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UltraViolet and Visible Spectrometry (UV/Vis)

* The information on this page is based on an original manuscript by Mr D. Irish, with the permission of the author.

Author’s Introduction

I joined Pye Unicam in the Autumn of 1973 as an assistant project leader. At that time the company employed around 1700 people. For the next 28 years (apart from a brief secondment to the marketing group), I held various roles within the development groups. Therefore, the above is a personal view of the company seen very much from a development perspective and also through the mists of time (article written in 2015). Many very skilled and committed people contributed to the company’s involvement in UV/Vis spectroscopy - in this short article I have managed to only mentioned a few - my apologies to all those whose names do not appear, but whose contribution to the Unicam UV story was immeasurable.

Over these 28 years the company would change beyond all recognition. It would go through numerous name changes: Unicam Instruments Ltd, Pye Unicam, Philips Scientific, ATI Unicam, Unicam Instruments, Spectronic Unicam and Thermo Spectronic. The organisation of the development group would change from a matrix organisation (with an electronics group, model shop and drawing office and project leaders requesting staff each month) to a small dedicated UV/Vis group of engineers and physicists.

The company would change from a ‘works order’ system - buying in components and making parts for maybe 100 instruments which when completed would go into a massive warehouse (in the 1970s at the nearby Coral Park, but prior to this within the York Street factory) to a just-in-time system where instruments were basically made to order and shipped to the customer as soon as it was built.

Company ownership would move from Philips, the Dutch electronics giant, to Analytical Technologies Inc (ATI) an American venture capital company and ultimately to Thermo Electron - a large American Instrumentation company that bought up many smaller instrument companies.

With these changes came changes in management styles and inevitably in personnel. The in house machine shop was sold off and various other functions, such as printed circuit board manufacture, outsourced. When Thermo split the company into separate companies along product lines, there were around 30 or 40 in the UV/Vis company.

What is UV/Vis Spectroscopy?

In its basic form the technique of UltraViolet and Visible Spectrometry (UV/Vis) is deceptively simple. By shining light of a known wavelength through a liquid sample and measuring how much gets through, information can be gleaned regarding the composition of the sample - in many cases the concentration of the chemical can be determined. If the instrument is a scanning instrument - that is a succession of wavelengths are passed through the sample, then a spectral curve can be produced and in some cases this will be used to determine what chemicals are present.

A typical instrument operates in the range 190nm to 1100nm. The human eye is sensitive between 400nm (blue) and 700nm (red). The lower limit of 190nm is placed by oxygen absorption bands in the atmosphere, and the upper limit by detector sensitivity. In measuring how much light gets through, it is usual to use an Absorbance Scale rather that straight transmittance. This is a log scale so an Absorbance of 0 = 100%T, 1A=10%T, 2A=1%T and 3A=0.1%T.

A UV/Vis spectrophotometer really is the workhorse of any chemistry lab. It was once said that in order to set up such a lab you need three things - a balance, a Bunsen burner and a UV/Vis Spectrophotometer. They will be found in hospitals (maybe checking the bilirubin level of new born babies), in pharmaceutical companies (maybe checking the right components in the right quantities have been added to the aspirin tablets) and indeed anywhere where a chemical sample needs to be analysed.

For a more detailed description of how UV/Vis spectroscopy works see the Pye Unicam booklet An introduction to UV/Vis Spectroscopy by J E Steward

The Early Years

To look at the history of Unicam and UV/Vis Spectroscopy, one has to go back to the immediate postwar period and start with one of its competitors:

The Beckman Du spectrophotometer had been developed in 1941 by Arnold Beckman. The UK in the late 40’s was basically broke with no cash to buy American made instruments. The story goes that the UK government loaned Unicam a Beckman DU instrument for a weekend and in essence were told to copy it - The Unicam SP500 was born! The government also loaned an instrument to Hilger Ltd who produced a similar model- the Uvispec. Interestingly both companies would ultimately be bought by Thermo.

