Back to Methodology List

1.0 Scope and Application:

1.1 Applicable Matrices: This method may be used to determine reactive mercury in filtered or unfiltered water samples.

1.2 Minimum Reporting Limit: The minimum reporting limit for this method is 0.04 ng/L (nanograms per Liter).

1.3 Dynamic Range: This method is designed for the measurement of reactive mercury (Hg) in the range of 0.04 - 0.8 ng/L. The upper range may be extended to higher levels with the selection of a smaller sample volume.

To top of page

2.0 Summary of Method:

Stannous Chloride (SnCl₂) is added to the sample to reduce the reactive Hg from the Hg^II to the Hg⁰ oxidation state. The Hg⁰ is purged onto gold-coated glass bead traps (sample). The mercury vapor is thermally desorbed to a second gold trap (analytical) and from that detected by cold vapor atomic fluorescence spectrometry (CVAFS).

To top of page

3.0 Safety Issues: Before beginning any of the procedures involved in this method, each individual must read and sign the Chemical Hygiene Plan developed for the lab. Specific safety concerns for each chemical can be found in the Material Safety Data Sheets for that chemical ñ all of which are located in the laboratory. Two extremely important areas for this method are addressed below.

3.1 Chronic mercury exposure may cause kidney damage, muscle tremors, spasms, personality changes, depression, irritability and nervousness. Due to the toxicological and physical properties of Hg, only highly trained personnel using extremely cautionary procedures should handle high concentration standards. These cautionary measures include the use of gloves and high volume hoods when preparing standards.

3.2 Strong acid solutions are employed in the cleaning of equipment, preparation of reagents and in sample preservation. Proper acid handling techniques should be employed whenever acids are being used. These techniques include the use of acid resistant clothing and the utilization of high volume fume hoods.

To top of page

4.0 Sample Preservative, Containers, and Holding Times:

4.1 Samples are preserved by the addition of 1mL of 6N trace pure hydrochloric acid (HCl). Samples are stored at 4°C until analysis.

4.2 Sample containers will consist of Teflon bottles cleaned at the laboratory. New Teflon bottles are rinsed with tap water, and cleaned by immersing in 4 N trace pure HCl heated to 65°C for at least 48 hour. Immediately following removal from the bath, the bottles are immersed in fresh reagent grade water and rinsed at least 3 times with reagent grade water. Following the rinsing step, each bottle is filled to 25% with 1% trace pure HCl and capped. The exterior of the bottles is allowed to air dry under a mercury-free class 100 laminar flow hood. Dry equipment is double bagged in new zip-type bags with the unique identifier and date cleaned written on the outer bag. After the initial 48 hr. cleaning, only 24 hr. is required.

4.3 Properly preserved samples may be held for up to 48 hours prior to analysis.

To top of page

5.0 Reagents and Standards:

5.1 Reagents: All reagents and/or dry chemicals used to make reagents must be of the highest purity available from the vendor and shown to be low in mercury. Upon receipt at the laboratory, containers will be marked with the date of receipt and stored in the appropriate areas. When reagents are mixed for use in this method, the person who mixes them will initial and date the reagent container.

5.1.1 Reagent water: Ultra pure reagent grade water shown to be > 18 M starting from pre-purified source (distilled, RO, etc.). The water is delivered through a 0.2 uM filter. All water is obtained from a Millipore Academic water purification system.

5.1.2 Hydrochloric Acid: EM Science trace pure HCl (containing less than 5 ng/L Hg) or equivalent.

5.1.3 Stannous chloride (SnCl₂). Add 100 g SnCl₂ to 50 mL concentrated HCl in a 500 mL Teflon bottle. Add 450 mL reagent water. Purge for 1 hour with Hg free N₂ at 300 mL/min. Prepare fresh every 6 months.

5.1.4 Nitrogen (N₂). Grade 5.0 (ultra high purity) that is passed through a gold bead trap attached to the outlet of the tank to remove any Hg.

