QA/QC: Quality Assurance and Control

• Quality assurance/quality control (QA/QC) is critical to maintaining data integrity.
• Data integrity is maintained through documented procedures, sample security, and monitoring of precision, accuracy, and contamination.
• Chemical measurements must produce accurate results to allow the user to make appropriate decisions.
• The result must be "fit for purpose”.

QA, QC & QMS

• Quality assurance (QA) is typically managed by a QA Department headed by a QA Manager.
• QA ensures that QC is being implemented to fulfil the Quality Management System (QMS) of the organization.
• Quality control (QC) involves the day-to-day activities designed to monitor the analytical process.
• These activities are also known as QC strategies or QC criteria.
• Quality Management System (QMS) is an overall, organization-wide system concerned with quality.
• QMS includes policies, guidelines, written protocols, Standard Operating Procedures (SOPs), and work instructions.

Reasons for QA & QC

• Human errors, also known as gross errors, can occur, such as mixing up results for two samples.
• Human errors should be small and are easily identified and corrected in a well-run laboratory.
• Errors in measurement have two components: a random component and a systematic component.
• Random errors typically arise from unpredictable variations of influence quantities.
• Random effects can cause variations in repeated observations of the measurand.
• Random errors of an analytical result cannot be compensated for but can be reduced by increasing the number of analyses.
• Systematic error is a component of error that remains constant or varies in a predictable way during analyses of the same measurand.
• Systematic error is independent of the number of measurements made.
• Systematic errors cannot be reduced by increasing the number of analyses under constant measurement conditions.
• Random and systematic errors lead to uncertainty in a measurement result.

Implementing Quality Control in a Fire Assay Laboratory

• A typical analytical process includes:
  • Sample Preparation
  • Weighing & fluxing
  • Fusion
  • Cupellation
  • Parting (acid digestion)
  • Instrumentation
  • Results processing
  • Reporting

INTERNAL QC STRATEGIES

• Internal QC strategies are documented and implemented in the laboratory as part of its analytical method.
• Geological blank: A sample of uncrushed rock or drill core with very low or non-detectable concentrations of the elements of interest.
  • It's included in the QC strategy to monitor contamination during sampling and handling.
• Method reagent blank (laboratory blank): Included during acid digestion and instrumental analyses.
  • Used to monitor contamination from reagents, such as acids and lab dilution water (1/20 samples).
• Geological Standard: A composite of naturally occurring geological material with a defined "accepted mean" and "error."
  • Used to monitor accuracy.
  • % Recovery = (Cmeasured / Caccepted) x 100
• Field Duplicate Sample (1 in 20 samples): Splits of drill core, reverse circulation (RC) cuttings, or outcrop from the same sampling interval.
  • These splits are bagged separately with separate sample numbers.
  • Used to calculate field, preparation, and analytical precision.
  • RPD = (Chigher - Clower) / X x 100
• Preparation Duplicate Sample: Splits of one sample taken after the coarse crush but before pulverizing (pulp).
  • Done routinely by the sample preparation laboratory (usually 1 in 40 samples). -Preparation duplicate captures error of sample size reduction in the preparation lab and the error of analyses.
• Pulp Duplicate Sample: Two separate weighings and analyses from one pulp.
  • Routinely done by labs (between 1 in 5 to 1 in 20 samples).
  • The pulp duplicate has the error of analyses.
• With duplicated samples, the relative percent difference between the two samples is calculated and compared with an accepted target (e.g., RPD = 5%).
  • RPD = (Chigher — Clower) / X x 100
• Blind Samples: Analysis of blind samples is a form of repeat analysis to check precision.
  • Replicated test portions are placed in the analytical batch by the laboratory supervisor.
  • The analyst is unaware of the identity of the test portions or that they are replicates.
  • This ensures the analyst has no preconceived ideas that the results should be related.

EXTERNAL QC STRATEGIES

• Certified Reference Materials (CRMs): Material comes with a certificate of analyses.
  • The certificate contains values of the analytes together with the associated uncertainty.
  • CRMs are analyzed to identify biases or determine the accuracy of the analytical method.
• Round Robin: Newly prepared geological standard is analyzed in replicate by a number of labs.
  • Used to calculate the "accepted mean" and standard deviation.
  • It is recommended to have at least 60 analyses using a minimum of 5 labs.
• Laboratory Proficiency Testing (or Interlaboratory Comparison Trials): Organized by an independent organization from outside.
  • The same sample is sent to many participating laboratories.
  • Laboratories compare their performance against others in the same industry.
  • It evaluates the overall competency of a participating laboratory.
  • Mandatory for testing laboratories accredited to ISO 17025 International Standard.