Holding Time & Preservation
EPA received many questions about hazardous waste test methods. The questions and responses for this category are listed below.
On this page:
- For SW-846 Method 1311, what are the holding times for the samples before leaching, the leachates before extraction, and the extracts before analysis?
- What are the preservation requirements for the leachates in Method 1311?
- What is the suggested holding time for a sample before performing the SW-846 methods?
- What is the current holding time for samples collected in the EnCore sampler and analyzed using SW-846 Method 5035?
- Holding time and preservation requirements for volatile organics analysis (VOA).
- Can H3PO4 be used for preservation for SW-846 Method 9060A?
- Low recovery of styrene and several other compounds in soil volatile organic analyte samples, likely caused by the bisulfate preservative.
- What is the EPA’s position with regard to extending a holding time for frozen soil samples?
- When an SW-846 method describes a holding time as "expires in 7 days", how is this holding time interpreted?
- What is the holding time for soil samples analyzed for hexavalent chromium by SW-846 Method 7196A?
- Use of preservatives for analysis of vinyl chloride or styrene using SW-846 Methods 5030/8260.
- Does ORCR observe the same holding time and preservations for SW-846 Method 7199 for hexavalent chromium allowed under 40 CFR 136?
- Can you provide more definitive guidance regarding the interpretation of “as soon as possible” in Methods 9040 and 9045?
- Holding time for SW-46 Method 8141B for organophosphorus pesticides.
- What is the recommended holding time for SW-846 Method 8082 for PCBs for aqueous, soil, and oil matrices?
- Is there a reference by EPA or others that addresses that no more than either 1% or 10% of a chemical preservative should be used when sampling liquid media?
- What is the recommended holding time for nitrate in soil, which is not addressed in SW-846 Chapter 3 or Method 9056A?
- Are the SW-846 Method 8330B Appendix A drying, sieving, and crushing steps included in the 14 day holding time?
- Where can I find information on sample holding times, preservation, and storage in SW-846?
- Differences in quality control (QC), preservation, and holding time recommendations among SW-846 parts.
For SW-846 Method 1311, what are the holding times for the samples before leaching, the leachates before extraction, and the extracts before analysis?
A table in Sec. 8.5 of Method 1311 indicates:
Sample must undergo TCLP within the following time periods:
SAMPLE MAXIMUM HOLDING TIMES [DAYS]
| From: Field Collection: To: TCLP Extraction |
From: TCLP Extraction To: Preparative Extraction |
From: Preparative Extraction To: Determ. Analysis |
Total Elapsed Time | |
|---|---|---|---|---|
| Volatiles | 14 | NA | 14 | 28 |
| Semi-volatiles | 14 | 7 | 40 | 61 |
| Mercury | 28 | NA | 28 | 56 |
| Metals, except Mercury | 180 | NA | 180 | 360 |
NA: Not Applicable
For the leachate that will be analyzed for organics (including volatiles, semivolatiles, and the herbicides), you have 14 days from the collection of the original sample until you have to start the leaching (extraction). For the metals, you have 180 days from collection until leaching, except for mercury, where leaching must start within 28 days.
The herbicides are grouped with the "semivolatiles" in Sec. 8.5 of the method, since both types of analytes are extracted with an organic solvent. The extractions of the semivolatiles and herbicides from the leachate must start within 7 days of the completion of the leaching procedure.
The determinative analyses for the semivolatiles and herbicides must be completed within 40 days of the completion of the solvent extractions. The determinative analyses for the volatiles must be completed within 14 days of the completion of the leaching procedure.
The determinative analyses for the metals must be completed within 180 days of the completion of the leaching procedure, except for mercury, where analyses must be completed within 28 days of the completion of the leaching procedure.
Other Category: Hazardous Waste Characteristics
What are the preservation requirements for the leachates in Method 1311?
As noted in Secs. 6.3 and 6.4 of Method 1311 (the Toxicity Characteristic Leaching Procedure), chemical preservatives shall not be added to samples before leaching. However, the samples may be refrigerated, unless refrigeration will result in irreversible physical changes to the waste.
According to Sec. 6.6, once leached, the portion of the leachate for the metals analyses must be acidified with nitric acid to a pH < 2, unless precipitation occurs, in which case, consult Sec. 7.2.14 of the method for instructions.
