Purpose
This Reference Material can be used to qualify the Absorbance scale, in the ultra-violet and visible region of the spectrum (250 nm to 850 nm) of spectrophotometers with spectral bandwidths not exceeding 10 nm.
Description and Discussion
These filters are equivalent to NIST SRM 2031c. A metallic coating is deposited on to a fused silica plate at a thickness that determines the transmission characteristics of the filter. The metallic surface is overlaid by an optically bonded cover plate, to protect it from oxidation, contamination, or physical degradation.
Note that SRM 2031a and SRM 2031b are no longer available from NIST, and were replaced by SRM 2031c. SRM 2031b used an evaporated silicon dioxide protective overcoating rather than a protective cover plate in the construction. We consider the bonded cover plate to be more durable than the overcoating method and have therefore retained the earlier design as per SRM 2031a and SRM 2031c. The filters are mounted in stress-free black-anodized aluminium alloy holders, with front and rear sliding covers that protect the filters when not in use. All individual references and sets are supplied with an empty filter holder for use as a measurement reference.
The spectrum of these filters is essentially flat from 250 nm to 850 nm.
Typical spectra
Absorbance and Transmittance values are certified at 250, 280, 340, 360, 400, 465, 500, 546.1, 590 and 635 nm.
These filters are based on a NIST SRM series whose values follow a sequence of Transmission rather than Absorbance values. Approximate values available are: 90% T (0.04 A), 50% T (0.3 A), 30% T (0.5 A), 10% T (1.0 A), 3%T (1.5 A) and 1% T (2.0A)
Instruments to be qualified should have a bandwidth of 10 nm or less.
Note: The measurement values given in this document are for guidance only. The Calibration Certificate accompanying the Reference Material gives the actual values measured at a bandwidth of 1nm.
As these filters attenuate the incident radiation partly by reflection, inter-reflections could be generated within the sample compartments of some spectrophotometers. This could affect the accuracy of measurements, and it is recommended that potential purchasers contact the manufacturer of their instrument to check its compatibility with metal-on-quartz filters.
Catalogue Number
|
|
Catalogue Number |
|
Metal-on-Quartz Filter set, NIST SRM 2031c |
RM-1Q3Q9Q |
The references are also available individually. Nominal certified transmission/absorbance values and catalogue number are given below. Any combination of references may be ordered as a set by combining the catalogue numbers as in the example above. An empty filter holder is supplied with each reference or set of references to be used as a measurement blank.
|
Nominal Transmittance and Absorbance Values |
Catalogue Number |
|
90% T (0.04 A) |
RM-9Q |
|
50% T (0.3 A) |
RM-5Q |
| 30% T (0.5 A) |
RM-3Q |
| 20% T (0.7 A) |
RM-2Q |
|
10% T (1.0 A) |
RM-1Q |
|
3%T (1.5 A) |
RM-Q3 |
|
1% T (2.0A) |
RM-Q1 |
| 0.1% T (3.0 A) |
RM-DQ1 |
| 0.01% T (4.0 A) |
RM-AQ1 |