From the wardrobe to the boxPH Meter
A PH Meter is an electronic device used to measure the PH of a liquid. It may also feature special probes for the measurement of the PH of solid and semi-solid samples. A typical PH Meter consists of a probe (a glass electrode) linked to an electronic device, which picks up the probe's signal, calculates the value of the corresponding PH which is then shown on the display.
The earliest PH Meters were produced in the late 30s in the USA by Arnold Orville Beckman and in Denmark by the company Radiometer. Beckman was an assistant at the California Institute of Technology when Glen Joseph, laboratory chemist at the California Fruit Growers Exchange, requested him to create an instrument capable of rapidly measuring the acidity of lemon juice. Beckman's invention led to the birth of Beckman Instruments Co., a company that was later renamed Beckman Coultier.
Today a vast range of pH Meters is available, ranging from simple portable devices similar to a large ball point pen, costing under a hundred Euros, up to complex laboratory devices which enable the mounting of several probes and computer interfacing. There are also probes designed for special applications and for difficult samples or work environments. A specific category of pH Meters is used in healthcare; they are usually applied in the detection of gastric pH during clinical gastroenterological investigations, often in conjunction with a digital signal recorder, fitted for 24 hours.
The evolution of the PH Meter through some examples
FIG. 1 - Ph-metro di Beckman (primo modello) anni 40-50 ca., Misure Altezza x Lunghezza x Larghezza (mm): 255x210x285 ca.
FIG. 2 - Ph-metro Beckman, SIMUS - Collezioni del Centro servizi CUTVAP (Donazione ARPAT) 1950 ca. Beckman Instruments Inc. South Pasadena, California, USA; Alluminio, bachelite, metallo, metallo cromato, plexiglas, rame; Misure Altezza x Lunghezza x Larghezza (mm): 193x240x285
FIG. 3 - Ph-metro “CL/2”, SIMUS - Collezioni del Centro servizi CUTVAP (Collezione strumento di Fisiologia), 1950 ca., Cassinelli & C. Milano, Italia; Alluminio, bachelite, metallo verniciato, plexiglass; Misure Altezza x Lunghezza x Larghezza (mm): 50x110x125
FIG. 4 - Ph-metro “115 A” con elettrodo, SIMUS - Collezioni del Centro servizi CUTVAP (Collezione strumenti di Fisiologia), 1960 ca., Photovolt Corporation – Martelli, New York, USA – Firenze, Italia; Alluminio, plastic, plexiglass; Misure Altezza x Lunghezza x Larghezza (mm): 125x350x132
FIG. 5 - Ph-metro Metrohm E300B, SIMUS - Collezioni del Centro servizi CUTVAP, 1960 ca., Metrohm, Herisau, Svizzera; Metallo cromato, metallo verniciato, plastica, plexiglass; Misure Altezza x Lunghezza x Larghezza (mm): 222x210x325
FIG. 6 - Ph-metro WTW, SIMUS - Collezioni del Centro servizi CUTVAP (Collezione strumenti di Ginecologia, Ostetricia e Pediatria), 1950 ca., WTW Wissenchaftlich Technische Werkstätten, Weilheim Obb., Germania; Bachelite, metallo cromato, plastica, vetro; Misure Altezza x Lunghezza x Larghezza (mm): 145x242x150
FIG. 7 - Moderno ph-metro (Source: Open University of Sri Lanka, 2014 Author: Gihan Jayaweera CC-BY-SA-3.0)
(Posiziona il mouse sulle immagini per leggerne le didascalie)
The following diagram illustrates the curve, which represents the size of a few spectrophotometers (taken as examples) over time:
Quartz photoelectric spectrophotometer, Cary & Beckman, 1941
Spectrophotometer
The spectrophotometer was invented in 1940 by Arnold J. Beckman. Before this date, chemical analysis was a long process, often requiring weeks to be completed, characterised by 25% mean precision rate. The spectrophotometer reduced analysis time to a few minutes and increased accuracy and precision rate of many units.
Performance problems of the earliest spectrophotometers were resolved through later modifications with the design of a B model characterised by a quartz wedge rather than a glass prism (thus improving the performance of the devices in the ultraviolet region), followed by a C model characterised by a higher resolution of ultraviolet dispersive wavelength. A new model, known as the DU, was released in 1941, featuring a hydrogen lamp and other improvements. It remained unchanged until more or less the second half of the 70s.
In 1981, Cecil Instruments produced a spectrophotometer controlled by a microprocessor, an automatic device, faster and more reliable compared to other versions at the time. In 1990 an external software for PC control was added, as well as an information display with spectra image. The instrument's development continues today, with a wide range of applications from science, medicine and even criminology.
Qui sopra: Spettrofotometro a fluorescenza, SIMUS - Collezioni del Centro servizi CUTVAP (Collezione di strumenti di Ginecologia, Ostetricia e Pediatria), 1972, Optica Milano, Italia; Alluminio, metallo sbalzato, plastica, plexiglass; Misure Altezza x Lunghezza x Larghezza (mm): 270x600x360
Qui sotto:Spettrofotometro UV-Vis Thermo Scientific, Helios Omega, anni 2000. Author: Viv Rolfe CC-BY-SA 4.0.
Qui sopra: Potenziometro “Jonosis”, SIMUS - Collezioni del Centro servizi CUTVAP (collezione strumenti di Oculistica) 1954, SIS – V. Manassi & C. Milano, Italia; Bachelite, metallo cromato, plexiglass Misure Altezza x Lunghezza x Altezza (mm): 190x385x270
A destra, potenziometro digitale attualmente in commercio
Potentiometer
A device which enables the measurement of differences in electric potential or electromotive forces which are compared with a standard electromotive force and without the absorption of current from the voltage source being measured. This comparison consists of the application of the standard electromotive force and the one to be measured, at the ends of a resistor (linear or circular), equipped with a sliding contact (cursor) so that they are in opposition; the cursor is regulated until the values of the unknown electromotive force and voltage are equal, indicated by a galvanometer indicating zero current and easily gauged.
The same name is used to denote a resistor with cursor (generally equipped with axis and control knob) used in aforementioned devices which are constructed in a variety of forms and are widely used in electrotechnical and electronic applications to reduce voltage supplied by a generator to a given, variable fraction, and to reduce voltage of electrical signals and therefore, for example, as a regulator of the gain of electroacoustic amplifiers, radio receivers etc.
Chromatograph
The Russian biochemist Mikhail Cvet has been attributed with the invention of chromatography, in 1906, when he first used this technique to separate chlorophyll from a plant extract. Cvet proceeded by placing a small amount of extract at the top of a glass tube filled with calcium carbonate and then washing the sample, by percolating petroleum down the ether column. As the substance flowed and washed away the sample, the latter separated into bands of different colour and each travelled to the bottom at different speeds. Cvet's experiment laid the foundations to modern chromatography.
Today this technique is applied to the analysis of colourless substances too, for transfer between complex phases of devices. Today the term chromatography generally refers to various separation techniques to be possibly applied to mixtures of substances and based on the distribution between two exchanging phases of the different compounds present in the mixtures and to be separated.
