Accessories FAQ

When should I use an achromatic collimating lens?

An achromatic doublet like the 74-ACR comprises two lenses and is designed to greatly reduce chromatic aberrations. The result is a consistent FOV for the sampling setup, where “contamination” of the spectrum caused by wavelengths outside the optimal FOV is eliminated. Typically, applications including absolute irradiance benefit the most from the use of an achromatic collimating lens.

Do collimating lens holder purchases include the collimating lens?

No, in most cases you will need to purchase lenses separately.

What is the response of Ocean Optics cosine correctors?

Our cosine correctors have 180° FOV with theoretical response close to Lambert’s cosine law, which states that the irradiance or illuminance measured will vary with respect to the cosine of the angle between the optical axis of the source and the normal to the detector. Radiance or luminance is constant in all directions.

Why choose quartz cuvettes versus plastic cuvettes?

Although more expensive, quartz cuvettes are more durable, have better chemical compatibility, and perform better optically than plastic cuvettes. Consider:

  • Quartz withstands mechanical strain and abrasion much better than plastic, and can be rinsed and wiped down many times without compromising optical clarity.
  • Many chemicals (including organics like acetone and toluene) cannot be used with acrylics as they will readily dissolve this plastic, while quartz cuvettes allow for measurement of corrosive and caustic species.
  • Plastic cuvettes tend to block UV transmission and may limit applications such as UV protein absorbance, whereas a Spectrosil® quartz cuvette will provide excellent performance from 170-2700 nm for continuous UV-Vis-NIR analysis.
  • Plastic cuvettes are disposable, eliminating clean-up time; are not fragile like quartz cuvettes; and perform well for many routine lab measurements.
What considerations should I take when handling cuvettes?

There are three main areas to account for when using cuvettes:

  • Ensure the cuvette is used in the same orientation each time it’s removed and replaced in the sample holder. Typically, there is a small “V” or similar mark on one side of the cuvette to guide you. Also, most cuvettes have two optically clear sides and two frosted sides; take care to ensure the clear path is used for light measurement.
  • Surface quality. Before placing a cuvette in the holder, use a Kimwipe® delicate task wiper or optical cloth to wipe finger oils or other interferences from the optical path. An unclean surface can create inconsistent and invalid shifts to the spectral response.
  • Sample changing. Some tests may require the cuvette to be removed between measurements due to the nature of the sample (viscosity, toxicity, etc.) or some experimental parameter. However, whenever possible it is ideal to maintain the cuvette in its relative position in the holder and change the sample via pipetting. Open-top cuvettes usually accommodate this transfer well. Perhaps the most effective approach is to use a slender transfer or Pasteur pipette to add and remove fluids. The tiny tip allows for suction of fluid from the corners, minimizing the carry-over volume. The typical procedure is to rinse the cuvette with the next sample to be analyzed at least three times. If the residual fluid is less than 10% of the wash fluid (it’s more likely to be 1% or less), the carry-over is reduced to 1/1000. Also, it’s important that the pipettes be washed with the sample and not allowed to touch or scratch the inside optical surfaces.
What is the “Z” dimension of Ocean Optics cuvette holders?

Our cuvette holders have a “Z” dimension of 15 mm, except for the legacy product USB-ISS-UV-VIS-2, which is 10 mm. Also, qpod® and qpod 2e™ temperature-controlled cuvette holders have a “Z” dimension of 8.5 mm.

The “Z” dimension is the optical height for placement of the light beam transmitting through the cuvette, and is especially important with small-volume sampling. This dimension is measured from the bottom of the cuvette to the height of ideal optical interface; your sample volume must cover this region to produce valid spectra.

Why are there fittings on the base of our CUV-series cuvette holders?

These are internal fluid channels designed to accept a constant-temperature water source for heating or cooling of the cuvette sample. The cuvette sample will equilibrate to some level between the water and ambient room temperatures, and a thermistor or other thermometer device may be used to confirm actual sample temperature. A more tightly controlled method of temperature regulation is available with the CUV-QPOD sample compartments.