The portions of the leachate to be analyzed for the organics must be preserved as described in the individual determinative methods. For volatiles, there is generally no need for further acidification, since the leachate is already at a pH below 7, which should retard any biological activity in the leachate. The portions of the leachate for volatiles, semivolatiles, and herbicides analyses must be stored with minimal headspace at 4° C.
Other Category: Hazardous Waste Characteristics
What is the suggested holding time for a sample before performing the SW-846 methods?
The recommended holding time for a sample before performing any of the SW-846 methods depends on the specific constituents, matrix, and type of sample to be tested. Certain constituents in waste can degrade faster than others, such as volatile organic compounds. General guidelines for holding times are outlined in the appropriate tables of Chapters 2, 3 and 4 of SW-846 however, the selection of preservation techniques and applicable holding times should be based on all available information, including the properties of the analytes of interest for the project, their anticipated concentration levels, the composition of the sample matrix itself, and the stated project-specific Data Quality Objectives (DQOs). Many preparation and determinative methods provide more definitive guidance for holding times and supersede the general guidance provided in Chapters 2, 3, and 4.
An example of the impact of exceeding the holding time is shown for TCLP Method 1311. When sample holding times are exceeded, the TCLP analytical results will be considered the minimum amount that could leach from the waste. An identical sample analyzed from the same waste within hold time might yield higher concentrations of toxicity characteristic constituents. If a sample exceeds recommended holding time and analysis demonstrates that concentrations are above the regulatory threshold for one or more constituents, then these concentrations can be treated as minimum values and the waste is hazardous for the toxicity characteristic. No further testing is required. If, on the other hand, a sample exceeds a recommended holding time and analysis demonstrates that concentrations are below the regulatory threshold for one or more constituents, further testing will be necessary to demonstrate that the waste is nonhazardous.
What is the current holding time for samples collected in the EnCore sampler and analyzed using SW-846 Method 5035?
The Office of Resource Conservation and Recovery's (ORCR) reviewed data from the manufacturer of the EnCore device. Those data suggested that samples could be held in the EnCore device for 48 hours without significant loss of volatile analytes. Subsequent data for freezing samples in the EnCore sampler also indicates a 48-hour limit without significant loss. As noted in Sec. 8.2.1.8 of Method 5035A, samples may be held for up to 48 hours before analysis, or before transfer to the glass vials used for the closed-system purge-and-trap device in the method. The overall holding time for the sample remains 14 days from collection to analysis. The same considerations apply to Methods 5021, 5032, and 8261 with respect to the EnCore sampler.
Other Category: Sampling
Holding time and preservation requirements for volatile organics analysis (VOA).
SW‐846 Chapter 4 recommends that for aqueous samples for 5030/8260 VOA when analysis for vinyl chloride and styrene are target compounds, an unpreserved vial be used and the holding time becomes within 7 days of collection. Our lab routinely analyzes aqueous MS/MSD samples from a large variety of sources (effluents, groundwater, surface water, etc.) that are preserved at a pH <2 with HCl with recoveries for these compounds well within 70‐130 percent. Because we typically spike the MS/MSD samples less than 48 hours from analysis we don’t have long-term stability data of these two compounds in preserved vials. Field samples are collected in 2 preserved vials and 2 unpreserved vials and we have analyzed samples that have detections of vinyl chloride and styrene from both preserved and unpreserved vials with statistically similar results.
The previous version of SW-846 Chapter 4 Table 4-1 recommended, for aqueous samples with no residual chlorine present, that "If vinyl chloride, styrene, or 2‐chloroethyl vinyl ether are analytes of interest, collect a second set of samples without acid preservatives and analyze as soon as possible."
In Update V, Chapter 4 (July 2014 rev 5) Table 4-1, that same recommendation was revised to "If compounds that readily degrade in acidified water (e.g., 2‐chloroethyl vinyl ether) are analytes of interest, collect a second set of samples without acid preservatives and analyze as soon as possible."
