Ray L. Williams Metropolitan Police Forensic Laboratory. London, England
Chemistry and biology are being applied ever increasingly to the investigation of crime. This article attempts to present some aspects of this renaissance in forensic studies
I should emphasize right at the beginning that any article of this nature is bound to contain a number of unavoidable biases. I am a physical chemist, and I have no doubt that if this paper were written by an organic chemist, a biochemist, a toxicologist, or a biologist, that the emphasis would be quite different ( I , 2). Furthermore, I would point out that although the United States and the UK have basically similar legal procedures, there are differences in the acceptance of scientific evidence which necessarily mean that what constitutes “proof’ in one court is not so regarded in another. In the UK, the Criminal Justice Act of 1967 permitted the use of written statements by scientists instead of their giving oral testimony. Counsel or the judge can still ask for the scientist to attend court, hut since then, the number of court appearances by expert witnesses has declined
dramatically. For the Metropolitan Police Laboratory, for example, in 1967 there were 7973 cases and 2336 court appearances: in 1972 with 36,814 cases, there were only 723 appearances. Written statements have to he quite brief. The experimental details on which the expert opinions are based are therefore kept to a minimum. This reduces the emphasis on which techniques are used in the examination and disguises the fact that there are considerable differences in what is regarded as acceptable as an identification. For example, some experts rely on crystal tests to identify a drug. Others may insist on spot tests plus thin-layer chromatography and gas chromatography data, whereas others insist on infrared, ultraviolet, and perhaps mass spectra in addition. The methods are not accentuated in the written statement, and it is up to the defence to raise this point in cross-examination if it thinks fit. The
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Figure 1. Evidential items and potential methods of examination 1076 A * ANALYTICAL CHEMISTRY, VOL. 45, NO. 13, NOVEMBER 1973
trend in English courts a t present seems to be to accept the facts, by whatever techniques they may have been obtained, and to dispute the interpretation. The situation therefore places Considerable responsibility on the expert witness in his attitude to analytical methods. I would he very surprised if the situation were exactly the same in all the courts in the U.S. Differences in emphasis are hound to occur, and hecause of this, there will he differences in the methods used, not only in the two countries hut also from lahoratory to laboratory. In this article, I am reflecting predominantly current British attitudes, particularly those prevailing in my own laboratory.
Forensic Scientist’s Role May I remind you first of all that the forensic scientist’s task is to assist the court in deciding whether or not a particular person has been involved in a crime. The scientist has items“exhibits”-suhmitted to him by the police for examination, and he has two questions to answer about anything of significance which he may find on the exhibits. Firstly, what is it? For example, is the dark stain on a jacket, blood? Are these tablets amphetamines? Secondly, if it is an item which can he associated indisputably with a suspect, it is identical with that found a t the scene of a crime, and what are the chances that this identity might he accidental? For example, is the flake of paint found on the clothing of a person thought to have robbed a house, the same as the paint on the window frame through which entry was made? What are the odds against a similar flake of paint turning up from some other source? The forensic scientist is conservative in his outlook, partly because over the years he has had to acquire his methods slowly and painfully: I have deliberately used the word painfully because the acquisition has heen accomplished against a background of growing work load, shortage of money for equipment, and in the face of some scepticism of the value of scientific evidence from the legal profession. The last factor, of course, is ahsolutely right every scientific method
Report
and deduction should be closely questioned and scrutinised when a person’s innocence or guilt depends there. on. However, the process has not been made easy by the tactics of some lawyers who have relied on emotive rather than rational criticism.
