U. S. Environmental Protection Agency. 1983.

Sample preservation. pp.xv-xx. In Methods for Chemical Analysis of Water and Wastes, EPA-600/4-79-020. U.S.E.P.A., Cincinnati, Ohio, USA.

TABLE 1:

RECOMMENDATION FOR SAMPLING AND PRESERVATION OF SAMPLES, ARRANGED ACCORDING TO MEASUREMENT

Complete and unequivocal preservation of samples, either domestic sewage, industrial wastes, or natural waters, is a practical impossibility. Regardless of the nature of the sample, complete stability for every constituent can never be achieved. At best, preservation techniques can only retard the chemical and biological changes that inevitably continue after the sample is removed from the parent source. The changes that take place in a sample are either chemical or biological. In the former case, certain changes occur in the chemical structure of the constituents that are a function of physical conditions. Metal cations may precipitate as hydroxides or form complexes with other constituents; cations or anions may change valence states under certain reducing or oxidizing conditions; other constituents may dissolve or volatilize with the passage of time. Metal cations may also adsorb onto surfaces (glass, plastic, quartz, etc.), such as, iron and lead. Biological changes taking place in a sample may change the valence of an element or a radical to a different valence. Soluble constituents may be converted to organically bound materials in cell structures, or cell lysis may result in release of cellular material into solution. The well known nitrogen and phosphorus cycles are examples of biological influence on sample composition. Therefore, as a general rule, it is best to analyze the samples as soon as possible after collection. This is especially true when the analyze concentration is expected to be in the low ug/1 range.

Methods of preservation are relatively limited and are intended generally to (1) retard biological action, (2) retard hydrolysis of chemical compounds and complexes, (3) reduce volatility of constituents, and (4) reduce absorption effects. Preservation methods are generally limited to pH control, chemical addition, refrigeration, and freezing.

The recommended preservative for various constituents is given in Table 1. These choices are based on the accompanying references and on information supplied by various E.P.A. Quality Assurance Coordinators. As more data become available, these recommended holding times will be adjusted to reflect new information. Other information provided in the table is an estimation of the volume of sample required for the analysis, the suggested type of container, and the maximum recommended holding times for samples properly preserved.

                           TABLE 1


                  Vol.                                 Holding
                  Req.  Container  Preservative        Time 
Measurement       (ml)  (note 2)   (notes 3,4)         (note 5)
-----------       ----  ---------  --------------      --------

Color               50   P,G       Cool, 4 deg. C      48 Hrs.
Conductance        100   P,G       Cool, 4 deg. C      28 Days
Hardness           100   P,G       HNO3 - pH below 2    6 Mos.
Odor               200   G only    Cool, 4 deg. C      24 Hrs.
pH                  25   P,G       None Req.           Analyze
                                                        Immediately
Residue
  Filterable       100   P,G       Cool, 4 deg. C       7 Days
  Non-filterable   100   P,G       Cool, 4 deg. C       7 Days
  Total            100   P,G       Cool, 4 deg. C       7 Days
  Volatile         100   P,G       Cool, 4 deg. C       7 Days
Settleable Matter 1000   P,G       Cool, 4 deg. C      48 Hrs.
Temperature       1000   P,G       None Req.           Analyze
                                                        Immediately
Turbidity          100   P,G       Cool, 4 deg. C      48 Hrs.

Dissolved          200   P,G       Filter on site,      6 Mos.
                                     HNO3 - pH below 2
Suspended          200             Filter on site       6 Mos. (8)
Total              100   P,G       HNO3 - pH below 2    6 Mos.

Chromium (6)       200   P,G       Cool, 4 deg. C      24 Hrs.
Mercury
  Dissolved        100   P,G       Filter,             28 Days
                                     HNO3 - pH below 2
  Total            100   P,G       HNO3 - pH below 2   28 Days

