Standard pH Values Research Articles

Accuracy of pH strip testing and pH liquid testing versus standard pH meter of gastric contents in critically ill patients: a diagnostic accuracy study

ObjectiveThe utilisation of pH level measurements from gastric contents may indicate the preferred tip position of a nasogastric tube or monitor the efficacy of stress ulcer prophylaxis in critically ill...

The effect of soil moisture content and soil texture on fast in situ pH measurements with two types of robust ion-selective electrodes

Abstract. In situ soil pH measurements with ion-selective electrodes (ISEs) are receiving increasing attention in soil mapping for precision agriculture as they can avoid time-consuming sampling and off-site laboratory work. However, unlike the standard laboratory protocol, in situ pH measurements are carried out at lower and varying soil moisture contents (SMCs), which can have a pronounced effect on the sensor readings. In addition, as the contact with the soil during in situ measurements should be relatively short, effects of soil texture could be expected because texture controls the migration of protons to the electrode interface. This may be exacerbated by the fact that the electrodes used for in situ measurements are made of less sensitive but more robust materials as compared to the standard glass electrode. Therefore, the aim of the present study was to investigate the effect of soil moisture and soil texture on pH measurements using robust antimony and epoxy-body ISEs pressed directly into the soil for 30 s. The SMC was gradually increased from dry conditions to field capacity. A wide range of soil texture classes were included, with sand, silt, and clay contents ranging from 16 % to 91 %, 5 % to 44 %, and 4 % to 65 %, respectively. An exponential model was fitted to the data to quantify the relationship between SMC and pH. The results show that an increase in SMC causes a maximum increase in pH of approximately 1.5 pH units, regardless of the type of pH ISE used. Furthermore, for sandy soil textures, a rather linear relationship between pH and SMC was observed, whereas, with decreasing mean particle diameter (MPD), the model had a pronounced exponential shape, i.e., a greater pH increase at low SMC and a plateau effect at high SMC. With increasing SMC, the pH values asymptotically approached the standard pH measured with a glass electrode in 0.01 M CaCl2 (soil : solution ratio of 1:2.5). Thus, at high SMC, subsequent calibration of the sensor pH values to the standard pH value is negligible, which may be relevant for using the sensor pH data for lime requirement estimates. The pH measurement error decreases exponentially with increasing soil moisture and increases with decreasing MPD. Using a knee point detection, reliable pH values were obtained for SMC > 11 %, irrespective of the pH ISE used. An analysis of the regression coefficients of the fitted exponential model showed that the maximum pH increase also depends on soil texture; i.e., the influence of soil moisture variation on the pH value increases with decreasing MPD. Moreover, the concavity of the exponential curve increases with decreasing MPD.

A Microfluidic pH Sensor with Temperature Compensation Based on Extended-Gate Field-Effect Transistor

PH sensors are widely used in food processing, health monitoring, water quality monitoring, and many other fields. The pH sensor applied in the health monitoring field can realize the real-time measurement of human health information and timely prevent the occurrence of diseases by improving people’s health levels. However, these sensors have some challenges in body fluid collection and temperature compensation. Here, we developed a pH sensor based on an extended-gate field-effect transistor (EGFET) with microfluidic channels and a temperature sensor to overcome these challenges. The sensor is prepared using a low-cost, solution-based process in which a temperature sensor is used for body temperature measurement and temperature compensation, and a microfluidic channel is used for body fluid collection. This pH sensor can measure both body temperature and pH of body fluid, where the temperature coefficient of resistance (TCR) of the temperature sensor is up to 5.17%, and the measurement result of body temperature is only 0.17 ℃ different from that of the gold standard. The pH sensitivity is 58.41 mV pH−1, and the pH value is only 0.066 deviating from the standard pH value. The sensor is expected to be used on a large scale in the applications of wearable health monitoring.