factors which I have just mentioned, many of these changes may seem less than new to the analytical chemist working in industrial, university, or big defence laboratories. Nevertheless, they are having a great impact on forensic science. The most important items which turn up as evidence are materials such as paint, glass, fibres, drugs, and poisons; inflammable substances from arsons; surface marks or striations typified by those made by tools, and those on bullets, and finally the biological fluids blood, semen, saliva, and sweat. In all these areas, considerable improvements have taken place in techniques of examination; these are outlined in Figure 1which shows their applicability to the materials I have listed above. The techniques fall into two groups-those in the top halfof the diagram deal with compounds, those in the lower half with elements. Some of the well-established standard methods are also shown to emphasize that they are still and will continue to he essential weapons in the forensic scientist’s armoury. Before considering these in detail, I must comment on one entirely physical development, viz., the use of the profile recorder (e.g., a Tallysurf) in measuring the scratches or marks
made by tools in the forcible entry into houses or coin boxes, telephone boxes, and so on. It is also equally applicable in the comparison of striation marks on bullets. Figure 2 gives profiles from a bullet recovered from a shooting and one fired from a queried weapon. The match in this example is good, hut the instrument does not take into account the severe distortions which often occur in the queried item. The technique is therefore used principally for sorting, the final examination still being made visually with a comparison microscope.
SEM in Police Work It is an obvious step in these examinations from an optical microscope to the scanning electron microscope (SEMI. This instrument has considerable advantages over the optical microscope, both in magnification and in depth of focus. It can therefore he used for looking a t striation marks of the order of microns in size, which could he located in sites which are inaccessible to the optical microscope, for example, the mark made by the firing pin of a gun on the base of a cartridge cap (3).Although the SEM has been relatively costly, particularly when fitted with X-ray microanalysis attachments, its versatility is such that the expenditure is justified
Analytical Methods Fortunately, the situation has improvedin all three respects over the last few years hut has left a legacy which substantially dictates which forensic methods are practicable. These must use relatively inexpensive equipment, he capable of application to a wide range of problems, be rapid in their operation, and preferably nondestructive! The parameters measured should he those giving good discrimination between two samples which are apparently the same; however, they must not he so discriminating that microheterogeneities within a single sample become significant. Let us now consider some areas where, in my opinion, there has heen rapid development. Because of the
Figure 2. Comparison of bullet striations by profile recorder ANALYTICAL CHEMISTRY, VOL. 45, NO. 13, NOVEMBER 1973
Figure 3. Matching of tool marks by split-field S E M . Total width of scratch
is 0.5 mm in big crime laboratories ( 4 ) . Moreover, a number of low-price machines are beginning to appear on the market which makes it possible for the smaller laboratories to consider its use. Quite recently, comparison or splitfield SEM has been achieved by van Essen and Morgan a t the Metropolitan Police Laboratory (5).Figure 3 shows how it is possible to match two specimens side by side in the SEM in a single examination rather than view them separately, take pictures, and try to produce a montage. The total width of the mark in this example is 0.5 mm, which emphasises that scratches on a micro scale can yield useful information.
Figure 4. Pyrograms
The SEM provides extremely valuable information of a different sort. The characteristic X-rays given off by the specimen when the scanning beam of electrons strikes it can be analysed to give both qualitative and quantitative information on the elements present in the specimen. Elements from about atomic number 5 upward can he examined in this way, and usually concentrations down to about the0.1% level can be detected in a volume of material potentially as small as a 10-p cube. This corresponds to an absolute sensitivity of about 10-12 gram of a particular element. Classical electron probe microanalysis by comparison has a sensitivity of the order of parts per million, hut it is rarely possible for a forensic laboratory to have sufficient funds to have both SEM and electron microprobe equipment. The SEM with X-ray analysis accessory is thus a good compromise. Moreover, it has the advantage that the area of specimen which is analysed is the same as that seen topographically by its secondary electron emission. The methcd is in addition virtually nondestructive. In the Metropolitan Police Laboratory in the first full year of operation, 114 cases were examined by the SEM, the majority of which could not be dealt with by any other method. The samples were 40% paints, each specimen being analysed for up to 10
'I
of two alkyd resins differina " in alvcerol-.
pentaerythritol composition. ( a ) Glycerol - pentaerythritol. 8.4:1 by weight.1 (b) Glycerol-pentaerythritol, 0.01 :1 by weight. Peak 1. acrolein; 2. methylacrolein:. 3.. benzene; 4, allyl alcohol
1
I,,
b
J" Time (min) 1 no .
