NATIONAL WATER QUALITY LABORATORY
TECHNICAL MEMORANDUM 98.01
November 10, 1997
To:
Chief, Office of Water Quality
Assistant Chief, Office of Water Quality
Assistant Chief Hydrologist for Technical Support
Regional Hydrologists
Chief, NAWQA
Chief, Office of Ground Water
Assistant Chief, Office of Ground Water
Chief, National Water Information System
Chief, Office of Hydrologic Research
Chiefs, Branches of Regional Research
District Chiefs
Regional Water Quality Specialists
Assistant Regional Hydrologists for NAWQA
District Water Quality Specialists
Chiefs, NAWQA Study Units
Chiefs, NAWQA National Synthesis Teams
Chief, Quality Water Service Unit, Ocala
Chief, Yucca Mountain Project
QA Manager, Yucca Mountain Project
Chief, Branch of Quality Systems
Employees, National Water Quality Laboratory
From:
Robert S. Williams, Jr., Chief
National Water Quality Laboratory
Branch of Analytical Services
Subject: Change in Ammonia plus Organic Nitrogen Minimum Reporting Level
Effective
date of
changes: November 10, 1997
Authors:
Charles J. Patton, Methods Research & Development Program,
(303) 467-8084, cjpatton@usgs.gov, and Juan Vasquez,
Supervisor, Nutrients Unit, (303) 467-8113, jvasquez@usgs.gov
Revision: None
Supplemental: None
SCOPE
This technical memorandum pertains to changes in the minimum reporting level
(MRL) for ammonia plus organic nitrogen in chilled and chilled-acidified
filtered and whole-water samples, effective November 10, 1997. Specifically it
announces that MRLs for these tests will be lowered from 0.2 milligrams of
nitrogen per liter (mg-N/L) to 0.1 mg-N/L (Table 1). The changes are the result
of a systematic evaluation of reporting levels for National Water Quality
Laboratory (NWQL) methods. Reporting level changes are based on an assessment
of analytical data for low-concentration samples.
Table 1. Reporting level changes for ammonia plus organic nitrogen methods
[WATSTORE, Water Data Storage & Retrieval System; N, nitrogen; ASF, automated
segmented-flow spectrophotometry; FIL, 0.45 um filtered; and WWR, whole water
recoverable]
____________________________________________________________________________
Minimum Reporting Level
(milligrams-N/liter)
Parameter NWQL _______________________
(WATSTORE) lab Effective
Constituent code* code Current Nov. 10, 1997
_____________________________________________________________________________
Ammonia + organic nitrogen as N, 00623D 1985 0.2 0.1
micro-Kjeldahl digestion,
colorimetry, ASF, FIL
Ammonia + organic nitrogen as N, 00625D 1986 0.2 0.1
micro-Kjeldahl digestion,
colorimetry, ASF, WWR
Ammonia + organic nitrogen as N, 00623E 1994 0.2 0.1
micro-Kjeldahl digestion,
colorimetry, ASF, FIL, acidified
Ammonia + organic nitrogen as N, 00625E 1995 0.2 0.1
micro-Kjeldahl digestion,
colorimetry, ASF, WWR, acidified
____________________________________________________________________________
*Letter following 5 digits represents method code.
BACKGROUND
>From 1986 until October 1, 1991, the NWQL determined ammonia plus organic
nitrogen (Kjeldahl nitrogen) using a semi-automated, block digester method
(Fishman and Friedman, 1989) similar to U.S. Environmental Protection
Agency (USEPA) method 351.2 (U.S. Environmental Protection Agency, 1993).
