Interpretation Of New Standard For Determination Of &Nbsp Value Of Textiles And Ph Value Of Aqueous Extracts

1, foreword

National standard GB/T7573-2009

This article mainly aims at (1), (2), (5), (7) modification part to carry out experimental analysis and explore more scientific and reasonable technical conditions.

2. Experiment part

This experiment is based on the implementation plan of GB/T7573-2009 "determination of pH value of textile water extraction solution". In view of the technical part of the new standard, the influence of 0.1mol/L KCl extraction medium, extraction time, experimental water, test time, sample humidity control and other factors on the determination of pH value of water extraction solution is emphatically discussed, so as to find the best way for testing and analysis in modern textile laboratory.

In addition to comparing the technical conditions of the experimental part, all other technical conditions of the experiment are carried out in accordance with GB/T7573-2009, without special explanation.

2.1 the influence of extraction medium and extraction time

2.1.1 three stage water (5 ~ 7.5) [1] extraction medium

Principle: water is a very weak electrolyte, and its ionization equation can be expressed as: H2O H++OH-

2.2 the influence of three grade water pH value

The new standard GB/T7573-2009 quoted the GB/T 6682-2008 "water specification and test method for analytical laboratories" and changed the pH value range of distilled water or deionized water to 5 to 7.5, which is wider than the experimental water specified in GB/T7573-2002.

In this experiment, the three grade water with pH 5.5 and 7.5 was selected as the extraction medium, respectively labeled as A and B. The pH of the extraction solution was determined to analyze the effect of three grade water in different pH interval on the test results.

Other technical conditions of the experiment were carried out in accordance with GB/T7573-2009's determination of the pH value of the aqueous extract of textiles.

2.3 effect of experimental time

In the experiment, we found that the time of glass electrode immersed in the extract affects the stability of the reading.

To get more accurate and reliable readings, glass electrodes do need to immerse in the extract for a period of time, so that the electrodes can respond. However, the immersion time is too long, which will cause the test data to drift, resulting in unstable reading. The experiment found that exposure to alkaline extractants in air for 10 min can lead to a reduction of pH value by more than 0.1. Over thirty minutes, the result of pH value can be reduced by more than 0.2. For acidic neutral neutral extraction, 30 min in air can cause the pH value to increase by 0.2.

This is because in an open laboratory environment, carbon dioxide in the air and other possible acidic (or basic) gases will be dissolved in the extract, affecting the concentration of H+ in the solution, thereby destroying the ion exchange balance and interfering with the experiment.

At present, the domestic laboratory basically adopts the open environment to conduct pH test on the extraction solution, so we finish the experiment operation as quickly as possible, so as to reduce the experimental error.

2.4 effect of humidity control on samples

GB/T7573-2009 "determination of pH value of textile water extract" cancelled the requirement of humidity control for test samples.

For the same sample, after two interlaboratory hygroscopic and non humidifying treatment experiments, it was found that the pH value of the extraction solution reproduced a larger regularity. Therefore, the humidification treatment of the test sample will affect the pH value of the extraction solution.

2.5 other factors

The preparation of the sample, the frequency and amplitude of the oscillation, the selection and maintenance of the electrode, the subjective judgement of the laboratory staff, and the laboratory environment will affect the accuracy of the determination of pH in the extraction solution.

Laboratory staff should pay more attention in daily work. The frequency selection should be reciprocating 60 times /min, rotating 30 weeks /min and amplitude 2cm.

The effective period of the electrode is generally 1 years. The electrode used for a long time will appear slow response and data drift, so new electrodes should be replaced in time.

3 conclusion

It is found by experiments that there are many factors that affect the accuracy of pH testing.

Starting from the comparison between the two standards of GB/T7573-2009 "determination of pH value of textile water extract" and "determination of pH value of textile water extraction solution", we have designed and implemented a large number of experiments. Experiments show that using 100ml 0.1mol/l KCl solution as extraction medium and extracting 1H + 5min can obtain satisfactory data with good reproducibility and high reliability, and at the same time improve work efficiency; the three grade water with different pH value ranges as an extraction solution has no obvious difference in the test results; the time of exposure to the laboratory opening environment has a great influence on the test results.

This experiment is carried out in the light of the present situation of the textile laboratory. It is suitable for the determination of the pH value of the textile water extract of most commercial commissioned tests. The determination of the pH value in the case of arbitration and laboratory equivalence should be carried out in accordance with the consistent intention of the two parties.

Although GB/T7573-2009's "determination of pH value of textile water extract" has been greatly improved than GB/T7573-2002 in terms of technical conditions, it is more scientific and reasonable. However, its specific implementation details need to be clarified and clarified. We expect GB 18401 - 2003 "national textile product basic safety technical specification" in the revised version of the revised version to be specified.

The water extracted from textile water is very limited. The ionic strength is small and the conductivity of the solution is low. The conductivity of the three grade water in the preparation of textile water extract is generally 2~5 S/cm. The resistance of the aqueous extract is very high. It is not negligible compared with other resistances in the measuring loop. At the same time, the change of pH caused by the instability of the liquid junction potential leads to a large drift of indication, and it is not easy to get the result of reappearance.

2.1.2 KCl (0.1mol/L) extraction medium

Principle: the KCl solution is a typical neutral solution, which is completely ionized in strong water with strong acid and strong base salt. K+ and Cl- do not change the concentration of H+ in water. That is, the ionization equilibrium of H2O H++OH- will not be destroyed. Therefore, KCl solution will not interfere with the pH value of the test solution itself. It can be used as an ionic strength regulator, increasing ionic strength and increasing electrical conductivity, thereby improving the stability of pH value.