I have some test results for Chromium (totals and dissolved) and the dissolved levels are higher than the totals How is this possible even though all quality controls are acceptable ? that's mean 100 % of chromium is in dissolved state?
Mr. Mushtaq Ahmad , thank you for your answer
for station 01; total is 0.081, dissolved is 0.098
for station 02; total is 0.105, dissolved is 0.130
for station 03; total is 0.106, dissolved is 0.097
for station 04; total is 0.099, dissolved is 0.179
only in station 03 the concentration was lower
The operation was though acceptable condition. The analysis were performed twice and obtained the same results. Is it possible that the samples were contaminated during the sampling?
in fact it is not possible this may be due to error in analysis , or in preparing extracts or chemicals ,or may be due to sample pollution or contamination of sample with pollutants please send the data and procedures for extracting available ant total amount .
Prof. Akram Othman Esmail. thank you for your answer
The samples were filtered with a filter paper 0.45μm and measured with atomic absorption spectrometer (Z-2700).
NB: the collected samples were acidified with nitric acid, for dissolved Cr the samples were filtred before acidification.
Acidification is not enough to determine any of your fractions
You need to digest both and using a proven method, maybe EPA 3015A
You also need to run several sets of negative controls
You error may come from many places, filters, acid, glassware, etc. Only the use of controls will lead you to ans answer
What you stated is impossible!
Take precaution and care to get rid of any possible contamination and error from the materials used - glasswares, chemicals, etc.
Always keep in mind the following research basics. You must have to run controls with the same reagents and conditions used (without sample material) parralel to your sample processing and estimation. Another important things are replicates which are must for any scientific estimation.
Then only you will be able to fix the errors and contaminations.
i believe this occur because cross contamination during sample preparation
If you measure dissolved Cr without digestion maybe you have some kind of positive interference in your matrix. Try to digest the sample after filtration (and take care of blanks)
This is a great thread. I ran into this from submitted lab results from an accredited lab.
Total , dissolved and available concentration values are differing for the same sample depending of type of chemicals used for extraction , for example increase in normality, strength or type of acids applying in extraction may gives different results.
Evaluate sampling issues. It can be that all the analyses are correct but taken from different place - consider a gold mine with a few nuggets.
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