The Viability of The Pasteurized milk with the addition Cinnamon (Cinnamomum burmannii) Extract

Generally, pasteurized milk in Indonesia has a relatively short shelf life of 5-7 days. Commercially, pasteurized milk has also experienced microbial contamination also found on day 7, so it cannot be stored for long. To avoid this, it is necessary to add natural ingredients, which are to maintain quality, by inhibiting the growth of pathogenic bacteria so the shelf life of pasteurized milk can be extended. One of these natural ingredients is cinnamon (Cinnamomum burmannii), which has antibacterial properties from its metabolite components. Cinnamon extract was added to pasteurized milk of as much as 0.5%. Cinnamon extract was obtained by the maceration method and concentrated using a rotary evaporator. This study used a completely randomized design (CRD) consisting of 5 storage treatments (0 days, 7 days, 14 days, 21 days and 28 days), each treatment was repeated 4 times. Parameters measured included pH analysis, total plate count and antibacterial activity against Escherichia coli and Staphylococcus aureus. The results of pH analysis showed that the average pH value of pasteurized goat’s milk added with cinnamon (Cinnamomum burmannii) extract and stored for 28 days ranged from 6.24 to 6.44, this value range had reached the standard pH value. The results of total plate count showed that the average bacterial growth ranged from 0.7 × 104 CFU/ml – 16.9 × 104 CFU/ml. Therefore, the results of the addition of cinnamon extract to pasteurized milk still met the standards of pasteurized milk. The addition of cinnamon extract with a concentration of 0.5% to pasteurized goat’s milk showed antibacterial activity by forming an average inhibition zone of 1.6 mm on S. aureus bacteria but was unable to inhibit the growth of Escherichia coli bacteria. Based on the results of the study, it can be concluded that the addition of 0.5% cinnamon extract to pasteurized milk can extend the shelf life of pasteurized milk up to 28 days but is unable to inhibit bacterial growth.

Effects of Calcination Temperature of Naturally Occurring Absorbents on Drinking Water Defluoridation

Currently, in Tanzania, fluoride removal from drinking water is treated mostly using the bone char method. The method has poor acceptability in some religious communities and also causes water quality deterioration in taste and odour if the bones are not properly prepared. The use of local natural adsorbents as an alternative is feasible with limitations of high levels of other impurities in treated water. Locally available gypsum, magnesite and bauxite were converted to adsorbents through calcination. The study was conducted to determine the removal efficiency, best calcination temperature and composite ratio of the three adsorbents for the removal of fluoride from natural drinking water with fluoride concentration as high as 16.7 mg/L. The adsorbent materials were calcined at different temperatures ranging between 3500C and 6000C. Batch experiments were performed and samples were collected at different contact time intervals of 2 minutes to 60 minutes, and residual fluoride was determined. Bauxite had the highest fluoride removal efficiency compared to gypsum and magnesite. The best calcination temperatures were 3500C, 4000C, 6000C for gypsum, bauxite and magnesite, respectively. The best calcination temperatures were used to prepare composites at different ratios of 1:2:3, 2:3:1 and 3:2:1, bauxite: gypsum: magnesite respectively. All the ratios gave low sulphate and iron as impurities within the recommended standards. The composites lowered fluoride concentration level to 1.53 mg/L, 2.07 mg/L, 2.60 mg/L for 1:2:3, 2:3:1, 3:2:1 ratios, respectively. In conclusion the study reveals that, it is possible for composites made of adsorbent calcinated at different optimum temperatures to give good results in fluoride removal from drinking water, as well as standard pH, iron and sulphate values in treated water.

