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SOP: 1012
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PREPARATION OF STANDARD SOLUTIONS
CONTENTS
1.0 SCOPE AND APPLICATION
2.0 METHOD SUMMARY
3.0 SAMPLE PRESERVATION, CONTAINERS, HANDLING AND STORAGE
4.0 INTERFERENCES AND POTENTIAL PROBLEMS
5.0 EQUIPMENT/APPARATUS
6.0 REAGENTS
7.0 PROCEDURES
7.1 Documentation
7.1.1 Lot Number 7.1.2 Logbook 7.1.3 Standard Solution Bottle
7.2 Organic Standards
7.2.1 Standards for Volatile Analysis 7.2.2 Standards for Semi-volatile Analysis 7.2.3 Standards for Pesticide/PCB Analysis
7.3 Inorganic Standards
8.0 CALCULATIONS
9.0 QUALITY ASSURANCE/ QUALITY CONTROL
10.0 DATA VALIDATION
11.0 HEALTH AND SAFETY
12.0 REFERENCES
These sections affected by Revision 0.
SUPERCEDES: SOP #1012; Revision 0.0; 11/20/00; U.S. EPA Contract EP-W-09-
SOP: 1012
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PREPARATION OF STANDARD SOLUTIONS
1.0 SCOPE AND APPLICATION
The objective of this Standard Operating Procedure (SOP) is to define procedures for preparing standards used in various analyses that are performed by SERAS laboratories. It also provides a uniform documentation and tracking system.
The procedures and requirements described in this SOP apply to all the standards prepared by SERAS analysts for all routine and non routine organic and inorganic analyses.
2.0 METHOD SUMMARY
Source standard materials or solutions will be purchased from commercial suppliers and then combined and/or diluted by the analyst with solvent(s) or reagent(s) specified in the analytical methods. The standards will be prepared at the concentrations specified in the associated analytical methods or SOPs.
An internal identification control number or SERAS lot number will be assigned to each source material purchased from suppliers, stock standard solution, intermediate standard solution (if appropriate), surrogate spike solution, matrix spike solution, instrument performance check standard solutions, and calibration standard solutions. This number will be documented in the sample digestion log, sample extraction log, and instrument run (analysis) log for each standard used in the data collection process.
3.0 SAMPLE PRESERVATION, CONTAINERS, HANDLING AND STORAGE
This section is not applicable to this SOP. Standard storage will be discussed in Section 9.0.
4.0 INTERFERENCES AND POTENTIAL PROBLEMS
Solvent, reagents, glassware, syringes, and other handling hardware may introduce artifacts and/or interferences to standard solutions. Only high purity materials ($99%) should be used for preparing standards. Solvents used to prepare pesticide/PCB and semi-volatile standards must be pesticide residue analysis grade or equivalent; purge-and-trap grade solvent must be used to prepare volatile standards; trace metal grade acids must be used for metals standards.
Soap residue on glassware may cause degradation of certain analytes. Aldrin, heptachlor, and most organophosphorus pesticides in particular will degrade in this situation. All glassware and syringes must be properly rinsed with designated solvents before use. It is recommended that only designated glassware and syringes be used to prepare standards to avoid cross-contamination.
Chromic acid may be useful to remove organic deposits from glassware; however, the glassware must be thoroughly rinsed with deionized water to remove the last traces of chromium. This is especially important if chromium is to be determined.
5.0 EQUIPMENT/APPARATUS
Class A volumetric pipettes (assorted sizes)
Class A volumetric flasks with ground-glass stoppers (assorted sizes)
Microsyringes, gas-tight preferred (assorted sizes)
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PREPARATION OF STANDARD SOLUTIONS
The letter "P" will be used for all standards prepared for pesticide/PCB analysis. For example, P11100015 represents the 15th pesticide standard prepared on November 10, 2000.
A two letter code will be used for all standards prepared for metal analysis. The codes are as follows: MS - stock standard; MI - intermediate standard; MW - working standard; and MQ - QA/QC standard. For example, MQ represents the second metal QA/QC standard prepared on May 28, 2000.
The letter "T" will be used for all standards prepared for tissue analysis by the Special Projects Group. The "T" will be followed by an "S", "V", or "P" to further represent semivolatiles, volatiles and pesticide/PCB standards, respectively. For example, TS10030002 represents the second semi-volatile tissue standard prepared on October 3, 2000.
The lot number of each standard used for analysis must be entered in the standard preparation logbook, the label on the standard solution container, the sample digestion logbook, sample extraction logbook, and the instrument run (analysis) log. Due to multiple standards prepared for the pesticide/PCB and toxaphene analyses, a separate sheet documenting the standards used will be included in the data package.
7.1. Logbook
A standard preparation logbook must be used by each lab to document all information listed below.
Lot number assigned
Standard solution identification (such as BNA Cal Std)
Compounds in the solution (refer to as Mix A, Mix B, etc) or affix the actual label in the logbook. Final concentration of each compound in the solution
Lot number of the source
NOTE: If source material was purchased from commercial vendor, enter the vendor's name, lot number, and catalog number. Maintain the certificate shipped with standard ampoule in a logbook, or three-ring binder.
