thermal preservation

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thermal preservation

Postby LAJ » Mon Jun 13, 2011 7:57 am

In accordance with TNI standards, bacteriological samples must be brought in on ice. Is this wet ice or can it be ice packs? This has been an ongoing conversation for many years. With the new standards coming out I would like to get the clarified.
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Re: thermal preservation

Postby pjunio » Wed Jun 15, 2011 8:40 am

The TNI Standards don't require that bacteriological samples be brought in on ice (but it's good practice to do so). The current language is as follows:

1.7.5 Sample Handling
a) Samples that require thermal preservation shall be considered acceptable if the arrival temperature of a representative sample container meets the method or mandated temperature requirement.
i) Samples that are delivered to the laboratory on the same day they are collected may not meet the requirements of Section 1.7.5.a). In these cases, the samples shall be considered acceptable if the samples were received on ice.
ii) If sample analysis is begun within fifteen (15) minutes of collection, thermal preservation is not required.
iii) Thermal preservation is not required in the field if the laboratory receives the sample and either begins the analysis or refrigerates the sample within fifteen (15) minutes of collection.

The presence of ice mitigates that samples may not have cooled to the required temperature, provided they are delivered to the lab on the day of sampling. I don't know of any place that we have defined ice as being wet or blue. From personal experience, blue ice doesn't cool as well as wet ice, so I would use wet ice.

To answer your question, then, my opinion is that either wet ice or blue ice would be acceptable under the language of the TNI Standard.
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Re: thermal preservation

Postby kchapman1 » Wed Jun 22, 2011 11:50 am

The EPA Drinking Water Lab Certification Manual mentions "ice" several times. In the chemical section it recommends "real" ice as it holds samples at <= 4 C more efficiently than "blue" ice. In the microbiological section it speaks of "icing" to keep samples at < 10 C, allowing samples taken within 2 hours to be outside of this requirement, but does not specify real or blue ice.
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Re: thermal preservation

Postby rcook » Wed Jul 13, 2011 9:16 am

I agree with pjunio. Whichever one can get to the temp is acceptable.
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Re: thermal preservation

Postby bray » Thu Jun 21, 2012 11:41 am

FYI, federal regulations state the following:

From the federal regulations for system sampling

§ 141.21 Coliform sampling.
Note 2 The time from sample collection to initiation of analysis may not exceed 30 hours. Systems are encouraged but not required to hold samples below 10 deg. C during transit.

From the federal regulations from the Surface Water rule

§ 141.74 Analytical and monitoring requirements.
Note 2 The time from sample collection to initiation of analysis may not exceed 8 hours. Systems must hold samples below 10 deg. C during transit.

From the federal regulations for groundwater monitoring

§ 141.402 Ground water source microbial monitoring and analytical methods.
Note 1 The time from sample collection to initiation of analysis may not exceed 30 hours. The ground water system is encouraged but is not required to hold samples below 10 °C during transit.

So only for surface water samples does the temp apply to transit. For the others simply noting the temperature is fine.

For WW the rule states that preservation is to be started within 15 minutes of collection but does not describe whether the sample must be at that temperature during transit.
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