Growth of Listeria monocytogenes in a Model High-Moisture Cheese on the Basis of pH, Moisture, and Acid Type

High-moisture, low-acid cheeses have been shown to support Listeria monocytogenes growth during refrigerated storage. Prior studies suggest that organic acids vary in their antilisterial activity and that cheeses of lower pH delay growth longer than those of higher pH; however, no standard pH value for Listeria control in cheese exists. The objective of this research was to create a predictive model to include the effects of acid type, pH, and moisture on the growth of L. monocytogenes in a model cheese system. Cream, micellar casein, water, lactose, salt, and acid (citric, lactic, acetic, or propionic) were combined in 32 formulations targeting 4 pH values (5.25, 5.50, 5.75, and 6.00) and two moisture levels (50 and 56%). Each was inoculated with 3 log CFU/g L. monocytogenes (five-strain mixture) after which 25-g samples were vacuum sealed and stored 8 weeks at 4°C. Triplicate samples were enumerated on modified Oxford agar weekly in duplicate trials. Model cheeses formulated with acetic and propionic acids inhibited growth (i.e., no observed increase in L. monocytogenes populations over 8 weeks) at pH ≤5.75, while those formulated with lactic acid inhibited growth at pH 5.25 only. In contrast, all model cheeses formulated with citric acid supported growth. Resulting growth curves were fitted for lag phase and growth rate before constructing models for each. The pH and acid type were found to significantly affect both growth parameters (P < 0.05), while moisture (50 to 56%) was not statistically significant in either model (P ≥ 0.05). The effects of acetic and propionic acid were not significantly different. In contrast, model cheeses made with citric acid had significantly shorter lag phases than the other acids tested, but growth rates after lag were statistically similar to model cheeses made with lactic acid. These data suggest propionic ∼ acetic > lactic > citric acids in antilisterial activity within the model cheese system developed and can be used in formulating safe high-moisture cheeses.

Corrosion protection of Cu by atomic layer deposition

Atomic layer deposition (ALD) is a vapor phase technique that is able to deposit uniform, conformal thin films with an excellent thickness control at the atomic scale. 18 nm thick Al2O3 and TiO2 coatings were deposited conformaly and pinhole-free onto micrometer-sized Cu powder, using trimethylaluminum and tetrakis(dimethylamido)titanium(IV), respectively, as a precursor and de-ionized water as a reactant. The capability of the ALD coating to protect the Cu powder against corrosion was investigated. Therefore, the stability of the coatings was studied in solutions with different pH in the range of 0–14, and in situ raman spectroscopy was used to detect the emergence of corrosion products of Cu as an indication that the protective coating starts to fail. Both ALD coatings provide good protection at standard pH values in the range of 5–7. In general, the TiO2 coating shows a better barrier protection against corrosion than the Al2O3 coating. However, for the most extreme pH conditions, pH 0 and pH 14, the TiO2 coating starts also to degrade.

Hydrogeochemistry and sulphate contamination of water environment around the coal stock pile in Tamabil, Sylhet

The study area Tamabil, Sylhet, is an important area in importing coal and its storing for supplying to different industrial uses in Bangladesh. This area is located in the north-eastern part of Bangladesh. Currently, the water environment in the study area is threatened by the processing of high sulphur coal, agricultural activities, and other anthropogenic effects. Hence, the protection of water resources in terms of quality and quantity from such contamination should be considered a serious issue. From this view point, this study intends to evaluate the hydrogeochemical characteristics and sulphate contamination of water bodies in the area. The hydrochemical evaluation of water for all samples has been carried out under standard laboratory methods with various diagrams, charts, and statistical methods. From the results of the laboratory testing, it has been observed that the water in the wells close to the coal stock pile is highly acidic (pH = 3.41), whereas the water shows the standard pH values as its distance increases from the stock area. The hydrogeochemical evaluation of water under the Piper chart implied that mixed type of water facies such as (i) Ca–Mg–Cl (38.7%), (ii) CaHCO3 (38.7%), (iii) NaCl (16.12%), and (iv) CaCl (6.4%) are dominant in the area. The Gibbs diagram showed the rock- and evaporation-dominant mixed environment, while the Durov Diagram reflected mixing–dissolution state with few in reverse ion-exchange condition. These results suggest that the major geochemical facies and evolution of water are prevailed by the carbonate rock dissolution and the weathering process. In the case of sulphate contamination, the overall concentration of sulphate falls within the standard limit of WHO and EQS, but this study observed that the intensity of SO4 is high in the samples adjacent to the coal stock pile. These scenarios entailed that the stored coal is primarily responsible for it while the sulphur content ranges from 1.42 to 7.26 Wt% (average 3.73 Wt%) of this coal. In addition, the leaching experiment of this coal shows that the pH values of the water reduce from 7 to 1.2, consequently increasing the acidity of the water environment around the area. In conclusion, this study recommends that (i) more cautious and watchful activity has to be taken to import, store, and use this coal; (ii) more precautions have to be considered to protect the water from such contamination to save the green environment as a whole for the present and future.