Volume or weight of source(s) used
Solvent or reagent used
Volume of solvent or reagent used
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PREPARATION OF STANDARD SOLUTIONS
Date of preparation
Signature of person preparing the standard
Expiration date of the standard
Signature and date of peer review
Comments, if necessary
7.1.3 Standard Solution Bottle
The following information must be transcribed to a logbook tracking preparation of the standard solution:
Lot number
Standard identification
Concentrations of the standards
Solvent used
Expiration date
Initials of chemist
7.2 Organic Standards
7.2.1 Standards for Volatile Analysis
- Log in all concentrated standard mixtures or individual standard(s) purchased from commercial vendors by following the procedures described in Section 7.1. A SERAS lot number must be assigned to each mixture or individual standard received.
- Determine the volumes of standard solutions to be prepared; calculate the dilution factor by using the equation provided in Section 8.0.
- Rinse all syringes and glassware with methanol to avoid cross-contamination. Make sure to rinse the plunger and the needle of the syringe and the stopper of the volumetric flask.
- Prepare the working 4-bromofluorobenzene (BFB) standard (50μg/mL) by the technique described below. A stock solution of 4-BFB in a methanol solution may also be purchased from a commercial vendor and used as a stock solution.
Fill the volumetric flask with methanol until it is approximately half full. Add the appropriate volume, precisely measured, of the stock BFB standard to the volumetric flask. Fill the flask with methanol so that the bottom of the solution meniscus lines up
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- Determine the volumes of standard solutions to be prepared; calculate the dilution factor by using the equation provided in Section 8.0.
- Rinse syringes and volumetric flasks with methylene chloride to avoid cross- contamination. Take care to rinse the plunger and the needle of the syringe and the stopper of the volumetric flask.
- Prepare the decafluorotriphenylphosphine (DFTPP) working standard using the technique described below or purchase from a commercial vendor.
Fill the volumetric flask with methylene chloride until it is approximately half full. Add the appropriate volume, precisely measured, of the concentrated DFTPP to the volumetric flask. Fill the flask with methylene chloride so that the bottom of the solution meniscus of the solution lines up with the mark on the neck of the flask. Stopper the volumetric flask and invert three times to mix well.
Transfer the solution to a clean amber glass bottle; label the bottle with information described in Section 7.1. A SERAS lot number must be assigned.
- Prepare the surrogate spike working solution by using the technique described below or purchase from a commercial vendor.
Fill the volumetric flask with acetone until it is approximately half full. Add the appropriate volume, precisely measured, of the base neutral and acid extractable concentrated standard mixtures into the volumetric flask. Fill the flask with acetone so that the bottom of the solution meniscus lines up with the mark on the neck of the flask. Stopper the volumetric flask and invert three times to mix well.
Transfer the solution into a clean amber glass bottle; label the bottle with information described in Section 7.1. A SERAS lot number must be assigned.
- Follow step 5 to prepare the matrix spike working solution. A source independent of calibration is used to prepare the matrix spike.
- A semi-volatile (BNA) stock standard solution (including surrogates) of 160 μg/mL will be prepared from concentrated standard mixtures purchased from commercial vendors. Alternatively, a 160 μg/mL base neutral and a 160 μg/mL acid extractable standard may be purchased from a commercial vendor and combined.
Transfer the solution to a clean amber glass bottle; label the bottle with information described in Section 7.1. A SERAS lot number must be assigned.
- Make various dilutions from the 160 μg/mL BNA standard to prepare the calibration standards. Each concentration level must be assigned a SERAS lot number. All documentation procedures described in Section 7.1 must be followed.
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7.2.3 Standards for Pesticide/PCB Analysis
- Log in all concentrated standard mixtures or individual standards purchased from vendors by following the procedures described in Section 7.1. A SERAS lot number must be assigned to each type of mixture and/or individual standard. These concentrated standard solutions will be used as stock solutions to prepare working standard solutions.
- Determine the volumes of standard solutions to be prepared; calculate the dilution factor by using the equation provided in Section 8.0.
- Rinse syringes and volumetric flasks with acetone followed by hexane to avoid cross contamination. Take care to rinse the plunger and the needle of the syringe and the stopper of the volumetric flask.
- Prepare surrogate spike working solution by following the technique described below.
Fill the volumetric flask with acetone until it is approximately one-third full. Add the appropriate volume of the concentrated stock standard purchased from the commercial vendor into the volumetric flask. Fill the flask with acetone so that the bottom of the solution meniscus lines up with the mark on the neck of the flask. Stopper the volumetric flask and invert three times to mix well.
Transfer the solution to a clean amber glass bottle; label the bottle with information described in Section 7.1. A SERAS lot number must be assigned.
- Follow step 4 to prepare matrix spike working solution using a separate source from that used for calibration.
- Prepare pesticide calibration standards by making various dilutions of the concentrated stock solutions purchased from commercial vendors.
