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January 8, 2018
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What are you digesting? We have purchased a Cold Block and are currently trialing it for fertilizer analysis. It is super quick compared to other digestion methods and data so far is looking good.

Original Poster1 point · 1 month ago

hiya labrat thanks for your reply

We mostly look at plant and soil samples

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We have tried it for plant when we had a demo model and the data looked reasonably good. We didn't quite have the time then to really nail it down but seemed to be OK. We haven't done any work with soils on it and I don't think we are planning to at this point. One thing with the Cold Block though is that is does seem to have corroded pretty quickly which we weren't expecting.

We have noticed for Plant Tissue samples that we get quite a bit of loss for these (on Elementar). We originally thought that it might be the purge but we also think it could be when the hot crucibles come out of the furnace, it could be creating a bit of a vacuum and bringing up the light plant samples. We thought this because it was really only happening on the first part of the sampler.

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Hi all, I am looking into our Soil Total Carbons and I have a few questions. We use an Elementar CNS and I would like to know the following; 1. Have had any trouble with C especially around consistency or any bias? 2. What weights do you all use? 3.How often are you replacing all of the tubes?

Thanks

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We've seen some issues with consistency with Carbon. We've been told that by the Elementar techs that Carbon shouldn't have any issues, that most issues affect nitrogen. As a result, I've been wondering about how good our calibration is. Our tubes don't last quite as long as alphaducks - reduction is about 5-600 samples, combustion and post combustion about 4000 samples. We use about 400mg for soils and 300mg for plants.

Something that has come up often here with these is the difficulty in emptying the combustion and post combustion tubes. Anyone got any tips to make it easier?

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Original Poster2 points · 7 months ago

Thanks for that info. We are getting about 5-600 from our reduction as well but we change the combustion and post combustion about every 1000 samples. We haven't pushed it to see how far we can go with this. We are using 400mg for soils and 200mg for plants. I think that a lot of our issues possibly could be coming from leaks in the system. For how to empty the combustion and post combustion tubes, we got given a tool to do this. It is a long piece of steel that has a jagged end that is used to break up the reagent in the tubes. Let me know if you want a pic of it.

We have 2 Perkin Elmer 350D ICP-MS's that we do Plant, Soil, Water and Fertiliser analysis on. They perform very well for us with minimal maintenance required. We ave also found that Perkin Elmer service is very good. As for Chloride, they can do it but not really at the ppm level.

Original Poster1 point · 1 year ago

We have occasionally seen a similar problem. it's a devil to track down. before I can help you can you answer a few quick questions?

What analytical finish are you using? Are you matrix matching your standards with your samples? is it present in your prep blank or calibration blank? Is the problem worse on hot days?

Some methods such as the Mixed indicator solution that some labs use in place of the phenolic method are very sensitive to high salt solutions. the other thing to remember is that ammonia can be quite volatile. make sure there are no uncapped sources of ammonia in the area where your instrument runs.

the other place I generally start looking is in the washing up process (if you are not using disposable tubes)

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We are using the phenolic finishing method on an FIA. Yes, samples and standards are matrix matched and standards are prepared fresh every month and are stored in the fridge. No it hasn't been noticed in the prep blank. I have noticed any correlation between the problem and hot days but it happens though winter as well. The lab is 24/7 air con controlled at 20 degrees C so i wouldn't think air temp would play a part. We have run a couple of trials around taking up ammonia from the atmosphere and I think it is the most likely source as we do use ammonium acetate for our cation extraction solution. The problem is slightly worse in winter which is our busy season.

Original Poster1 point · 1 year ago

Judging from the fact it's not in you prep blank we can assume that the source is not in your KCl or water which leaves (IMHO) either airborne transfer. or some sort of interferon in the sample prehaps.

I am pretty unfamiliar with the Phenolic method. someone else maybe able to shed more light on it

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Yeah that's the conclusion that we have come to. Apparently there can be a positive interference for samples with high turbidity. It's just a matter of determining which one it is.

We seem to be having some intermittent NH4 contamination that we can't seem to find the source of. The amount of contamination is always about the same level, 0.5-1ppm in solution, and it does't affect blanks. This is on the 1.7M KCl extractable NO3+NH4 test (I see another post mentioning NO3-N, we have had troubles with that as well but not to the same extent as NH4-N). Has anybody come across this before? And if so, what did you do to over come it?

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