Laserfiche WebLink
( r +_ ~ <br />UI A'Y G'^ ~ w« ~~@S <br />-9 <br />SA~iI'LE PRGSLRVA"fIUN <br />Complete and uncyuivocal preservation of s;unples, either domestic sewage, industrial wastes, or <br />natural waters, is a Practical impossibility. Regardless o(ihc muure of the sample, complete stability <br />for every constituent can never be achieved. AI hest, preservation Icclmiqucs can only retard the <br />chemica) and bological changes Ihal inevilahly continue after the s;unple is rcnurved from the parent <br />source. The changes that take place in a sample arc either clirmical or biological. In the former case, <br />certain changes occur in the chemical stniclure of ihc. anxlilucnls Ih;+t arc a function of physical <br />conditions. Metal cations may precipitate as hydroxides or form complexes with otl+cr constiu+cnts; <br />cations or anions may change valence stales under certain reducing or oxidizing conditions; other <br />conslitucnts may dissoh•e: or volatilize wish the passage of time. Metal cations nr+y also ndseuh onto <br />surfaces (glass, plastic, quartz, etc.), such ^s, imn and Icad. Iholagical diangcs taking place in a <br />sample may change the valence of an clement or a radical to a different valence. Soluble constituents <br />may be converted to organic;dly hound materials in cell structures, or cell lysis may result in release <br />of cellular material into solution. The well known nitrogen and phosphorus c~clcs arc cxarnplcs of <br />biological influence on sample composition, l hcreforc, as a general rulr, it is hest u+ analyze the <br />samples as soon as possible after culleclion. This is especially true when the analyze atncculration is <br />expected to be in the low ug/I range. <br />+ Methods of prescrvatum :uc rcl:rtivcly limited and arc nuendcd gu+crallp to (11 retard hu+log+c;+1 <br />action, (2) retard hydrolysis of chemical compounds and complexes, (t) reduce volaulily of <br />constituents, and (4) reduce ahsrnption effects. Prescrvatioo +neih++ds arc generally limited to pH <br />control, chemical addition, refrigeration, and freezing. <br />The recommended prescrvatice for various constiWCnts iti given in -fable I.'fhese choices arc based <br />on the accompanying references ;md on information supplied by various Qu;dity Assurance <br />Coordinators. As mare dau+ become avcilablc, these recommended holding times will he adjusted to <br />reflect new information. Other information provided in the table is an estimation of the volume of <br />santplc required for the :urdysis. the suggested type of container, and ilic maxinnun recommended <br />holding tinter for s:+nyilcs propel ly picscrvcd. <br />s~ <br />_. _ _ _ I ` d <br />