High performance liquid chromatography (HPLC) is a valid and reliable technique that has become a practical tool in many laboratories. The HPLC Analytical Laboratory faces problems that can waste time and resources. One of the most common problems in HPLC is the quality of the solvent/mobile phase. Contaminants in the solvent can affect the performance of HPLC in a variety of ways (Safavizadeh
et al., 2020, Safavizadeh
et al., 2021, Snyder
et al., 2012).
In the HPLC analysis, water is essential in the preparation of mobile phases and samples. If impurities are present in the moving phase, they can amplify the background signals. In this way, the base noise and drift increase or cause other phenomena, such as negative peaks or unknown peaks during slope washing. Also, the presence of impurities in the sample solutions can cause unknown peaks. HPLC grade water is a type of water that loses its impurities due to the distillation process (Arabi
et al., 2020, Wang and Kasperski, 2018)
.
In fact, water is boiled and distilled using special devices, and finally HPLC grade water is obtained by separating gases and suspended mineral particles. Depending on the type and amount of distillation, this water can be up to 95 pure. As a result, there are almost no minerals in it. This water is used for various and important purposes (Saini
et al., 2017)
.
Ordinary water, or treated city water, does not contain any pollutants or dangerous salts. However, it is not completely pure and contains salts, such as calcium and magnesium. These minerals, which are found in mineral water, do not pose a threat to the health of the body, and sometimes even their presence is necessary for the better functioning of the body organs. However, sediments left by these salts may in some cases pose a threat to human health (Senevirathne
et al., 2018)
.
HPLC grade water, in addition to being free of salts and minerals, has no calories or sugar. On the other hand, the most important difference between this water and municipal water is how it is processed. HPLC grade water is obtained by the process of evaporation at high pressure. For this reason, it can be said that HPLC grade water is the product of changes in the structure of urban drinking water (Zhang
et al., 2017)
.
HPLC grade water does not contain any solutes. For this reason, it does not have the property of contrasting with some chemicals. This feature has led to the use of HPLC Grade water in laboratories and scientific and research centers for activities, such as dissolving chemicals or even washing laboratory dishes. On the other hand, the highest consumption of this water is in the pharmaceutical industry and medical applications due to its high purity. You have seen the smallest example of using HPLC grade water in chemistry and food analysis (Ghafurian
et al., 2019)
.
One of the most important properties of HPLC grade water is that it does not leave any sediment due to evaporation or excessive use. For this reason, it is also used to keep car batteries moist, since ordinary water sediment can damage the battery and eventually the car engine after a while (Senevirathne
et al., 2018)
.
HPLC grade water is also used to make raw materials in various factories, especially food. The purity of this water has led many people to drink it instead of municipal water. Measuring pH, oxidizing materials, and residues after evaporation in this type of water is not practical due to measurement problems of this purity (Zhang
et al., 2017)
.
HPLC grade water free of any minerals is essential. Drinking this water, although in many cases recommended for some people with certain diseases, but also carries risks. The purity of this water reduces the error in the tests and increases the accuracy and has a very high impact on the results (Ouyang
et al., 2017). The present study aimed to evaluate the quality of HPLC grade water available in the market for the first time
.
Materials and Methods
Thirty samples of HPLC grade water were purchased from the relevant stores in Tehran during the period of January 1st to February 1st 2020. The samples had 5 domestically produced samples and 25 foreign samples.
The electrical conductivity was measured using COND 7310 conductivity meter, WTW Co., Germany, and its standard limit according to Iranian standard 1728 is 0.01 MS/s.
In general, the instructions for measuring silica in water were generally divided into the five or six categories as follows:
Dye formation: For 50 ml of the sample, 10 ml of 1 + 1 hydrochloric acid and 2 ml of ammonium molybdate reagent were added to the sample in rapid sequence. They were mixed at least 6 times and placed on the mixer for 5 to 10 min. Two ml of dissolved oxalic acid was added to the sample and mixed thoroughly again. After 2 to 15 min, the color value was recognized, the desired time was calculated from adding oxalic acid to the sample. Given the yellow color of the sample may follow the beer rule, it was better to read the color value with a photometer.
In order to find some unreacted silica solids, the sample was digested with NaHCO3 before the dye formation step. Certainly this amount of digestion is not sufficient to convert all amounts of unreacted silica molybdate to reacted silica molybdate. Silicate compounds as well as silicate polymers have a high melting point with alkalinity at high temperatures. The digestion step can be omitted if all known silicates react with molybdate. Then, 200 mg of NaHCO3 was added without digestion and placed in digestion reactors for 1 h. The analysis cannot be stopped in time, but all the steps must be continued until the end. Fifty ml of Nessler tube was carefully transferred to it and its value was marked (Regnault
et al., 2004, Toppner, 2014).
Preparation for colorimetry (or determination of turbidity): For each sample that needs to be prepared, there was a separate blank or control sample. For the measurement, two of the above cases should be made according to the function of the instructions. The necessary reagents should be added to one of them, and the other sample, which is the control and blank sample, should be oxalic acid and hydrochloric acid, without adding Molybdate. The control sample or blank without any molybdenum was put in the device and did not show the device below (Paul
et al., 2019).
Calculations and measurements: The device was turned on and the absorption rate was reduced to zero with HPLC grade water and all the standards were read, including control reagents, in front of the HPLC grade water blank. Plot micrograms of silica eventually appeared in the 55 ml solution for reading in the Fluorimeter. The blank sample was put in the machine and a standard was applied for each group of samples, so that the calibration curve drawn by the machine was not disturbed (Regnault
et al., 2004, Toppner, 2014).