The reason for this change followed discussion in the Workgroup regarding the requirement of a second set of unpreserved vials for analysis of styrene and vinyl chloride. Stability studies were conducted and the stability data for vinyl chloride and styrene were felt to be reasonably comparable by the group. Therefore, the Workgroup dropped the unpreserved requirement for those two compounds, but not for 2‐chloroethylvinyl ether, as the study data did not address 2‐chloroethylvinyl ether. It is still the recommended guidance that unpreserved samples be run for 2‐chloroethylvinyl ether.
Other Category: 8000 series
Can H3PO4 be used for preservation for SW-846 Method 9060A?
Method 9060A states, “In instances where analysis cannot be performed within 2 hr from time of sampling, the sample is acidified (pH < 2) with HCl or H2SO4.” However, our instrument manufacturer recommends using H3PO4 for preservation. Can H3PO4 be used for preservation for Method 9060A?
Method 9060A is on the list of method defined parameters (MDPs). Therefore, it must be followed exactly as written without deviation, even if substituting H2SO4 with H3PO4 is recommended by the instrument manufacturer. That being said, you can always seek permission for the substitution from your regulator or client. It will be rare that they grant permission, but depending on the circumstances for using the method, they may allow it. Be prepared to show equivalency data that the substitution works.
Other Category: 9000 Series
Low recovery of styrene and several other compounds in soil volatile organic analyte samples, likely caused by the bisulfate preservative.
We have observed low recovery of styrene and several other compounds in some soil VOA samples. After conducting some research, we found that the sodium bisulfate preservative is likely to be responsible for the low recoveries.
Chapter 4 – Table 4‐1 of SW‐846 recommends that a second set of samples without acid preservatives be collected and analyzed as soon as possible if the compounds (e.g., vinyl chloride, styrene, and 2-chloroethyl vinyl ether) are analytes of interest. EPA 5035 does not provide another preservation option, aside from sodium bisulfate, for low concentration soil method unless the sample is effervescent.
An updated Method 5035A (Draft Revision 1, July 2002) is available and posted on the “Validated Test Methods Recommended for Waste Testing” page. The information provided in Appendix A of Method 5035A was based on EPA’s evaluation of currently available data and technology as applied to the most appropriate sample handling and preservation procedures in order to minimize the loss of volatile organic compounds (VOCs) during the collection and analysis of aqueous and solid materials. The intended users of this Appendix guidance are those individuals and organizations involved in the collection and preparation of samples for VOC analyses during the characterization of solid materials under the Resource Conservation and Recovery Act (RCRA). See Appendix A for guidance on selecting an appropriate sample collection and preservation technique that are suitable for VOC analyses to meet the data quality requirements or objectives for the intended use of the results.
Table A-1 in Appendix A of 5035A recommends VOC Sample Preservation Techniques and Holding Times with a variety options using physical and chemical preservations and compound applicability.
Ultimately, holding times and preservation requirements are typically set by the regulator or data user in a project-specific QAPP.
Other Category: 8000 series
What is the EPA’s position with regard to extending a holding time for frozen soil samples?
What is the EPA’s position with regard to extending a holding time for frozen soil samples? For example, can the holding time be extended to one year for PAHs by SW-846 8270?
Table 4‐1 in Chapter 4 of SW‐846 presents the holding times recommendations for the EPA Office of Resource Conservation and Recovery (ORCR) with respect to organic analytes by SW‐846 methods. Footnote "a" of Table 4‐1 states: “The information presented in this table does not represent EPA requirements, but rather it is intended solely as guidance. Selection of containers, preservation techniques and applicable holding times should be based on the stated project specific data quality objectives.”
Alternative preservation and/or holding times are difficult to apply universally. A study using archived samples can be performed (for example) but the conclusions are very likely to be applicable only to the actual samples included in the study.
It is important to note that other federal and state government agencies may impose additional sample storage and holding time requirements than the ones recommended in SW‐846 Chapters 3 [for inorganics] and 4 [for organics] and specific methods [e.g., Method 8270D for semivolatiles] for their program or project use and needs.
Laboratories should consult data users and adhere to the sample storage and holding time requirements stipulated in the project QA plans to ensure generated data meets specific program and/or project needs.
When an SW-846 method describes a holding time as "expires in 7 days", how is this holding time interpreted?