SIMULASI PH AIR UNTUK AIR BOILER DAN AIR CHILLER PADA MESIN PRODUKSI REFRIGERATOR DENGAN MENGGUNAKAN LOGIKA FUZZY

&lt;p&gt;The need for water is very important for the production process, the water quality must also be considered the pH value so that the water is suitable for use in boilers or chillers. Seeing from these needs a simulation was made on matlab R2017a using a fuzzy toolbox that can find out the water quality with fuzzy mamdani method. This fuzzy logic simulation can determine the standard value of boiler water pH (10.5-11.5) and the standard pH value of chiller water (6-8) in the production machine. The methods in fuzzy logic used are mamdani and centroid methods as deffuzification with R2017a matlab simulation tool. The fuzzy inference system used is the mamdani method. This study made a simulation of mamdani method that can determine the quality of the PH water produced by using fuzzy logic. Chiller water pH can be used if iron ion values (0-2 ppm), silica ions (50-150 ppm), Total Dissolved Solid (TDS) (500-1000 ppm), total Hardness (100-200 ppm), M-alkalinity (500-750 ppm) from the standard value, the pH of the chiller water can be proven to reach a water pH value of 6-8. Boiler water pH can be used if iron ion values (0-2 ppm), silica ions (100-150 ppm), Total Dissolved Solid (TDS) (2000-3500 ppm), total Hardness (0-3 ppm), M-alkalinity (700-800 ppm) from the standard value, the pH of boiler water can be proven to reach a water pH value of 10.5-11.5.&lt;br /&gt;Keywords: fuzzy logic, Mamdani method, pH of boiler water&lt;/p&gt;

Development of fluorescent pH sensors based on a sol-gel matrix for acidic and neutral pH ranges in a microtiter plate

In this study, two typical pH-sensitive dyes, fluorescein amine (FA) and 8‑hydroxypyrene‑1,3,6‑trisulfonic acid trisodium salt (HPTS), were doped with two types of silica particles. The dye-doped silica particles were entrapped in a mixture of 3‑glycidoxypropyltrimethoxysilane (GPTMS) and 3-aminopropyltrimethoxysilane (APTMS) sol-gel matrix (GA) and a polyurethane hydrogel (PU) to prepare stable pH-sensitive membranes in a microtiter plate. Four pH-sensing membranes prepared at the bottom of wells in 24-well microtiter plates showed high sensitivity, fast recoverability, and good photostability. Supporting materials with fast ion transport properties were used to produce a pH-sensing membrane with rapid response time. The membranes entrapped with FA-doped silica particles had a dynamic detection range from pH 2 to pH 6, while the membranes entrapped with HPTS-doped silica particles had a dynamic detection range from pH 5 to pH 8. Dye-leaching from the pH-sensing membranes did not occur due to tight binding of functional groups in the dyes (FA and HPTS) to the sol-gel GA matrix, the doping of dyes in the silica particles, and the addition of an anti-fading agent (DABCO). Four pH-sensing membranes were used to measure the pH of wastewater. The measured results were consistent with standard pH values.

Brain aging: Evaluation of pH using phosphorus magnetic resonance spectroscopy.