Figure 5. GC analy80 sis of quina1 barbitone in acetone by use of (a) flame ionization, (b) therm- g -60 ionic detectors. 1 mc Each represents 40 two-pl injections at concentration of 0.02 pglfil; note difference in solvent peak
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ANALYTICAL CHEMISTRY, VOL. 45, NO. 13, NOVEMBER 1973
elements, frequently for each layer when the specimen was multilayered. Two examples indicate the value of the SEM in case work. In one instance, $119,000 worth of selenium was stolen in an armed robbery. Clothing from a person believed to have been involved in the attack was examined in the Laboratory and a small fragment about 0.2 X 0.2 mm found on one of the shoes. Analysis showed it to be pure selenium. In the second case, some ceremonial regalia were recovered from a car abandoned after a robbery a t Arundel Castle; they included an Earl Manhal's baton coated with ruby glass. Two control pieces of the latter were compared with a fragment measuring 0.9 x 0.2 mm found on the instep of a shoe worn by a suspect. Table I gives an analysis of the controls and queried item which are in excellent agreement for all elements present except silicon. Laser Probe The use of the laser microprobe in analysis in many ways parallels that of the SEM (6, 7). In this instrument a pulse of energy from a laser is used to vapourise a small amount of material from a preselected part of the specimen, The vapour then triggers an electric discharge between two graphite electrodes, and the resulting uvvisible emission can be analysed by a spectrograph in the usual way. It is possible to adjust the size of the areas of sample analysed from 10 to 250 q n in diameter. Only a small crater is produced; hence, it is possible to obtain analyses within individual layers in a paint-chip. Alternatively, the laser can be defocussed and because of the consequent low penetration, surface films on samples can be analysed. Sensitivities range from 0.1% concentration for small craters to 0.01% for large ones, Le., 10-lo to 10-11 gram absolute sensitivity. Other items, such as alloys, can be analysed by this method, but glass, because of its transparency to the laser pulse, has to he pelleted with graphite powder. The smallest sample of this material that can he handled is thus about a milligram, and the sensitivity is limited to elements present in greater than 150-200 ppm concentrations. AAS Applications There are indications that problems arising in glass analysis may be overcome by atomic absorption spectrometry (AAS) where the greater sensitivity in terms of concentrations enables many trace elements to be determined. The equipment is also relatively inexpensive and can yield quantitative results readily. Hitherto,
trace elements in the lowest concentration ranges have had to be measured either by spark source mass spectrometry or neutron activation analysis. Neither of these, however, has been widely used in forensic casework, partly because the high cost of the equipment restricts it to a few laboratories, partly because the techniques are time consuming, and partly because special training is needed for their operation. In the UK, the practice has been to use the methods for acquiring reference data. For example, analyses down to trace elements levels have been carried out by the Home Office Central Research Establishment (HOCRE, which was set up in 1966 specifically to carry out research in forensic disciplines for the benefit of the operational laboratories in England and Wales) over 1000 samples of glass, mainly window glass, using mass spectra and NAA (8, 9). An evaluation of these results has shown that maximum discrimination between samples can be obtained by measuring the concentrations of about a dozen elements, including vanadium, titanium, strontium, rubidium, and arsenic. It is therefore possible, in principle, to choose for operational forensic laboratories cheaper and more specific methods of analysis to look for these elements. AAS is one such technique, having high sensitivity particularly when used with a heated graphite furnace (Massman) ( I O ) for vapourizing the sample. There are difficulties in handling small glass samples, particularly because of the large differences in concentrations of the important elements. Dissolution in hydrofluoric acid followed by dilution of aliquots to the right concentration range for the AA spectrometer may prove satisfactory. The major problem is then the determination of those elements such as calcium, which have insoluble fluorides. The other difficulty which arises with the use of the graphite furnace is when an element, e.g., barium, forms a refractory carbide. However, if the concentration is greater than a few parts per million, emission spectrography can be used to overcome this. Atomic absorption spectrometry, particularly now that multielement lamps are available, can also be used for many other types of sample as in the estimation of the levels of toxic metals in biological specimens, for instance. One such toxicological application has been the detection of thallium at a level of several parts per million in the cremation ashes of a man previously thought to have died from natural causes. No thallium could be found in controls from the
