Measurement precision and range. To evaluate measurement precision, 10 consecutive headspace moisture measurements of a 50-mL clear glass vial containing
16 capsules of a gelatin encapsulated dry product were taken at 40 °C. Measurement precision, expressed by the percent relative
standard deviation (% RSD) of the 10 consecutive readings, was 1.1%.
Table V: Summary of key attributes of the various headspace-moisture techniques examined in the study.
Measurement precision also was evaluated by repetitive measurements of several saturated salt solutions at 25 and 40 °C. An
individual vial containing a specified saturated salt solution was prepared for each measurement (see Tables VII and VIII).
As Figures 6a and 6b show, % RSD values increased as the % RH value decreased.
The ability of the FMS 1400 headspace-moisture analyzer to accurately measure relative humidity values close to 0% RH and
100% RH also was evaluated (see Table VI and Figure 6b). Five 50-mL clear vials containing USP water (with an expected relative
humidity of 100%) and equilibrated at 40 °C were measured. The results (mean = 98.8%, RSD = 0.4%) suggested that the Lighthouse
instrument can measuring up to 100% RH with a high degree of accuracy. At the low end, five 50-mL clear vials containing dried
desiccants (with an expected relative humidity of 0%) and equilibrated at 40 °C were measured. The results (mean = 0.8%, RSD
= 37.5%) suggested acceptable performance at the low end of the expected relative humidity range as well, although with less
Table VI: Examination of the specificity of the FMS 1400.
This article introduced a novel nondestructive technique that is based on frequency modulation spectroscopy for the measurement
of moisture activity in optically transparent packages. The technique appears to be a promising tool with reasonable method
specificity, measurement precision, method precision, accuracy, linearity, range, and excellent analyst-to-analyst and time
stability. The ability to make moisture activity measurements nondestructively for samples in a sealed glass container also
enables new applications and offers significant advantages over traditional techniques.
Table VII: Accuracy and linearity for measurements at 25 °C for the FMS 1400.
The sealed system avoids all sample-handling issues during the measurement because the samples are not exposed to the environment.
Furthermore, there is no interference from preceding measurements or concerns for leakage (because the sealed stopper-vial
system provides an excellent barrier). Some applications enabled by this technique not offered by traditional techniques include
measurement of moisture activity in optically transparent packages (e.g., lyophilized products) without breach of package, measurements of samples sealed in an inert gas atmosphere, and monitoring
of moisture exchange between samples in real time. The high cost of the instrument will, however, restrict widespread application
of this technique.
Table VIII: Accuracy and linearity for measurements at 40 °C for the FMS 1400.