What is the difference between the CUV-QPOD and CUV-QPOD-2E temperature-regulated cuvette holders?

The CUV-QPOD-2E has the control electronics incorporated into its body and comes with control software; the CUV-QPOD requires a separate controller. Pricing is comparable for both.

As the diagram demonstrates, light enters a bifurcated fiber assembly and then splits into two legs, each leg transmitting light to a sample. Light interacts with each sample and transmits through a second set of fibers, each of which connects to a port on the FOS-2X2-TTL.

On the spectrometer side of the setup, a bifurcated fiber assembly collects light from the FOS-2X2-TLL and funnels it to the spectrometer. With the FOS-2X2-TTL in place, you can activate the shutter on either light channel to get “clean” data from each sample. An alternative is to add a second spectrometer channel to monitor the second sample.

How does the fiber optic variable attenuator accessory work?

Fibers screw into collimating lenses on both sides of the FVA-UV, transmitting light across a metal disk into which a slit has been cut. The width of the slit varies as a function of the manually adjusted radial wheel position. Rotating the wheel allows you to vary the attenuation from the closed position (no light) to fully open.

When should I use a Gershun tube?

Using a Gershun tube restricts the field of view of your sampling setup to a known value. Here’s an example: You’re collecting light emitted from a large projection screen in a movie theater. With a bare optical fiber, which has a 25° FOV, you may collect light from the entire screen. With the Gershun tube, you can adjust that FOV to 6°, for example, and collect light from a smaller part of the screen. This would allow you to compare spot to spot uniformity in brightness or color.

Are integrated cuvette holder-light source products like the USB-ISS-UV-VIS-2 available as standalone products?

Yes, but you will still need to plug them into the appropriate spectrometer (Flame or USB2000+/USB4000). In addition to discrete cuvette holders and light sources, there are options with similar functionality including the ecoVis light source and CUV-FL-DA direct-attach cuvette holder.

How do I use a linear variable filter for fluorescence?

Linear variable filters (LVFs) are useful tools for setups where high-pass, low-pass or bandpass filters are required. The filters are epoxied into slide carriers so you can move the transmission or blocking band through each filter’s wavelength range.

Where you place the LVFs is also important:

  • Pre-sample. Use an in-line filter holder and a low-pass LVF-LL filter to block excitation energy from a light source above a certain wavelength, so that the light does not interfere with the fluorescence of the sample. The device is situated between the lamp and the sample. If the sample is in a cuvette, you can achieve the same result by using a cuvette holder adapter to secure the filter and then positioning the illumination fiber so that it transmits through the filter to the sample.
  • Post-sample.By placing a filter holder and a high-pass LVF-HH between the sample and the spectrometer or detector, you can block excitation energy in the fluorescence region by passing light above a certain wavelength. You can achieve the same result with the cuvette holder adapter fixturing the LVF on the “read” port of the cuvette holder.
  • Pre- and post-sample. You can combine pre- and post-filtering to further remove unwanted excitation signal from the fluorescence signal.

Also, LVFs can be used to reduce the stray light in absorbance measurements by limiting the illumination light to the wavelength band of interest. The LVF-HL lets you adjust both the wavelength and bandwidth of the filtering. The filter can be used either in-line or in a cuvette holder on either the illumination or read side of the holder.

What reflectance standard should I use?

Reflectance measurements are a ratio of the reflected light spectrum to the incident light spectrum. Since there is no way to directly collect all the light incident on a surface, reflectivity is usually measured relative to a reference standard. A reflectance standard can be used to calibrate and verify your spectral reflectance measurements.

The reflectance standard chosen should be similar in reflectivity to the sample to keep signal levels about the same during measurement and ensure the best S:N. The WS-1 diffuse reflectance standard is our most popular, since it is matte white in color and is >98% reflective from 250-1500 nm (then >95% reflective up to 2200 nm). The WS-1-SL can be a good choice when working in the field or in dirty environments, since it can be smoothed, flattened and cleaned if it gets pitted or dirty.

