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Introduction

The traditional use of the spectrophotometer is to measure the absorbance or transmission

of a clear or translucent liquid or solid. Typically UV/VIS/NIR spectroscopy applications

include reaction kinetics, quantitative analysis or the identification of the chemical

constituents in a substance. The measurement of reflectance offers an added dimension to

the spectroscopy capabilities of your spectrophotometer, the analysis is no longer limited

to the portion of the beam that penetrates the sample. Accordingly, the analysis is no

longer limited to samples that are clear or translucent. The DRA provides the means of

measuring absorbance or transmission of opaque, turbid and reflecting substances.

Figure 1. The external DRA.

Figure 2. The external DRA viewed from

the back.

There are three versions of the diffuse reflectance accessory that operate over different

wavelength ranges.These are specified

below. While all of the following variations are

available, the configurations indicated by ticks in the table below offer optimal operation.

(External DRA

900)

(External DRA

1800)

(External DRA

2500)

Cary

4000

Cary

5000

Cary

6000i

The Varian 900, 1800, 2500 External Diffuse Reflectance accessory (DRA) consists of a

150 mm diameter integrating sphere. The sphere is easily installed in the sample

compartment of the instrument and features an inbuilt high performance photomultiplier

tube (PMT). The DRA also has a Lead Sulfide (PbS) or InGaAs detectors which become

active Varian 2500 External DRA. The coating is Polytetrafluoroethylene (PTFE), which

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