5.1.5 Argon (Ar). Grade 5.0 (ultra high purity) that is passed through a gold bead trap attached to the outlet of the tank to remove any Hg.

5.2 Standards: Upon receipt at the laboratory or on the day of preparation, containers should be labeled with the date received or made and the initials of the person preparing them. The stock and substock standards should by stored outside of the clean laboratory to prevent contamination of the entire lab.

5.2.1 Stock standard (1000 mg/L): Commercially available Hg standard verified against a NIST standard reference material. All subsequent standards are prepared using the stock standard. Before preparing other standards, ensure the expiration date of the stock standard has not been exceeded.

5.2.2 Substock standard (1000 ng/mL): Dispense approximately 50 mL of reagent grade water and 5 mL of BrCl into a 100 mL mercury clean class A volumetric flask. Pipette 100 µL of the stock standard (1000 mg/L) and bring to volume with reagent water. To clean the volumetric flask, fill to approximately 80 % total volume with 30% HCl, place the ground glass stopper on its side over the opening to prevent pressure buildup, and heat to near boiling on a hotplate for 8 hours.

5.2.3 Working standard (1 ng/mL): Dispense approximately 50 mL of reagent grade water and 1 mL of BrCl into a 100 µL mercury clean (sec. 5.2.2) class A volumetric flask. Pipette 1.0 mL of the substock standard (1000 ng/mL) and bring to volume with reagent water. This working standard must be compared to the previous working standard and agree within ± 5%. Working standard should be prepared fresh every 6 months.

5.3 Quality control sample (QCS): The quality control sample will be prepared from a Hg source different from that used to prepare the standards routinely used for analysis. The QCS is used during analysis runs to verify calibration of the detector. Due to the fact that Hg source standards are only commercially available in concentrated solutions serial dilutions are necessary. The serial dilutions necessary are outlined below.

5.3.1 Quality control stock standard (10,000 mg/L): Commercially NIST certified standard reference material 3133. All subsequent quality control standards and samples are prepared using this stock standard. Before preparing other standards, ensure the expiration date of the stock standard has not been exceeded.

5.3.2 Quality control substock standard (10,000 ng/mL): Dispense approximately 50 mL of reagent grade water and 5 mL of BrCl into a 100 mL mercury clean (sec. 5.2.2) class A volumetric flask. Pipette 100 µL of the quality control stock standard (10,000 mg/L) and bring to volume with reagent water.

5.3.3 Quality control working standard (10 ng/mL): Dispense approximately 50 mL of reagent grade water and 1 mL of BrCl into a 100 mL mercury clean (sec. 5.2.2) class A volumetric flask. Pipette 100 µL of the quality control substock standard (10,000 ng/mL) and bring to volume with reagent water. This quality control working standard must be compared to the previous quality control working standard and agree within ± 5%.

5.3.4 Quality control sample (0.5 ng/L):

5.3.4.1 Dispense approximately 750 mL of reagent grade water and 5 mL of concentrated HCl into a mercury clean (sec. 5.2.2) 1.0 L class A volumetric flask. Pour this solution into a mercury clean 5 L Teflon bottle.

5.3.4.2 Dispense approximately 750 mL of reagent grade water into the same volumetric flask used in sec 5.3.4.1. Pipette 0.250 µL of the quality control working standard (sec. 5.3.3) into the volumetric and dilute to volume. Add this solution to the 5 L bottle from sec. 5.3.4.1.

5.3.4.3 Fill the same volumetric used previously to volume and add to the 5 L bottle containing the HCl, and the quality control working standard. Repeat an additional 2 times to bring the final volume to 5 L.

5.3.4.4 The QCS is then split into 8 ñ 500 mL and 4 ñ 250 mL mercury clean Teflon bottles. A new QCS needs to be prepared when 500 mL of the previous QCS remains or in one month, whichever is shorter. The new QCS must be verified against the previous QCS and agree within ± 10%.

