I am working on different heavy metals with a very low concentration (eg. less than 1ppm). please suggest some possible reasons. My absorption values are coming like 0.0023, 0.0036 etc.
This depends on the instruments detection limit (DL)
For example, if your instrument DL (0.004 Abs) this mean you should start your calibration form this point.
The first standard (Abs) must be ≥ 0.004.
Its been years for me in lab with AA spectrophotometer. I dont remember calculating measuring or absorbance, just making standards of known concentrations, developing response curve, measuring unknown samples and nearest known value. If concentration were too high, I had to turn burner to right angle. Some elements may work better with flame emission. New equipment may use new measures.
When you construct calibration curve you should be take in consideration the signal of the first standard above the nosy area (above detection limit signal of AAS instrumen) to achieve acceptable characteristic concentration value for the curve
Yes, noise was a factor to detection limit. I think detection limit might be standard that was at least two times the noise factor. I attached a recording strip chart to record all responses to Perkin Elmer AAS. I was trained my Professor Pickett, Analytical Chemist in Agriculture Dept. at University of Missouri in the 1970s. During about 4 years of work, I dont remember many problems. I think once in a while, I had to clean or replace the fine tubing that pulled in sample. Alot of care in cleaning glassware, mixing standards, following procedures. I dont remember, but probably filtering of at least some samples to remove excessive particles.
Thank you Mahmoud Ghuniem sir for your answer. My instrument has detection limit of 1 ppb ( 1microgram/l). so I think my values are correct.
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