Jenway Genova Nano Data Sheet

Application note: A09-012A
Accuracy and precision of the Genova Nano
Introduction
The Jenway Genova Nano spectro­photometer combines a micro volume accessory with the dedicated life science measurement modes of the Genova Plus as well as those of a standard spectro­photometer. The Genova Nano is able to measure sample volumes as low as 0.5µl with a high degree of accuracy, reproducibility and speed. This ability conserves precious samples, reduces the need for dilution and eliminates the requirement for cuvettes. Cleaning is quick and simple: wiping the read heads with a lint­free cloth removes all trace of the sample, allowing faster change over between samples and therefore increasing sample throughput.
and precision is a measurement of repeatability or reproducibility. The Genova Nano is specified to an absorbance accuracy of +/-2% at 260nm and a precision of <
0.005A between 0 and 1A (at 0.5mm path length). This application note demonstrates this specification on eight individual units and also shows concentration reproducibility when measuring in dsDNA mode.
Materials and Methods
Each of the Genova Nano units was calibrated using the certified calibration standard solution provided following the instructions detailed in the user manual.
To determine absorbance accuracy, the unit was set up in multiwavelength mode to measure at 260nm and 330nm. The unit was zeroed using 2µl of the calibration blank solution then 2µl aliquots of the calibration standard solution were measured. Following each measurement, the sample was wiped off the read head using a lint-free wipe. This test was performed at both at 0.5mm and
0.2mm path lengths and on each individual unit. 10 successive readings were used for data analysis.
Fig. 1: Applying samples to the read head of the micro volume accessory.
An important requirement for measurement of micro volumes is accuracy and precision. Accuracy is defined as how close the measured parameter is to a defined value
jenwayhelp@bibby-scientific.com
www.jenway.com
Tel: +44 (0)1785 810433
Fig. 2: A droplet of sample is shown on the Genova Nano read head.
In order to measure absorbance precision or repeatability, a sample of green food colouring (Supercook, Leeds, UK) was used. This contains a mix of tartrazine (E102) and Green S (E142). The absorbance spectrum
of the food colouring shows a peak at 430nm and a trough at 520nm (Fig. 3), therefore these wavelengths were chosen for measurement. The food colouring was diluted with water to give an absorbance between 0 and 1 in a path length of 0.5mm.
Fig. 3: Visible spectrum of green food colouring measured using the microvolume accessory at
0.5mm path length showing a peak at 430nm and trough at 520nm.
In a similar manner to the absorbance accuracy test, the unit was set up in multiwavelength mode, however this time measurements were made at 430nm and 520nm. The instrument was zeroed using 2µl of water then 2µl aliquots of the food colouring solution were measured. Following each measurement, the sample was wiped off the read head using a lint-free wipe. This test was performed at 0.5mm path length on each individual unit. 10 successive readings were used for data analysis.
For measurement of concentration repeatability, the unit was set up in the Life Science Multiwavelength mode with the following parameters:
a. Wavelength 1 = 260 b. Wavelength 2 = 280 c. Wavelength 3 = 230 d. Wavelength 4 = 330 e. Sum = (xF1*(A1-A4))-(xF2*(A2-A4)) f. F1 = 50 for dsDNA g. F2 = 0 h. Units = µg/ml
The sample used was Calf thymus DNA (Sigma, D3664) diluted to approximately 100µg/ml with nuclease-free water. Measurements were performed as described previously. The instrument was zeroed using 2µl of water then 2µl aliquots of the DNA solution were measured. Following each
measurement, the sampls was wiped off the read head using a lint-free wipe. This test was performed at 0.5mm path length on each individual unit. 10 successive readings were used for data analysis.
Results
In order to minimise any factors which may interfere with a reading it is recommended, when performing micro volume measure­ments, that a reading is also made at a second reference wavelength (where the absorbance of the sample is very low and unchanging) in order to perform a background correction. In each of the measurements shown here, background correction was performed at 330nm for the calibration solution and DNA and at 520nm for the green food colouring. For analysis the absorbance at the background wavelength was subtracted from that of the measurement wavelength.
Results for the absorbance accuracy tests are shown in Fig. 4.
Fig 4: Absorbance accuracy tests on 8 individual Genova Nano units at 0.5mm path length (top) and 0.2mm path length (bottom). The centre unbroken line on each graph represents the expected absorbance value of the standard solution. The broken lines are set +/- 2% from the expected value. The mean of 10 consecutive readings are shown.
jenwayhelp@bibby-scientific.com
www.jenway.com
Tel: +44 (0)1785 810433
+ 2 hidden pages