To top of page

6.0 Quality Control: Each analyst must demonstrate the ability to generate acceptable accuracy and precision with this method. This includes the ability to reproduce standards, establish acceptable daily detection limits (DDL), produce acceptable relative percent differences between replicates, and produce spike recoveries that meet acceptance criteria.

6.1 Bubbler blanks: A bubbler blank is prepared by adding 500 µL of SnCl₂ to a bubbler containing approximately 125 mL of mercury free water. The water in the bubbler can be reagent grade water or sample water but must first be reduced with SnCl₂ and purged for 20 minutes to remove all Hg. Blanks are critical to the reliable determination of Hg at low levels. Frequent analysis of bubbler blanks is required to demonstrate freedom of system contamination and the absence of carry over from one sample or standard to the next.

6.1.1 Acceptance criteria: No bubbler blank must contain more than 25 pg of Hg. A daily detection limit (DDL) is calculated each day prior to analysis of samples. The DDL is computed using the following formula:

DDL= ((3 x ) x RF_m) / 0.125 L

= standard deviation among peak areas found for a set of bubbler blanks purged simultaneously on all bubblers

RF_m = ratio of concentration to peak area from the standard curve (sec. 6.2.1)

The acceptable value for the DDL must be 0.04 ng/L or less.

6.1.2 Corrective Actions:

6.1.2.1 If a bubbler blank is found to contain more than 25 pg Hg, at the beginning of the day, another set of bubbler blanks should be run to ensure the entire system has been purged and that the value is true. If this second set blanks is also out of control the analyst must isolate and correct the problem before continuing.

6.1.2.2 If a bubbler blank is found to contain more than 25 pg Hg, during the course of the day's analyses, the system is out of control and data produced on that bubbler should be rerun or carefully evaluated and flagged as being suspect.

6.1.2.3 If the DDL exceeds 0.04 ng/L, another set of bubbler blanks should be run to ensure the entire system has been purged and that the value is true. If this second set blanks is also out of control, the analyst must isolate and correct the problem before continuing.

6.2 Standards: A standard is prepared by adding a known volume of working standard and 500 µL of SnCl₂ to a bubbler containing approximately 125 mL of mercury free water. The water in the bubbler can be reagent grade water or sample water but must first be reduced with SnCl₂ and purged for 20 minutes to remove all Hg.

6.2.1 Acceptance criteria: A mean response factor (RF_m) is calculated at the beginning of the day from the ratio of mass to peak area (ng/PA) for 4 standards of different concentrations (sec. 7.6.11). The RSD among the ng/PA ratios of the standards must 10%.

RSD (%) = ( / mean) x 100

= standard deviation among four standards

6.2.2 Corrective action: If the RSD of the standards fails to meet acceptance criteria, an additional set of standards must be run to ensure no operator error exists. If the second set of standards still does not meet acceptance criteria, the analyst must isolate and correct the problem before continuing.

6.3 Quality control sample: A QCS must be analyzed subsequent to calibration but prior to sample analysis. A QCS must also be analyzed approximately every ten samples and at the end of the analytical batch.

6.3.1 Acceptance criteria: The recovery of the QCS must be between 80 and 120% (0.4 and 0.6 ng/L) of the expected value.

6.3.2 Corrective actions:

6.3.2.1 If the initial QCS analysis fails to meet acceptance criteria, an additional QCS must be run to ensure no operator error exists. If the second QCS still does not meet acceptance criteria, the analyst must isolate and correct the problem before beginning analysis.

6.3.2.2 If the QCS, analyzed subsequent to a batch of samples, fails to meet acceptance criteria, an additional QCS must be run to ensure no operator error exists. If the second QCS still does not meet acceptance criteria, the instrument is recalibrated and the QCS is analyzed until it demonstrates statistical control has been reestablished. After control has been reestablished, all routine samples analyzed since the last acceptable QCS measurement are reanalyzed.

6.3.2.3 If the QCS analyzed prior to or subsequent to a batch of samples fails to meet the acceptance criteria, the samples in that batch must be reanalyzed or flagged appropriately.