This was followed in 1952 by the SP600. (NOTE: The National Archives contains a report on the preliminary inspection of a Unicam SP600 by the chemical inspectorate at the Woolwich Arsenal)

By 1967 the range consisted of the SP500 and SP600 manual instruments, together with the SP1300 colorimeter. Also making an appearance were the SP800 UV/Vis and the SP700 UV/Vis/Nir instruments

The SP700 (launched around 1958) was very much a copy of the Cary 14 - then regarded as the "Rolls Royce" of spectrophotometry. Howard Cary was the designer behind the Beckman DU but left Beckman to set up his own company following a dispute with Beckman over the merits of single v double beam spectrophotometers (a debate which subsequently was to be replayed during the development at Unicam of the SP 8-700 in the 1980s).

The SP3000 was in many ways ahead of its time when launched in the late 1960s and the design incorporated many novel features. It covered the full UV/Vis/Nir range and was the first UV/Vis spectrophotometer with digital readout. It also incorporated an automatic sample changer so it could be loaded with up to 50 samples and left unattended. The project leader was David Shrewsbury who subsequently went on to head up chromatography development. It won a Queens Award for technological achievement and also other industry awards, but sadly only a few were sold. An assessment of its performance was published in The Analyst in 1972. The concept of an automatic sample changer led on to a family of automatic chemistry analysers(AC1, AC4).

The SP8000 was primarily a ‘value engineered’ SP800 and the main performance difference was a more sensitive 1A scale rather than the 2A of the SP800 (both provided by logarithmetically cut combs driven to produce a ‘null’ between the beams).

The 1970s 0nwards

SP1800 & SP1700 marked the start of using diffraction gratings rather than prisms as the dispersing element. They were double beam instruments. The SP1800 had an analogue readout and The SP1700 incorporated a digital display and could be connected to an external chart recorder. The project leader for both these products was Mike Sharpe.

Led by project leader Mike Wilkinson, The SP30 was a double beam non scanning instrument aimed primarily at rate analysis. It was an unusual instrument in that there was a vertical casting with the optics fastened to the front of it and the electronics at the rear. It was an 8nm band-pass instrument and used a Monk Gillieson monochromator with a 600 lpmm diffraction grating. The baseline drift was always a concern due to electronics warm up and it often struggled to meet its specification.

Unicam had taken its eye off the ball as far as very low cost non scanning instruments were concerned. The SP600 was definitely old technology and many competitors had entered this market slot. The answer was the SP6, project lead: Bob Kydd. Based around the same monochromator as the SP30 used, it employed two phototubes which were changed over by a manual lever. The covers were made of two vacuum formings with a metal band round the middle - rather like a suitcase. The top cover was not, therefore totally rigid, but despite this perceived weakness, it sold over 1000 per year and the basic design was to carry forward into the PU8600 series and its variants for many years to follow. The strap line for the advert was ‘Every lab should have one’.

1976 saw the introduction of the SP8100, SP8200 & SP8250. The mechanics and optics of this family of double beam scanning instruments were to form the backbone of the main Unicam UV/Vis instrument family for many years as they migrated into the 8-300, 400, 500 & 8800 series. The design was based around an Ebert monochromator and used an EMI 9558 end window photomultiplier. A large sample compartment with a wide beam separation allowed a wide range of specially designed accessories to be accommodated. In addition the 8-100 accepted a range of electronic based accessories which plugged into the top control area of the instrument. Mike Sharpe was project leader for the 8-100 and Tony Moss for the accessories, some of which were manufactured in house, some by Specac, a specialist spectroscopy accessory company in Kent, and some by Hansatech in Kings Lynn - once part of the Pye empire in East Anglia. The 8-100 typically sold around 500 instruments per year.

