Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:3:p4
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 3 (pt 4/9)
Character Range: 724595–727380

confidence interval
When results are qualified with standard deviations (SD) or their multiples (for example, 'x ± SD'), these are taken to be their confidence limits. This means that a result of 10±4 mg/kg would have confidence limits (CLs) of 6 and 14 mg/kg and a confidence interval (CI) from 6 to 14 mg/kg (APHA 2005). In a normal distribution, 95% of results are found within approximately twice the standard deviation of the mean (e.g. '95% CI = x ± 2SD'). Further clarification of these terms may be found in standard statistics texts.

    3.2.3         Limits of detection and reporting

3.2.3.1         Method detection limit
The method detection limit (MDL) is the concentration of analyte which, when the sample is processed through the complete method, produces a response with a 99% probability that it is different from the blank (NATA Technical Note 17). It is derived by:
    * analysing at least 7 replicates of a sample with a concentration close to the estimated MDL, and determining the standard deviation
    * calculating the MDL as follows
MDL = t * Std Deviation, using a one-sided t distribution where, for 7 replicates, t= 3.14 for 99% confidence levels.

3.2.3.2         Limit of Reporting
The limit of reporting (LOR) is the practical quantification limit (PQL), and is the lowest concentration of an analyte that can be determined with acceptable precision (repeatability) and accuracy under the stated conditions of a test (NATA Technical Note 17). It is calculated as follows (APHA 2005):

LOR = PQL = 5 x MDL

The LOR should be at or below the relevant HIL, HSL or EIL and should be equal to the lowest calibration standard (as expressed in units of mg/kg of soil sample).

3.3              Laboratory Batch QC procedures
The laboratory should adopt, at a minimum, the QC concepts and procedures described below and be able to demonstrate:
    * method proficiency within the laboratory
    * conformance to the performance characteristics expected of the method
    * confidence in the results produced.
Recommended QC procedures for all soil analyses are described in US EPA SW-846 Chapter 1: 'Quality Control'.

    3.3.1         Process batch and QC interval
For the purposes of QC requirements and QC monitoring intervals, a laboratory process batch is deemed to consist of up to 20 samples that are similar in terms of matrix and test procedure, and are processed as one unit for QC purposes. If more than 20 samples are being processed, they are considered as more than one batch.

    3.3.2         Method blank
This refers to the component of the analytical signal that is not derived from the sample but from reagents, glassware, analytical instruments, etc. It can be determined by processing solvents and reagents in exactly the same manner