Walmsley et al Flexible dialyser membrane.

dialyser membrane would continuously flex as samples ofdifferent protein concentrations are analysed the peakheight of a specimen does not necessarily reflect itscreatinine level. In the authors’ experience this producesmany bizarre peak shapes within every batch and the lastpeak is always higher than expected. One way of minimisingconformational changes in the dialyser membrane is to raisethe waste donor stream Of the dialyser. However, under theseconditions small changes in conformation still occur due tothe elasticity in the membrane, and the last peak in everybatch is still higher than expected. A-satisfactory solution tothis problem has been found by minimising pressuredifferences between samples. A plasma creatinine analyserhas been operated for the last 18 months using a samplediluent of sodium chloride (300 mmol/1) and 10 g/1 of Brij

35. Over 75,000 specimens were analysed during this time. Ahigher concentration of 30 g/1 is not used, in order to reducethe possibility of phase separation when samples of high totalprotein are analysed ].

ACKNOWLEDGEMENTThe authors wish to acknowledge the financial support from theMedical Research Council of New Zealand and constructive discussionswith Dr C. M. Andre.

REFERENCES[1] Walmsley, T. A., Clin. Chim. Acta, 1979, 99, 53-57.[2] Technicon Method No. AAII-11, 1970, Technicon Instrument

Corporation, Tarrytown, New York.

A bichromaticmethodfor the enzymaticdetermination of serum triglycerideswith the Gemsaec Fast analyserP. Bijster*, H. L. Vader and C. L. J. VinkClinical Laboratory, St. Joseph Hospital, Aalsterweg 259, Eindhoven (The Netherlands).

IntroductionFully enzymatic methods for the determination of serumtriglycerides may be carried out in either .a kinetic or anequilibrium mode. Both kinetic and equilibrium methodshave been adapted for use on centrifugal analysers.Kinetic(orfixed-time rate) analyses are carried out by adapting thereaction conditions to achieve first or pseudo-first-orderkinetics 1-5]. Equilibrium analyses on centrifgual analysersdeal with some special problems concerning the initialabsorbance reading [1,6]. If a slight lag-phase is present inthe first stage of the reaction some analysers can read aninitial absorbance during this time. Otherwise ’zero-time’.extrapolation procedures must be used despite the difficultiesthese present. Another drawback of equilibrium analyses,especially for centrifugal analysers, is the long reaction time.A fully enzymatic equilibrium method adapted to the

Gemsaec Fast analyser which takes less than two minutes ofinstrument time is described. It is a modification of themethod described by Bucolo.et al [7]. in this procedure thetriglycerides are released and hydrolysed by a mixture oflipase and 0t-chymotrypsin. Subsequently, the releasedglycerol is converted to glycerol-l-phosphate in the presenceof glycerol kinase and ATP. Phosphoenol pyruvate, includedin the reagent, is converted by pyruvatekinase to pyruvateresulting in the regeneration ATP from ADP. The reductionof pyruvate to lactate in the presence of lactate dehydro-genase with concurrent oxidation of NADH2 to NAD+ isused as the indicator reaction. Both the hydrolysis and theelimination of glycerol are carried out at 37 C in the transferdisc outside the analyser within 10 minutes.

To minimise optical interferences, the absorbance of thereaction mixture is read after 10 minutes at two wavelengths,

*Correspondence to this author

202

namely 340 nm and 380 nm. There is no optical interferenceby lipemic sera as the absorbances are determined after com-plete hydrolysis of the lipids. The concentration oftriglycerides is calculated by subtracting the absorbancedifferences (A 340 nm A 380 nm) of the reagent blank anddeterminations compared to that of a glycerol standard.

