Starna

Like its liquid counterpart, the didymium glass filter produces characteristic peaks that make it suitable for use as a wavelength reference material in the visible region of the spectrum

Glass filters mounted ‘stress free’ in an anodised aluminium Glass filter containing didymium (a mixture of neodymium
& praseodymium) oxide, mounted stress free in an anodised aluminium holder. As a solid material the didymium glass filteris physically more robust than the equivalent liquid cell, and can therefore be used in more demanding environments, making it especially useful as a routine wavelength check. Sliding window covers are provided to protect the surface from damage when not in use. Variations from melt to melt of the glass can cause small uncertainties in peak position, soeach Starna filter is individually certified.

The spectrum shows 11 characteristic and well-defined peakscovering the wavelength range from 430 nm to 890 nm.

Approximate peak wavelength values (in nm) are: 431, 473, 513, 529, 573, 585, 685, 741, 749, 807, 879.

Note: The above values are for guidance only. Because theabsorption bands are asymmetric, measured values will bespectral bandwidth dependent. The Calibration Certificateaccompanying each Starna Didymium Glass Reference gives actual values measured at bandwidths of 0.10, 0.25, 0.50,1.00, 1.50, 2.00 and 3.00 nm, and only these certified values should be used for instrument qualification. On request, Starna can provide certified values at other wavelengths andbandwidth values.

COMPOUND

Catalogue  Number

Didymium glass filter

RM-DG

The DMV Bio-cell from Starna is the elegant solution to direct, accurate measurement of nucleic acids or proteins in low volume biological samples. The Bio-cell is compatible with any conventional UV spectrophotometer and its magnetic closure design facilitates rapid filling and emptying and easy cleaning, providing cost-effective, easy-to-use low-volume analysis. For those working in the regulated environment, Starna's expertise in cell technology is combined with Performance Qualification using specially developed Certified Reference Materials to give truly validated measurements and the ultimate confidence in results.

• Direct low volume analysis of nucleic acids and proteins
• Available with 2.5, 1.0 and 0.6 μl volumes
• High accuracy and reproducibility
• Validated measurements
• Certified Reference Materials for OQ/PQ
• Certified path length option
• Compatible with all major UV/Visible spectrophotometers

Precision micro-machining techniques and advanced materials are used to create a patented high energy optical system, so that low volume samples can be measured accurately and reproducibly across a wide absorbance range. The DMV-Bio Cell is available in 0.5, 0.2 and 0.125 mm path lengths for direct measurement of sample volumes of less than 2.5 μl (down to 0.6 μl) for all life science applications. If required, these path lengths can be certified. Cells are available with Z heights of 8.5 mm or 15 mm to suit a wide range of instrument designs

Like its liquid counterpart, the holmium glass filter produces characteristic peaks that make it suitable for use as a wavelength reference material in the UV and visible regions of the spectrum (240 nm – 640 nm). Unlike the liquid cell, however, It is not adopted by all the Pharmacopoeias for wavelength qualification.

It is accepted for this purpose by the following bodies:

United States Pharmacopeia
American Society for Testing and Materials
Therapeutic Goods Administration (Australia)
British Pharmacopoeia

Glass filter containing holmium oxide, mounted stressfree in an anodised aluminium holder. As a solid material the holmium glass filter is physically more robust than the equivalent liquid cell, and can therefore be used in more demanding environments, making it especially useful as a routine wavelength check. Sliding window covers are provided to protect the surface from damage when not in use. Variations from melt to melt of the glass can causesmall uncertainties in peak position, so each Starna filter is individually certified.

The spectrum shows 11 characteristic and well-defined peakscovering the wavelength range from 240 nm to 640 nm.

Approximate peak wavelength values (in nm) are: 242, 279, 288, 334, 361, 419, 446, 454, 460, 537, 638

Note: The above values are for guidance only. Because the absorption bands are asymmetric, measured values will bespectral bandwidth dependent. The Calibration Certificateaccompanying each Starna Holmium Glass Reference givesactual values measured at bandwidths of 0.10, 0.25, 0.50, 1.00, 1.50, 2.00 and 3.00nm, and only these certified values should be used for instrument qualification. On request, Starna can provide certified values at other wavelengths andbandwidth values.

COMPOUND

Catalogue  Number

Holmium glass filter

RM-HG

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 6.5 nm.

These filters are equivalent to NIST SRM 2013a. A metallic coating is deposited on to a quartz plate at a thickness that determines the transmission characteristics of the filter are determined by the thickness of a metallic coating deposited on a quartz plate. The metallic surface is overlaid by an optically bonded cover plate, to protect it from oxidation, contamination, or physical degradation.

Note that SRM 2013a is no longer available from NIST, having been replaced by SRM 2013b, that differs from the prior series by using 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. 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.

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 5nm 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.

The references are also available individually. Nominal certified transmission/absorbance values and catalogue number are given below. Any combination of references can 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.

These references can be used to qualify the absorbance accuracy and linearity of visible spectrophotometers with a spectral bandwidth of 6.5 nm or less, over the wavelength range 440 -635 nm.

Measurements made with these references will be accepted as evidence of instrument qualification by:

• • United States Pharmacopeia
• • American Society for Testing and Materials
• • Therapeutic Goods Administration (Australia)
• • British Pharmacopoeia

Glass filters mounted ‘stress free’ in an anodised aluminium holder. The use of Schott NG-type glasses has been used for over thirty years for the validation of the absorbance scale and linearity of spectrophotometers in the visible region. Filters with a wide range of transmission and absorbance values can be produced. The spectrum of these filters is essentially flat over the range of calibration.

