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How to use ion chromatography to detect lactic acid content?

Since polylactic acid is formed by the polymerization of lactic acid, can the content of lactic acid in it be tested? This article introduces how to use ion chromatography to test the new material polylactic acid

Polylactic acid (polylactide,; polylactic acid,; PLA), also known as polylactide, is a polyester polymer obtained by polymerization of lactic acid as the main raw material. It uses renewable biomass such as corn, cassava, and straw as raw materials. Broad and renewable. After use, polylactic acid products can be composted and degraded into CO2 and water to realize the cycle in nature without polluting the environment. This is very beneficial to environmental protection and is recognized as an environmentally friendly material.

This test uses Wanyi ion chromatograph IC6000 to draw a lactic acid standard curve and share the ion chromatography method for the determination of polylactic acid content in biodegradable materials.

Instruments and equipment required for ion chromatography:

Ion chromatograph: IC6000, conductivity detector;
Autosampler: AS3100;
Oil bath device (with stirring function);
One-tenth electronic balance;

Take 0.3g of the sample, accurately weigh it, transfer it to a round bottom flask, add 40mL NaOH solution (1mol/L) and gently shake to make the sample immersed in the solution, add a condenser, and place the flask in a 100°C oil bath. 1h, turn on the magnetic stirring (20rpm) at the same time, take out and cool down after 1h to obtain the degradation liquid. Transfer all the degradation liquid to a 100mL volumetric flask and dilute to the mark with water. Then dilute the degradation solution 200 times, take the diluted sample, and pass it through the activated RP column-H column-0.45μm needle filter to remove the first 1-2mL filtrate, and take the filtrate into an ultrafiltration centrifuge tube for centrifugation (10000rpm) 10min, transfer the filtrate to the sample bottle to be tested.
Note: 1. The RP column is first passed through 10 mL of methanol, then 15 mL of pure water, and activated for 30 minutes
H column passes through 10mL pure water and activates for 30min
2. Since the sample contains macromolecular organic matter, this test uses a strong alkali solution to degrade it. To avoid incomplete sample degradation and possible irreversible damage to the chromatographic column by the degradation solution, the RP column is used to remove the degradation in this test. For organics in the liquid, the H column neutralizes the degradation liquid.

Ion Chromatography Conditions

Chromatographic column Shodex SI-52 4E 4×250mm+Wayeal HS-5AG 4.6×50mm
Eluent 3.6mM Sodium carbonate
Flow rate 0.8mL/min
Column temperature 45℃ Conductivity cell temperature 50℃
Current 30mA Injection volume 25μl

Test chromatogram

                          Standard curve series concentration table(μg/mL)
Name        1       2        3       4       5
L-lactic acid    1.235      2.45     4.90     9.80    19.6

Standard curve test chromatogram

Lactic acid standard curve test chromatogram


Sample test chromatogram

Ion chromatography has high sensitivity and good selectivity. Using ion chromatography to determine polylactic acid is simple and fast.



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