The SP8-200, project led by Bob Francis broke new ground in various ways. It was a microprocessor controlled instrument, incorporating an Intel 4004 chip, the first commercially available microprocessor, and very crude by today’s standards! The main control panel of the SP8-100 - mostly rotary knobs and pushbuttons were replaced by an array of leds and buttons. There was much debate within Unicam as to who would want to buy one of these new-fangled devices and what benefit did the microprocessor confer - in the end the instrument was made in pretty small quantities by a section of Unicam that specialised in making ‘one offs’. Unicam’s first software engineer was Paul Houghton. The product became the world’s first microprocessor controlled UV/Vis instrument, beating arch rivals Perkin Elmer by a couple of weeks in 1978. The SP8250 was an SP8200 with the addition of a pre-monochromator to reduce stray light to negligible levels. However with the advent of holographic gratings in the standard instruments, this performance improvement was minimal.

A number of competitors has by now entered the marketplace with lower cost scanning instruments. Work therefore started on the design of a low cost scanning instrument. The design was to incorporate a rubber belt drive similar to that used in Philips tape recorders. Philips had an office where you could ask the question "where did that component come from?" and back came the answer "from the Philips rubber band factory of course!" Philips really did make everything those days. It was soon realised that a more efficient route to a lower cost instrument was to reengineer the SP8100 chassis. Reengineering the SP8-100 consisted of replacing the expensive end window photomultiplier with a side window one, and replacing the top deck electronics with a thinner moulded box containing a single PCB with all functions on it. Various other cost savings were made in the product-line and the SP8-300 & SP8-400 were launched in 1980. The project leader was Doug Irish. A further variant was the SP8-500 which added a second box of electronics along the top of the instrument, and incorporated an off the shelf microprocessor board. The project leader was Bill Woods and around 150 of this variant were made.

PU8800-team: David Griggs, Doug Irish, Tony Moss, Jim Steward & Mark Farrow

The PU8800 was launched 1982 and was based on the optics of the SP8100 series, but with new electronics and a VDU to display results. The development lab had both 50Hz and 60HZ electrical supplies and a Commodore PET computer was purchased in the States (circa 1979) long before they were available in the UK as it could be run from the lab supply. This was used to design the screen displays on the PU8800 and the similarities in the chunky letters and numbers between the Commodore and the PU8800 are very evident. The main top cover was of moulded plastic foam - a technique that would feature in many subsequent instruments. The project leader was Tony Moss, seen in the middle of the PU8800 team picture (right).

Interestingly, the 2015 Thermo brochure for UV/Vis, the PU8800 features as an example of the pedigree and heritage of Thermo UV:

The PU8800 replaced the SP8200, the SP8-500 and many of the top end 8100 packages. However Unicam again had a gap in its catalogue with the introduction by its competitors of several lower cost scanning instruments - the response to this was to effectively cut the price of the PU8800 whilst a new strategy was formulated.

To plug the gap, Unicam merchandised the Spectronic 1201 as the Unicam SP7-500. There is a nice irony here as subsequently both companies were bought by Thermo and their activities merged.

Meanwhile the SP6 series had been revisited. In particular the floppy suitcase style cover was replaced with a moulded foam cover. In addition an ‘upmarket’ version, incorporating a microprocessor, the PU8600 was introduced. The project leader was Mike Bennett and in the fullness of time, the product would undergo one more facelift to become the 5-600 series.

By the early 1980s the basic scanning chassis of the PU8800 was showing its age and Unicam scanning instruments were again not competitive on price in the market place. Doug Irish was seconded from development to the marketing department to work alongside Chris Cottrell in the specification of a new scanning instrument where price was to be the number one priority. He subsequently returned to development as project leader for the new instrument. Lessons had been learnt from the PU8800 with its built in VDU in that the VDU market was fast changing so it was quickly appreciated that any VDU had to be an external one.