6.4 Duplicates: All samples are run in duplicate.

6.4.1 Acceptance criteria:

6.4.1.1 For samples with concentrations exceeding 0.2 ng/L the acceptance criteria is a relative percent difference (RPD) of 10%.

RPD (%) = ((|X₁ - X₂|) / Mean) x 100

X1 = Measured value of first replicate

X2 = Measured value of second replicate

6.4.1.2 For Samples with concentrations 0.2ng/L the acceptance criteria is an absolute difference (AD) of ± 0.02 ng/L.

6.4.2 Corrective action:

6.4.2.1 If the RPD or the AD between the two replicates is greater than 10% or 0.02 ng/L, respectively, the sample is analyzed a third time.

6.4.2.2 If the relative standard deviation (RSD) between the three replicates is greater than 10 %, the sample is flagged and/or analyzed a fourth time.

RSD (%) = ( / mean) x 100

= standard deviation among three replicates

6.5 Matrix spike: A matrix spike is prepared by adding a known concentration of working standard to a sample. A matrix spike must be analyzed each run or every tenth sample whichever is greater.

6.5.1 Acceptance criteria: Percent recovery for a matrix spike must fall between 90 and 110%.

% Recovery = ((|Mass - (sample conc. x volume spiked in liters)|) / Mass of spike) x 100

6.5.2 Corrective actions:

6.5.2.1 If the percent recovery falls beyond the range of 90 to 110%, another sample from the set must be spiked.

6.5.2.2 If percent recovery for the second spike falls beyond the range of 90 to 110%, the batch of samples analyzed for that day are flagged identifying either high or low recovery.

To top of page

7.0 Procedure:

7.1 Comments: The samples are collected using ultra clean sampling techniques.

7.1.1 Interferences:

7.1.1.1 Free halogens: The destruction of the gold traps exists if they are exposed to free halogens resulting in low mercury values. This can be avoided with the addition of a soda lime trap directly upstream of the sample traps during purging.

7.1.1.2 Water vapor: Water vapor may collect on the gold traps during the purging step. If water vapor is present on the traps this will give a false peak during analysis. This can be avoided with the addition of a soda lime directly upstream of the sample traps during purging.

7.1.1.3 Carrier gas: The fluorescent intensity of the detector is strongly dependent on the inertness of the carrier gas. The dual amalgamation step virtually eliminates quenching due to impurities in the carrier gas, but it is the analystís responsibility to ensure high purity inert carrier gas and a leak free analytical train.

7.1.2 Helpful hints:

7.1.2.1 Working with detection limits in the parts per trillion range, protecting these samples from contamination cannot be over emphasized. The greatest difficulty in low level mercury analysis is preventing the samples from becoming contaminated. Extreme caution must be used throughout the preparation, collection and analysis procedures to avoid contamination.

7.1.2.2 It is very important that the laboratory air be low in both particulate and gaseous Hg. The mercury in the air can be reduced with the use of gold-coated cloth at the intakes of the laminar flow hoods.

7.1.2.3 If cloudy residue becomes apparent on the inside of the bubblers, dissolve approximately 2 grams of Potassium Hydroxide in 250 mL of reagent water and allow to soak for 1 hr.

7.2 General Description: Refer to section 2 of this procedure for a summary of this method.

7.3 Labware:

7.3.1 All-plastic pneumatic fixed-volume and variable pipettors in the range of 5 µL to 10 mL.

7.3.2 Analytical balance capable of measuring to the nearest 0.1 g.

7.4 Sample preparation: No sample preparation is required.

7.5 Instrumentation:

7.5.1 Purging and preconcentration:

7.5.1.1 Regulator capable of supplying 30 psi of pressure.

7.5.1.2 Various sizes of Teflon tubing and fittings.

7.5.1.3 Flow meter(s) capable of maintaining a N₂ flow of 300-400 mL/min.

7.5.1.4 Needle valve to shut off N₂ flow to bubblers.

7.5.1.5 Gold coated glass bead traps: The gold coated glass bead traps are constructed of a 7 mm quartz tube, 4" long and with a constriction at 1 " from the outlet end. A quartz plug is placed into the inlet end, about 0.7 g (3.5 cm in the tube) of gold coated beads are added and the inlet end is plugged with another piece of quartz wool. Female fittings for gold traps are made from small pieces of 6 mm i.d. monobarb Teflon tubing. Heating " Teflon tubing and sealing one end by pinching with a pliers until cool creates end plugs.