MaterialsEskalab triglyceride reagentEskalab substrate vials (89804) and Eskalab glycerol kinasevials (89802), obtained from Smith Kline Instruments, Inc.,Sunnyvale, California 94086, USA, were dissolved in hi-distilled water according to the manufacturer’s recommend-ations. The reactants in the reagent mixture have thefollowing approximate concentrations:

Substrate mixtureReduced nicotinamide adenine dinucleotidePyruvate kinaseLactate dehydrogenaseMgZ+Lipaseot-chymotrypsinPhosphoenol pyruvateBovine serum albuminAdenosine triphosphateBuffer: (pH 7.1 : 0.2)Potassium dihydrogen phosphatedi-Potassium hydrogen phosphate

0.3 mmol/10.8 x 103IU0.7 x 103IU

6 mmol/1300 x 103 IU13 x 103IU0.8 mmol/1

1.7 g/10.5 retool/1

10 mmol/163 mmol/1

Glycerol kinase suspensionGlycerol kinase not less than 20 IU/vial.

Journal of Automatic Chemistry

Bijster et al Enzymatic.determination of serum triglycerides with the Gemsaec Fast analyser.

Combined reagent10pl Of the glycerol kinase suspension were added per ml ofthe substrate solution and the reagent was mixed.

Glycerol standards100% Glycerol, purchased from Fluka A. G., Buchs S. G.(Prod. no 49770) was used as the primary standard. Thewater content of the 100% glycerol was checked bymeasuring the relative viscosity at 20.0C [8]. As asecondary standard Precimat glycerol standard, obtainedfrom Boehringer Mannheim GmbH, Germany, was used.This is a stabilised aqueous solution of glycerol whichcontains 2.29 mmol/1 glycerol, corresponding to a trigly-ceride concentration of 2.29 mmol/1. This standard waschecked with aqueous dilutions (v/v) of 100% glycerol.

Ethanolic potassium hydroxide (ca. 0.5 mol/1)3.30 g 85% Potassium hydroxide p.a. (Merck art. 5033) weredissolved in 10 ml bidistilled water, under cooling with tapwater. 96% Ethanol p.a. (Merck art. 972) was added to afinal volume of 100 ml.

Magnesium sulphate solution (0.15 mol/1)3.70 g Magnesium sulphate 7 aq. p.a. (Merck art. 5886)were dissolved in 50 ml bidistilled water and bidistilledwater was added to a final volume of 100 ml.

Boehringer test-combination triglyceridesAll reagents in this kit (no. 124966), purchased fromBoehringer Mannheim GmbH, Germany, were dissolvedin bidistilled water according to the manufacturer’srecommendations.

Turbidity standard5 g Hexamethylene tetramine (Merck art. 4343) were dis-solved in 30 ml bidistilled water and brought to a finalvolume of 50 ml. 0.5 g Hydrazine sulphate (BDH ’analar’no. 10121) were dissolved in the same way to a final volumeof 50 ml. Both solutions were combined (1:1) to a stock-standard. The working-standard was prepared by dilution of12 ml stock-standard with bidistilled water to a volume of50 ml.

Apparatus1. ENI-Gemsaec centrifugal analyser obtained from Electro-

Nucleonics Inc., Fairfield, New Jersey 07006, USA, withoptional addition of a Digital Decwriter II and an ENI-Gemsaec rotoloader IV with Micromedic Systems auto-matic pipettes.

2. LKB ultrolab system 2074 calculating absorptiometerobtained from LKB Produkter AB, Bromma 1, Sweden.

3. A Vitatron Photometer UFD, was used as a nephelometerwithout optical filters, obtained from Vitatron, Dieren,The Netherlands.

MethodsThe transfer discs are prewarmed to the incubation temper-ature (37C) before they are loaded. 10/al Bidistilled water,standard, control or serum sample, dispensed with 80saline followed by 500 /al combined reagent (see Materials)are pipetted into well C of the transfer disc. Positions 1,2 and 3 of the transfer disc contain bidistilled water, reagentblank and a glycerol standard respectively.