The Unicam machine shop had recently undergone quite a transformation with the introduction of a Trumpf sheet metal machine so much of the design (with the exception of the top cover) would be based around sheet metal. Major debates were held over the style of user interface, but eventually the idea of a mouse driven system (very much a novelty in those days) was agreed upon. The instrument was to be a pseudo double beam instrument (only one beam was accessible in the sample compartment, but to help improve drift figures, a silica plate in the beam reflected 4% or so of the light onto a photodiode so that in effect a double beam system was created). Two microprocessors were used - a Z80 to cope with all the low level stuff, driving stepper motors etc. and a Motorola 68008 to do all the number crunching and graphics display. To get the colours right on the display, advice was sought from the BBC team that developed Teletext and Ceefax.

Hewlett Packard had introduced their diode array instrument which could produce near instantaneous scans, so a fast scan speed was also deemed a ‘must have’. During the course of development some residual absorbance drift was still apparent due to the temperature coefficient of the photomultiplier. Steve Cooke and Mike Sharpe came up with an ingenious electronic compensation for this which was patented. (Patent No. US4832491 (A) - Method of and apparatus for spectroscopically analyzing samples).

The development of the software proved to be Herculean task - experts from Logica were brought in and warned we had embarked on too big a task as a unique operating system needed to be developed. Work progressed with an army of software engineers (we were constantly reminded of Brookes ‘The mythical man month’, as more and more software engineers and contractors were piled into the project), but eventually in 1986 the 8700 was launched. The advert and short form brochure were in a very different style to the usual Philips material and the main brochure carefully did not say how many beams the instrument had! With its eye-catching user interface, it instantly became a success, becoming the market leader in several major markets. Unicam was back selling five or six hundred scanning instruments per year. The instrument would feature in one of the James Bond Films when Philips sponsored the film production and James used Philips goods throughout the film.

UV Series team
UV Series team

Although the performance of the PU8-700 equalled that of double beam instruments from competitors, its pseudo double beam design was inevitably a perceived weakness in the market place. The next family of instruments to be developed was the UV Series which reverted to a traditional double beam design and based on a stable optical cast base plate. It was available in either a Local control version, or as a ‘blind bench’ controlled by a PC and Vision software. By now, the pharmaceutical industry in particular, were demanding features to prove the instrument was working correctly when an analysis was carried out and so a major sales thrust of the product was around the sophisticated self-test facilities built into the hardware and the corresponding software facilities in the Vison control software.

Several versions of the product were available, including one using an end window PMT to cope with turbid samples.

Attention next turned to the bottom end of the market and the 5625 series. The optical design was fundamentally quite old and the aberrations of the Monk Gillieson monochromator limited its band-pass to 8nm. Many analyses required a band-pass of under 2nm and the constantly falling prices of electronics meant many instruments in this class now offered built in scanning capability. Thus the Helios range of spectrophotometers were designed. These were built around a Seya-Namioka monochromator, requiring a concave diffraction grating (thus eliminating the need for a collimator mirror) and virtually all the mechanical components were plastic and produced by injection moulding. Interestingly, many years previously, a plastic optical base had been developed to prototype stage but it had been deemed too risky to adopt. The tooling cost was enormous, but the piece part cost minimal. By now Unicam was owned by Thermo so the tooling budget had to be signed off by them. Over a period of time variants aimed at specific industries were produced. Thus the Aquamate and the Biomate were launched. Amongst the key people in the development of this family of instruments were Steve Hartwell, Barrie Hatten and Alan Biggs.

In parallel with the main instrument development a significant team continued to refine the Vision PC based software. Much emphasis was placed on all the aspects of traceability and security required by the pharmaceutical industry as defined in CFR11 by the FDA in America. Gordon Chambers was the software engineer looking after the group.

The Evolution series of instruments was to be the last family of UV/Vis instruments to be developed in Cambridge (around 2002). Certain components of the UV series were becoming obsolete and Evolution was effectively its replacement. Much discussion took place as to what was the primary target market and it was agreed this should be life sciences. The implication of this was for a small beam of light in the sample compartment (to pass through small cells) and also a double beam instrument with a wide beam separation (to allow cell changers to operate). A major innovation was to incorporate a Xenon flash lamp as the light source, so eliminating the need for the traditional deuterium and tungsten lamps.