7.5.1.6 Bubblers: The bubblers are 250 mL borosilicate glass flasks with the standard 24/40 tapered neck. The sparging stopper has a coarse glass frit that extends to the bottom of the flask.

7.5.1.7 Soda lime traps: The soda lime traps are constructed of a 10 mm i.d. Teflon tube with custom machined Teflon end plugs. The traps are filled with 4-8 mesh soda lime. The traps are pre-purged for 20 min before collection of a sample onto a gold trap. Soda lime traps should be repacked every 2-3 days.

7.5.2 Desorbtion and analysis:

7.5.2.1 Analytical train: A CronTrol model XT multi outlet timer controls the analytical system. The timer is connected to 2 variable current transformers and 2 cooling fans. The transformers are connected to Nichrome coils that are wrapped to fit around the sample traps and the analytical trap. First the sample trap is heated to 425°C with a ramp time of 2 minutes. Then the analytical trap is heated. After the heating of each coil, the fans are activated to cool the traps.

7.5.2.2 Detector: The detector is a commercially available Model 2500 CVAFS Mercury Detector from Tekran (Toronto, ON) equipped with a mass flow controller capable of measuring 30 mL/min.

7.5.2.3 Integrator: The detector analog output is connected to a Hewlett Packard Model HP3395 integrator and the peak areas are recorded.

7.6 Initial start-up, calibration and sample analysis:

7.6.1 Check pressure in Argon tank to verify adequate volume for the day's analyses.

7.6.2 Adjust mass flow controller at detector to read 30.0 mL/min.

7.6.3 Check baseline at detector, acceptable baseline readings are from 0.0050 and 0.0250. If the baseline is out of that range, adjust by turning the offset knob. Record date, initial reading and adjusted reading in the instrument notebook.

7.6.4 Start burning the set of eight sample traps: While these traps are being burned proceed with step 7.6.5.

7.6.4.1 Remove the plugs from the ends of the first trap and place it into the analytical train by threading it, with the id number downstream, through the center of the Nichrome wire coil. Center the Nichrome wire over the gold beads and press, in sequence the buttons labeled Prog, 3, and run on the Crontrol timer.

7.6.4.2 After the 6-minute cycle is complete repeat the steps in 7.6.4.1 for each of the remaining traps.

7.6.4.3 You need to have 4 traps burned before your step 7.6.5 is complete. You have 8 traps and four bubblers. The bubbling of samples takes 20 minutes and the burning of 4 traps takes 24 minutes, you will be bubbling a round of samples while burning (analyzing) the previous round. This is the cycle you will follow throughout the day.

7.6.5 Remove the caps from the inlet and outlet of the bubblers and thoroughly rinse the bubblers with reagent grade water.

7.6.6 Dispense approximately 125 mL of reagent grade water into each of the bubblers and add1.0 mL of SnCl₂ .

7.6.7 Attach the nitrogen line with the attached pretrap to the inlet of the bubbler, the soda lime trap to the outlet of the bubbler, tighten the sparging stopper, and begin purging at 300 mL/min with nitrogen. Allow to purge for 20 minutes.

7.6.8 After this initial purging, shut off the flow to the bubblers, add 500 µL of SnCl₂, attach a clean gold trap to the end of the soda lime trap and proceed as in 7.6.7. This represents a bubbler blank.

7.6.9 When the 20-minute purging cycle for the bubbler blanks has elapsed, remove the gold traps from the end of the soda lime traps, cap both ends of the gold traps, and shut-off the flow to the bubblers.