Acidity            100   P,G       Cool, 4 deg. C      14 Days
Alkalinity         100   P,G       Cool, 4 deg. C      14 Days
Bromide            100   P,G       None Req.           28 Days
Chloride            50   P,G       None Req.           28 Days
Chlorine           200   P,G       None Req.           Analyze
                                                        Immediately
Cyanides           500   P,G       Cool, 4 deg. C,     14 Days (7)
                                     NaOH - pH over 12
                                     0.6g ascorbic
                                     acid (6)
Fluoride           300   P,G       None Req.           28 Days
Iodide             100   P,G       Cool, 4 deg. C      24 Hrs.
Nitrogen
  Ammonia          400   P,G       Cool, 4 deg. C,     28 Days
                                     H2SO4 - pH below 2
  Kjeldahl, Total  500   P,G       Cool, 4 deg. C,     28 Days
                                     H2SO4 - pH below 2
  Nitrate          100   P,G       Cool, 4 deg. C,     28 Days
   + Nitrite                         H2SO4 - pH below 2
  Nitrate (9)      100   P,G       Cool, 4 deg. C,     48 Hrs.
  Nitrite           50   P,G       Cool, 4 deg. C,     48 Hrs.
Dissolved Oxygen
  Probe            300  G bottle   None Req.           Analyze
                          + top                         Immediately
  Winkler          300  G bottle   Fix on site         8 Hours
                          + top      and store
Phosphorus
  Ortho-P,          50   P,G       Filter on site,     48 Hrs.
    dissolved                        Cool, 4 deg. C
  Hydrolyzable      50   P,G       Cool, 4 deg. C,     28 Days
                                     H2SO4 - pH below 2
  Total             50   P,G       Cool, 4 deg. C,     28 Days
                                     H2SO4 - pH below 2
  Total,            50   P,G       Filter on site,     24 Hrs.
    dissolved                        Cool, 4 deg. C,
                                     H2SO4 - pH below 2
Silica              50   P only    Cool, 4 deg. C      28 Days
Sulfate             50   P,G       Cool, 4 deg. C      28 Days
Sulfide            500   P,G       Cool, 4 deg. C,     7 Days
                                     add 2 ml zinc
                                     acetate plus
                                     NaOH - pH over 9
Sulfite             50   P,G       None Req.           Analyze
                                                        Immediately

BOD               1000   P,G       Cool, 4 deg. C      48 Hrs.
COD                 50   P,G       Cool, 4 deg. C,     28 Days
                                     H2SO4 - pH below 2
Oil & Grease      1000   G only    Cool, 4 deg. C,     28 Days
                                     H2SO4 - pH below 2
Organic carbon      25   P,G       Cool, 4 deg. C,     28 Days
                                     H2SO4 or HCI to
                                     pH below 2
Phenolics          500   G only    Cool, 4 deg. C,     28 Days
                                     H2SO4 - pH below 2
MBAS               250   P,G       Cool, 4 deg. C      48 Hrs.
NTA                 50   P,G       Cool, 4 deg. C      24 Hrs.

2. Plastic (P) or Glass (G). For metals, polyethylene with a polypropylene cap (no liner) is preferred.

3. Sample preservation should be performed immediately upon sample collection. For composite samples each aliquot should be preserved at the time of collection. When use of an automated sampler makes it impossible to preserve each aliquot, then samples may be preserved by maintaining at 4 deg. C until compositing and sample splitting is completed.

4. When any sample is to be shipped by common carrier or sent through the United States Mails, it must comply with the Department of Transportation Hazardous Materials Regulations (49 CFR Part 172). The person offering such material for transportation is responsible for ensuring such compliance. For the preservation requirements of Table I the Office of Hazardous Materials, Materials Transportation Bureau, Department of Transportation has determined that the Hazardous Materials Regulations do not apply to the following materials: Hydrochloric acid (HCl) in water solutions at concentrations of 0.04% by weight or less (pH about 1.96 or greater); Nitric acid (HNO3) in water solutions at concentrations of 0.15% by weight or less (pH about 1.62 or greater); Sulfuric acid (H2SO4) in water solutions at concentrations of 0.35% by weight or less (pH about 1.15 or greater); Sodium hydroxide (NaOH) in water solutions at concentrations of 0.080% by weight or less (pH about 12.30 or less).

5. Samples should be analyzed as soon as possible after collection. The times listed are the maximum times that samples may be held before analysis and still considered valid. Samples may be held for longer periods only if the permittee, or monitoring laboratory, has data on file to show that the specific types of sample under study are stable for the longer time, and has received a variance from the Regional Administrator. Some samples may not be stable for the maximum time period given in the table. A permittee, or monitoring laboratory, is obligated to hold the sample for a shorter time if knowledge exists to show this is necessary to maintain sample stability.

6. Should only be used in the presence of residual chlorine.

7. Maximum holding time is 24 hours when sulfide is present. Optionally, all samples may be tested with lead acetate paper before the pH adjustment in order to determine if sulfide is present. If sulfide is present, it can be removed by the addition of cadmium nitrate powder until a negative spot test is obtained. The sample is filtered and then NaOH is added to pH 12.

8. Samples should be filtered immediately on-site before adding preservative for dissolved metals.

9. For samples from non-chlorinated drinking water supplies conc. H2SO4 should be added to lower sample pH to less than 2. The sample should be analyzed before 14 days.