When the method describes a holding time as "expires in 7 days", how is this holding time interpreted (i.e., does the holding time expire on the 7th day at 23:59 or on the 7th day at collection time)?
Holding times should be from the documented time a sample was collected, not based on midnight of the last day. For example, if a semivolatile water sample (with a holding time of 7 days) was taken at 8:30 am on Tuesday, October 15, 2013, then the laboratory can extract that sample at any time up until 8:30 am on Tuesday, October 22, 2013 and be considered within the method's holding time.
Holding times are distinctions in the methods to try to reduce the effect of degradation on the results due to analyte decomposition, reaction, evaporation and any number of other effects of time on a sample matrix. However, a line has to be drawn somewhere for unacceptable losses and the method's holding time represents the best data available as to when the analysis is still completely valid. If an exact sample collection time is known, then the exact time should be used in calculating the holding times. If the collection time is recorded to the hour, the holding time should be interpreted to the hour. If the collection time is recorded to the hours and minutes, the holding time should be interpreted to the hours and minutes.
Ideally, laboratories should try to do the required preparation steps (i.e., extraction, digestion, etc.) in advance of the hold time's expiration so as to avoid hold time problems.
What is the holding time for soil samples analyzed for hexavalent chromium by SW-846 Method 7196A?
What is the holding time for soil samples analyzed for hexavalent chromium by Method 7196A? The method appears to say 24 hours; however, I understand that there is guidance in the SW‐846 manual that the holding time is 30 days to extraction and then 7 days from extraction to analysis.
Method 7196A is used to determine the concentration of dissolved hexavalent chromium in TCLP extracts and ground waters for which the hold time is 24 hours as the method specifies. These types of samples are not stable and need to be analyzed more quickly. However, for soils there is a separate extraction step before the analytical steps described in 7196A. The extraction method gives a more stable extract than groundwater or a TCLP extract, hence the holding time can be longer before analysis. The extraction method is 3060A where Section 6.4 says, "hexavalent chromium has been shown to be quantitatively stable in field moist soil samples for 30 days from sample collection. In addition Cr(VI) has also been shown to be stable in the alkaline digest for up to 168 hours (7 days) after extraction from soil." Guidance is also given in SW-846 Chapter 3, Table 3-2 where it says aqueous samples have a holding time of 24 hours and solids have 30 days to extraction and 7 days from extraction to analysis.
In summary, for waters or TCLP extracts, the holding time is 24 hours to analyze by Method 7196A or Method 7199. For soils, the holding time is up to 30 days from sample collection before extracting by Method 3060A, then up to another 7 days to analyze the 3060A extracts by Method 7196A (colorimetric) or Method 7199 (ion chromatography).
Other Category: Inorganic
Use of preservatives for analysis of vinyl chloride or styrene using SW-846 Methods 5030/8260.
SW‐846 Chapter 4 recommends that aqueous samples for 5030/8260 VOA when analysis for vinyl chloride and styrene are target compounds, an unpreserved vial is used and the holding time becomes within 7 days of collection. Our lab routinely analyzes aqueous MS/MSD samples from a large variety of sources (effluents, groundwater, surface water, etc.) that are preserved at a pH <2 with HCl with recoveries for these compounds well within 70‐130 percent. Because we typically spike the MS/MSD samples less than 48 hours from analysis we don’t have long-term stability data of these two compounds in preserved vials. Field samples are collected in 2 preserved vials and 2 unpreserved vials and we have analyzed samples that have detections of vinyl chloride and styrene from both preserved and unpreserved vials with statistically similar results.
For aqueous samples with no residual chlorine present, the previous version of SW-846 Chapter 4 Table 4‐1 recommended that "If vinyl chloride, styrene, or 2‐chloroethyl vinyl ether are analytes of interest, collect a second set of samples without acid preservatives and analyze as soon as possible."
In Update V, Chapter 4 (July 2014 rev 5), that same recommendation was changed to "If compounds that readily degrade in acidified water (e.g., 2‐chloroethyl vinyl ether) are analytes of interest, collect a second set of samples without acid preservatives and analyze as soon as possible."