7.6.10 Analyze the gold traps as in 7.6.4.1-7.6.4.2. While these traps are being burned proceed with step 7.6.11.

7.6.11 Pipette 25, 50, 75, and 100 µL of the working standard into bubblers 1,2,3,and 4, respectively, add 500 µL of SnCl₂, attach a clean gold trap to the end of the soda lime trap and proceed as in 7.6.7. This represents your standards.

7.6.12 Analyze the gold traps as in 7.6.4.1-7.6.4.2. While these traps are being burned proceed with step 7.6.13.

7.6.13 Add approximately 125 mL of the QCS (sec. 6.2) to bubbler 1, add 500 µL of SnCl₂, attach a clean gold trap to the end of each soda lime trap and proceed as in 7.6.7. The QCS establishes system control when it meets the acceptance criteria outlined in sec. 6.2. The additional bubbler blanks demonstrate the amount of carry-over if any exists.

7.6.14 Analyze the gold traps as in 7.6.4.1-7.6.4.2. While these traps are being burned proceed with step 7.6.15.

7.6.15 Begin analyzing samples following the chart listed below.

Round	Bubbler 1	Bubbler 2	Bubbler 3	Bubbler 4
Blanks	BB1	BB2	BB3	BB4
Standards	0.025 ng	0.050 ng	0.075 ng	0.100 ng
QCS/blanks	QCS	BB2	BB3	BB4
Sample set A	S1	S2	S3	S4
Sample set B	S5	S6	S7	S8
Sample set A	S1	S2	S3	S4
Sample set B	S5	S6	S7	S8
Blanks	BB1	BB2	BB3	BB4
QCS/blanks	SPIKE	QCS	OOPS	OOPS
Sample set C	S9	S10	S11	S12
Sample set D	S13	S14	S15	S16
Sample set C	S9	S10	S11	S12
Sample set D	S13	S14	S15	S16
Blanks	BB1	BB2	BB3	BB4
QCS/blanks	OOPS	OOPS	QCS	SPIKE

BB = bubbler blank

SX = sample

SPIKE = matrix spike

OOPS = sample whose replicates do not meet acceptance criteria (sec. 6.4.1)

To analyze a sample, pour off the volume of water in the bubbler from the previous analysis, tare the bubbler on the scale, add approximately 125 mL of sample to the bubbler, add 500 µL of SnCl₂ and proceed as above.

7.6.16 All samples need to be bracketed by standards, if the sample peak area is greater than the highest standard, either a higher standard is analyzed or the sample is analyzed using a smaller sample volume.

7.7 Calibration and performance documentation: During the analysis run, the analyst must evaluate the calibration data, bubbler blank values, QCS recovery, and RPDs for duplicate analyses to ensure acceptance criteria (sec. 6.0) are being met. The following information must be recorded in the mercury logbook.

7.7.1 Date of analysis.

7.7.2 Type and date prepared for reagents and standards used.

7.7.3 Name of analyst.

7.7.4 Identification of bubbler contents, volume analyzed, instrument response, and sample trap identification for each analysis performed.

7.7.5 Comments pertaining to special samples run, problem samples, corrective actions taken, and results of any calculations performed to ensure acceptance criteria are being met.

7.8 Shut-down:

7.8.1 After the last sample has been purged, the following steps must be performed to properly store the bubblers until the next analysis run.

7.8.1.1 Shut off N₂ flow at the needle valve and at the tank regulator.

7.8.1.2 Remove the N₂ line from the inlet and the soda lime trap from the outlet of the bubblers.

7.8.1.3 Thoroughly rinse the bubblers and the sparging stoppers with copius amounts of reagent grade water.

7.8.1.4 Fill the bubblers to approximately 95% volume with reagent grade water, add 5 mL of concentrated HCl, and fill remaining volume.

7.8.1.5 Carefully replace the sparging stopper, cap the inlet and outlet of the bubbler and return to the laminar flow hood.

