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FAQ for ALACC 2015

1) Section 5.9.1 of the Guidelines discusses use of CRMs and RMs as quality control samples.  What 
level of traceability is required for an organism used as a QC sample/positive control to 
determine method accuracy for microbiological tests, and how can the microbial count be 
determined? 

The microbiological QCS organism is traceable from date of possession, preferably to a
Type culture collection such as ATCC, NCTC, etc. The working culture is inoculated
into an enrichment broth, and after a defined incubation period (ex. overnight), is diluted
and the density is determined (e.g. by enumerating using non-selective media or by using
a densitometer, spectrophotometer, McFarland standard or equivalent) to estimate the
CFU/mL of inoculum. Once the density of the inoculum has been verified by one of
these means, it may be used for either media QC or sample batch QC as a measure of
relative recovery (note: inoculum density may be determined concurrently with testing).
 
2)  Appendix A, Table 1 contains a requirement for weekly conductivity verification of DI systems.  
Does the requirement for weekly verification apply to the conductivity meter that is used to 
monitor the DI system? 

The requirement for DI systems is for verification of the water.  Requirements for 
verification of conductivity meters are contained in the Table 1 section on “pH meters, 
ion selective, and related conductivity equipment.”  The laboratory sets an appropriate 
frequency for conductivity meter verifications with consideration of the criticality of the 
measurement (i.e., is it a reported result?) and accreditation body requirements.
 
3)  Appendix A, Table 1 contains a requirement for weekly conductivity verification of DI systems.  
Does a continuous conductivity monitor meet the requirements of weekly monitoring? 

Section 5.5.2 states that Appendix A, Table 1 provides minimum requirements.  Greater 
frequencies or continuous will fulfill this requirement. 

4)  Appendix A, Table 1 contains a requirement to verify detector response of chromatographic 
systems with an analytical standard at mid‐range concentration with each batch.  Does this 
allow for use of an analytical standard at the lower end of the calibration curve to match sample 
concentrations rather than at mid‐range of the calibration curve? 

Table 1 sets a minimum requirement.  Use of an analytical standard at a level below the 
mid‐range of the calibration curve is more difficult due to increased method variability 
as you approach the LOQ and would meet the minimum requirement of Table 1. 

5)  Appendix A, Table 1 contains a requirement for weekly conductivity testing of DI systems.  Some 
laboratories may go more than a week without operation.  Was the intent of the requirement to
be “week of  
use”? 

Yes, the intent is that the water be tested each week of use. 

6)  Does ALACC:2015 Section 5.9.1 require the use of a QCS (full method, in matrix and known value)
 for qualitative microbiological methods?


No.  The first paragraph of Section 5.9.1 of the ALACC Guidelines provides a number of
examples of quality control samples, but does not require the use of specific types in specific
situations.  The use of qualitative quality control samples (e.g., positive/negative controls) is
suitable for qualitative methods.