Diffraction gratings

With the move from prisms to diffraction gratings as the dispersing element came a number of challenges. Not least was that the major suppliers of gratings were all major instrument makers as well, and so direct competitors of Pye Unicam. Disputes would arise as to whether a particular grating was within specification or not. In particular the characterisation of the stray light properties of an individual grating was almost impossible to define.

Gratings were made by replicating from a master. The master was produced on a special ruling engine - of which there were very few in the world. The gratings used in the Unicam instruments had 1200 lpmm or 600 lpmm (lines per mm). A replica would then be produced (rather like gramophone records used to be produced) and aluminised.

A research project was agreed at Unicam to better understand the stray light performance of gratings. Apparatus was constructed to scan gratings with a laser to quantify their performance. Doug Irish was the experimentalist and Mike Sharpe the theoretician. At roughly the same time, SIRA (the Scientific Instrument Research Association) proposed a collaborative project to be led by Dr Arthur Tarrant to investigate stray light. All the major players in the industry (manufacturers and users) contributed funds to the project. It became a bit of a ‘race’ as to who would publish and eventually the Unicam paper was accepted by Optica Acta. Ed Loewen a world authority on gratings sent a very complementary letter and the results now feature in his classic text on gratings. Mike Sharpe subsequently wrote a ‘popular’ version for the journal Analytical Chemistry.

Meanwhile, Dr Michael Hutley at the National Physical Laboratory (NPL) had developed a process for producing blazed gratings using an interferometric process (commonly referred to as holographic gratings). These were made by using a powerful laser beam to form an interference pattern in photoresist on a quartz substrate. By sheer good fortune the laser wavelength used produced gratings with all the right properties for use in a UV/Vis spectrophotometer. The process was patented by NPL - Patent No 1384281 in the name of the Secretary of State for trade & Industry and with the title ‘Improvements in or relating to the formation of photographic records’ (an obscure title to help keep it from competitors) and licenced to Pye Unicam. Bob Francis took on the role of setting up the process in a specially constructed clean room at Cambridge in the mid-1970s and Chris Evans became the optics production manager responsible for making them and subsequently the concave gratings used in the Helios range.

It was anticipated that the stray light performance of these new gratings would be significantly better than the performance of the ruled ones. (Basically the ‘lines’ were straighter with fewer imperfections and a master rather than a replica was to be fitted into the instruments). However when the day came to fit one into an instrument little difference was observed. Eventually it was realised that as part of the design the grating was overfilled with light and the mount which held the grating was scattering a significant amount of light. A mask was introduced at a conjugate point so that the grating was under filled and the stray light performance of the instrument improved by a factor of ten over its predecessors. Unicam was now able to fit master holographic gratings into every instrument with a significant competitive advantage on stray light specification.

Bob Francis also turned his attention to the issue of protecting the surface of the mirrors used in spectrophotometers. The mirrors were made by evaporating aluminium onto the glass substrate. The aluminium is very delicate and also oxidises with age, so loosing UV reflectivity. Magnesium Fluoride had been used for many years as a possible protective coating - it prevented the oxidisation but was itself a very soft coating. Bob perfected the technique of coating the mirrors with a layer of quartz by a sputtering process, so producing an incredibly tough coating for the mirrors. His ‘party piece’ when delivering a talk on the subject was to produce a toothbrush from his coat pocket and vigorously demonstrate how the mirror could be cleaned!

The overall optical superiority of Unicam instruments thus became a major part of its advertising campaigns.


Finding suitable cost effective detectors for UV/Vis instruments was always a challenge. For many years, the top of the range instruments used end window photomultipliers (typically EMI 9558) or the specially selected ones with extended red response. Eventually smaller side window photomultipliers (with much better red response) would take over from the end window variant.

At the other end of the product range, phototubes were used for many years. Photodiodes were a tantalising possibility, with excellent red response but little or no UV response. Enter into the story the Philips Nat Lab at Eindhoven. This was the days of the big corporate laboratory and the Nat Lab was big! Dr Knipenburg of the labs arranged for Mike Sharpe to go on secondment to Eindhoven to develop a UV sensitive photodiode specifically for Unicam. The result was an excellent photodiode that was used for many years in the 8-600 families of instruments.

