Preparing Trace Level Calibration Standards
These instructions are specifically for preparing mercury standards at trace levels for the NIC RA-4300FG+ and previous models. These instructions will only work with the NIC direct purge systems and are not intended for use with other analyzers.
When working at trace mercury levels, it is a best practice to reduce the number of surfaces that your calibration standards, diluents, and reagents come in contact with. These instructions have been created with this in mind, and they are field tested and proven by many of our customers.
Stock Solutions Required:
- Stock 1,000 mg/L Hg as HgCl2 (mercury chloride) [AGS Scientific Part No. 2080-04-01]
- Stock BrCl (bromine monochloride), prepared by adding concentrated HCl to bromide/bromate solution [AGS Scientific Part No. 1000-02-02]
- Distilled Water (deionized water may be used, but we have found distilled water to be the lowest in background mercury)
Other Items Required:
- Certified Pre-cleaned 50-mL Disposable Polypropylene Digestion Tubes [AGS Scientific Part No. 3000-12-01]
- Dedicated pipettor for 0.5 to 5 mL volume transfers (pipettes dedicated to trace level mercury analysis are preferred)
- Dedicated pipettor for 1 to 1,000 uL volume transfers (pipettes dedicated to trace level mercury analysis are preferred)
- Dedicated pipettor for 20 to 200 uL volume transfers (pipettes dedicated to trace level mercury analysis are preferred)
- Pipettor tips for each of the above pipettors
Preparing Working/Intermediate Solutions:
- 0.1% v/v BrCl Solution: In a 50-mL digestion tube, add 50 uL of the Stock BrCl, and then dilute to the 50-mL mark on the digestion tube with distilled water. This solution will be used for cleaning only.
From this point forward, you will use the 0.1% BrCl solution to clean all pipette tips before use by first drawing up the volume to be used of this cleaning solution, then dispensing it into a waste container. You will then draw up the volume of standard (or other solution) that you are pipetting with that same tip still attached. After transfer is completed, dispose of that pipette tip appropriately. This process will help eliminate contamination sources when working at low and sub part per trillion concentrations.
- 0.5% v/v BrCl Blank Solution: In a 50-mL digestion tube, add 250 uL of the Stock BrCl, and then dilute to the 50-mL mark on the digestion tube with distilled water. You may need to prepare at least two sets of this diluent solution, depending on how many total calibration and method blanks you will analyze (5-mL per blank measurement).
- 10 mg/L Intermediate Calibration Standard: In a 50-mL digestion tube, add 250 uL of stock BrCl solution, 500 uL of stock 1,000 mg/L Hg solution, and then dilute to 50-mL precisely with distilled water. It is very important to be very accurate in the transfer and dilution of all calibration standard solutions. This solution is stable and should be stored for future use.
- 1 mg/L Intermediate Calibration Standard: In a 50-mL digestion tube, add 250 uL of stock BrCl solution, 50 uL of stock 1,000 mg/L Hg solution, and then dilute to 50-mL precisely with distilled water. It is very important to be very accurate in the transfer and dilution of all calibration standard solutions. This solution is stable and should be stored for future use.
- 0.1 mg/L Intermediate Calibration Standard: In a 50-mL digestion tube, add 250 uL of stock BrCl solution, 500 uL of intermediate 10 mg/L Hg solution, and then dilute to 50-mL precisely with distilled water. It is very important to be very accurate in the transfer and dilution of all calibration standard solutions. This solution is stable and should be stored for future use.
- 10 ug/L Intermediate Calibration Standard: In a 50-mL digestion tube, add 250 uL of stock BrCl solution, 50 uL of intermediate 10 mg/L Hg solution, and then dilute to 50-mL precisely with distilled water. It is very important to be very accurate in the transfer and dilution of all calibration standard solutions. This solution should be prepared fresh each week.
- 1.0 ug/L Intermediate Calibration Standard: In a 50-mL digestion tube, add 250 uL of stock BrCl solution, 50 uL of intermediate 1.0 mg/L Hg solution, and then dilute to 50-mL precisely with distilled water. It is very important to be very accurate in the transfer and dilution of all calibration standard solutions. This solution should be prepared fresh each week.
- 0.1 ug/L Intermediate Calibration Standard: In a 50-mL digestion tube, add 250 uL of stock BrCl solution, 50 uL of intermediate 0.1 mg/L Hg solution, and then dilute to 50-mL precisely with distilled water. It is very important to be very accurate in the transfer and dilution of all calibration standard solutions. This solution should be prepared fresh each week.
Preparing Final Working Calibration Solutions:
- Set up a sample tube rack with fresh disposable sample tubes for the RA-4300FG+ (or previous model) Mercury Analyzer. If running EPA 1631, the method requires three calibration blanks followed by at least 5 non-zero calibration standards. We recommend a total of 6 non-zero calibration standards at concentrations of 0.5, 1.0, 5.0, 10, 50, and 100 ng/L (ppt) Hg.
- In the first three tubes, add 5 mL of the 0.5% v/v BrCl blank solution. These are your three calibration blanks. You may then go ahead and add 5 mL of the blank solution to as many tubes as are needed to complete the Method Blanks for your analysis batch.
When pipetting the standard solutions below, take care to inject it directly down into the solution and not onto the tube walls. Also take care to get a full, accurate injection of the standard solution. A best practice is to not rush through the pipette injection, but instead use a gradual, smooth stroke for injection.
- 0.5 ng/L Working Standard: Directly to a sample tube, add 4.95 mL of 0.5% v/v BrCl solution followed by 25uL of 0.1 ug/L intermediate calibration standard solution.
- 1.0 ng/L Working Standard: Directly to a sample tube, add 4.90 mL of 0.5% v/v BrCl solution followed by 50uL of 0.1 ug/L intermediate calibration standard solution.
- 5.0 ng/L Working Standard: Directly to a sample tube, add 4.95 mL of 0.5% v/v BrCl solution followed by 25uL of 1.0 ug/L intermediate calibration standard solution.
- 10 ng/L Working Standard: Directly to a sample tube, add 4.90 mL of 0.5% v/v BrCl solution followed by 50 uL of 1.0 ug/L intermediate calibration standard solution.
- 50 ng/L Working Standard: Directly to a sample tube, add 4.95 mL of 0.5% v/v BrCl solution followed by 25uL of 10 ug/L intermediate calibration standard solution.
- 100 ng/L Working Standard: Directly to a sample tube, add 4.90 mL of 0.5% v/v BrCl solution followed by 50 uL of 10 ug/L intermediate calibration standard solution.
Always dispose of unused BrCl and mercury standard solutions using proper disposal procedures.
Additional Tip for Success: Make sure that you always close the caps on any BrCl solutions when not being used. The BrCl oxidant has a very strong affinity for mercury, and it will capture it from the ambient air. This is also a reason that we recommend preparing only small batches of these reagents in small digestion tubes, so that the exposure to ambient air over time is reduced.
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