After an incubation at 37C for 10 minutes the hydroly-sis of the triglycerides and elimination of glycerol has beencompleted and the transfer disc is placed into the Gemsaecanalyser and the run is started. The analyser is operated at37C and the first reading at 340 nm is taken after 10seconds (IR 10). Thirty seconds after the vacuum blast(mixing) the wavelength is-changed to 380 nm and thesecond reading is taken 60 seconds after the first reading(RI 60, NR 2).

The computer instructions are as followsIR 10 AD 3RI 60 CD 2NR 2 HI 2.5SC 2.29 LO 0.5KT 1.0 SA 0.4TF 1.0 RM 2TC XX

To calculate correctly the total glycerol concentration ofthe samples, the first printout must be disregarded and anadditional computer program must be used (see Manual SKI).This program performs the following calculations using theabsorbances stored in the computer memory"

1. A340 Aas0 Delta in which A340 absorbance at340nm

Aa 80 : absorbance at380nm

2. Deltablank Deltasamples A corrected

3. A corrected unknownx glycerol concentration of standard

A corrected standard (mmoi[1)total glycerol concentration ofunknown (mmol/1)

Results were compared to the manual enzymatic methodafter saponification with ethanolic KOH (see Materials)which was performed according to the manufacturers recom-mendations. In routine clinical chemistry, the triglycerideconcentration is obtained by subtracting 0.11 mmol/1 ascorrection for the mean free glycerol concentration,, from themeasured value [9]. Otherwise the concentration of ’free’glycerol may be estimated, separately.

Experiments and resultsWavelength choiceThe glycerol concentration of an aqueous glycerol solutionis generally measured by determining the absorbancedifference between the reagent blank and the sample relativeto the absorbance difference between the reagent blank and astandard at one wavelength (340 nm). When optical ’normal’sera diluted in the combined reagent as described earlier areanalysed in this way, the triglyceride concentrationwill bedecreased by approximately 0.1 0.2 mmol/1.

As it is impossible to read the initial absorbance of thereaction mixture at the Gemsaec Fast analyser, an altern-ative approach is to measure the absorbance of the reactionmixture at two wavelengths, after completion of hydrolysisand elimination of glycerol. The choice of the second wave-length, next to the fixed 340 nm, is based on several factors.Firstly, interference caused by haemolytic and ictedcsamples must be minimised. Secondly, the sensitivity of theassay must be guaranteed and thirdly, the practical.handlingof the assay on the Gemsaec analyser is of importance.

To evaluate the possible colorimetric interferences spectrawere measured of haemolytic and icteric sera in the reactionmixture without glycerolkinase against the same mixturewithout these pigments. These experiments showed thatminimum interference of haemolysis was given if the secondwavelength is about 375 nm. To evaluate the interferencecaused by icteric samples spectra of icteric sera with a highand low percentage conjugated bilirubin were measured. Asthe absorption minimum for both spectra is about 340 nm itappeared that for minimising the interference of bilirubinthe best choice for the second wavelength is about 340 nm.

The sensitivity of the assay is dependent on theabsorbance difference between 340 nm and the second wave-length. The choice of a high wavelength (>390 nm) willguarantee good sensitivity (a large absorbance difference)but, as stated above, will cause erroneous results especiallywhen assaying icteric samples. The choice of a low wave-

Volume 2 No. 4 October 1980 203

Blister et al, Enzymatic determination of serum triglycerides with the Gemsaec Fast analyser..

length (<370 nm) will result in minimal interference causedby icteric samples but pronounced interference caused byhaemolytic samples and loss of sensitivity. In prac.tice, thechoice of 380 nm as the second wavelength offers a reasonablecompromise. The interference of pigments at this wavelengthis acceptable and the sensitivity is guaranteed as the correctedabsorbance (Delta blank Delta sample) for a triglycerideconcentration of 2.3 mmol/1 (reference range 0.84 1.94) is36% higher than the corrected absorbance at 370 nm.Furthermore, changing the wavelength during the assay onthe Gemsaec spectrophotometer from 340 nm to 380 nmand calibration and checking the cuvettes at both wave-lengths presents no practical problems as the same filterrange can be used.