Neutral Density Filters

In order to check that the instrument is giving the correct reading, it is necessary to have an absorbance standard - a substance whose absorbance is accurately known. The traditional method was to make up a standard solution of potassium dichromate, but this of course relied heavily on the skill of the analyst making up the solution correctly. A joint programme between Unicam and the National Physical Laboratory devised a set of neutral density filters in special stress free mounts covering the range up to 3A. The people at Unicam involved were Mike Sharpe and Barry Popplewell. There were many novel features of the filter system - they were made to incredibly tight tolerances and parallelism. Initially they were used by Unicam service engineers but eventually were made available to customers and indeed to competitors.

Meanwhile the National Bureau of Standards (the American version of the National Physical Laboratory) also developed a set of neutral density filters, but only covering up to 2A.

Unicam became accredited under UKAS for the calibration of filters traceable to the NPL and several years later, following considerable involvement and visits by Unicam staff to NIST in Washington, Unicam also became accredited under NVLAP with traceability to NIST. Unicam were invited by NIST to present a special paper at a symposium they organised at the Pittcon 1999 Conference and also presented at the National Conference of Standards laboratories held in Toronto in 2000. Unicam staff were also heavily involved as members of the working party to produce National guidelines for valid analytical measurements using UV/Vis Spectrophotometry.

The UV Spectrometry Group

The UV Spectrometry Group was a small scientific society, originally known as the Photoelectric Spectrometry Group, that had its origins in the post-war years and acted as a ‘self-help’ group for Beckman DU owners - spare parts were in short supply and took ages to come from the USA. The group published an annual bulletin and organised several scientific meetings per year. The intention being that the presented papers would be published in the bulletin. Often the meetings would be joint ones with similar groups - The Infra-Red Discussion Group, The Colour Group, or the Spectroscopy Group of the Institute of Physics.

It became the tradition that Unicam provided the secretary to the Group - someone from the development dept., so it was not perceived as a marketing ploy by the firm, although of course Unicam paid for things like all the postage costs. Perkin Elmer usually provided the treasurer. Secretaries from Unicam included David Shrewsbury, Mike Wilkinson, Doug Irish and Mike Sharpe. The chairman was usually an academic or significant person from the pharmaceutical industry. This meant that the meetings were usually held in pretty prestigious venues such as universities, the Royal Institution, The Welcome Foundation etc. The group also published a series of books on UV spectrometry and a number of Unicam people contributed chapters to the books - Tony Moss, Doug Irish, and John Hammond. Klaus Mielenz of the American National Bureau of Standards wrote a very complimentary review of one of the books.

As UV spectroscopy became a routine laboratory tool, the Group inevitably went into decline and was wound up - its assets were handed to the British Association of Spectroscopists.

The Legacy

In around 2003, Thermo took the decision to consolidate all molecular spectroscopy in Maddison, the home town of Nicolet (The manufacturer of Infra-Red spectrophotometers). However the association of Cambridge with UV/Vis Spectroscopy still lives on as it has spawned a number of other companies: -

In 1968 Cecil Tarbet, an employee of Unicam, left to set up his own business, Cecil Instruments which continues to design and manufacture UV/Vis Spectrophotometers.

Later, in the 1980s, Tony Moss and Mike Mills also left to set up Camspec instruments. For a long while this was based in Cambridge, but on the retirement of Tony it was sold to a company in Leeds.

LKB Biochrom set up on the Cambridge Science Park. Whilst not actually set up by Unicam folk, many senior people now work there whose first introduction to UV/Vis was at Unicam.


Sources: 1. Original manuscript Mr D. Irish,   2. The History and Pedigree of Unicam Instruments, Martin Long, 1999,   3. Private communications with Chris Barrett & Jim Steward

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