7.8.2 After the last sample trap has been burned, leave the trap in the analytical train to avoid contamination from room air. Reduce flow at the mass flow controller to the minimum flow allowable (approximately 2 mL/min).

7.9 Maintenance, maintenance records and Responsibilities:

7.9.1 Gold traps attached to regulators on the N₂ and Ar tanks should be burned clean every time a tank is changed.

7.9.2 Nichrome wire temperature should be checked quarterly.

7.9.3 Detector lamp driver voltage should be checked quarterly. If voltage exceeds 12.5, the lamp should be adjusted or replaced according to manufacturers guidelines.

7.10 Calculations:

7.10.1 Uncorrected concentrations: The uncorrected (for additions of mercury from preservation and bromination) concentrations must be calculated during analysis to ensure acceptance criteria are being met. The following formula is used to calculate the uncorrected concentration for environmental and QC samples.

C = ((PA_s ñ BB_m) x RF_m) / V_s

C = concentration in ng/L

PA_s = peak area of sample, in PA units

BB_m = mean bubbler blank, in PA units (sec. 6.1)

RF_m = mean response factor, in ng/PA unit (sec. 6.2)

V_s = volume of sample purged, in liters

7.10.2 Final (corrected) concentrations: Raw data from the mercury logbook is entered into an EXCEL spreadsheet that calculates final concentrations using the same basic formula as above. The uncorrected value is than adjusted by subtracting additional Hg added to the sample during preservation.

7.11 Data validation and evaluation: After the data has been entered into the EXCEL spreadsheet, someone other than the analyst must verify that no values have been incorrectly entered in either the log book or the spreadsheet. The data is then evaluated carefully by the QC officer to ensure all data quality objectives have been met for the run and that the data seem reasonable. Data is evaluated as to reasonability if historical data from a site exists.

7.12 Reporting:

7.12.1 Reporting units: Total mercury as ng/L Hg.

7.12.2 Reporting levels and significant figures:

7.12.2.1 Report to the nearest 0.01 ng/L for values less than 10 ng/L.

7.12.2.2 Report to three significant figures for values exceeding 10 ng/L.

7.12.3 Data transfer: After the data has been verified in the EXCEL spread sheet it may be transferred to the customer via e-mail, hard copy, or the internet.

To top of page

8.0 Archiving: All raw data produced in the laboratory is archived in a filing cabinet located in the laboratory managerís office. Hard copies of EXCEL spreadsheets and data reports are archived with raw data. All electronic data is archived on the laboratory managerís computer, which is backed up to tape daily.

To top of page

9.0 References:

9.1 Method source:

U.S. Environmental Protection Agency, 1996, Draft Method 1631: Mercury in Water by Oxidation, Purge and Trap, and Cold Vapor Atomic Fluorescence Spectrometry: EPA 821-R-96-012, Office of Water, 32 p.

Olson, M.L. Cleckner, L.B., Hurley, J.P., Krabbenhoft, D.P., Heelan, T.W. 1997, Resolution of matrix effects on analysis of total and methyl mercury in aqueous samples from the Florida Everglades: Fresenius Journal Analytical Chemistry. 358: 392-396

9.2 Deviations from source method and rationale:

9.2.1 Reactive mercury is operationally defined by this method as being the from of mercury that is easily reducible with the addition of SnCl₂. Method 1631 is used for the analysis of total Hg where all forms of Hg are oxidized with bromine monochloride (BrCl) then reduced with SnCl₂. This method skips the BrCl step and only reduces a slightly acidified sample with SnCl₂.

9.2.2 Gold coated glass bead traps are used in place of sand traps. There are two advantages to glass beads 1) less back pressure and 2) the ability to handle higher temperatures during analysis which provides cleaner burning traps (Olson et al 1997).

9.2.3 To increase the confidence in the analytical result obtained using this procedure, all samples are analyzed in duplicate, which is not required in Method 1631.

9.2.4 Method 1631 establishes bubbler blank control limits at 50 pg. This method sets the control limits for bubbler blanks at 25 pg.

To top of page