Very important aspects of aging include age-related changes occurring in the brain. The aim of the present study was to identify the standard pH value in the entire brain volume using phosphorus magnetic resonance spectroscopy in healthy individuals of both sexes in different age groups, and then to determine whether there are differences in these values. A total of 65 individuals aged 20-32 years (mean age 24.5 ± 2.1 years, 31 women and 34 men) and 31 individuals aged 60-81 years (mean age 64.9 ± 5.5 years, 17 women and 14 men) were studied. The phosphorus magnetic resonance spectroscopy examination was carried out using a 1.5-T magnetic resonance system. The signal was acquired from the volume of interest that covered the whole brain. A vast majority of the examined individuals had slightly alkaline brain pH regardless of age. In the ≥20 years group, pH was 7.09 ± 0.11, and in the ≥60 years group, the average pH was 7.03 ± 0.05. This comparison of the pH identified in all the tested individuals shows a negative correlation of pH with age. The present findings might provide a valuable basis for further research into "healthy aging" as well as pathology in older adults. Geriatr Gerontol Int 2018; 18: 881-885.

The effect of different composition of ternary mixtures of emulsifying salts on the consistency of processed cheese spreads manufactured from Swiss-type cheese with different degrees of maturity

The scope of this work was to investigate the dependence of selected textural (texture profile analysis, TPA) and viscoelastic properties of processed cheese on the composition of ternary mixtures of emulsifying salts [disodium hydrogenphosphate, DSP; tetrasodium diphosphate, TSPP; sodium salt of polyphosphate (with mean length n ≈ 20), P20; and trisodium citrate, TSC] during a 60-d storage period (6±2°C). The processed cheese samples [40% wt/wt dry matter (DM) content, 50% wt/wt fat in DM content] were manufactured using Swiss-type cheese (as the main raw material) with 4 different maturity degrees (4, 8, 12, and 16 wk of ripening). Moreover, the pH of the samples was adjusted (the target values within the range of 5.60–5.80), corresponding to the standard pH values of spreadable processed cheese. With respect to the individual application of emulsifying salts (regardless of the maturity degree of the Swiss-type cheese applied), the samples prepared with P20 were the hardest, followed by those prepared with TSPP, TSC, and DSP. Furthermore, a specific ratio of DSP:TSPP (1:1) led to a significant increase in the hardness of the samples. On the whole, the hardness of all processed cheese samples increased with the prolonging storage period, whereas their hardness significantly dropped with the rising ripening stage of the raw material utilized. In all of the cases, the trends of hardness development remained analogous, and only the absolute values differed significantly. Moreover, the findings of TPA were in accordance with those of the rheological analysis. In particular, the specific ratio of DSP:TSPP (1:1) resulted in the highest gel strength and interaction factor values, followed by P20, TSPP, TSC, and DSP (used individually), reporting the same trend which was demonstrated by TPA. The monitored values of the gel strength and interaction factor decreased with the increasing maturity degree of the Swiss-type cheese used. The intensity of the rigidity of the samples showed an analogous relationship to the intensity of the gel strength; the higher the gel strength of the sample, the more inflexible the product is expected to be.

Splenic Doppler Resistive Index for Early Detection of Occult Hemorrhagic Shock After Polytrauma in Adult Patients

The objective of this study was to evaluate whether direct assessment of splenic circulation by splenic Doppler resistive index (Doppler RI) is a clinically useful noninvasive method for an early detection of occult hemorrhagic shock after polytrauma in adult patients. Splenic Doppler RI was measured in 49 hemodynamically stable adult patients admitted to the emergency department because of polytrauma. Renal Doppler RI was also determined in 20 patients. Spleen size, Injury Severity Score, systolic blood pressure, heart rate, blood lactate, standard base excess, pH, hemoglobin, and inferior vena cava diameter values were recorded at admission and at 24 h. Patients were grouped according to whether signs of hemorrhagic shock did (n = 22) or did not (n = 27) occur within the first 24 h from admission. Patients who developed hemorrhagic shock had significantly higher splenic and renal Doppler RI, higher Injury Severity Score, and lower standard base excess at admission. By multivariate logistic regression, splenic Doppler RI resulted to be a predictor of hemorrhagic shock development within the first 24 h from admission. Splenic Doppler RI may represent a clinically useful noninvasive method for early detection of occult hemorrhagic shock and persistent occult hypoperfusion after polytrauma in adult patients.