container of the ashes or from the ground wherein the ashes were interred ( 1 2 ) . Trace metals in paints could also be measured by AAS if necessary, but an alternative approach to paint comparison is to identify the matrix which carries the pigment. In the past, various methods such as IR spectroscopy, effect of solvent, or methanolysis combined with gas chromatography of the resulting methyl esters have been used. Pyrolysis GC The advent of Curie-point pyrolysers (12),however, has made possible the rapid and reproducible thermal decomposition of polymeric materials. A small quantity of paint (10-20 Fg) is attached to a ferromagnetic wire which is inserted in a small induction furnace. Induction heating raises the temperature of the wire to its Curie point in a few microseconds, and the pyrolysis products are swept by carrier gas into a gas chromatograph. The resulting chromatograms are characteristic of particular polymers and can be used in a “finger print” fashion for identification of the material by reference to collections of standard pyrograms. If the compounds giving rise to some of the peaks in the chromatogram can be identified, e.g., by using gas chromatography/mass spectrometry, then it is possible to infer the type of polymer without reference to standard pyrograms. Even resins prepared from the same starting materials, but in varying proportions, can be differentiated by this technique (Figure 4 ) . As an example, the case may be quoted where the pyrogram was obtained of a black speck of material found embedded in the skull of a 38 year old woman who had died from head injuries. It turned out to be that of a styrenated alkyd, a coating used for tools; it matched similar pyrograms from paint on the tool kit of an abandoned car from which the wheel ANALYTICAL CHEMISTRY, VOL
brace was missing. There is no need to point out the significance! The extension of pyrolysis GC to the characterisation of other organic materials is quite obvious. Pyrograms of top-soil extracts, adhesives from items such as Sellotape, carpet backings, and fibres, to name but a few, can be dealt with quite easily (13). The latter use promises to be of great potential since fibres are of great evidential value, and a lot of effort has already been devoted to trying to improve their characterisation. For example, the use of beam condensers and micro-KBr discs to obtain the IR spectrum of 2-3 mm length of a single fibre is already well established ( 1 4 ) .The extraction of the colouring matter from a fibre by use of a suitable solvent such as dimethylformamide, followed by thinlayer chromatographic separation of the component dyes, is also being used increasingly by forensic chemists. It should, in the latter instance, be a relatively simple matter to develop means of obtaining absorption spectra from these chromatographic spots, since it already is possible to obtain their fluorescence spectra by use of microspectrofluorimeters. Pyrolysis GC, because of its ease of operation, is a powerful addition to these methods. Chromatographic Applications The importance of GC and mass spectrometry in the identification of drugs and poisons is beyond dispute, as shown by the large number of papers published on this topic (25-18). New sources of ions for mass spectrometry (viz., chemical ionization, field ionization, and field-desorption ionization) are significant, not only for simplifying the spectra but also in extending the range of mass spectrometry to difficult volatile materials (33). However, it is worth commenting on a strictly GC development, viz., selective detectors. Some of these 45, NO. 13, NOVEMBER 1973
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such as the electron capture detector (19) are well known and can be used in forensic work to enhance the sensitivity of detection of a drug by preparing, for example, its perfluoracyl derivative. Others, such as the thermionic detector ( 2 0 ) ,are sensitive only to compounds containing nitrogen and phosphorus. This means that the work-up of material before GC analysis can be greatly reduced. The specificity of the detector ensures that only the compounds of interest (e.g., barbiturates with nitrogen or organic pesticides with phosphorus) are “seen” by the gas chromatograph, and coextractants which would previously have interfered with the identification pass through