the injector in the torch. If this is set to zero, then the plasma may be sitting on the injector and this causes overheating of the injector, potential blockage and eventually, the torch melt.
You should run with the aux flow set to a flow of ~1 L/min.
Your plasma gas flow has also been reduced from the default value of 12 L/min. Not sure if that was a deliberate choice.
I expect with that change, you will not experience any further torch melt issues.
Thanks Eric for all of that information, its very insightful.
Regarding the aux. flow and plasma flow settings; I am using these settings because I've found that it offers optimum signal intensity for the analyte of interest (in this case Zn). I've have previously read literature which states that some labs run an OES without the aux. flow switched on and haven't stated any issues of torch melt downs. I just assumed that the ICP Expert software would prevent you from choosing instrument settings that would damage the instrument components or at least warn you? Like with RF power where you can only select from min. 1.2 up to max of 1.5 power. Is this not the case? Also the engineer didn't suggest this as a possibility when they performed their call out and instrument review.
I suspect if I increase the aux. flow up to ~1 L/min that will have quite an impact on my signal intensity which may be an issue for trace element analysis. However I do value your input as I'm relatively new to ICP-OES and so may need to strike a balance in my development work going forward between optimising for the analytes and ensuring instrument settings are appropriate.