The repeated adjustment of the wavelength scale at thechosen wavelengths is sufficiently exact.

LinearityA series of glycerol standards was prepared by diluting 100%glycerol (primary standard) with bidistilled water (v/v).The primary standards were assayed four times and theglycerol concentrations were calculated against the secondaryPrecimat glycerol standard. The results (Figure 1) show thatthere is good linearity over the range of glycerol concen-trations from 0 up to 7.5 mmol/1 (max. deviation fromcalculated glycerol concentration 0.5%). Furthermore, theresults show that the stated glycerol concentration of thePrecimat standard is correct.

PrecisionThe within-run precision was determined by assaying serumpools with different triglyceride concentrations in three runs.In each. run aliquots of the same serum were pipetted in 13wells of the transfer disc. The’ results are presented in Table1. The day-to-day precision was determined by assaying thecontrol serum liponorm (Boehringer Mannheim GmbH) oncea day in duplicate..The results over a period of 32 days are.also shown in Table 1.

AccuracyThe automated bichromatic enzymatic method wascompared to a manual enzymatic method, the Boehringertest-combination triglycerides. Seventy-three sera wereanalysed by both methods. The results are shown in Figure2. The correlation curve, calculated according to Lindley[10] assuming that the variances in x and y are equal, isdescribed by the eqUation

y 1.03x 0.05with a coefficient of correlation of 0.996. The data followeda normal distribution, checked with the Kolmogorov-Smirnov-test 11 (a 0.05).

Interference of haemoglobinAny interference of haemolysis with this bichromaticmethod was investigated. Blood from a healthy donor wascentrifuged after clotting and the blood clot was washedtwice with 0.9 g/1 NaCI. Erythrocytes were haemolysed by

Table 1. Within-run and day-to-day precision of three sera and one control serum, respectively

SampleMean (mmol/1) concentration of triglyceridesStandard deviation (mmol/1)Coefficient of variation (%)Number of samplesNumber of days

Within-runA B

0.49 1.810.0122.6

13

0.0261.4

13

3’190.0481.5

13

Day-to-dayLiponorm

1.930.0482.5

32

Table 2. Influence of haemolysis on the determination of triglyeerides

Haemoglobinconcentration

(mmol/1)

0.000.030.060.120.23

Qualitative haemolysisaccording to Frank

et al 121

2+3+4+

Expected triglycerideconcentration

(mmol/1)

2.162.152.142.122.08

Measured triglycerideconcentration

(mmol/1)

2.162.182.202.212.23

Apparent increase intriglyceride concentration

(mmol/1)

0.000.030.060.090.15

ca,c lOy told al lo31

Figure 1. Glycerol concentrations measured by the dualwavelength method on the Gemsaec Fast analyser of aseries of glycerol standards prepared by diluting 100%glycerol with bidistilled water (V/v).

Figure 2. Comparison ofthe triglyceride concentrations of73 sera analysed with the dual wavelength method on theGemsaec Fast analyser and with a manual enzymaticmethod after saponification with ethanolic KOH.

204 Journal of Automatic Chemistry

Bijster et al Enzymatic determination of serum triglycerides with the GemsaecJFast analyser.

