The instrument linear range using NIST OD standard solutions was higher than that observed for the process linear range for
all spectrophotometers. Therefore, a conservative linear range based on the process linear range was set for each spectrophotometer.
Models A, B, and C had a linear range of 0.2–4.0 dilution OD and the Model D had a reduced linear range of 0.2–1.6 dilution
Model B was the most accurate and most precise spectrophotometer relative to the Model A spectrophotometer over the linear
range of 0.2–4.0 dilution OD. No correction factor was required for this spectrophotometer.
Model C had high precision but reduced accuracy across the linear range compared to Model B when predicting the Model A OD.
Therefore, this spectrophotometer would require a correction factor or a reduced linear range to be used as a replacement
in fermentation processes.
Model D did not have sufficient accuracy or precision relative to Model A OD, and was not desirable as a replacement spectrophotometer.
The authors would like to thank Bill Wagner for troubleshooting and experimental design support, and Valerie Pferdeort for
assisting with sample analysis during experiments.
Carin Gray* is a senior associate scientist, Rick Burdick, PhD, is principal quality engineer, and Arun Tholudur, PhD, is principal engineer, all at Amgen, Longmont, CO, firstname.lastname@example.org
1. J. Neter et.al., Applied Linear Statistical Models, Fourth Edition, (McGraw Hill/Irwin 1996) pp. 167–169.