The STAN-SSH high reflectivity specular reference standard is the best choice when measuring very shiny surfaces, but it varies in reflectivity from 85-98% over its range of 250-2500 nm. This can be accounted for in OceanView software by uploading the reflectance values and correcting for the reflectivity of the standard. This data comes automatically with the STAN-SSH-NIST calibrated reference standard (250-2400 nm). If no correction is applied, OceanView will assume the standard is 100% reflective at all wavelengths, giving distorted data.

At the other extreme, the STAN-SSL low reflectivity specular reflectance standard is best for surfaces with low specular reflectance values like thin film coatings, anti-reflective coatings, blocking filters and substrates. It has just ~4.0% reflectance from 200-2500 nm.

How do I choose between a bifurcated optical fiber assembly and a fiber splitter?

Bifurcated fibers are a good choice for routing equal amounts of light from a light source to two different locations, and from a single sample to two spectrometers configured for different wavelength ranges (UV-Vis and Vis-NIR).

Fiber splitters are useful for mixing light from two different locations and delivering it through a single fiber to a spectrometer or sample. With a splitter, you can combine illumination from two different light sources, or mix light collected from two different sampling points before delivery to a spectrometer.

Fiber splitters have lower transmission efficiency than bifurcated fibers due to the inefficient geometrical overlap between the fiber cores at their junction point. This effectively eliminates splitters with small core diameter fibers for most applications, as their thicker cladding diameter results in minimal geometric overlap.

What core diameter optical fiber (patch cord) should I use for my application?

Use a smaller diameter fiber for routing high light levels, as in absorbance and irradiance measurements, and a large diameter fiber for low light level applications such as fluorescence. We offer fibers in core diameter sizes ranging from 8 µm to 1000 µm, but recommend 400 μm fibers as a good starting point for most applications.

What is the field of view of standard Ocean Optics optical fibers?

Our fibers have FOV of ~25°. Adding an accessory like a collimating lens or cosine corrector to the end of a fiber allows users to adjust the FOV, collection efficiency and spatial resolution of their setup.

When should I use an optical fiber with a linear keyed SMA 905 connector?

Keyed SMA 905 connectors are useful to achieve the same relative fiber orientation to the spectrometer, which can be critical for high-precision measurements or certain complex fiber designs. Additionally, patch cords with linear keyed SMAs may provide improved efficiency in spectrometers with a tall detector, such as those in the QE Pro, Maya2000 Pro, or NIRQuest optical benches.

Are NeoFox optical oxygen sensors used for gas or liquid phase measurements?

Ocean Optics optical oxygen sensors are compatible in both gas and liquid phases. Dissolved oxygen measurements are critical in fields such as medical, biological, marine and beverages. While aqueous DO2 measurements are the most common, Ocean Optics oxygen sensors also are compatible in common process fluids such as alcohols, fuels and high-oxygen-capacity fluorocarbon fluids.Since these fluorescent chemical sensors work on the principle of partial pressure, the conversion from these ppO2 values to the typical mg/L (ppm) units requires some information about the liquid system properties. This may include salinity levels and/or Henry’s coefficients to determine relative affinity of oxygen into that system

What analytes have been detected using SERS substrates from Ocean Optics?

We have numerous analytes with our SERS substrates using a QE Pro-Raman spectrometer and 785 nm probe, as shown in the table below. Limits of detection will vary with the sensitivity of the Raman instrument used for measurement.

