New Method for Particulate Carbon and Particulate Nitrogen
In Reply Refer To:
Mail Stop 412 June 1, 2000
Office of Water Quality Technical Memorandum 2000.08
Subject: New Method for Particulate Carbon and Particulate Nitrogen
Starting June 1, 2000, the National Water Quality Laboratory (NWQL) offers
a new, high-temperature combustion method (USEPA 440.0) for the
determination of particulate (suspended) carbon and particulate (suspended)
nitrogen in water. The analytes determined by method 440.0 are total
particulate carbon (TPC), particulate inorganic carbon (PIC), particulate
organic carbon (POC), and total particulate nitrogen (TPN). The POC
fraction determined by method 440.0 will replace the previous,
wet-oxidation method--TWRI method O-7100-83 (parameter and method codes
00689 A; NWQL lab code 305--for suspended organic carbon (SOC). New
filtration options for processing samples collected for dissolved organic
carbon (DOC) determinations--TWRI method O-1100-83 (parameter and method
codes 00689 A; NWQL lab code 305--will also become available. Changes in
terminology required by the new method are listed below.
*NOTE:
The required GF/F glass fiber filters have not reached the NWQL as of June
1, 2000. Last minute refinements to the Teflon filtering unit design have
delayed delivery of this piece of equipment, but all required supplies
should be available by mid-June, 2000.
Definitions:
1. TPC--parameter and method codes 00694 A; NWQL lab code 2606. All
organic and inorganic carbon retained on the GF/F, glass fiber filters used
to process samples for USEPA method 440.0 are included in the TPC fraction.
TPC is a direct determination.
2. PI--parameter and method codes 00688 A; NWQL lab code 2608. All
inorganic carbon that remains on GF/F, glass fiber filters after organic
carbon has been removed by thermal fractionation are included in the PIC
fraction. PIC is a direct determination.
3. POC--parameter and method codes 00689 B; NWQL lab code 2611. The POC
fraction is the calculated difference between the TPC and PIC fractions
(POC = TPC -- PIC).
4. SOC--parameter and method codes 00689 A; NWQL lab code 305. This was
the NWQL's routine method for SOC. SOC is defined as Organic carbon
retained by silver membrane filters (0.45 micrometer (um) nominal pore
size) after the inorganic fraction has been removed by acidification and
purging with a stream of oxygen. This method will be run only on a custom
basis at NWQL after September 30, 2000.
5. TPN--parameter code (pending) and method code A; NWQL lab code 2607.
All organic and inorganic nitrogen retained on the GF/F, glass fiber
filters used to process samples for USEPA method 440.0 are included in the
TPN fraction. TNP is a direct determination.
In principle, TPN concentration corresponds to the difference between
Kjeldahl nitrogen concentrations determined for a whole-water and
filtered-water sample pair. At present, however, there is
insufficient data to permit replacement of Kjeldahl nitrogen
determinations with TPN determinations. Guidance on using TPN data
will be issued early in calendar year 2001 after statistical analysis
of TPN data collected over the next six months.
6. DOC--Direct measurement of organic carbon in filtrates that pass
through 0.45 um silver membrane filters, 0.45 um Gelman Supor-- capsule
filters, or 0.7 um GF/F glass fiber filters. There is no significant
difference among results using any of these three filters. Samples
processed with each filter will, however, have a separate method code to
document the method used. New method codes for these filtration options
are tabulated below.
|-----------------------------+-----+-------------+-------|
| | Lab | ParameterCod| Method|
| Parameter | Code| e | Code |
|-----------------------------+-----+-------------+-------|
| DOC, silver filter | 113 | 00681 | A |
|-----------------------------+-----+-------------+-------|
| DOC, Supor filter, acid |2612 |00681 | D |
| preserved | | | |
|-----------------------------+-----+-------------+-------|
| DOC, GF/F filter, acid | 2613| 00681 | C |
| preserved | | | |
|-----------------------------+-----+-------------+-------|
On October 1, 2000, the NWQL will change laboratory and method codes for
DOC determinations from 113 A to 2612 D on all standard schedules that
include DOC determination. All three DOC lab codes will continue to be
available, however, at the request of the projects.
Why the change?
The need for these new methods was prompted by the difficulty to obtain
silver filters from the sole supplier. The increasing price and decreased
availability of these filters prompted a request from the Office of Water
Quality (OWQ) to the Methods Research and Development Program (MRDP) at
NWQL to investigate alternatives to the silver filter for processing
organic carbon samples. The new methods announced in this memorandum are
the result of this investigation. The MRDP program, in close cooperation
with the Carbon Unit at the NWQL, has adapted this USEPA approved method
for use at the NWQL. Performance validation of USEPA method 440.0 has been
successfully completed and parameters included in method 440.0 can now be
routinely requested at the NWQL.
