Mercury One LTD
Specialists in Mercury Analysis
Holding Time Study for Mercury 1631E and 245.7 Analysis
Introduction
Method 1631E and 245.7 for the analysis of Mercury provides two different holding times depending upon sample analysis requirements. If the sample must be transferred to another vessel for digestion or dissolved mercury must be analyzed, the sample must be transported to the laboratory with in 48 hours of sampling to start digestion. If the sample is being analyzed for total mercury and in-bottle digestion is being employed, a 28 day hold time is acceptable. This study is to determine if the integrity of the sample is maintained over that 28 day using in bottle digestion.
Scope
A large sample (2.5L) of effluent is taken at a local wastewater treatment plant. The total time of holding before splitting is 5 hours. The sample is then transported to the laboratory and split into 28 different bottles. Each bottle represents from day 1 to day 28. A pipette is used to take 50 ml of sample aliquots from the original sample bottle and placed in each of the 28 bottles. One ml of BrCl digestate is added to the bottle. The bottle is then set aside for 24 hours at room temperature for digestion. Analysis is performed after the 24 hour digestion time.
Procedure
A 50ml class A pipette is used to take a sample aliquot and placed into a digestion bottle. The bottle is labeled “Day 1”. This procedure is repeated 27 more times until 28 bottles are filled. Each bottle represents a holding time based upon days of holding from 1 to 28 days. The BrCl digestion acid is added to the bottle marked day 1 and held for analysis 24 hours after the digestion acid is added. Once the 24 hour period is up the sample is analyzed. This procedure is repeated each day until all 28 split samples (28 days) have been digested and analyzed. Thus sample 28 is held with out digestion acid added until the 28th day upon which the BrCl acid is added and held 24 hours for analysis.
Analysis
The sample was analyzed using the standard operating procedures established for method 1631E.
Results
The table below is a tabulation of the results from day 1 to day28.
All concentrations are in ng/L
Day 1 / 1.79 / Day 8 / 1.89 / Day 15 / 1.99 / Day 22 / 2.15Day 2 / 2.14 / Day 9 / 2.41 / Day 16 / 2.04 / Day 23 / 2.11
Day 3 / 2.10 / Day 10 / 2.15 / Day 17 / 4.14 / Day 24 / 2.07
Day 4 / 1.97 / Day 11 / 2.11 / Day 18 / 2.07 / Day 25 / 1.98
Day 5 / 2.08 / Day 12 / 2.16 / Day 19 / 2.12 / Day 26 / 2.14
Day 6 / 2.21 / Day 13 / 2.06 / Day 20 / 2.10 / Day 27 / 2.17
Day 7 / 2.02 / Day 14 / 2.09 / Day 21 / 2.07 / Day 28 / 2.16
Conclusion
The 28 day hold time works very well and as the 1631E and 245.7 procedure allow, the digested sample can be held up to 90 days. Based upon above data it is clear the in-bottle digestion works very well and the 28 day hold is not a problem.
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