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TNI Standards Guidance

Disclaimer: This material represents the opinion of its authors. It is intended solely as guidance and does not include any mandatory requirements except where such requirements are referenced. This guidance does not establish expectations of being implemented universally, exclusively, in whole, or in part.

This guidance does not establish or affect legal rights or obligations and is not finally determinative of the issues it addresses. It does not create any rights enforceable by any party in litigation with TNI, its accreditation bodies, or affiliated institutions. Any decisions made by TNI regarding requirements addressed in this guidance will be made by applying the applicable standards, policies or procedures to the relevant facts.


Module: Microbiology

Subject: Chlorine Residual in Sample

Question 1

A microbiology sample comes in with remaining chlorine residual. What should be done now?

Likely you will reject the sample and ask the client for a new sample. Establish whether the sampler took the specimen correctly?  Was the chlorine residual intentional? Remind client about preservative and discuss sampling technique with client. Check sample bottles for Na2S2O3.

Involve Sample Receiving, the client and the sampler in the root cause investigation and the resolution process. Notify the client, project manager, and the personnel or service provider that prepares and issues bottles to clients (whether in-house or contracted).

Review sampling techniques with client and sampling personnel (as possible). Reject the sample and request resampling. Ensure that lab follows its procedure for client notification of sample rejection.


2009 & 2016 TNI

2009 TNI V1M2 and 2016 TNI Rev. 2.1 V1M2
4.0 Management Requirements §4.1.2 and 4.1.5 a, h & i
4.2 Management §4.2.1 and §
4.7 Service to the Client (ISO/IEC 17025:2005(E), Clause 4.7) §4.7.1 a&b, w/ Note 2.

4.9 Control of Nonconforming Environmental Testing Work (ISO/IEC 17025:2005(E), Clause 4.9) §4.9.1 a thru e and §4.9.2
4.11 Corrective Action (ISO/IEC 17025:2005(E), Clause 4.11) §4.11.1 thru 4.11.5
4.13 Control of Records §
5.4 Environmental Methods and Method Validation §5.4.1 first paragraph
5.8 Handling Samples and Test Items (ISO/IEC 17025:2005(E), Clause 5.8)

5.8.6 Additional Requirements – Sample Acceptance Policy

The laboratory shall have a written sample acceptance policy that includes the following:

a) proper, full, and complete documentation, which shall include sample identification, the location, date and time of collection, collector's name, preservation type, sample type and any special remarks concerning the sample;

b) proper sample labeling to include unique identification and a labeling system for the samples with requirements concerning the durability of the labels (water resistant) and the use of indelible ink;

c) use of appropriate sample containers;

d) adherence to specified holding times;

e) sufficient sample volume to perform the necessary tests;

f) procedures to be used when samples show signs of damage, contamination or inadequate preservation; and

g) qualification of any data that do not meet the above requirements.

5.8.7 Additional Requirements – Sample Receipt Protocols The laboratory shall implement procedures for verifying and documenting preservation. If the sample does not meet the sample receipt acceptance criteria listed in this Standard, the laboratory shall either:

a) retain correspondence and/or records of conversations concerning the final disposition of rejected samples; or

b) fully document any decision to proceed with the analysis of samples not meeting acceptance criteria.

i) The condition of these samples shall be noted on the chain of custody or transmittal form and laboratory receipt documents.

ii) The analysis data shall be appropriately qualified on the final report.


1.7 Technical Requirements

1.7.5        Sample Handling

b)       Microbiological samples from known chlorinated sources (such as wastewater effluent), unknown sources where chlorine usage is suspected (such a new client or a new source) and all potable water sources (including source water) shall be checked for absence of chlorine residual.

Laboratories that receive samples from potable water sources (including source water) that have a demonstrated history of acceptable preservation may check a sample from each source at a frequency of once per month if:

i)        the laboratory can show that the received sample containers are from their laboratory;

ii)       sufficient sodium thiosulfate was in each container before sample collection to neutralize at minimum 5 mg/l of chlorine for drinking water and 15 mg/l of chlorine for wastewater samples;

iii)       one container from each batch of laboratory prepared containers or lot of purchased ready-to-use containers is checked to ensure efficacy of the sodium thiosulfate to 5 mg/l chlorine or 15 mg/l chlorine as appropriate and the check is documented;

iv)      chlorine residual is checked in the field and actual concentration is documented with sample submission.