PROGRAMS AND PLANS--Preservation of water samples for chemical analysis



               SUPERSEDED BY QWB TECH MEMO 80.26

                                          January 5, 1972

QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM NO. 72.09

Subject:  PROGRAMS AND PLANS--Preservation of water samples
          for chemical analysis

Various Quality of Water Branch and Division memoranda have 
recommended the addition of mercuric chloride to samples 
collected for determination of nitrogen and phosphorus 
species, organic carbon, and chemical oxygen demand so as to 
prevent changes in the samples due to microbiological 
activity prior to analysis.  Similar instructions are 
contained in "Methods for Collection and Analysis of Water 
Samples for Dissolved Minerals and Gases" (TWRD Book 5, 
Chapter A1) and in "Selected Procedures for Biological and 
Microbiological Investigations"  (USGS Open-file Report).

Because of the interferences of mercury in some analytical 
methods used for analysis of the above samples, the 
possibility of contamination with the mercuric chloride 
solution of equipment later used for sampling for toxic 
metals, and the problems connected with disposal of mercury-
containing samples after analysis, the Quality of Water 
Branch advises all offices of the Water Resources Division to 
stop using mercuric chloride as a preservative for water 
samples.  Instead, bacterial action should be minimized by 
chilling the samples in the field immediately after 
collection, preferably to 1-4 deg. C, and maintaining this 
low temperature until the analysis is performed.  It should 
not be frozen, as this can result in irreversible chemical 
and physical changes in the sample.  Samples should be 
shipped by the fastest practicable means to the respective 
laboratories and the samples analyzed as soon as possible by 
the laboratories.

Dwight Ballinger, Chief, Analytical Quality Control, EPA, has 
agreed to this change for the EPA-GS transfer program, 
however they will require that 1 ml conc. H2SO4 per liter of 
sample be used in addition to cooling as a preservative for 
samples to be analyzed for ammonia, organic nitrogen, 
phosphorus species, organic carbon and chemical oxygen 
demand.  Current studies by the WRD Analytical Methods Unit 
suggest that chilling is as effective in preventing 
microbiological activity in water samples as the addition of 
mercuric chloride, and that the two methods in combination 
probably offer no advantage.  Testing is continuing.

Questions on the stated policy or on preservation procedures 
should be directed to this office.



                              W.H. Durum
                              Chief, Quality of Water Branch

WRD Distribution:
A, B, FO-L, PO