the machine almost unnoticed (Figure 5). It is almost superfluous to add a note of caution at this stage; the technique is applicable only to those circumstances where it is desired to know whether a particular compound is present or not. The second application of gas chromatography is one of which petroleum chemists are already well aware. It is in the characterisation of hydrocarbons. It is now fairly commonplace with arson cases to extract the debris from the fire and to identify the incendiary material according to its type, whether it is aviation spirit, gasoline, light oil, heavy oil, diesel fuel, and so on. Capillary columns are used for this. Occasionally, if the police are fortunate enough to find the arsonist with fuel in his possession, it is possible to say whether that particular fuel was used to cause the fire. Not all hydrocarbons are amenable
With built-in computer compatibility, the RS-I can be readily interfaced into your lab data acquisition system. An optional interface is available for low cost “CAT” signal averagers. Typical applications of the RS-1 include: Analysis of aqueous solutions Investigation of competitive Analysis of reaction products including products trace impurities and many more. The RS-1 Fact File contains reprints of technical articles about the RS-1, application data sheets, specifications, and prices. Use reader service number for your copy, or contact Norcon.
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ANALYTICAL CHEMISTRY, VOL. 45, NO. 13, NOVEMBER 1973
Figure 6. HPLC analysis of an engine oil by use of (a) fluorescence, (b)
ultraviolet detectors
to forensic problems. This, in my opinion, is one of the most important developments which is taking place at present. The basis of the method is the production by a living organism (be it human, horse, or rabbit) of antibodies which react specifically with foreign substances, termed antigens, which may be introduced into the body (29, 30). Antigens have to be macromolecules or larger for this response to take place, so that if it is desired to produce antibodies specific to a small molecule, such as LSD, cannabis, or heroin, it has to be coupled to a carrier-usually albumen. The small molecule is then termed a hapten. Schematically, the sequence for the production of a specific antiserum is thus: Figure 7. Methods of immunoassay
Hapten
Bovine
Albumen
to gas chromatography. Some are too involatile, and the development of high-pressure liquid chromatography (HPLC) has opened up new possibilities for the analysis of these and other difficult substances such as the more polar or thermally unstable drugs. There are many examples in the literature of analyses of the latter types of compound (21-23). In the Metropolitan Police Laboratory, for instance, it has been used for the identification of benzodiazepine metabolites in toxicological samples. A more commonplace example is the estimation of LSD by use of a fluorescence detector. The sensitivity is quite high. For example, by use of a microcell and a spectrofluorimeter as detector, quantities of LSD as low as 10 pg in a 5-pl injection can be detected for aqueous LSD solutions ( 2 4 ) . With hydrocarbons, the analysis of engine lubricating oils by HPLC looks quite promising ( 2 5 ) .As the oil in the engine gets progressively older, many degradation products appear, including polynuclear aromatics whose proportions seem to be characteristic of the particular engine. The use of different detectors, such as uv absorption, fluorescence, and refractive index, increases the versatility of the technique in a similar fashion to gas chromatography (Figure 6). It is also possible to use reagents such as dansyl chloride and 7-chloro-4-nitrobenzo oxadiazole to convert many drugs to fluorescing derivatives prior to the HPLC separation. Lloyd has used a different technique for tackling this problem, viz., synchronous scanning of the fluorescence spectrum ( 2 6 ) .In this, the excitation monochromator and the monochromator analysing the fluorescence spectrum are scanned synchronously
with a fixed and predetermined wavelength interval between them. Highly characteristic and reproducible spectra are thereby produced, and a sensitivity comparable to liquid chromatography is achieved. One example of the use of the method is a murder case in which oil on the weapon was matched against oil from the scene of the crime. Fluorescence Spectra Fluorescence has a high intrinsic sensitivity so that it is well suited to the characterisation of the small objects that occur in forensic work. Fortunately, the development of a number of microspectrofluorimeters has been reported in the literature ( 2 7 ) ,and one such instrument has been constructed in the M.P. Laboratory. The apparatus is used frequently for fibre identification in which it