A neutron crystallographic analysis of a cubic porcine insulin at pD 6.6

The p K a values of ionizable amino acid side chains are tabulated in standard textbooks. However, whether a certain amino acid side chain in a protein is charged or not cannot be estimated from standard pH values measured from protein solutions. Protonation and deprotonation of various ionizable amino acid residues were observed by a neutron diffraction experiment and discussed on the basis of the charged states estimated by the p K a values of the amino acid residues. The neutron diffraction study has been carried out at 2.7 Å resolution on cubic porcine insulin at pD 6.6 using the BIX-4 single crystal diffractometer at the JRR-3 reactor of the Japan Atomic Energy Agency. For the present work, a large single crystal of 2.7 mm 3 (=2.0 × 1.7 × 0.8 mm) was obtained by dialysis. The structure refinement was carried out using the program CNS. The resulting R cryst is 21.6% and the R free is 29.1% at a resolution of 2.7 Å. In the case of His B5, both N π and N τ of an imidazole ring are protonated at pD 6.6, but at pD 9 only N π is protonated. In contrast, for His B10, both N π and N τ are protonated at pD 6.6 as well as at pD 9. The ionization states of several amino acids in porcine insulin have been obtained at pD 6.6 and they are compared with those at pD 9 obtained by neutron diffraction as well as those at pH 6.50 and 6.98 obtained by X-ray diffraction. In this manuscript, the difference between these forms will be discussed.

Prediction of electrophoretic behaviour of a series of quinolones in aqueous methanol

Quinolones are a family of antibacterial agents used in human and veterinary clinics. The examination of protonation equilibria is essential because their antibacterial activity is pH-dependent. In this work, dissociation constants of quinolones in MeOH–water mixtures were obtained using capillary electrophoresis. The method is based on a model that relates electrophoretic mobility of the solute with pH. The effect of pH, p K a and activity coefficient on electrophoretic behaviour was considered. Standard pH values for buffer solutions were previously determined in MeOH–water mixtures, and the pH can thus be measured in these media as in water. This model is also used to obtain the optimum conditions for the separation of a series of substances because it allows one to predict the resolution between adjacent peaks from a few experimental data.

Demonstration of increasing standard pH value of lacrimal fluid with increase of flow rate.

To test the hypothesis that pH value of human tears is affected by flow rate. After stimulation with a drop of 70% alcohol into the ipsilateral nasal cavity tears from the left eyes of 30 healthy volunteers were collected with glass capillaries while flow rate of tear secretion was registered. The pCO(2), actual and standard pH were determined in the collected samples with the Astrup method: Standard pH is defined as the pH of the sample that has been equilibrated at 37 degrees C with a gas mixture having pCO(2)=40 mmHg. The flow rate correlated positively and significantly with both the standard pH value (r=0.503, p<0.01) and the pCO(2) (r=0.517, p<0.01) while there was no correlation between the actual pH and the flow rate. Loss of CO(2) from the sample is a cause of serious uncertainty in tear pH determination. A positive flow rate-pH relationship was found for human tears when the uncertainty was removed by determination of the standard pH.

Capillary electrophoresis in mixed aqueous-organic media: Effect of tetrahydrofuran on mobilities, dissociation constants and separation of a series of quinolones

The influence of the composition of aqueous-tetrahydrofuran mixtures on the electrophoretic behaviour of nine quinolones was studied in order to predict the optimum conditions for their separation. The effect of pH, pK a and activity coefficients on electrophoretic behaviour was established. Standard pH values for buffer solutions of the NIST scale as previously determined in THF-water were used in accordance with IUPAC rules. pH was therefore measured for these media as for water. The pK a values of quinolones were determined from the electrophoretic mobilities-pH data pairs in different THF-water mixtures. The electrophoretic resolution between pairs of substances was then predicted in order to obtain the optimal experimental conditions for separation methodologies.