The reason for this change followed discussion in the Workgroup regarding the requirement of a second set of unpreserved vials for analysis of styrene and vinyl chloride. Stability studies were conducted and the stability data for vinyl chloride and styrene were evaluated by the group. Based on the available information and the stability results, the Workgroup dropped the unpreserved requirement for those two compounds (i.e., styrene and vinyl chloride), but not for 2‐chloroethylvinyl ether, as the study data did not address 2‐chloroethylvinyl ether. It is still recommended that unpreserved samples be run for 2‐chloroethylvinyl ether.
Does ORCR observe the same holding time and preservations for SW-846 Method 7199 for hexavalent chromium allowed under 40 CFR 136?
There appears to be a discrepancy in EPA 7199 Revision 0 for analysis of hexavalent chromium. The method and Chapter Three of SW-846 both state that the hold time is 24 hours, yet the method indicates the use of a preservative to achieve a pH of 9‐9.5. 40 CFR Chapter 136 allows the use of EPA 218.6 in which using a buffer and adjusting the pH to 9.3‐9.7 extends the hold time to 28 days. The fact that 7199 mentions the buffer but then does not extend the hold time seems like an error. Does the Office of Resource Conservation and Recovery observe the same holding time and preservations for hexavalent chromium allowed under 40 CFR 136?
The holding times and sample preservation information found in SW-846 Chapter 3 and Method 7199 are intended as guidance. Holding times and preservation requirements a lab has to follow are typically set by data users (e.g., a regulator) or specified in a project-specific QAPP. They may specify the method be followed exactly as written, or they may allow the 28-day hold time mentioned in footnote 20 in 40 CFR Part 136.3, Table II to be followed. The footnote is reproduced below but it contains a caveat that prevents the use of the 28 day holding time as a default value in all circumstances:
"20To achieve the 28-day holding time, use the ammonium sulfate buffer solution specified in EPA Method 218.6. The allowance in this footnote supersedes preservation and holding time requirements in the approved hexavalent chromium methods, unless this supersession would compromise the measurement, in which case requirements in the method must be followed."
The caveat "unless this supersession would compromise the measurement" is important and some would argue it's intention is to use the shorter hold-time guidance in 7199 or shorter hold time specification in 218.6 unless it is proven that the longer hold time does not compromise the measurement for samples from a given site. This proof would require analyzing an aliquot of sample(s) from a site within the shorter hold time, then rerun another aliquot of the same samples later within the longer hold time and see if they had any significant change. If there is no change, the longer holding time would be acceptable. If there is a change, the laboratory is in a precarious situation if they used the longer holding time for the reported samples (i.e., the data would have to be qualified, and possibly rejected). A regulator, data user, or QAPP may choose the safest approach and just specify the shorter hold times.
Other Category: Inorganic
Can you provide more definitive guidance regarding the interpretation of “as soon as possible” in Methods 9040 and 9045?
Methods 9040 and 9045 for pH both say that samples should be analyzed as soon as possible. 40 CFR 136 Table II defines the maximum holding time for Hydrogen ion (pH) as 15 minutes.
Can you provide more definitive guidance regarding the interpretation of “as soon as possible”?
Methods 9045D and 9040C can be done in the field, but often field conditions cannot be controlled and may be unfavorable for accurate analyses. The methods are generally meant to be used in a laboratory setting under controlled conditions.
Because of potential changes from microbial activity, or shifts in chemical equilibrium, sample pH should be taken as soon as possible upon receipt at the laboratory. It is expected pH of collected samples would be analyzed within a few hours of laboratory receipt, and not the next day. The method is written to be followed sequentially with no undue delay between steps, except for the one hour settling time for soils in Section 7.2.2 or 15 minutes settling time for wastes in Section 7.3.2 of 9045D. Also, keep in mind that Methods 9045D and 9040C are Method Defined Parameter (MDP) methods that must be followed exactly as written with no modifications.