often happens that two fibres of apparently the same colour have different fluorescence spectra. A more novel application has been the comparison of a fluorescent marker powder used to tag some bank notes with a single small crystal found in the pocket of a suspect. It is worth noting in connection with fluorescence spectroscopy that it is relatively easy by small additions to the fluorimeter to measure the phosphorescence of a substance (28). When this can be excited, it provides a second identifiable parameter which is often more characteristic than the fluorescence spectrum. For instance, the rodenticide, warfarin, can be distinguished quite readily by this method. Immunological Methods I would like to discuss now the application of immunological methods
Anti-Hp-BSA antibodies
Hp-BSA conjugate
Extraction
A n i ma I
Anti-Hp antiserum
I have, of course, grossly oversimplified this procedure, but once a specific antiserum has been made, it can be used to detect the presence of a drug in a complex mixture by a t least four ways (Figure 7). In radioimmunoassay, a quantity of radioactively labelled hapten is needed (31).This is complexed to the antibody. When the test sample is added to this, if it contains the hapten (e.g., heroin), this will displace the radiohapten from the antibodyantigen complex in the usual massaction fashion. In consequence, the radioactivity of the antibody-hapten complex (which can be precipitated out) falls, and the radioactivity of the supernatant liquid rises. The method is quantitative and sensitive to levels of about pg/ml. One of the most interesting applications of this by Taunton-Rigby and her colleagues has been the detection of LSD in the urine of subjects who had taken 200pg doses (32).The concentration in the urine was about 1000 pg/ml. A variation on this process is in spin immunoassay ( 3 3 ) .In this method, a quantity of hapten is electron spin labelled by attaching a stable free radial to it. The lines in the ESR spectrum of the antibody-labelled hapten complex are broad; when the labelled hapten is displaced from the complex by unlabelled hapten from the test solution, its ESR spectrum becomes sharp-lined. The sensitivity is about 0.1 pg/ml. The two other methods are more biochemical in nature. The first relies on absorbing the hapten onto red blood cells; these then can be used as the equivalent of a “spot” reagent. If an excess of antisera is added to the
ANALYTICAL CHEMISTRY, VOL 45, NO. 13, NOVEMBER 1973
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hapten in the unknown solution, unused antisera will remain after the interaction ( 3 4 ) .Addition of the mixture to the red-cell-hapten complex will then cause these to agglutinate. If there is no free antiserum, then the cells remain unaffected. Enzyme inhibition relies on the inactivation of an enzyme previously coupled to the hapten, when this complex is itself bound by the antihapten antibody. Addition of more hapten displaces the hapten-enzyme complex from the antibody. The enzyme is no longer inactive and can be detected by its reactions (35). None of the antisera is absolutely specific. Usually each antiserum will complex with molecules of similar structure to that of the hapten for which it is intended, but the complex is so weak that the concentration of the “foreign” molecule has to be at least 1000 times greater than that of the true hapten to produce the same response. This usually is well within the range of detection of more conventional means of analysis and can therefore be confirmed or not.
lines are still in the research or development stages; the remainder are fully operational methods. Blood enzymes and proteins are frequently polymorphic and can be examined by electrophoretic methods (38).These are all based on separation of the blood enzymes or proteins by migration through a gel under the influence of an electric field. The gel acts as a molecular sieve, and the rate of migration is also affected by the electrical charge on the protein. It is clearly impossible to separate completely all the different components in the serum by this process. However, just as with selective detectors in gas chromatography, it is possible
to develop colour reactions specific to a particular enzyme. For example, with phosphoglucomutase (PGM) the sequence of reactions is as follows, with the production of a blue-coloured formazan in the presence of PGM. Treating an electrophoretic plate with such a reagent will then only show the presence of that enzyme and ignore the other components. Moreover, the catalytic role of the enzyme ensures very high sensitivity because it can transform many molecules of the reagent. With PGM there are three forms PGM-1, PGM2 , and PGM 2-1, corresponding to 58.4, 5 5 , and 36.1%, respectively, of the British population (38).