adding bidistilled water and the suspension was homogen-ised in a mortar. After centrifuging the suspension fivetimes for 30 minutes at 4000 rpm the haemoglobin sol-ution had a haemoglobin concentration of 5.5 mmol/1and a triglyceride concentration of 0.1 mmol/1. A seriesof dilutions with pooled serum was prepared. The expectedtriglyceride concentration of the haemolytic sera werecalculated from the triglyceride concentration of the pooledserum (2.16 mmol/1) and the dilution factors obtainedafter the addition of the haemoglobin solutions. The trig-lyceride concentrations of the different haemolytic serumsamples were determined in duplicate on the Gemsaecanalyser by the bichromatic enzymatic method. The fourhaemolytic samples were categorised qualitatively in fourclisses (1+, 2+, 3+ and 4+) according to Frank et al [12].Table 2 shows the results of these experiments. From theseresults it is evident that the presence of haemoglobin inserum results in an apparent increase of the triglycerideconcentration. The authors consider that the influence ofhaemolysis which is acceptable for practical purposes asthe triglyceride concentration of a very haemolytic (4+)sample (which rarely occurs) with an expected triglycerideconcentration of 2.00 mmol/1 (reference range 0.841.94 mmol/1) will be increased by about 8%.

Interference of bilirubinIn order to investigate the interference with the bichromaticmethod caused by bilirubin, a series of dilutions with salinewere made of four different icteric sera, with a high percent-age conjugated bilirubin (mean 73%). The diluted sampleswere assayed on the Gemsaec analyser in duplicate with sub-strate without the addition of glycerol kinase to evaluatethe optical interference. The results are presented in Table 3.From these results it is evident that the presence of bilirubinin serum results in an apparent increase of triglyceride con-centration. For example, the triglyceride concentration of anicteric serum- with a total bilirubin concentration of100 pmol/1 (reference range 5-14/amol/1) and an expectedtriglyceride concentration of 2.00 mmol/1 (reference range0.84 1.94 mmol/1) will be increased by about 10% whenassayed with this method. As the spectra at about 340 nm ofsera with high concentrations of unconjugated bilirubin inthe reaction mixture are almost the same as the spectra ofsera with high concentrations of conjugated bilirubin, theinterference of unconjugated bilirubin on the assay is notquantified.

Interference by turbidityA series of turbid samples prepared by dilution of a stronglylipemic serum pool of 10 patients (triglyceride concentration10.1 mmol/1) with saline was assayed, to evaluate thecapability of the combined reagent to clear up sera with ahigh content of chylomicrons. The turbidity of the sampleswas measured in duplicate on a nephelometer, that wasadjusted to an arbitrary transmission of 40% with theturbidity standard. The samples were analysed in duplicateon a Gemsaec analyser diluted with combined reagent with-out the addition of glycerol kinase to evaluate the influenceof turbidity on the corrected absorbance. The results are

Table 3. Influence of total bilirubin concentration on thedetermination of triglycerides

Total bilirubinconcentration

(ktmol/1)0

5O100150200250

A corrected + SD (Deltablank Delta sample)

0.000 + 0.0010.007 + 0.0010.016 + 0.0010026 + 0.0020.036 + 0.0030.047 + 0.005

Apparent increasein triglycerideconcentration(mmol/1)

0.00O.O80.190.320.440.57

Table 4. Influence of turbidity on the determination oftriglycerides

Dilutionfactorlipemic

serum pool

undiluted2x4x8x

12x18x

Nephelo-merry %

transmission

29.329.623.217.012.1

A corrected(Delta blank

-Deltasample)

-0.017-0.007-0.003-0.0010.0000.000

Apparentdecrease intriglyceride

concentration

(mmol/1)0.210.080.040.010.000.00

shown in Table 4. From the results it is clear that evenstrongly lipemic sera are sufficiently cleared by the combinedreagent. For example, the triglyceride concentration of the2 x diluted pooled serum (strongly lipemic) with an expectedtriglyceride concentration of 5.0 mmol/1 was decreased byabout 1.5%. Only extreme milky sera cause falsely loweredtriglyceride concentrations but this will not cause erroneousresults as these sera will have a high triglyceride concentra-tion and dilution will be necessary to prevent crossing theupper limit of !inearity (7.5 mmol/1).