AnalyteClassificationLimit of DetectionLaser Wavelength (nm)
Food & Agriculture
AcetamipridNeonicotinoid insecticide1 ppm785
Aflatoxin B1AflatoxinNo SERS ActivityNA
BardacInsecticide1 ppm785
CaptanFungicide1000 ppm785
CarbophenothionOrganophosphate insecticide1 ppm785
CarbofuranCarbamate pesticide1000 ppm785
ChlorpyrifosOrganophosphate insecticide1 ppm785
ClothianidinNeonicotinoid insecticide10 ppm785
CoumaphosInsecticide1 ppm785
Crystal VioletFungicide10 ppt785
DeoxynivalenolMycotoxinNo SERS ActivityNA
DichlorvosOrganophosphate insecticide100 ppm785
N,N-diethyl-meta-toluamide (DEET)Insect repellent1 ppm785
DiphenylamineDiphenyl fungicide1 ppm785
FipronilInsecticideNo SERS ActivityNA
FludioxonilPyrrole fungicide10 ppm785
FolpetFungicide1000 ppm785
ImidaclopridInsecticide1 ppm785
Malachite GreenFungicide1 ppb785
MalathionOrganophosphate insecticide1 ppm785
MelamineFood adulterant1 ppm532 or 785
MethomylCarbamate pesticide100 ppb785
MetofluthrinInsect repellent10 ppm785
PermethrinInsecticide1 ppm785
PhosaloneOrganophosphate insecticide1 ppm785
PhosmetOrganophosphate insecticide1 ppm785
ProfenofosOrganophosphate insecticide10 ppb785
ThiamethoxamInsecticide1 ppm785
ThiramFungicide and animal repellent1 ppm785
TransfluthrinInsecticide10 ppm785
TribufosOrganophosphate pesticide1 ppm785
TrichlorfonOrganophosphate insecticide1 ppm785
    
Illicit Drugs
CocaineStimulant1 ppm785
CodeineOpiate100 ppb785
HeroinOpiate1 ppm785
KetamineHallucinogen100 ppm785
MDMAStimulant10 ppm785
MethamphetamineStimulant1 ppm785
MorphineOpiate10 ppb785
Tetrahydrocannibinol (THC)Psychotropic (Cannabis)1 ppm785
Dyes
Rhodamine BDye1 ppm785
Rhodamine 6GDye1 ppm785
Ru(Bpy)3Dye1 ppb785
    
Biologicals
Albumin (bovine)Protein500 ppm785
Albumin (human)Protein500 ppm785
E. coliBacteriumUnknown785
GlucoseSugarNo SERS ActivityNA
HemoglobinProteinNo SERS ActivityNA
    
Antibiotics
CeftiofurAntibiotic10 ppm785
PenicillinAntibiotic10 ppm785
TetracyclineAntibiotic10 ppm785
Miscellaneous
AcetateSaltNo SERS ActivityNA
1-aminohydantoin HClAnti-cancer agent1 ppm785
Bitrex (denatonium benzoate)DenaturantNo SERS ActivityNA
BPETaggant/Marker100 ppt785
GeosminFlavor compoundsNo SERS ActivityNA
GtMIBFlavor compoundsNo SERS ActivityNA
2-methylisoborneol (MIB)Flavor compoundsNo SERS ActivityNA
2-naphthalenethiolFlavoring agent100 ppb785
NicotinamideVitamin10 ppm785
OxalateNutrientNo SERS ActivityNA
1,10-phenanthrolineHeterocyclic organic100 ppb785
(-)-RiboflavinVitamin10 ppm785
Semicarbazide HClDetection agent10 ppm785

Light Sources

What is the different between the DH-2000 and DH-2000-BAL combination deuterium-tungsten halogen light sources?

All deuterium sources have an alpha line, a sharp spectral feature centered at 655 nm. This feature and other deuterium lines produce “unbalanced” output in the deuterium and halogen sources. Simply adjusting the integration time of the spectrometer to suppress the alpha line does not solve the problem as the efficiency of the system at UV wavelengths drops significantly, compromising signal-to-noise performance.

A system of proprietary internal mirrors and filters eliminates the D-alpha, D-beta and Fulcher lines in the deuterium source, producing a “smoother” spectrum across the entire wavelength range and eliminating problems associated with saturation. By comparison, most combination UV-NIR sources can be adjusted for relative intensity only.

Regulatory

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