The holding time of "Analyze as soon as possible" is not clearly defined for SW-846, but is only recommended as a qualitative goal. In 2007, the definition for “immediately” was established as 15 minutes for the NPDES Program (40 CFR 136, Table II), however, that does not apply to the RCRA program and SW-846. Even though SW-846 Method 9040C (and Method 9045D) are MDP methods and must be followed prescriptively, Section 6.0 of Method 9040C on holding time is not prescriptive. The method authors recognized changes in pH begin as soon as a sample is put into a container and specified that samples should be analyzed as soon as possible. If they meant to analyze by an exact time, the method authors would have put that time into the method. Instead, they left it up to the user to do what is feasible as soon as possible. SW-846 also makes a distinction between "must" or "shall" language that is mandatory, as opposed to guidance language like "should" or "may". Note that Section 6.0 of Method 9040C uses the word "should".
The actual holding time for pH analysis should be specified in the quality assurance plan under which the sample was collected and agreed‐upon by all stakeholders involved, including those who have to measure the pH (be it in the laboratory or in the field). In the laboratory, we recommend performing the analysis within a few hours of receipt, and not the next day.
Other Categories: 9000 Series, Characteristics
Holding time for SW-46 Method 8141B for organophosphorus pesticides.
The SW-846 method 8141B for Organophosphorus pesticides looks to have added a requirement for 7 day holding times for solids. This appears to be a change in practice over what’s been accepted previously as a 14 day holding time.
Method 8141B (Rev 2, February 2007), posted online, states in Section 8.4 "Begin extraction of either aqueous or solid samples within 7 days of collection."
This is much more specific than the language in 8141A, which only referenced Chapter 4 and gave a 48-hour requirement for the derivatization of extracts. From the lack of specificity in earlier versions, we can see where laboratories might have assumed 14 days was the hold time as it was not spelled out clearly one way or the other in 8141A or Chapter 4 regarding organophosphorus pesticides.
Table 4-1 in Chapter 4 (Rev 5, October 2012) addresses the holding times for organochlorine pesticides and semivolatiles, but not for organophosphorus pesticides. The reason Method 8141B calls for lowering the hold time for this specific group of target compounds was based on a study (by D. J. Munch, and C. P. Frebis, on "Analyte Stability Studies Conducted during the National Pesticide Survey," ES & T, 1992, Vol 26, 921-925), cited as Reference 12 in the method. This study showed that the organophosphorus pesticides were not stable, with many compounds degrading before the 14-day hold time would have taken place.
Section 9.1 of 8141B states: "When inconsistencies exist between QC guidelines, method-specific QC criteria take precedence over both technique-specific criteria and those criteria given in Chapter One, and technique-specific QC criteria take precedence over the criteria in Chapter One." Therefore, the determinative method's criteria would supersede the general guidance in Chapter 4. Therefore, all samples for Method 8141B (both soils and waters) need to be extracted within 7 days to be considered acceptable.
Other Category: 8000 Series
What is the recommended holding time for SW-846 Method 8082 for PCBs for aqueous, soil, and oil matrices?
40 CFR 136 specifies a one-year holding time for PCBs. SW-846 Chapter 4 states “none”.
What is the recommended holding time for Method 8082 for the aqueous, soil, and oil matrices?
SW-846 gives "Recommended Holding Times" in Chapter Four of the SW-846 Compendium: Organic Analytes, Table 4-1.
Footnote "a" of Table 4.1 states: "The information presented in this table does not represent EPA requirements, but rather it is intended solely as guidance. Selection of containers, preservation techniques and applicable holding times should be based on the stated project-specific data quality objectives." Therefore, if the samples were not collected for CWA compliance (40 CFR 136), the hold time for PCBs is usually specified in a site-specific QAPP. Many QA/QC programs, QAPPs, and laboratories usually default to the recommended holding times for SVOCs (7 days water, 14 days soil from sample collection to extraction, and 40 days from extraction to analysis).
It is important to note that PCBs are quite stable compounds in environmental and waste samples, and a holding time prior to extraction of the sample may not be warranted. However, once extracted, it is advisable to analyze the sample within 40 days because, while the PCBs will likely not degrade, the solvent could evaporate over time, biasing the result high.
Other Category: 8000 Series
Is there a reference by EPA or others that addresses that no more than either 1% or 10% of a chemical preservative should be used when sampling liquid media?
There is no known reference that specifically addresses that issue or sets a limit. There are so many preservation situations, depending on the analyte, the method, and the sample matrix, it would be difficult to make a general statement that would be valid for every case or even many cases. There may be cases where more than 10% of a preservative by volume may be needed to reach a particular state. For example, alkaline wastes may need more than 10% by volume of acid to reach a desired pH for metals preservation.