DiscussionAn enzymatic analysis based on an equilibrium measurementhas the advantage over a kinetic measurement thattemperature or drugs have no influence on the kinetics ofthe reaction. In addition, a linear reaction curve is notnecessary. The difficulty in adapting an equilibrium analysisto the Gemsaec analyser is that it is impossible to take anearly absorbance reading. Chong-Kit et al [6] have solvedthis problem and introduced a ’zero-time extrapolation’ bymeans of an extrapolation factor. The authors evaluated abichromatic reading after completion of the reactions whichreplaces the ’zero-time extrapolation’. A bichromatic readingmay introduce errors caused by pigments and/or turbidity.Data presented here shows that these interferences caused byhaemoglobin and bilirubin are not completely minimisedby this bichromatic reading. However, the influence ofhaemolysis only becomes important at haemoglobin concen-trations that seldom occur in practice and the authorsconsider that this method is acceptable for practical purposes.The interference of bilirubin is the result of the choice ofthe second wavelength. There is an almost linear relationbetween the bilirubin concentration and the apparentincrease in triglyceride concentration; for every 50 /amol/1bilirubin the triglyceride concentration of an icteric sampleis increased by 0.1 mmol/1. The interference caused bylipemic turbidity is excluded as the absorbances are deter-mined after complete hydrolysis of the lipids.

The disadvantage of a long hydrolysis time (10 minutes)is limited because the incubation takes place outside theGemsaec analyser. During this incubation the precedingbatch is run, calculated and the necessary administrationcan be performed. In principle this enzymatic analysis ofserum triglycerides can be performed on every spectro-photometer with variable wavelength setting and on therecently introduced bichromatic analysers after hydrolysisof glycerides. The choice for the Gemsaec analyser is basedon the advantage this system offers (economic reagent use,good precision, easy calculation of results, clear presentation,statistical evaluation).

ACKNOWLEDGEMENTSThe authors wish to thank Gist-Brocades Farmaca Nederland BV andSmith Kline Instruments, Inc. for their cooperation in this study andMrs Geboers-van der Have for her assistance in the preparation ofthe manuscript.

Volume 2 No. 4 October 1980 205

Bijster et al Enzymatic determination of serum triglycerides.with the Gemsaec Fast analyser.

REFERENCES [7][l] Tiffany, T. O., Morton, J. M., Hall, E. M. and Garrett, A.S., [8]

Clinical Chemistry, 1974, 20, 476.[2] Ziegenhorn, J., Clinical Chemistry, 1975, 21, 1627.[3] Wentz,. P. W., Cross, R. E. and Savory, J., Clinical Chemistry, [9].

1976, 22, 188.[4] Grossman, S. H., Mollo, E. and Ertingshausen, G., Clinical [10]

Chemistry, 1976, 22, 1310.[5] Wakayama J. E. and Swanson, J. R. Clinical Chemistry, 1977, [11]

23, 223.[6] Chong-Kit, R. and McLaughlin, P., Clinical Chemistry, 1974, [12]

20, 1454.

Bucolo, G. and David, H., Clinical Chemistry, 1973, 19, 476.Wolf, A. V., Brown, M. G. and Prentiss, P. G. in ’Handbook ofChemistry and Physics’ Ed. Weast, R. C., CRC Press, Cleveland,Ohio, D-206.Stinshoff, K., Weisshaar, D., Staehler, F., Hesse, D., Gruber, W.and Steiner, E., Clinical Chemistry, 1977, 23, 1029.Lindley, D. V., Supplement Journal Royal Statistical Society,1947, 9, 218.Massey, F. J., Journal American Statistical Association, 1951,46, 68.Frank, J. J., Bermes, E. W., Bickel, M. J. and Watkins, B. F.,Clinical Chemistry, 1978, 24, 1966.

A clinical appraisal ofthe Greiner G300clinical chemistry analyser

M.J. Hallworth and S.G. ArcherDepartment of Clinical Biochemistry, Addenbrooke’s Hospital, Hills Road, Cambridge CB2 2QR.

and J.G. LinesDepartment of Clinical Chemistry, William Harvey Ho’spital, Ashford, Kent TN24 OLZ.