Fill the volumetric flask with hexane until it is approximately one-third full. Add the appropriate volumes, precisely measured, of the concentrated pesticide standard mixture, alpha-chlordane standard, gamma-chlordane standard, and surrogate standard mixture purchased from the commercial vendor to the volumetric flask. Fill the flask with hexane so that the bottom of the solution meniscus lines up with the mark on the neck of the flask. Stopper the volumetric flask and invert three times to mix well. Transfer the solution to a clean amber glass bottle; label the bottle with information described in Section 7.1. A SERAS lot number must be assigned to each concentration level prepared.
- Prepare toxaphene calibration standards by making various dilutions of the concentrated stock solution purchased from the commercial vendors.
Fill the volumetric flask with hexane until it is approximately one-third full.
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information described in Section 7.1. A SERAS lot number must be assigned.
- Transfer the remaining stock standard solutions to vials lined with Teflon. Store in the refrigerator.
7.3 Inorganic Standards
- Log in all concentrated standard solutions or individual element standards purchased from commercial vendors by following the procedures described in Section 7.1. A SERAS lot number must be assigned to each type of mixture and/or individual element standard. These concentrated standard solutions will be used as stock solutions to prepare intermediate solutions.
- Determine the volumes of standard solutions to be prepared; calculate the dilution factor by using the equation provided in Section 8.0.
- Rinse volumetric flasks and pipettes with 10% nitric acid, followed by deionized water.
- Intermediate Standard Solutions
Fill approximately one-tenth of the volumetric flask with deionized water; add an appropriate volume of concentrated nitric acid to produce 5% HNO 3 at final volume; add the appropriate volume of the concentrated stock solution. Fill the flask with deionized water so that the bottom of the solution meniscus lines up with the mark on the neck of the flask. Stopper the volumetric flask and invert three times to mix well.
NOTE: Use the appropriate volumes of concentrated nitric and hydrochloric acids for mixed-acid standards.
Transfer standard solutions to high density polyethylene bottles; label the bottle with the information described in Section 7.1. Assign a SERAS lot number to each stock or intermediate solution.
- Secondary Standard Solutions
The secondary standard solution will be prepared from the intermediate standard solution for AA analysis. Follow the procedure described in step 4. Assign a SERAS lot number for each concentration level prepared.
- Working Standard Solutions
For furnace AA analysis, the working standard solution will be automatically prepared by the instrument during analysis by serially diluting the secondary standard solution.
For flame AA or ICP analysis, the working standard solutions are prepared from the intermediate standard by the analyst following the technique described in step 4.
All working standard solutions are only prepared when needed in very small quantities. To ensure the traceability of standards used for all sample analyses, the following
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PREPARATION OF STANDARD SOLUTIONS
information must be documented on the instrument printouts or calibration log sheets: the source lot number and the preparation date of the working standards. The signature of the chemist who prepared the working standard solution for AA or ICP analysis must also be documented.
- Quality Control Standard (QCS)
Concentrated QCS will be purchased from commercial vendors. The preparation procedures specified by the vendor will be followed. A SERAS lot number must be assigned to the working QCS. All documentation requirements described in Section 7. must be followed at all times.
8.0 CALCULATIONS
The following equation can be used to prepare diluted standard solutions.
C 1 V 1 = C 2 V (^2)
where,
C 1 = concentration of analyte in the stock or intermediate standard solution to be diluted V 1 = volume of stock or intermediate standard to be used C 2 = final concentration of the standard solution to be prepared V 2 = total volume of the standard solution to be prepared
EXAMPLE: If 10 mL (V 2 ) of a 2-μg/mL (C 2 ) standard will be prepared from a 20-μg/mL (C 1 ) stock or intermediate standard, the volume of the stock or intermediate standard to be withdrawn can be calculated by using the above equation:
20 μg/mL (C 1 ) x V 1 = 2 μg/mL (C 2 ) x 10 mL (V 2 )
V 1 = (2 μg/mL x 10 mL)/20 μg/mL = 1 mL
To prepare the 2-μg/mL solution, 1 mL of the 20-μg/mL standard will be added into a 10-mL volumetric flask which contains approximately one-third of the proper solvent or reagent. The proper solvent or reagent will be added to the mark and mixed well.
9.0 QUALITY ASSURANCE/QUALITY CONTROL
- All standards must be documented in the standard logbook with information specified in Section 7.1.
- Peer review must be conducted on every entry in the logbook for correctness in content and concentration. When each page of the standard logbook is filled out, the analyst must bring the logbook to the Group Leader for signature. In some cases, the peer and the Group Leader may be the same individual.
- All standards purchased from commercial suppliers must be verified for content and concentration
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U.S. Environmental Protection Agency. September 1986. Office of Solid Waste and Emergency Response, Test Methods of Evaluating Solid Waste, Third Edition, SW-.
U.S. Environmental Protection Agency. May 1999. Contract Laboratory Program, Statement of Work for Organic Analysis, Multi-Media, Multi-Concentration , Document Number OLM04.2.
U.S. Environmental Protection Agency. Contract Laboratory Program, Statement of Work for Inorganic Analysis, Multi-Media, Multi-Concentration , Document Number ILM04.0.