However, in all situations, good laboratory practices should be followed to record the actual amount, type, and concentration of preservative used in any study. That way, dilutions due to preservative can be corrected, and method blanks can be prepared with the same amount of preservative. The data quality objectives (DQOs) of the study at hand will dictate whether the dilutions need to be corrected or if the dilutions due to preservative addition can be ignored.
What is the recommended holding time for nitrate in soil, which is not addressed in SW-846 Chapter 3 or Method 9056A?
SW-846 Chapter 3 and Method 9056A don’t address holding time for nitrate in soil; what is the recommended holding time?
If nitrogen speciation in soil is needed (i.e., nitrite and nitrate), it is important to analyze as soon as possible because of the possibility of conversion from nitrite to nitrate. Microbial activity can cause changes over time.
Method 9056A is not clear on the holding time for solid matrices. Some holding times for solids are based simply on holding times for aqueous matrices (e.g., metals holding time for soils and waters is 180 days) and others are based on assumptions about constituent stability in solid versus aqueous matrices (e.g., holding time to extraction for semivolatile organic compounds is 7 days for waters and 14 days for soils).
For analysis of nitrogen as nitrate using either SW‐846 Method 9056 or EPA Methods for the Chemical Analysis of Water and Waste (MCAWW) Method 300.0, a holding time not to exceed 48 hours from collection through extraction and analysis for speciation of inorganic nitrogen is recommended, considering that nitrogen species conversion can happen relatively quickly regardless of the matrix.
Other Category: 9000 Series
Are the SW-846 Method 8330B Appendix A drying, sieving, and crushing steps included in the 14 day holding time?
Method 8330B says that the holding time is the same as semivolatiles, which SW-846 Chapter 4 lists as 14 days from sample collection. Are the 8330B Appendix A drying, sieving, and crushing steps included in the 14 days or does the 14 days start after the sample is dry?
If you have to follow the method prescriptively, the drying, crushing, and sieving parts of the sample preparation would need to be completed within 14 days; prior to the extraction phase of the preparation. When the extraction begins, the 14-day hold time clock stops. We realize that this presents a problem for 8330B, as the potentially explosive samples must be dried at room temperature.
Reference 17 from 8330B may be useful as it discusses the drying, crushing and sieving parts, and it includes information on a holding time study. The data in that reference, at least for the compounds chosen, indicates that the 14-day hold time is not an issue. We advise to seek guidance for your holding time question from your regulator or data user (e.g., DoD).
Using the performance-based approach and methods innovation rule (MIR) with Method 8330B, if you can demonstrate a longer hold time is supported for your compounds of interest on representative samples for your study, then your regulatory agency may allow a longer period of time to complete sample preparation before extraction.
Other Category: 8000 Series
Where can I find information on sample holding times, preservation, and storage in SW-846?
Where can I find information on sample holding times, preservation, and storage in SW-846?
SW‐846 provides general guidance on holding times, preservation, and storage container materials on Table 3‐1 in Chapter Three of the SW-846 Compendium: Inorganic Analytes and in Chapter Four of the SW-846 Compendium: Organic Analytes, Table 4-1.
In many cases, the individual methods provide more specific guidance on preservation and holding time that supersedes the guidance in the chapters.
Differences in quality control (QC), preservation, and holding time recommendations among SW-846 parts.
When there are differences in the quality control (QC) recommendations between Chapter One, a general method (e.g. 8000), and a determinative method (e.g. 8082), what is the proper precedence? Would recommendations for preservation and holding time follow the same precedence as QC?
The precedence for holding time and preservation is the same as that for QC. According to Chapter Two of SW-846, QC guidance specific to a given analytical technique (e.g., extraction, cleanup, sample introduction, or analysis) may be found in general methods 3500, 3600, 5000, 7000, and 8000.
When inconsistencies exist between the information in a chapter, a general method, or a specific method, method-specific QC criteria take precedence over both criteria found in the general method and those criteria given in Chapter One. QC criteria in general methods take precedence over the criteria in Chapter One.
Other Categories: QA/QC, General