Common use of DETECTION LIMITS Clause in Contracts

DETECTION LIMITS. ▇▇ (2005) presents the method used to estimate detection limits for the PILS- IC sulfate and nitrate data. Table 4-2 reports the reliable range of results for both sulfate and nitrate as defined by the lower limit of detection (LLD) and by the lower and upper limit of quantification (LLQ, ULQ). The lower limit of detection was estimated from the lowest calibration standard concentration with an IC detector response (analyte peak) signal-to-noise ratio greater than three. The baseline noise of a chromatogram is affected by the hardware and operating conditions of the IC (column type, eluant composition and concentration, solution (including water) quality, degree of internal IC temperature fluctuation, whether or not the eluant is degassed, and whether or not a suppressor is used). The lower limit of quantification (LLQ) was the lowest concentration within the linear range, just as the upper limit of quantification (ULQ) was determined by the highest concentration within the linear range. For sulfate, the LLD did not correspond to the LLQ because although chromatogram peaks were clearly distinguishable from the baseline at the lowest concentration standard, concentrations below Level 2 did were nonlinear (i.e., the Milli-Q and Level 1 standards were typically above the regression line generated from the calibration data). ▇▇▇▇▇▇ et al. (2003) documented that past field studies have also witnessed detectable sulfate and nitrate peaks during blank runs, possibly attributable to DI water (sulfate) and background NOx entering through ineffective denuders (nitrate). Table 4-2. Detection limits (reliable ranges) for sulfate and nitrate by PILS-IC. Sulfate (μg/m3) Nitrate (μg/m3) LLD LLQ ULQ LLD/LLQ ULQ Sample loops 0.03 0.33 33 0.02 22 Concentrator pre-columns 0.05 0.53 53 0.04 35 Reported values are not true method detection and quantifiable limits, but rather are operational definitions based on the calibrations standards corresponding to an IC conductivity signal-to-noise ratio greater than three (LLD) and the calibration standards denoting the linear range (or at the extreme values of the calibration standard concentration range if linear to that concentration).