Reflectoquant® Malic Acid Test, Catalog No. 16128/1
Malic acid (malate) is oxidized to oxalacetate by NAD under the catalytic effect of malate
dehydrogenase. In the presence of diaphorase, the NADH formed in the process reduces a tetrazolium
salt to a red formazan, the concentration of which is determined reflectometrically.
2. Measuring Range and Number of Determinations
||Number of Determinations
|1.0 - 60.0mg/l malic acid
Beverages, e.g. wine and fruit/vegetable juice, after appropriate dilution (see section 6).
Food after appropriate sample pretreatment
4. Influence of Foreign Substances
After appropriate dilution or sample pretreatment, the determination is not interfered with
by the concentrations of foreign substances usually present in beverages and food.
5. Reagents and Auxiliaries
|The analytical test strips are stable at least up to the date stated on the pack when
stored in the closed tube at +2 to +8°C.
Tube containing 50 analytical test strips
1 Bar code strip
Other Reagents and Accessories:
L(-)-Malic acid, Cat. No. MX0119
Buffer solution pH 7.00 Titristar®, Cat. No. BX1635/1
Reflectoquant® Dilution Set, Cat. No. 17990/1
Liquid samples can be analyzed after appropriate sample pretreatment, e.g. after dilution with
distilled water. In the case of dilutions of 1:50 or higher (e.g., 1ml of sample + 49ml of water),
interferences due to intrinsic colorations can be neglected even in very intensively colored
To exclude interferences due to foreign substances, at least the following dilutions
|Fruit and Vegetable Juices:
|The Reflectoquant® Dilution Set is appropriate for this dilution.|
Observe the instructions for the reflectometer. The following applies to the Malic Acid Test:
Measurement Procedure A.
Stored reaction time: 300 sec.
|Press the START button of the reflectometer and - this is imperative - at the same
time immerse both reaction zones of the analytical test strip into the measurement. Sample
for approximately 2 seconds. Allow excess liquid to run off via the long edge of the strip onto
an absorbent paper towel.
insert the test strip all the way into the strip adapter with the reaction zone facing the display.
After the end of the reaction time, read off the result from the display in mg/l malic acid.
The result is stored automatically.
Notes on Measurement:
- The two reaction zones change color differently.
- Concerning the result of the analysis, the dilution (see section 6) must be taken
Result of analysis = measurement value x dilution factor
- Serial Measurements:
After the first measurement, it is possible to run further measurements by pressing
the START button. In this case, however, a stopwatch is required since the countdown
function of the reflectometer is available only once per series.
Protect the reaction zones from light during the reaction time.
All results are individually shown and automatically stored.
8. Method Control
To check analytical test strips, equipment, and handling:
Dissolve 0.250g of L(-)-malic acid in buffer solution pH 7.00, make up to 100ml with this
buffer solution and mix. Malic acid content: 2500mg/l.
Dilute this standard solution with distilled water to 25mg/l malic acid and analyze as
described in section 7.
- Reclose the tube containing the test strips immediately after use.
- At the end of each workday, cleanse the strip adapter thoroughly with water or ethanol.