Glucose-1-phosphate
PGM with glucose-1,6-diphosphate
4
t
6-Phosphogluconate
Glucose-6-phosphate
Blood Groupings
So far, I have been discussing chemical aspects of forensic science; progress in the biological field has also been great. Some of this, one would like to believe, is the result of stimulus from either physics or chemistry. Developments in blood grouping are such that one can now think about the possibility of blood being as unique an identification as a fingerprint. It is also becoming possible to derive additional information from blood; for example, whether it is from a man (36) or woman (37);whether or not it is menstrual blood. Figure 8 summarises the situation in general terms: those areas bounded by dotted
Glucose-6-phosphate dehydrogenase
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NADP
NADPH Phenazine methosulphate
I J
MTT formazan
MTT (tetrazolium)
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Figure 8. Examination and grouping of bloodstains
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BAT
Origin
Figure 9. Erythrocyte acid phosphatase
phenotypes
automated, and the results of a grouping can be presented on a recorder chart (38).The Gm and Inv systems based respectively on antigens in the IgG and in the IgG, IgM, and IgA fractions of the blood have also been examined carefully, and it is hoped to put them into routine case work this year (40). The present situation for grouping is summarised in Figure 10 which gives frequency distributions for the British population. If we take the most commonly occurring section of each group (Table 11),the overall discrimination is 1in 100 of the UK population: if we take some of the rarer sections, a discrimination of 1in 200,000,000,000is attained, which can cope with the whole world population at present! Matters are less satisfactory with
The most recent enzyme system to be put into case work is erythrocyte acid phosphatase (EAP) which can be detected by its fluorescence under UV light. Figure 9 shows some of the variants possible with EAP. There are three homozygous forms A. B, and C, corresponding to 12.9, 35.4, and 0.2% population and three heterozygous forms BA, CA, and CB, corresponding to 42.7, 3.3, and 5.5% population (39).
Serological grouping systems based on antibody-antigen reactions are complementary to the electrophoretic systems. The AB0 and M N systems have been in forensic use for some time, while Rhesus grouping is now equally well established and gives excellent discrimination since it divides the population into at least 15 different phenotypes. The method has been MN ____
-
A A/S A/C others
M MN
29
N
21
Rh (Rhesus)
AB0
%
%
A B 0
50
%
42 8.5 47
Rh-
rr
R1R2 13
Hb(haemog1obin) % normal adult 14.5 British Negroes
Rzr
RED CELL ANTIGENS
Ro
RPr
4
I
rare
Hp(haptoglobin) % 1-1 16 2-1 48 2-2 35
15 35
BODY
12 2 1 SECRETOR STATUS
GROUPS nonsecretors 23%
4 RED CELL ENZYMES
EAP %
A B
c
BA CB CA
13 35 0.2 43 5.5 3
ADA ~
PG M- _ _
%
%
58 1 2-1 36 2 5.5
90 1 2-1 9 0.2 2
AK _ % 1 91 2-1 9 2 0.2
_
_ PGD_ % A 96 A/C 4 C 0.04
%
A 28 British Negroes B 72 AB onlyfoundlncertain Negresses "
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Table II. Probabilities of Occurrence of Most Common and Rare Sub-Groups in Blood Grouping Systems System
Commonest
AB0
0
Rh
Rlr
%
Rarer
47 34
AB Several
