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Appendix H: An Example of In-house QC from a New Zealand Laboratory

Metals

Table A9: Typical QC used with each batch of analytical soil samples for inductively coupled plasma - mass spectrometry analysis

Typenfection, trou Frequency Warning limit(a) Control limit(b) Action on failure
Blank Beginning of each run   < detection limit Repeat whole run
Duplicate   10% 20% Repeat whole run
Spikes       Not used(c)
QC standard(d) Beginning of each run 10% 20% Fix problem (usually instrumental) before repeating run
QC sample(e) 3 per batch 10% 20% Re-digest samples and re-analyse
Certified reference material At validation, then as required   Within certified range Re-digest samples and re-analyse

Notes:

a) Warning limit - Variation outside which the laboratory would take special note of the analyses QC trends.

b) Control limit - Maximum acceptable variation outside which analyses would usually be repeated.

c) Spiked soil samples are not used as it is virtually impossible to spike a soil in a way that has the same form as the analyte already in the matrix.

d) Obtained from an independent source to the working standards used.

e) A thoroughly homogenised sample that has been well characterised by multiple analyses over time.

 

Volatile (VOC) and semi-volatile organic compound (SVOC) analysis

Table A10: Typical QC used for VOC and SVOC analysis on soils

Type Frequency Typical acceptance criteria
Blank Every batch or 20 samples < half detection limit or 5% of regulatory limit
Replicate Every 10-20 samples Generally 20% of the relative percent difference. Can be up to 100% of the relative percent difference of the mean concentration depending on the matrix
Spikes Every 10-20 samples 30-150% recovery SVOCs depending on matrix
80-120% recovery for VOCs
Surrogates Every sample 30-110% recovery SVOCs depending on matrix
80-120% recovery for VOCs
Certified reference material (CRM) Monthly for SVOC samples;
no CRM available for VOC
Within certified range

Total petroleum hydrocarbons (TPH)

Table A11: Typical QC used for TPH analysis on soils

Type Frequency Typical acceptance criteria
Blank Every batch or 20 samples < half detection limit or 5% of regulatory limit
Replicate Every 10-30 samples 20-100% relative percent difference of the mean concentration depending on the matrix
Spikes Every 10-30 samples 20-150% recovery depending on the matrix
Surrogates Not used  
Diesel QC sample Every batch or 20 samples 15% relative percent difference of the mean concentration depending on the instrument
Certified reference material Monthly Within certified range