In 1991, projected increases in demand for Kjeldahl nitrogen determinations
brought on by the National Water Quality Assessment Program (NAWQA) Program
spurred efforts at the NWQL to improve data quality and production capacity for
this test. To this end, changes in both the digestion procedure and
colorimetric method used to determine ammonia in sample digests were developed,
validated, and implemented. Modifications to the block digestion procedure
involved halving sample and digestion reagent volumes as described by Jirka and
others (1976) and using a pair of block digesters as described by Bowman and
Delfino (1982)--one set at the desolvation temperature, the other set at the
digestion temperature--rather than a single block digester that ramped between
the two temperatures during the 4-hour course of the digestion. The
Jirka/Bowman modifications to the block digestion procedure, along with an
improved cleaning procedure for digestion tubes, resulted in significant
decreases in the time required to digest samples and in reagent blank
concentrations. Complete details of the modified digestion procedure have
been reported previously (Patton and Truitt, 1992). An automated colorimetric
method to determine ammonia in sample digests also was developed and validated.
In this automated procedure, a microporous polypropylene membrane allows ammonia
to pass into the analytical stream but excludes particulate and ionic components
in sample-digest matrices that would otherwise interfere in the analysis. The
salutary effects of these modifications, which have been in place at the NWQL
since October 1, 1991, are apparent in yearly average NWQL blind blank (reagent
water) Kjeldahl nitrogen concentrations (Table 2).
Table 2. Yearly concentration averages and standard deviations
for NWQL Kjeldahl nitrogen blind blank samples. Note method
change in the 1992 water year.
[mg-N/L, milligrams of nitrogen per liter; n, number of points]
____________________________________________________________________
Kjeldahl nitrogen concentration (mg-N/L)
__________________________________________________________
Year Dissolved n Whole-water n
____________________________________________________________________
1990 0.11 +/- 0.17 59 0.13 +/- 0.27 60
1991 0.10 +/- 0.11 49 0.11 +/- 0.13 46
1992 -0.04 +/- 0.05 47 -0.04 +/- 0.06 51
1993 0.01 +/- 0.06 53 0.00 +/- 0.06 51
1994 0.00 +/- 0.04 52 0.00 +/- 0.05 52
1995 -0.01 +/- 0.06 135 0.02 +/- 0.07 139
1996 0.00 +/- 0.06 67 0.01 +/- 0.06 68
____________________________________________________________________
EFFECT ON DATA BASE
The minimum reporting level change will cause a shift in the nondetection
(less than) concentration in the data base. Historical reporting levels
are not being changed in the data base.
REFERENCES
Bowman, G.T., and Delfino, J.J., 1982, Determination of total
Kjeldahl nitrogen and total phosphorus in surface waters and
wastewaters: Journal of the Water Pollution Control
Federation, v. 54, no., 9, p. 1324-1330.
Fishman, M.J. and Friedman, L.C., eds., 1989, Methods For
Determination Of Inorganic Substances In Water And Fluvial
Sediments-Nitrogen, ammonia plus organic, colorimetric, block
digestor-salicylate-hypochlorite, automated-segmented flow:
U.S. Geological Survey TWRI, Book 5, Chapter 1A, pp 327-330.
Jirka, A.M., Carter, M.J., May, Dorothy, and Fuller, F.D., 1976,
Ultramicro semiautomated method for simultaneous determination
of total phosphorus and total Kjeldahl nitrogen in
wastewaters: Environmental Science and Technology, v. 10, no.
10, p. 1038-1044.
Patton, C.J. and Truitt, E.P., 1992, Methods of analysis by
the U.S. Geological Survey National Water Quality Laboratory-
Determination of total phosphorus by a Kjeldahl digestion
method and an automated colorimetric finish that includes
dialysis: U.S. Geological Survey Open-File Report 92-146, 39 p.
U.S. Environmental Protection Agency, 1993, Methods for the
determination of inorganic substances in environmental
samples: Cincinnati, Ohio, Environmental Monitoring and
Support Laboratory, EPA/600/R-93/100, August 1993, 79 p.
Supersedes: None
Key Words: Ammonia + organic nitrogen, Kjeldahl nitrogen,
minimum-reporting level, MRL
Distribution: See above plus the Netnews usgs.labnews and .water.quality,
WRD Secretaries; Field and Project Offices;
Hydrologic Technicians; and http://wwwnwql.cr.usgs.gov/