Internal & External Checks: Quality Assurance, Control, and Assessment Measures

Quality monitoring in production lines and industrial processes needs to be assessed on two basic factors – assessing the accuracy (how close your results are to actual figures) and gauging the precision (the repeatability of the results). The various aspects involved in this process can be divided into quality assessment measures, and quality assurance/control.

Let’s look at these aspects and understand them in a little more detail.

Quality Control and Assessment Measures

Quality control (QC) is the procedure for determining the validity of analytical procedures and specific sampling. Once the analysis is complete, quality assessment is performed to measure the accuracy and overall precision of your data. These can further be broken down into internal and external checks.

Internal Checks –

These checks are performed by field volunteers and employees at project sites and laboratories:

  • Field Blanks –  Deionized water used as a sample to identify contamination or errors in sample analysis and collection.
  • Positive and Negative Plates (for Bacteria) –  Filtering the buffered rinse water in the same way as the samples for testing results in negative plates. These are used to test the sample for laboratory bacteria contamination. Filtering water which you know contains bacteria, in the same way as the samples for testing, results in positive plates. These are used to detect contaminants or procedural errors which could inhibit bacterial growth.
  • Field Duplicates – Duplicate samples which the same person taking the original sample, or another, collects at the same place and time, to establish analysis and sampling precision.
  • Lab Replicates – Samples that are divided into subsamples before analyzing, so the results can be compared to gauge the precision of measurements, or to incubate optimal bacteria colonies for counting.
  • Spike Sample – A known solution of the indicator that is being measured, which is dissolved into the sample to increase the concentration by a calculable amount. This is compared with actual measurements to test the accuracy.
  • Calibration Blank – Deionized water used to set the instrument to “zero” by processing it as a sample. Blanks are used to periodically check for “drift” in instruments. You can pinpoint sources of contamination by comparing against a field blank.
  • Calibration Standards – One or multiple standard concentrations of a particular indicator against which instruments can be calibrated. These can be used before running the test or for converting the reported units to another system of measurement (like mg/L to absorbance).

External Checks

These are tests performed by a QC-lab or non-volunteer staff at the site, which are then compared to the results of tests performed at the project lab:

  • External Field Duplicates – A duplicate of the sample collected at the site, which is then analyzed by an independent sampler at the same time and place. This is used to assess the precision of the laboratory analysis.
  • Split Samples – A duplicate sample created by splitting the lab sample. The project lab and an independent lab analyze one sample each and the results are then compared.
  • Outside Lab Analysis of Duplicate Samples – Field duplicates, either external or internal, are sent to an independent lab for analysis. The results are compared with the measurements of the project lab.
  • Knowns – Samples labeled with identified concentrations which, before performing the first sample run, are sent by the QC lab to the project lab to be analyzed for certain indicators. The results are compared with samples of known concentrations and the project lab reports any discrepancies to the QC lab.
  • Unknowns – Similar to knowns, but the concentrations are not communicated to the project lab. The results of the findings are compared with the known values by the QC lab and any problems found are reported to the project lab.

Any discrepancies that are discovered with these methods are reported, followed by processes for identifying the problems, their causes and possible solutions.

Steps to Quality Assurance and Control

Quality assurance (QA) is typically a broad plan for maintaining quality, which encompasses monitoring activities, proper documentation, training, study design, monitoring processing activities and data analysis/management.

  1. You should consult with your program advisor and/or the technical team while developing and implementing QA and QC measures, to help maintain data quality and fulfill requirements.
  2. Locate an independent quality control lab to perform any external checks that are needed.
  3. Assess your capabilities and resources, both human and financial, to determine the limitations to the in-house quality checks you can perform.

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