Ionization Constants of o-Phthalic Acid and Standard pH Values of Potassium Hydrogen Phthalate Buffer Solutions in Glycerol + Water Solvent Mixtures at Normal and Subzero Temperatures

Determination of primary standards for pH measurements in glycerol + water solventmixtures has been carried out based on reversible emf measurements of the cellPt|H2|KHPh (m PS) + KCl (m Cl)|AgCl|Ag|Ptwhere KHPh denotes the potassium hydrogen phthalate buffer solution of molalitym PS = 0.05 mol-kg−1, at glycerol mass fractions w G = 0.2 and 0.4, within thetemperature range −10 to 40°C. A multilinear regression procedure as a functionof electrolyte molality, glycerol mass fraction w G, and temperature T has beenapplied for the data processing leading to the values of primary standards pHPS.These can be represented by the following regression equationpHPS = (4.007037±0.001113) + (3.55844±0.01776)x G+(0.39622±0.01410)z + (4.3084±0.3377)z 2− (50.66±10.53)x G z 2 + (457.10±78.48)x G 2 z 2where z = (T − 298.15)/298.15. Parallel values of the first ionization constantof o-phthalic acid (H2Ph; benzene-1,2-dicarboxylic acid, the parent acid of KHPh),which are essential for the above calculations, have been determined fromreversible emf measurements of the cellPt|H2|H2Ph (m 1) + KHPh (m 2) + KCl (m 3)|AgCl|Ag|Ptover the range of solvent composition and temperatures mentioned above.

Chromatographic behaviour of ionizable compounds in liquid chromatography. Part 1. pH scale, p Ka and pH S values for standard buffers in tetrahydrofuran–water

The solvent characteristics of tetrahydrofuran (THF)–water mixtures that have an influence on the chromatographic behaviour of ionizable compounds in liquid chromatography (LC) were investigated (Debye–Hückel parameters, pH scale, LC-useful range, solvatochromic parameters). Solute properties, such as the p K a values of the acids used to prepare reference standard buffer solutions used in LC, depend on the composition of the mixture. The p K a values in several THF–water mixtures were subjected to factor analysis in order to determine how many factors affect the variation in the data sets, and then to target factor analysis to identify these factors. The influence of solvatochromic parameters on the interactions between acidic groups and the solvents studied was identified and quantified. Standard pH values, pH S, for the seven primary reference buffer solutions of the NIST scale and for acetate buffer in THF–water mixtures containing 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70% and 100% (w/w) THF were determined using IUPAC standardization rules. The quasi-lattice–quasi-chemical (QLQC) theory of preferential solvation was applied to obtain the degree of preferential solvation of hydrogen ions in these media in order to explain the variation in pH S values obtained over the range of mixtures studied. The relationships obtained allow calculation of the pH S values of the standard buffers in THF–water mixtures. Thus pH measurements in these media can be performed as in water. The chromatographic behaviour of the solute can then be related to the real pH value of the mobile phase used.

Improved traceability of pH measurements.

Traceability is a prerequisite for the comparability and uniformity of measurements. Although pH-measurements are carried out on a large scale in laboratory and industry, the problems involved in the traceability of pH values have not adequately been solved in the past. The comparability of pH measurements is limited, among other parameters, by the accuracy of the pH values of the standard buffer solutions used to calibrate the pH meter-electrode assemblies. The measured pH(X) value must be traceable to primary standard pH(PS) values through an unbroken chain of comparisons, all values having stated uncertainties. A new primary standard measurement device for pH is used to certify primary pH reference materials from which these secondary reference materials can be derived.