A range of 18 filters is available from Starna, covering absorbance values from approximately 0.04 A to 3.5 A (see How to Order, below). Originally, these filters were manufactured with selected transmission values. Available transmission values and equivalent absorbances are: All Starna neutral density filters are manufactured and certified in accordance with the ‘Technical Specification for Certification of Spectrophotometric NIST Traceable Reference Materials’ (NIST Special Publication 260-140).

This recommends calibration at 440 nm, 465 nm 546.1 nm 590 nm and 635 nm, and Starna filters are certified at these wavelengths. NIST also lists three specifications for neutral density filter Standard Reference Materials (SRMs): SRM 930e, SRM 1930 and SRM 2930. These specifications also stipulate the maximum spectral bandwidth to be used at these wavelengths for certification measurements:

For those users wishing to work to these specifications, sets of filters equivalent to these SRMs are available (see How to Order). For convenience, but to comply with the SRM specifications, all certification measurements are made at a SBW of 1.0 nm. These sets consist of three filters together with an empty aluminium holder, to be used as a blank

These SRMs were originally specified in transmittance, the specified nominal transmittance and approximate absorbance values are given below: Certificate values are given in both %T and Absorbance.

NIST Equivalent SRM Sets

Three specifications for neutral density filter Standard Reference Materials (SRMs) are listed by NIST: SRM 930e, SRM 1930 and SRM 2930. For those users wishing to work to these specifications, sets of filters equivalent to these SRMs are available:

Visible Spectrophotometer Qualification Set

This is a convenient way of qualifying a visible spectrophotometer for photometric accuracy, linearity and wavelength accuracy.

These references can be used to qualify the absorbance accuracy and linearity of near-infrared spectrophotometers with a spectral bandwidth of 6.5 nm or less, over the wavelength range 800 nm - 3200 nm.

Glass filters mounted ‘stress free’ in an anodised aluminiumholder. The use of Schott NG-type glasses is well established for the validation of the absorbance scale and linearity of spectrophotometers in the near-infrared region.

The spectrum of these filters is relatively flat over most of the range of calibration, but with significant deviation above 2700 n

Calibration values (in % Transmission and Absorbance) are certified at 1100, 1700, 2210, 2500 and 2850 nm. Three filters are available, designated, R1 R3 and I1. Approximate values are:

1100 nm

1700 nm

2210 nm

2500 nm

2850 nm

Catalogue Number

%T

A

%T

A

%T

A

%T

A

%T

A

20

0.70

40

0.40

47

0.32

49

0.31

2

1.83

RM-R1

25

0.59

46

0.34

53

0.28

55

0.26

3

1.54

RM-R3

33

0.48

53

0.28

59

0.23

60

0.22

6

1.25

RM-I1

Set of all 3 filters as above

This exceptionally wide-range filter contains a mixture of rare earth oxides and provides 20 peaks for wavelength calibration between 335 nm in the UV and 1945 nm in the NIR. It is equivalent to NIST SRM 2065.

Nominal peak wavelength values (in nm) are: 335, 345, 361, 375, 386, 402, 418, 485, 538, 583, 642, 748, 804,976, 1076, 1151, 1222, 1366, 1469, 1945

COMPOUND

Catalogue  Number

Wide Range Wavelength Reference

RM 2065

These Reference Materials can be used to qualify the Stray Light (or Stray Radiant Energy) of ultraviolet and visible spectrometers.

Glass cut-off filters that allow stray light to be checked, nominally at 280 nm,360 nm and 450 nm. Note that variations from melt to melt of the glass can cause variation in these wavelengths, up to ± 10 nm, so each Starna filter is individually certified. Sliding window covers are provided to protect the surface from damage when not in use.

Stray light, also called Stray Radiant Energy or Power, is any light reaching the detector that is outside the Spectral Band Width selected for analysis by the monochromator. It can be due to optical imperfections or stray reflections within the monochromator itself or to light leaks or other effects in the rest of the optical system. As the detector cannot discriminate between the analytical wavelength and the stray light, the stray light contributes to the detector signal and introduces an error in the measured absorption. The stray light is not absorbed even at high concentrations of the absorbing species, so its effect is a negative deviation from the linear relationship between concentration and absorbance (the Beer-Lambert law) on which most quantitative determinations are based. 

Stray light is wavelength and instrument dependant. It can be present at any wavelength but is most noticeable when the energy throughput of the system at the analytical wavelength is relatively low, and any stray light will be comparatively more significant. At these wavelengths, any deterioration in the instrument optics or light source will exaggerate the apparent stray light, so it is desirable to check it on a regular basis, as it is an excellent way of monitoring the condition of the instrument optics.

The usual way of assessing stray light is to measure, at the desired analytical wavelength, a sample that totally absorbs the radiation at that wavelength, but transmits at all other wavelengths. Any light detected by the instrument is then stray light. 

Practically, the usual method is to use cut-off filters that cut off all light near the analytical wavelength and transmit at all higher wavelengths. The certified wavelength is that at which the spectrum transitions 2.0 A.  Below this wavelength, within the indicated usable range, any indication of light transmission must be stray light. 

Material 

Cut-off 

Catalogue Number 

WG275

280 nm 

RM-G275 

GG380

355 nm 

RM-G380 

GG475

450 nm 

RM-G475 

This exceptionally wide-range filter contains a mixture of rare earth oxides and provides 20 peaks for wavelength calibration between 335 nm in the UV and 1945 nm in the NIR. It is equivalent to NIST SRM 2065.

Nominal peak wavelength values (in nm) are: 335, 345, 361, 375, 386, 402, 418, 485, 538, 583, 642, 748, 804,976, 1076, 1151, 1222, 1366, 1469, 1945

COMPOUND

Catalogue  Number

Wide Range Wavelength Reference

RM 2065