IntroductionThe demands on clinical chemistry laboratories over the lasttwo decades have grown so rapidly that automated multipleanalysis upon single samples is now the only practicablemethod of providing a routine clinical chemistry service inall but the smallest hospitals. A large variety of equipment iscommercially available for performing this task rapidly andeconomically,whilst maintaining high standards of analyticalquality. Any new instrument must therefore equal or betterthe established standards of precision, and must use analyticalmethods producing results as close as possible to referencemethods for each analyte.

Thework which follows sets out to determine the precisionand accuracy of the Greiner G300 analyser in routine useand to examine both the analytical capability of the instru-ment and also the contribution it can make towards handlingthe workload of the clinical chemistry laboratory.

The Greiner G300 analyser is a third-generation instrument,which essentially comprises up-dated modifications of theGreiner Selective Analyser (GSA II) which has been availablefor six years. In the United Kingdom, the GSA II was firstformally evaluated by Skinner and Wilding [I] in 1975, anda more comprehensive evaluation has recently been producedby Carlyle et al [2] who made their study over a considerableperiod of routine use.

The present evaluation was planned as a rapid assessmentof the clinical utility of the new.G300. Following exhibitionat the 3rd European Congress of Clinical Chemistry (Brighton,June 1979), a prototype instrument was transported toCambridge and was operational for this clinical trial the dayafter arrival. Over the next five days a series of experimentsdesigned to rapidly assess the per-formance of the G300under routine conditions was performed.

Instrument descriptionThe instrument is a discrete analytical system capable ofperforming up to 30 different analyses on a single specimen.Methods for 20 analyses are already fully documented, and

the repertoire is being extended by further tests as they areadapted to the G300 from the GSA II.

The G300 is physically smaller than the GSA II and hasimproved process control facilities. The number of analyseson each specimen and the rate of analysis remain the same,but the handling of emergency and paediatric samples isfaster and more convenient than on the GSA II. A washingcycle for process tubes is a new feature of the G300 andcontrasts advantageously to the disposable process tubesused by the GSA II. Carlyle et al [2] found that the cost ofprocess tubes considerably exceeded the cost of reagentsfor most tests, therefore .the economic saving is appreciable.

The G300 comprises a 30 place sample carrier and samplingunit, a conveyor belt system on which the process tubesused for reactions are supported and moved, and a ighoto-meter unit with associated electronics. The analysis timefrom sampling to measurement of the final optical densityis 13.4 minutes. The reaction time is variable between 36seconds and 12.6 minutes according to the position of thereagent dispensers within the incubator unit, and the opticaldensity may be read at the wavelength of any one of eightmercury lines, between 334 and 623 nm. The same samplecan be dispensed into a pair of process tubes, and up to fourdifferent reagents added to each tube. In this manner blankmeasurements can be determined when required. The oper-ator selects the tests to be performed on each specimen bymeans of a keyboard next to the sample tray. Commonly-requested groups of analyses (biochemical profiles) can beselected by means of a single key, and some examples ofprofiling rates are shown in Table 1. It is possible to intro-duce any urgent investigation into the middle of the batchof other analyses, or to perform only a few necessary testson a small sample of serum, while performing a wider profileon the remainder of the batch. Emergency samples are placedin the next available space in the sample tray, the operatoridentifies the sample as an emergency, and keys in the testrequired: the instrument then positions the emergencysamples under the sampling unit, samples sufficient serum

206 Journal of Automatic Chemistry

Submit your manuscripts athttp://www.hindawi.com

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation http://www.hindawi.com Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttp://www.hindawi.com

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

The Scientific World JournalHindawi Publishing Corporation http://www.hindawi.com Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

Journal of

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation http://www.hindawi.com Volume 2014

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

CatalystsJournal of