Description of the method:
At collection sites, sample volumes (typically between 20 and 200 mL,
depending on particulate load) are processed through 25-um diameter, GF/F
glass fiber filters with 0.7 um nominal pore size. The filters have been
baked by the manufacturer to reduce carbon and nitrogen blanks to
negligible concentrations. Filters are folded in half, transferred to
aluminum foil pouches, and shipped to the NWQL by overnight express at 4C.
Filters are stored at or below -20C at the NWQL and are dried in an oven
overnight at 50C prior to analysis. Dried filters are transferred to
nickel sleeves for TPC and TPN analysis by high-temperature combustion
(975C) with an Exeter Analytical elemental analyzer. A duplicate filter
for each sample is pre-combusted in a muffle furnace to remove organic
carbon and then analyzed for PIC when it is desirable to differentiate the
organic and inorganic contributions to TPC--that is, POC = TPC - PIC.
Details of the new analytical method will be available as an NWQL technical
memorandum from the NWQL home page
(wwwnwql.cr.usgs.gov/Public.html).
Change in field methods for TPC and PIC samples:
Two previous OWQ technical memoranda (00.05 and 00.07) listed the required
supplies and equipment needed to submit samples for TPC and POC. A
detailed standard operating procedure for field procedures is attached to
this memorandum and will be posted on the OWQ web site. This procedure
will be reformatted in the near future and included as a revised section in
the National Field Manual for Collection of Water-Quality Data.
The new methods require three filters to be submitted with each sample.
The first filter will be analyzed for TPC, and the second for PIC. The
third filter will serve as a back up in case one of the first two filters
is damaged in processing. The NWQL will also routinely process about 10
percent of these "extra" filters as part of their internal quality-control
process.
Change in DOC field methods:
The NWQL method for DOC determinations will remain the same, but there are
now more flexible options for filtering the samples at collection sites. A
study at NWQL showed no significant difference between DOC concentrations
when filtered with the silver filter and GF/F glass fiber filter. A larger
data set (unpublished data) provided by George Aiken at the National
Research Program in Boulder, Colorado showed no significant difference in
DOC concentrations from samples filtered with the silver filter and the
Gelman Supor capsule filter. Thus samples filtered with any of these three
filters may be submitted for DOC analysis. All DOC samples that are
filtered with the glass fiber or Gelman capsule filter must be acidified
with 1 mL of 4.5 N sulfuric acid (Quality of Water Services Unit Item No.
Q438FLD) per 120 mL of sample. Note that this is the same solution used to
preserve WCA nutrient samples. Samples filtered with the silver filter
should continue to be chilled but not preserved with sulfuric acid.
Implementation of the new methods:
The new TPC, PIC, POC, and TPN methods are available at NWQL on June 1,
2000. Districts may start submitting samples as soon as the required
supplies are delivered. The old SOC method will continue to be available
through the end of the 2000 water year. After this date it will only be
available as a custom method. Some ongoing programs may choose to continue
using the old method at least until the end of the water year, but we
recommend that samples using both methods be collected to provide some
overlap for quality-assurance purposes.
Acknowledgements:
The availability of the new methods is the product of a collaborative
effort by several groups. The Ocala Quality of Water Supply Section first
brought our attention to the shortage of silver filters and the likelihood
that the shortages would only get worse. The MRDP researched the question
of using a new type of filter and evaluated available analytical options.
The speed with which this method was implemented would have been impossible
without the full cooperation of Carl F. Zimmerman, Carolyn Keefe, and
Kathryn Wood, who developed method 440.0 at the Chesapeake Biological
Laboratory (CBL) in Solomons, Maryland. In November 1999, these
individuals provided technical training in method 440.0 to Jacob Gibs, Jim
Kammer, and Charles Patton at the CBL. CBL also provided analytical
services crucial to method 440.0 evaluation and validation at the NWQL.
Under the direction of Charles Patton at MRDP and in close cooperation with
the Carbon Unit at the NWQL, equipment was purchased and the methods
adapted for use at NWQL. MRDP and the Carbon Unit met all deadlines in
completing the method evaluation and prove out for this method. Jacob Gibs
from the New Jersey District and Kathy Fitzgerald, OWQ, evaluated the field
procedures and helped to develop the new filtering apparatus. They also
revised the field procedures published in the National Field Manual to
include the new methods.
Questions on laboratory procedures outlined in this technical memorandum
should be directed to Charles Patton (cjpatton@usgs.gov) at NWQL and
questions about field procedures should be directed to Kathy Fitzgerald
(kkfitz@usgs.gov) in OWQ or Jacob Gibs (jgibs@usgs.gov) in the New Jersey
District.
Janice R. Ward /s/
Acting Chief, Office of Water Quality
Attachment: SOP of field procedures
This memorandum is a supplement to OWQ Technical Memoranda 2000.05 and
2000.07.
Distribution: All WRD Employees