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  #1  
Old 12/28/2007, 06:04 PM
imafishy! imafishy! is offline
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need accurate measure of salinity levels

Hi,

I'm currently doing some research on ocean contamination, and since it's winter break, our school laboratory is closed.

However, all I need is salinity level measurements on four water samples. I was just wondering if anybody here has a refractometer I can borrow/use, it should only take at most a hour.

I live in the Pasadena area, so I can just drop by anytime this week, preferably today.

Thanks for helping me out!!!

-Jeff
  #2  
Old 12/28/2007, 06:19 PM
lowbudget lowbudget is offline
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you can come by my place. 10 minutes from pasadena.
  #3  
Old 12/28/2007, 07:52 PM
five.five-six five.five-six is offline
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how accurate do you need to be? and how precise do you need to be? are you checking, salinity as you stated, specific gravity, or refractive index?

I only ask because those terms are often interchanged, though they are not really interchangable
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  #4  
Old 12/28/2007, 08:22 PM
imafishy! imafishy! is offline
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Thanks for the replies,

I just need the measurement of salt levels. The reason I need the measurements to be accurate is because out of the four ocean water samples, I need to see if two of them came in contact with freshwater. I'm not sure how accurate or precise it needs to be, but the more accurate and precise the measurements are, the better.
  #5  
Old 12/28/2007, 08:30 PM
five.five-six five.five-six is offline
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then you do not need accuracy, you just need precisoin. any refractomiter should do the trick
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  #6  
Old 12/29/2007, 10:39 AM
imafishy! imafishy! is offline
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yep, I'm just looking to use a refractometer.

Does anyone else have one that I could possibly use?

Thanks!
  #7  
Old 12/29/2007, 11:36 AM
Orochimaru Orochimaru is offline
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I think you need accuracy more than precision. What is the point of getting the same results six times and they are all wrong and way far from the actual values? That only means you are consistant in your test method but doesn't mean you are doing it right. If this data are important, you should perform at least three to six replicates testing of each sample. Since this is only using a refractometer, I don't think you will need to do precison because the testing only involes putting a drop of sample onto the meter. Not very hard.

"accuracy is the degree of conformity of a measured or calculated quantity to its actual (true) value. Accuracy is closely related to precision, also called reproducibility or repeatability"
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  #8  
Old 12/29/2007, 01:10 PM
raskal311 raskal311 is offline
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Swing by your LFS and borrow theirs.
  #9  
Old 12/29/2007, 02:43 PM
five.five-six five.five-six is offline
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Quote:
Originally posted by Orochimaru
I think you need accuracy more than precision. What is the point of getting the same results six times and they are all wrong and way far from the actual values? That only means you are consistant in your test method but doesn't mean you are doing it right. If this data are important, you should perform at least three to six replicates testing of each sample. Since this is only using a refractometer, I don't think you will need to do precison because the testing only involes putting a drop of sample onto the meter. Not very hard.

"accuracy is the degree of conformity of a measured or calculated quantity to its actual (true) value. Accuracy is closely related to precision, also called reproducibility or repeatability"
if he just wants to find out which samples have been diluted, then it does not matter if the mesurements are correct, just consistnt, and a fairly high level of resalution, refractomiter will work fine
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  #10  
Old 12/29/2007, 07:44 PM
Orochimaru Orochimaru is offline
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If the he doesn't care about the the accuracy of the measurement, I am not sure why anyone would measure anything at all. I don't doubt the refractometer is sufficient for what he is looking for but he did ask for accuracy in his second post. Precision only applies if he is planning to test each sample multiple times. If he is only testing one sample at time then it is accuracy that he needs. The only time you would need precision is when you want to see whether your methodology or instruments are functioning properly so you test the same sample again and again to prove the instrument or method is consistent. In this case he wants to know whether some samples are contaminated or not, he is not going to test each of the samples multiple times is he? If he refractomer is as accurate as we believe it is to be, there is no need to test each sample multiple times is there? Hence it is not precision( aka % relative standard deviation) that he wants but accuracy.
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  #11  
Old 12/30/2007, 06:26 PM
Harley-J Harley-J is offline
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ahhh..I am in Santa Clarita..by magic mountian..if you need a refractometer i got one..about 1/2 hour from you...
so if you want precision or accuracy, which ever suits your fancy..Let me know..
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