Читать книгу pH of the Skin: Issues and Challenges - Группа авторов - Страница 46

The rubber cap covering the lateral electrode-filling aperture should be lifted and immediately replaced once daily before measurements as to allow atmospheric pressure compensation [24]. Prior to use, the pH meter should be equilibrated for at least 20 min in the same room where measurements will be recorded [2, 7]. It is desirable to maintain room temperature between 20 and 22°C and the relative humidity between 40 and 60% to minimize sweating by the participant [2].

The pH meter must be calibrated in accordance to the instructions of the manufacturer [7, 12]; usually this implies calibration prior to use, but longer intervals may be prescribed based on the frequency of use and the age of the electrode [2]. With high frequency measurement, periodic verification against a standard buffer may also be required [7]. Calibration with at least 2 stable calibration buffers, usually at a pH of 4 and 7, should be performed.

Prior to measurement, the participant should be relaxed and acclimated for at least 20 min at the above-mentioned room temperature and relative humidity in order to avoid errors that could arise due to temperature and sweating [2]. Also, skin positions to be measured should not be occluded by clothing. Measurement of skin surface pH should be made on anatomical positions appropriate for the particular study design. In clinical settings, the standard anatomical position is the (mid) volar forearm. The skin on the measurement position may be wiped using a clean, dry, oil- and lotion-free tissue paper or filter paper to remove excess sebum or other residues [7, 12]. The use of water to clean the skin is not recommended, as it will influence the skin surface pH. The flat measuring surface of the pH electrode should be moistened with deionised water prior to it being applied to the skin (as to avoid contamination). The electrode should be held at a right angle to the skin and with gentle pressure applied in order to obtain optimal contact between the electrode’s measuring surface and the skin surface [7]. Excessive pressure must be avoided, as it will most likely affect the extraction of material from the skin and expunge water between the electrode and the skin [2]. If possible, measurements should be performed by the same person, as to avoid inter-individual operator variability. Measurements should be recorded upon obtaining a stable signal (as is defined by the instrument manufacturer) [7, 12]. It is recommended to make 3 sequential measurements on the same anatomical position, each adjacent to the other. The lag-time between these sequential measurements should be as short as possible [7]. If more than one anatomical position is to be measured, it is recommended that all measurements on one anatomical position be completed before moving to the next position [7, 12]. If pH measurements are made at time intervals on a specific anatomical position, the area of measurement should be demarcated so as to ensure that all measurements are performed in exactly the same positions. Dermatological marking pens, photographs or templates may be used to demarcate measurement positions on the skin. The electrode should also be regularly inspected between measurements for possible contamination with sebum and other substances, and if present, it should be eliminated [2]. Finally, if skin surface pH measurements are recorded in conjunction with other skin barrier function measurements, such as transepidermal water loss and skin hydration, skin surface pH should be measured last, as the water applied onto the skin with pH measurement will affect the other measurements [12].